Myelodysplasia/Myeloid leukemia factor: Biological Overview | References
Gene name - Myelodysplasia/Myeloid leukemia factor
Cytological map position - 52D2-52D3
Function - Transcriptional regulation
Keywords - protein stabilization; regulation of cell proliferation involved in compound eye morphogenesis, regulates Lozenge during hematopoetic development, crystal cells, regulates assembly of the COP9 signalosome complex, regulator of Dref
Symbol - Mlf
FlyBase ID: FBgn0034051
Genetic map position - chr2R:11823360-11827597
Classification - Myelodysplasia-myeloid leukemia factor 1-interacting protein
Cellular location - cytoplasmic and nuclear
Defining the function of the genes that, like RUNX1, are deregulated in blood cell malignancies represents an important challenge. Myeloid leukemia factors (MLFs) constitute a poorly characterized family of conserved proteins whose founding member, MLF1, has been associated with acute myeloid leukemia in humans. To gain insight into the functions of this family, the role of the Drosophila MLF homolog was investigated during blood cell development. mlf controls the homeostasis of the Drosophila hematopoietic system. Notably, mlf participates in a positive feedback loop to fine tune the activity of the RUNX transcription factor Lozenge (LZ) during development of the crystal cells, one of the two main blood cell lineages in Drosophila. At the molecular level, these data in cell cultures and in vivo strongly suggest that MLF controls the number of crystal cells by protecting LZ from degradation. Remarkably, it appears that the human MLF1 protein can substitute for MLF in the crystal cell lineage. In addition, MLF stabilizes the human oncogenic fusion protein RUNX1-ETO and is required for RUNX1-ETO-induced blood cell disorders in a Drosophila model of leukemia. Finally, using the human leukemic blood cell line Kasumi-1, it was shown that MLF1 depletion impairs RUNX1-ETO accumulation and reduces RUNX1-ETO-dependent proliferation. Thus, it is proposed that the regulation of RUNX protein levels is a conserved feature of MLF family members that could be critical for normal and pathological blood cell development (Bras, 2012).
Development of the hematopoietic system relies on the activity of several signaling pathways and transcription factors that have been conserved from mammals to fly. Drosophila has emerged as a model organism to gain insight into the gene regulatory networks controlling hematopoiesis. Deregulation of these networks lies at the origin of several diseases in humans, including leukemia and lymphoma. Interestingly, these hematologic malignancies are frequently associated with recurring chromosomal abnormalities. Along with their clinical prognostic value, these rearrangements have led to the identification of many genes involved in the etiology of cancer; thus, characterizing the function of these genes in normal and pathological blood cell development is of particular interest (Bras, 2012).
One notorious gene identified by cloning translocation breakpoints is RUNX1/AML1, which is affected by the t(8;21) (q22;q22) translocation found in ~15% of all cases of acute myeloid leukemia (AML). RUNX1 belongs to the RUNX transcription factor family, which is characterized by the presence of a highly conserved DNA binding domain. RUNX proteins activate or repress transcription in a context-dependent manner, thereby regulating cell proliferation and differentiation in a variety of metazoans. In particular, RUNX genes have been shown to regulate hematopoiesis in both vertebrates and Drosophila. For instance, RUNX1 plays a prominent role in definitive hematopoietic stem cell emergence, as well as in megakaryocyte and lymphocyte differentiation in mammals, and mutations affecting RUNX1 are among the most frequent genetic abnormalities associated with blood cell malignancies in humans. These alterations promote leukemia by altering RUNX1 dosage or by producing mutant proteins that act as dominant negative and/or display neomorphic activities, as for RUNX1-ETO, the product of the t(8;21)(q22;q22) translocation, which comprises the RUNX1 DNA-binding domain fused to the transcriptional corepressor ETO. In Drosophila, the RUNX factor Lozenge (LZ) is specifically expressed in and required for development of one of the two main blood cell types: the crystal cells, a megakaryocyte- like lineage that participates in clotting. In fact, LZ interacts and cooperates with the pan-hematopoietic GATA transcription factor Serpent (SRP) to activate the crystal cell differentiation program. This cooperation is conserved in mammals, where it controls megakaryopoiesis and hematopoietic stem cell development. Moreover, reminiscent of the situation in humans, RUNX1-ETO expression in the Drosophila LZ+ blood cell lineage induces a preleukemic phenotype characterized by a switch of cell fate from differentiation to self-renewal. Thus, Drosophila provides a valuable model for studying the normal and oncogenic functions of RUNX factors during hematopoiesis (Bras, 2012).
The myeloid leukemia factor (MLF) family comprises a small group of evolutionarily conserved genes whose founding member was first identified as the target of the t(3;5)(q25;q35) translocation associated with myelodysplastic syndrome (MDS) and AML. This translocation generates a fusion protein between the N-terminal region of nucleophosmin (NPM; a multifunctional nucleolar protein) and most of MLF1. Whereas NPM, which is involved in other translocations, seems to act by providing a dimerization domain and a nucleolar targeting sequence (Rau, 2009), little is known about MLF1 activity. Significantly, however, increased MLF1 expression correlates with poor prognosis in AML and with malignant progression in MDS, and MLF1 ectopic expression affects the myeloerythroid lineage switch and cell cycle progression in cell cultures (Yoneda-Kato, 2005; Winteringham, 2004; Williams, 1999). Nonetheless, MLF1 function in hematopoiesis remains poorly defined. Only one MLF gene is present in Drosophila, whereas there are two MLF paralogs in vertebrates (Ohno, 2000). As in mammals, MLF encodes a nucleocytoplasmic shuttling protein with no recognizable structural domain apart from a 14-3-3 binding motif (Sugano, 2007). However, its in vivo function remains unclear, given that mlf mutant flies are subviable and do not exhibit any obvious developmental defect (Martin-Lannerée, 2006; Bras, 2012 and references therein).
Given the conservation between MLF proteins and the parallels between mammalian and fly blood cell development, this study assessed whether MLF controls hematopoiesis in Drosophila. In particular, it was found that mlf expression is activated in the crystal cells by SRP/LZ, and that mlf regulates the expansion of this lineage. At the molecular level, the data indicate that MLF controls the number of crystal cells by protecting LZ from proteasome- mediated degradation. Interestingly, human MLF1 is able to substitute for mlf function in the crystal cell lineage. Furthermore, mlf is required for the activity and stable expression of the human leukemogenic protein RUNX1-ETO in Drosophila, whereas human MLF1 depletion causes a decrease in RUNX1- ETO protein and impairs RUNX1-ETO-dependent proliferation in human leukemic blood cells. Thus, it is proposed that the control of RUNX levels is a conserved function of MLF proteins that play an important role in the control of blood cell homeostasis (Bras, 2012).
Although deregulation of MLF1 has been linked to AML, the physiological role of MLF family members in hematopoiesis remains largely unknown. Focusing analysis on Drosophila hematopoietic development, this study has demonstrated that MLF controls blood cell homeostasis. In particular, strong evidence is provided that MLF is required to stabilize the RUNX factor LZ during crystal cell development. In addition, the findings suggest that the regulation of RUNX activity by MLF is conserved in humans, where it could play an important role in leukemogenesis. These findings reveal MLF's regulatory function in the control of crystal cell production. Actually mlf, which exhibits a rather ubiquitous expression pattern, is highly expressed in these blood cells, and mlf expression in this lineage is activated by SRP/LZ. MLF controls crystal cell number in a cell-autonomous manner, chiefly by impinging on LZ levels. It is proposed that the induction of mlf expression by SRP/LZ contributes to crystal cell development by stabilizing LZ. As such, this gene regulatory network forms a two-component positive feedback loop that drives development forward by stabilizing the expression of lineage-specific regulators. These findings also show that MLF controls lymph gland homeostasis, where it seems to promote hematopoietic progenitor maintenance. Although some of the factors controlling lymph gland development have been identified, no RUNX factor has been implicated in prohemocyte maintenance, suggesting that MLF has other partners in these cells. Of interest, MLF has been shown to bind Su(fu) and to possibly antagonize its function (Fouix, 2003). Because Su(fu) negatively regulates both Hh and Wnt pathways, which are required for prohemocyte maintenance, their premature differentiation in mlf mutants could result from increased Su(fu) activity. It is anticipated that deciphering MLF's mode of action in the lymph gland will provide valuable insight into the regulation of blood cell progenitor fate (Bras, 2012).
Along with revealing the role of MLF in hematopoiesis, these findings shed light on the function and regulation of LZ. It was found that decreased LZ levels in mlf mutant larvae resulted in an increased number of circulating LZ+ cells, but did not block these cells' differentiation, suggesting that low levels of LZ are sufficient to induce crystal cell differentiation. In addition, expansion of the pool of LZ+ cells might reflect a slowdown in the cells' rate of differentiation or a direct function of LZ in controlling blood cell proliferation or apoptosis. Along this line, LZ was shown to promote cell death in the eye, notably by regulating the expression of the Drosophila homolog of the Wilms' tumor gene 1 (WT1). Alternatively, decreased LZ levels may make crystal cell progenitors more susceptible to proliferative cues from the Notch pathway, which regulates larval crystal cell numbers. In mammals, RUNX1 acts mostly as a brake on blood cell progenitor proliferation, and decreased RUNX1 dosage, as well as MDS/AML-associated mutations or translocations affecting RUNX1, tend to promote aberrant self-renewal. Interestingly, RUNX1-ETO also promotes hematopoietic progenitor cell expansion in Drosophila, and both WT1 overexpression and activation of the Notch signaling pathway have been linked to RUNX1-ETO-induced AML. Given these similarities, characterizing the function of LZ in the control of crystal cell number may have broader implications (Bras, 2012).
Notwithstanding the evolutionary distance between human and fly, the human MLF1 protein rescued mlf-associated crystal cell defects, including LZ down-regulation, whereas mlf and MLF1 were required for the stable expression of RUNX1-ETO in Drosophila and human leukemia cells, respectively. Thus, the regulation of RUNX turnover seems to be a conserved function of MLF family members. The proteasome was found to regulate RUNX1-ETO as well as other RUNX proteins in human cells, and the current data indicate that LZ is degraded in a proteasome-dependent manner in the absence of mlf. An important area of future inquiry will be to determine more precisely how RUNX stability is regulated by MLF. This is of particular interest given that altered RUNX levels are associated with several diseases in humans, including familial platelet disorders and AML for RUNX1 and cleidocranial displasia for RUNX2. Actually, the slightly reduced LZ levels that were observed in mlf mutant eye discs suggests that the regulation of RUNX stability by MLF is not restricted to the hematopoietic system. Moreover, few genes required for RUNX1-ETO-induced AML have been identified so far, and the data suggest that MLF1 is a critical component for RUNX1-ETO leukemogenic activity. Indeed, along with the MDS/AML-associated t(3;5) translocation that generates the NPM-MLF1 fusion protein, MLF1 overexpression was correlated with malignant progression. The mechanisms underlying the oncogenic activity of NPM-MLF1 or MLF1 remain largely unknown, however. Similarly, the function of MLF1 in mammals remains poorly characterized. Exploring the relationship between MLF and RUNX factors could shed further light on MLF's role and mode of action (Bras, 2012).
Blood cell development is controlled by an intricate network of genes, the activity of which must be tightly controlled to ensure proper cell lineage choice, proliferation, and differentiation. The current findings show that the dynamic and coordinated control of gene expression through positive feedback loops participates in the fine-tuning of hematopoiesis, and provides a framework for future investigations of the cross-regulatory interactions that control blood cell fate. Finally, the results open up new avenues of research into the mode of action of MLF family members as conserved regulators of RUNX protein stability, and it is envisioned that Drosophila will provide a powerful model for deciphering MLF's function in hematopoiesis and leukemia (Bras, 2012).
Proper blood cell development requires the finely tuned regulation of transcription factors and signaling pathways activity. Consequently mutations affecting key regulators of hematopoiesis such as members of the RUNX transcription factor family or components of the Notch signaling pathway are associated with several blood cell disorders including leukemia. Also, leukemic cells often present recurrent chromosomal rearrangements that participate in malignant transformation by altering the function of these factors. The functional characterization of these genes is thus of importance not only to uncover the molecular basis of leukemogenesis but also to decipher the regulatory mechanisms controlling normal blood cell development. Myeloid Leukemia Factor 1 (MLF1) was identified as a target of the t(3;5)(q25.1;q34) translocation associated with acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) more than 20 years ago. Further findings suggested that MLF1 could act as an oncogene or a tumor suppressor depending on the cell context and it was shown that MLF1 overexpression either impairs cell cycle exit and differentiation, promotes apoptosis, or inhibits proliferation in different cultured cell lines. Yet, its function and mechanism of action remain largely unknown (Miller, 2017).
MLF1 is the founding member of a small evolutionarily conserved family of nucleo-cytoplasmic proteins present in all metazoans but lacking recognizable domains that could help define their biochemical activity . Whereas vertebrates have two closely related MLF paralogs, Drosophila has a single mlf gene encoding a protein that displays around 50% identity with human MLF in the central conserved domain. In the fly, MLF was identified as a partner of the transcription factor DREF (DNA replication-related element-binding factor), for which it acts a co-activator to stimulate the JNK pathway and cell death in the wing disc. MLF has been shown to bind chromatin, as does its mouse homolog, and it can either activate or repress gene expression by a still unknown mechanism. MLF also interacts with Suppressor of Fused, a negative regulator of the Hedgehog signaling pathway, and, like its mammalian counterpart, with Csn3, a component of the COP9 signalosome, but the functional consequences of these interactions remain elusive. Interestingly the overexpression of Drosophila MLF or that of its mammalian counterparts can suppress polyglutamine-induced cytotoxicity in fly and in cellular models of neurodegenerative diseases. Moreover phenotypic defects associated with MLF loss in Drosophila can be rescued by human MLF1. Thus MLF function seems conserved during evolution and Drosophila appears to be a genuine model organism to characterize MLF proteins (Miller, 2017).
Along this line, the role of MLF during Drosophila hematopoiesis has been studied. Indeed, a number of proteins regulating blood cell development in human, such as RUNX and Notch, also control Drosophila blood cell development. In Drosophila, the RUNX factor Lozenge (Lz) is specifically expressed in crystal cells and it is absolutely required for the development of this blood cell lineage. Crystal cells account for ±4% of the circulating larval blood cells; they are implicated in melanization, a defense response related to clotting, and they release their enzymatic content in the hemolymph by bursting. The Notch pathway also controls the development of this lineage: it is required for the induction of Lz expression and it contributes to Lz+ cell differentiation as well as to their survival by preventing their rupture. Interestingly, the previous analysis revealed a functional and conserved link between MLF and RUNX factors. In particular, MLF was shown to control Lz activity and prevent its degradation in cell culture, and the regulation of Lz level by MLF is critical to control crystal cell number in vivo. Intriguingly, although Lz is required for crystal cell development, mlf mutation causes a decrease in Lz expression but an increase in crystal cell number. In human, the deregulation of RUNX protein level is associated with several pathologies. For instance haploinsufficient mutations in RUNX1 are linked to MDS/AML in the case of somatic mutations, and to familial platelet disorders associated with myeloid malignancy for germline mutations. In the opposite, RUNX1 overexpression can promote lymphoid leukemia. Understanding how the level of RUNX protein is regulated and how this affects specific developmental processes is thus of particular importance (Miller, 2017).
To better characterize the function and mode of action of MLF in Drosophila blood cells, this study used proteomic, transcriptomic and genetic approaches. In line with recent findings, MLF was found to bind DnaJ-1, a HSP40 co-chaperone, as well as the HSP70 chaperone Hsc70-4, and that both of these proteins are required to stabilize Lz. It was further shown that MLF and DnaJ-1 interact together but also with Lz via conserved domains and that they regulate Lz-induced transactivation in a Hsc70-dependent manner in cell culture. In addition, using a null allele of dnaj-1, it was shown to control Lz+ blood cell number and differentiation as well as Lz activity in vivo in conjunction with mlf. Notably, w mlf or dnaj-1 loss leads to an increase in Lz+ cell number and size due to the over-activation of the Notch signaling pathway. Interestingly, these results indicate that high levels of Lz are required to repress Notch expression and signaling. A model is proposed whereby MLF and DnaJ-1 control Lz+ blood cell growth and number by promoting Lz accumulation, which ultimately turndowns Notch signaling. These findings thus establish a functional link between the MLF/Dna-J1 chaperone complex and the regulation of a RUNX-Notch axis required for blood cell homeostasis in vivo (Miller, 2017).
Members of the RUNX and MLF families have been implicated in the control of blood cell development in mammals and Drosophila and deregulation of their expression is associated with human hemopathies including leukemia. The current results establish the first link between the MLF/DnaJ-1 complex and the regulation of a RUNX transcription factor in vivo. In addition, these data show that the stabilization of Lz by the MLF/DnaJ-1 complex is critical to control Notch expression and signaling and thereby blood cell growth and survival. These findings pinpoint the specific function of the Hsp40 chaperone DnaJ-1 in hematopoiesis, reveal a potentially conserved mechanism of regulation of RUNX activity and highlight a new layer of control of Notch signaling at the transcriptional level (Miller, 2017).
MLF binds DnaJ-1 and Hsc70-4, and these two proteins, like MLF, are required for Lz stable expression in Kc167 cells. In addition, these data show that MLF and DnaJ-1 bind to each other via evolutionarily conserved domains and also interact with Lz, suggesting that Lz is a direct target of a chaperone complex formed by MLF, DnaJ-1 and Hsc70-4. Of note, a systematic characterization of Hsp70 chaperone complexes in human cells identified MLF1 and MLF2 as potential partners of DnaJ-1 homologs, DNAJB1, B4 and B6, a finding corroborated by Dyer (2017). Therefore, the MLF/DnaJ-1/Hsc70 complex could play a conserved role in mammals, notably in the regulation of the stability of RUNX transcription factors. How MLF acts within this chaperone complex remains to be determined. In vivo, this study demonstrated that dnaj-1 mutations lead to defects in crystal cell development strikingly similar to those observed in mlf mutant larvae, and these two genes were shown to act together to control Lz+ cells development by impinging on Lz activity. The data suggest that in the absence of DnaJ-1, high levels of MLF lead to the accumulation of defective Lz protein whereas lower levels of MLF allow its degradation. Thus it is proposed that MLF stabilizes Lz and, together with DnaJ-1, promotes its proper folding/conformation. In humans, DnaJB4 stabilizes wild-type E-cadherin but induces the degradation of mutant E-cadherin variants associated with hereditary diffuse gastric cancer. Thus the fate of DnaJ client proteins is controlled at different levels and MLF might be an important regulator in this process (Miller, 2017).
This work presents the first null mutant for a gene of the DnaJB family in metazoans and the results demonstrate that a DnaJ protein is required in vivo to control hematopoiesis. There are 16 DnaJB and in total 49 DnaJ encoding genes in mammals and the expansion of this family has likely played an important role in the diversification of their functions. DnaJB9 overexpression was found to increase hematopoietic stem cell repopulation capacity and Hsp70 inhibitors have anti-leukemic activity, but the participation of other DnaJ proteins in hematopoiesis or leukemia has not been explored. Actually DnaJ's molecular mechanism of action has been fairly well studied but there are only limited insights as to their role in vivo. Interestingly though, both DnaJ-1 and MLF suppress polyglutamine protein aggregation and cytotoxicity in Drosophila models of neurodegenerative diseases, and this function is conserved in mammals. It is tempting to speculate that MLF and DnaJB proteins act together in this process as well as in leukemogenesis. Thus a better characterization of their mechanism of action may help develop new therapeutic approaches for these diseases (Miller, 2017).
As shown in this study, mlf or dnaj-1 mutant larvae harbor more crystal cells than wild-type larvae. This rise in Lz+ cell number is not due to an increased induction of crystal cell fate as we could rescue this defect by re-expressing DnaJ-1 or Lz with the lz-GAL4 driver, which turns on after crystal cell induction, and it was also observed in lz hypomorph mutants, which again suggests a post-lz / cell fate choice process. Moreover mlf or dnaj-1 mutant larvae display a higher fraction of the largest lz>GFP+ cell population, which could correspond to the more mature crystal cells. It is thus tempting to speculate that mlf or dnaj-1 loss promotes the survival of fully differentiated crystal cells. RNAseq data demonstrate that mlf is critical for expression of crystal cell associated genes, but both up-regulation and down-regulation of crystal cell differentiation markers were observed in mlf or dnaj-1 mutant Lz+ cells. Also these changes did not appear to correlate with crystal cell maturation status since alterations were found in gene expression in the mutants both in small and large Lz+ cells. In addition the transcriptome did not reveal a particular bias toward decreased expression for 'plasmatocyte' markers in Lz+ cells from mlf- mutant larvae. Thus, it appears that MLF and DnaJ-1 loss leads to the accumulation of mis-differentiated crystal cells (Miller, 2017).
The data support a model whereby MLF and DnaJ-1 act together to promote Lz accumulation, which in turn represses Notch transcription and signaling pathway to control crystal cell size and number. Indeed, an abnormal maintenance of Notch expression was observed in the larger Lz+ cells as well as an over-activation of the Notch pathway in the crystal cell lineage of mlf and dnaj-1 mutants or when Lz activity was interfered with. Moreover the data as well as previously published experiments show that Notch activation promotes crystal cell growth and survival. Importantly too the increase in Lz+ cell number and size observed in mlf or dnaJ-1 mutant is suppressed when Notch dosage is decreased. Yet, some of the mis-differentiation phenotypes in the mlf or dnaj-1 mutants might be independent of Notch since changes in crystal cell markers expression seem to appear before alterations in Notch are apparent. At the molecular level, the results suggest that Lz directly represses Notch transcription as this study identified a Lz-responsive Notch cis-regulatory element that contains conserved RUNX binding sites. The activation of the Notch pathway in circulating Lz+ cells is ligand-independent and mediated through stabilization of the Notch receptor in endocytic vesicles. Hence a tight control of Notch expression is of particular importance to keep in check the Notch pathway and prevent the abnormal development of the Lz+ blood cell lineage. Notably, Notch transcription was shown to be directly activated by Notch signaling. Such an auto-activation loop might rapidly go awry in a context in which Notch pathway activation is independent of ligand binding. By promoting the accumulation of Lz during crystal cell maturation, MLF and DnaJ-1 thus provide an effective cell-autonomous mechanism to inhibit Notch signaling. Further experiments will now be required to establish how Lz represses Notch transcription. RUNX factors can act as transcriptional repressors by recruiting co-repressor such as members of the Groucho family. Whether MLF and DnaJ-1 directly contribute to Lz-induced-repression in addition to regulating its stability is an open question. MLF and DnaJ-1 were recently found to bind and regulate a common set of genes in cell culture. They may thus provide a favorable chromatin environment for Lz binding or be recruited with Lz and/or favor a conformation change in Lz that allows its interaction with co-repressors. The scarcity of lz>GFP+ cells precludes a biochemical characterization of Lz, MLF and DnaJ-1 mode of action notably at the chromatin level but further genetic studies should help decipher their mode of action. While the post-translational control of Notch has been extensively studied, its transcriptional regulation seems largely overlooked. The current findings indicate that this is nonetheless an alternative entry point to control the activity of this pathway. Given the importance of RUNX transcription factor and Notch signaling in hematopoiesis and blood cell malignancies, it will be of particular interest to further study whether RUNX factors can regulate Notch expression and signaling during these processes in mammals (Miller, 2017).
The human myeloid leukemia factor 1 (hMLF1) gene was first identified as an NPM-hMLF1 fusion gene produced by chromosomal translocation. In Drosophila, dMLF has been identified as a protein homologous to hMLF1 and hMLF2, which interacts with various factors involved in transcriptional regulation. However, the precise cellular function of dMLF remains unclear. To generate further insights, the behavior of dMLF protein was examined using an antibody specific to dMLF. Immunostaining analyses showed that dMLF localizes in the nucleus in early embryos and cultured cells. Ectopic expression of dMLF in the developing eye imaginal disc using eyeless-GAL4 driver resulted in a small-eye phenotype and co-expression of cyclin E rescued the small-eye phenotype, suggesting the involvement of dMLF in cell-cycle regulation. The molecular mechanism was examined of interactions between dMLF and a dMLF-interacting protein, dCSN3, a subunit of the COP9 signalosome, which regulates multiple signaling and cell-cycle pathways. Biochemical and genetic analyses revealed that dMLF interacts with dCSN3 in vivo and glutathione S-transferase pull-down assays revealed that the PCI domain of the dCSN3 protein is sufficient for this to occur, possibly functioning as a structural scaffold for assembly of the COP9 signalosome complex. From these data the possibility is proposed that dMLF plays a negative role in assembly of the COP9 signalosome complex (Sugano, 2008).
MLF family proteins are novel intracellular factors whose in vivo functions remain largely unknown. This study analyzed the function of Drosophila MLF through its expression pattern, subcellular localization and molecular mechanisms of binding to a dMLF-interacting protein to generate further insights into dMLF and MLF family proteins. It is reported that dMLF proteins are largely cytoplasmic in early blastoderm embryos prior to cellularization, although they progressively accumulate in the nuclei thereafter. In addition, strong cytoplasmic localization of dMLF was observed in cultured Kc cells in a previous study. However, in this study, immunostaining of Drosophila embryos and cultured cells revealed that dMLF primarily localizes in the nucleus in early embryos and mainly in the nuclear envelope with a slight accumulation in cytoplasm and nucleoplasm in cultured cells. Accumulation in the peripheral region of the inner nuclear membrane was also observed in some embryos, consistent with the reported nuclear localization of dMLF with some concentration inside the nuclear envelope and in the perinuclear region in the salivary glands of Drosophila larvae. The discrepancies are probably not due to the antibodies used in the experiments, because these results are found using another antibody. Thus, differences between observations may result from variation in the physiological conditions of cells and/or fixation processes for immunostaining analyses (Sugano, 2008).
In a previous study, MLF1 in cultured mammalian cells was seen to localize in both the cytoplasm and the nucleus. It was also noted that MLF1 was not evenly distributed in the cytoplasm, but was more concentrated in the perinuclear region including centrosomes. In addition, it has been suggested that MLF1 translocates between the nucleus and cytoplasm. In this study, dMLF was detected not only in the nucleoplasm, but also in the nuclear envelope during early embryogenesis. Taking the available information, it is likely that dMLF shuttles between the cytoplasm and the nucleus depending on other protein factors or physiological conditions of cells. Indeed, it has been reported that mammalian MLF1 interacts with 14-3-3zeta, which is involved in subcellular localization and shuttling between the nucleus and cytoplasm. Immunoblot analysis with anti-dMLF IgG suggested that some modified forms of dMLF protein are present in embryonic and larval-pupal stages. It has been reported that a serine kinase recruited by MADM phosphorylates MLF1 at the 14-3-3 binding motif in mammals. As with MLF1, both MADM and 14-3-3 are also conserved in Drosophila, and it is possible that dMLF also interacts with Drosophila MADM to become phosphorylated. It is also conceivable that 14-3-3 interacts with phosphorylated dMLF and affects its subcellular localization, although it remains to be confirmed that dMLF does in fact undergo phosphorylation (Sugano, 2008).
In this study it was observed that the dMLF-induced small-eye phenotype was suppressed by a half-dose reduction in the dCSN3 gene. These observations appear to be consistent with the report describing that knockdown of CSN3 rescued hMLF1-induced growth inhibition of NIH 3T3 cells (Yoneda-Kato, 2005). It has been reported that amino acids 50-125 of hMLF1 are required for CSN3-binding (Yoneda-Kato, 2005). In the case of Drosophila, amino acid region 1-202 is necessary for the interaction between dMLF and dCSN3. Therefore, in both mammals and Drosophila, the C-terminal region of MLF appears to be dispensable for CSN3 binding (Sugano, 2008).
This study has shown that dMLF interacts genetically with cyclin E, and dCSN3 was identified as a dMLF-interacting protein. GST pull-down assays revealed that dCSN3 interacts with dMLF via its PCI domain. It has been reported that the C-terminal half of CSN1 and CSN2 encompassing the PCI domain is required for incorporation of the subunit into the CSN complex in mammals. It has also been suggested that the N-terminal part of CSN3 is not essential for binding to CSN1 and CSN2, in contrast to the PCI domain in the C-terminal part of CSN3. Furthermore, mutational analysis showed that PCI domains are important for assembly of the regulatory particle of the 26S proteasome in budding yeast. Thus the PCI domain may function as a structural scaffold to assemble the CSN complex and its dMLF binding may inhibit the integration of dCSN3. It is reported that a null mutation in csn4 results in a complete loss of the entire CSN complex in Drosophila, indicating that deletion of one subunit of the CSN complex may lead to disassembly of the entire complex. Therefore, it is possible that this might occur with masking of dCSN3 by dMLF. Multiple CSN subunits can be found in subcomplexes of molecular mass lower than the intact 500 kDa CSN complex, and individual CSN subunits are also linked through protein-protein interactions to a broad range of cellular processes. Genetic analyses of flies expressing dMLF revealed a genetic interaction with cyclin E, implying negative regulation of cyclin E functions in vivo. It has been shown previously that the CSN regulates degradation of cyclin E in Drosophila. It is therefore hypothesize that the proper function of CSN requires regulation of integration of the CSN complex by dMLF binding to CSN3 (Sugano, 2008).
To examine the involvement of cell death, flies expressing dMLF were crossed with others expressing an apoptosis inhibitor protein, p35. The small-eye phenotype induced by dMLF overexpression was not suppressed by expression of p35. It is therefore suggested that the phenotype is not due to induction of apoptosis. However, the dMLF-induced small-eye phenotype was enhanced by expression of p35. There are no clear interpretations to these observations at the moment. Further analyses are necessary to address this point (Sugano, 2008).
Myeloid leukemia factor 1 (MLF1) was first identified as part of a leukemic fusion protein produced by a chromosomal translocation, and MLF family proteins are present in many animals. In mammalian cells, MLF1 has been described as mainly cytoplasmic, but in Drosophila, one of the dMLF isoforms (dMLFA) localized mainly in the nucleus while the other isoform (dMLFB), that appears to be produced by the alternative splicing, displays both nuclear and cytoplasmic localization. To investigate the difference in subcellular localization between MLF family members, the subcellular localization of deletion mutants of dMLFA isoform was examined. The analyses showed that the C-terminal 40 amino acid region of dMLFA is necessary and sufficient for nuclear localization. Based on amino acid sequences, it is hypothesized that two nuclear localization signals (NLSs) are present within the region. Site-directed mutagenesis of critical residues within the two putative NLSs leads to loss of nuclear localization, suggesting that both NLS motifs are necessary for nuclear localization (Sugano, 2007).
In human, the myeloid leukemia factor 1 (hMLF1) has been shown to be involved in acute leukemia, and mlf related genes are present in many animals. Despite their extensive representation and their good conservation, very little is understood about their function. In Drosophila, dMLF physically interacts with both the transcription regulatory factor DREF and an antagonist of the Hedgehog pathway, Suppressor of Fused, whose over-expression in the fly suppresses the toxicity induced by polyglutamine. No connection between these data has, however, been established. This study shows that dmlf is widely and dynamically expressed during fly development. The first dmlf mutants were isolated and analyzed: embryos lacking maternal dmlf product have a low viability with no specific defect, and dmlf mutant adults display weak phenotypes. dMLF subcellular localization in the fly and cultured cells was monitored. Although generally nuclear, dMLF can also be cytoplasmic, depending on the developmental context. Furthermore, two differently spliced variants of dMLF display differential subcellular localization, allowing the identification of regions of dMLF potentially important for its localization. Finally, it was demonstrated that dMLF can act developmentally and postdevelopmentally to suppress neurodegeneration and premature aging in a cerebellar ataxia model (Martin-Lanneree, 2006).
In Drosophila and vertebrates, Suppressor of fused [Su(fu)] proteins act as negative regulators of the Gli/Ci transcription factors, which mediate the transcriptional effects of Hh signalling. This study sought novel partners of Su(fu) in fly using the two-hybrid method. Most of the Su(fu) interactors thus identified are (or are likely to be) able to enter the nucleus. This study focused on one of these putative partners, dMLF, which resembles vertebrate myelodysplasia/myeloid leukaemia factors 1 and 2. dMLF binds specifically to Su(fu) in vitro and in vivo. Using a novel anti-dMLF antibody, it was shown, that dMLF is a nuclear, chromosome-associated protein. A dMLF transgene was overexpressed in the fly using an inducible expression system. dMLF over-expression disrupts normal development, leading to either a lethal phenotype or adult structural defects associated with apoptosis and increased DNA synthesis. Furthermore, the dMLF-induced eye phenotype is enhanced by the loss of Su(fu) function, suggesting a genetic interaction between Su(fu) and dMLF. It is proposed that Su(fu) and dMLF act together at the transcriptional level to coordinate patterning and proliferation during development (Fouix, 2003).
Organogenesis involves cell proliferation followed by complex determination and differentiation events that are intricately controlled in time and space. The instructions for these different steps are, to a large degree, implicit in the gene expression profiles of the cells that partake in organogenesis. Combining fluorescence-activated cell sorting and SAGE, genomic expression patterns were analyzed in the developing eye of Drosophila. Genomic activity changes as cells pass from an uncommitted proliferating progenitor state through determination and differentiation steps toward a specialized cell fate. Analysis of the upstream sequences of genes specifically expressed during the proliferation phase of eye development implicates the transcription factor DREF and its inhibitor dMLF in the control of cell growth in this organ (Jasper, 2002).
To monitor the genome-wide gene transcription profiles associated with the different phases of eye development, defined subsets of cells isolated from eye imaginal discs were analyzed. These groups of cells were distinguished by the specific expression of green fluorescent protein (GFP) under the control of the Gal4-UAS system. Three distinct cell populations were purified from dissected third instar eye imaginal discs by fluorescence-activated cell sorting (FACS) of trypsin-dissociated cells. The first pool (referred to as GMR−; see below) contained cells from the region before the MF and represents the pluripotent, proliferative stage of eye development. The second pool of cells (GMR+) includes cells in the morphogenetic furrow, the second mitotic wave, as well as cells engaged in differentiation and patterning programs. Expression of GFP under the control of the GMR-Gal4 driver is restricted to the second pool of cells and can be used to distinguish the two cell populations. The third cell pool that was isolated represents a late stage of organogenesis, a group of already determined cells that are undergoing differentiation into specialized photoreceptor and cone cells. These cells were sorted based on GFP expression under the control of the sevenless enhancer/promoter (using sevGal4), which is transiently active in R3/R4 photoreceptor precursors and whose expression during ommatidial development becomes confined to R1, R6, R7, and the cone cells (Jasper, 2002).
The transcriptome of the three cell pools was quantitatively analyzed by serial analysis of gene expression (SAGE). SAGE was chosen as a method, since it allows accurate genome-wide quantification of mRNA levels in minute amounts of cellular material, without the need for amplification of the RNA pool by strategies that are prone to distortion of relative RNA representation. SAGE libraries were constructed from the sorted GMR−, GMR+, and Sev+ cell pools. Close to 20,000 tags were sequenced from each library, generating expression data for 4,279 different genes (tags present twice or more times in the 57,441 tags of the combined libraries) (Jasper, 2002).
SAGE tags were annotated using recently described databases and by BLAST searches against the Drosophila genome. Similar to results in the analysis of embryonic expression patterns, about 20% of the identified tags had no match to the Drosophila genome. Six percent had multiple matches and 4% matched the genome in regions without predicted genes. A large fraction (34% of all tags) matched the genome 3' to a predicted gene, indicating alternative 3' end processing and incomplete annotation of the genome sequence (Jasper, 2002).
The majority of tags appeared at comparable frequency in the three libraries, indicating constant expression levels of the corresponding genes. A tag derived from the transgene RNAs encoding GFP and Gal4 was abundant in the GMR+ and Sev+ libraries, while found only once in the GMR− library, illustrating the validity of the data and the purity of the sorted cell preparations. The SAGE data was confirmed by performing RNA in situ hybridization on eye imaginal discs for selected genes that were differentially represented in the different libraries. These experiments corroborated the differential expression of virtually all genes for which an informative signal could be obtained (28 out of 29). For many other genes, the data matched earlier reports of specific expression in the analyzed cell populations (e.g., toy, capt, sdk, lz; mdelta, B-H1 and ru (Jasper, 2002).
Classification of the differentially expressed genes into functional categories based on published data or on sequence similarities provides an overview of the general changes in cellular functions as cells transit from proliferation to the patterning and differentiation stages of organ development. Not surprisingly, many of the genes that are downregulated upon cessation of cell proliferation and at the onset of differentiation encode proteins involved in DNA replication and cell proliferation. These include genes specifically induced at the transition from G1 to S phase of the cell cycle, such as pcna (mus209) and ribonucleoside-diphosphate reductase (rnrL), as well as the replication licensing factors mcm2 and mcm5 (Jasper, 2002).
Other genes that are expressed at elevated levels in the proliferating cells of the GMR− pool encode products with functions in metabolism and the regulation of protein synthesis. This is consistent with the reported deleterious effect of mutations in some of these genes on cell proliferation and growth, such as for und, eIF4A, Asp-tRNA synthetase, bellwether, and bonsai. The similar expression patterns of a group of proteasome subunits can be rationalized by the high degree of regulated protein turnover in proliferating tissues. Altogether, 93 genes were identified that are upregulated significantly in the GMR− pool and that have tentatively assigned functions in cell growth and proliferation (Jasper, 2002).
When eye imaginal disc cells enter the MF, they transit from the growth phase to the patterning phase of organogenesis and initiate specific differentiation programs. Consistent with this change of function, the cells posterior to the furrow upregulate specific cell adhesion and signal transduction molecules. These include proteins involved in the regulation of cellular adhesiveness and the cortical cytoskeleton such as Paxillin, Spectrin, Ankyrin, and α-Actinin, which show elevated expression levels in the GMR+ and Sev+ libraries. It is conceivable that such proteins mediate dynamically changing cell contacts as ommatidial clusters undergo rotation movements within the plane of the epithelium. Furthermore, differentiation markers such as genes involved in synaptic organization and axonal pathfinding begin to be upregulated in the GMR+ library and are yet more highly represented in the Sev+ library. Many of the mRNAs that are most prevalent in the latter library are involved in neuronal differentiation and signaling. Genes that are selectively transcribed in differentiating photoreceptors, as identified by their exclusive expression in the Sev+ cell population, include the cell type-specific transcription factors rough, lozenge, BarH1, and E(spl)mdelta. rough encodes a homeodomain transcription factor expressed in photoreceptors R2, R3, R4, and R5, whereas lozenge encodes a Runt domain transcription factor known to be expressed in cone cells and in all photoreceptors that arise from the second mitotic wave (R1, R6, and R7). The homeodomain transcription factor BarH1 is specifically expressed in R1 and R6 cells. E(spl)mdelta is a bHLH transcription factor expressed in R4 and R7. These transcription factors act in combination with specific signaling events to direct cell fate decisions within ommatidial clusters. The expression of the AT-rich interaction domain (ARID) transcription factor Retained, in a subset of photoreceptors as identified in this study, might contribute to this combinatorial genetic control of cell specification (Jasper, 2002).
In summary, the group of genes that was identified by SAGE to be specifically expressed in the differentiating cells of the eye imaginal disc overlaps to a significant degree with the regulators of photoreceptor differentiation previously identified by genetic means. This underscores the reliability of the method and supports the notion that genes that were designated as differentiation specific by SAGE, but have not yet been characterized genetically, may make important contributions to eye development. A further analysis of these genes thus holds the promise of providing significant new insights into the molecular biology of retinal development (Jasper, 2002).
It was reasoned that the coordinated regulation of groups of genes at specific stages of organogenesis might correlate with the presence of similar regulatory sequence motifs in their promoter regions. To identify such putative cis-acting elements, an unbiased computational approach was employed that would identify nonrandom sequence patterns in sequences proximal to the transcription start site of coregulated genes. Such algorithms have been employed successfully to identify genetic regulatory networks in the yeast genome. The AlignACE server was used to screen for nonrandom patterns within 1,000 bp upstream of the transcription start site of a set of 23 coregulated growth-related genes as well as a set of 23 differentiation-specific genes. In this way, one DNA element (TATCGATA) was identified that occurs in the upstream regions of genes implicated in cell growth and proliferation ahead of the MF. This motif is identical to the DNA replication-related element (DRE). DREs, in combination with E2F-responsive elements, control expression of genes involved in DNA replication including pcna. DREF, the transcription factor that binds to DREs, acts as a regulator of DNA synthesis in the Drosophila eye imaginal disc and is expressed predominantly in proliferating cells of the eye disc. The AlignACE results were confirmed by searching for DREs in the upstream region of a larger group of GMR−-specific genes as well as in the 23 differentiation-specific genes used for the second AlignACE search. Strikingly, 14 of 41 tested GMR−-specific genes contain a perfect match and 10 more contain a sequence closely resembling the 8 bp consensus DRE sequence within 1,000 bp of their transcription start site. In many cases, DREs or DRE-related sequences are found clustered with other DREs or with consensus binding sequences for E2F, another cell cycle-promoting transcription factor. In contrast, only 1 out of 23 tested differentiation-specific genes contained a DRE in the examined promoter regions. However, in the upstream sequences of this group of genes, a different motif resembling the binding site for the transcription factor Glass was found frequently. Glass is required for photoreceptor differentiation and is expressed in all cells posterior to the MF (Jasper, 2002).
The prevalence of DREs in genes that are associated with the proliferative state of the GMR− cell population suggests that the transcription factor DREF, possibly in concert with E2F, regulates a genetic program of cellular proliferation and growth during the early stages of eye development. In such a scenario, the downregulation of genes containing DRE sequences in their promoter region in the cells in and behind the MF (represented by the GMR+ and Sev+ pools) is likely to be a consequence of a suppression of DREF activity. One mechanism to explain the downregulation of DREF activity in the MF involves a known inhibitor of DREF, myelodysplasia/myeloid leukemia factor (dmlf). As indicated by the increased presence of dMLF-derived SAGE tags in the GMR+ and Sev+ libraries, and confirmed by in situ hybridization, dMLF expression is specifically upregulated in the MF and to a lesser degree posterior to the MF, thus coincident with the proposed suppression of DREF activity. Induction of dmlf in the MF might thus limit DREF function when cells prepare for differentiation. To test this model, DREF was ectopically expressed in the cells behind the MF. Earlier reports suggested that DREF overexpression leads to increased DNA synthesis behind the MF. Additionally, a significant increase of mitotic cells in this area was found, as visualized by immunostaining for phosphorylated histone 3, a specific marker for mitotic cells. These data thus suggest a function of the DREF/dMLF system in the control of a cell growth and proliferation program during organogenesis (Jasper, 2002).
Intracellular inclusions of abnormally long polyglutamine tracts and neurotoxicity are the hallmarks of several hereditary neurodegenerative disorders, including Huntington's disease (HD). In Drosophila melanogaster, dMLF, an ortholog of human myeloid leukemia factors, hMLF1 and hMLF2, suppressed polyglutamine toxicity and colocalized with the inclusions. In transfected primary rat neuronal cultures, dMLF and its orthologs reduced the morphological phenotypes and inclusions. Furthermore, dMLF reduced the recruitment of CBP and Hsp70 into the inclusions, both of which are among many essential proteins apparently trapped in the inclusions. These data suggest that a possible mechanism of suppression by dMLF is via the sequestration of polyglutamine oligomers or inclusions (Kim, 2005).
The toxicity of an abnormally long polyglutamine [poly(Q)] tract within specific proteins is the molecular lesion shared by Huntington's disease (HD) and several other hereditary neurodegenerative disorders. A genetic screen in Drosophila, devised to uncover genes that suppress poly(Q) toxicity, yielded a Drosophila homolog of human myeloid leukemia factor 1 (MLF1). Expression of the Drosophila homolog (dMLF) ameliorates the toxicity of poly(Q) expressed in the eye and central nervous system. In the retina, whether endogenously or ectopically expressed, dMLF co-localized with aggregates, suggesting that dMLF alone, or through an intermediary molecular partner, may suppress toxicity by sequestering poly(Q) and/or its aggregates (Kazemi-Esfarjani, 2002).
The transcription factor DREF regulates proliferation-related genes in Drosophila. With two-hybrid screening using DREF as a bait, a clone encoding a protein homologous to human myelodysplasia/myeloid leukemia factor 1 (hMLF1) was obtained. The protein was termed Drosophila MLF (dMLF); it consists of a polypeptide of 309 amino acid residues, whose sequence shares 23.1% identity with hMLF1. High conservation of 54.2% identity over 107 amino acids was found in the central region. The dMLF gene was mapped to 52D on the second chromosome by in situ hybridization. Interaction between dMLF and DREF in vitro could be confirmed by glutathione S-transferase pull-down assay, with the conserved central region appearing to play an important role in this. Northern blot hybridization analysis revealed dMLF mRNA levels to be high in unfertilized eggs, early embryos, pupae and adult males, and relatively low in adult females and larvae. This fluctuation of mRNA during Drosophila development is similar to that observed for DREF mRNA, except in the pupa and adult male. Using a specific antibody against the dMLF, immunofluorescent staining of Drosophila Kc cells was performed, and a primarily cytoplasmic staining was obtained, whereas DREF localizes in the nucleus. However, dMLF protein contains a putative 14-3-3 binding motif involved in the subcellular localization of various regulatory molecules, and interaction with DREF could be regulated through this motif. The transgenic fly data suggesting the genetic interaction between DREF and dMLF support this possibility. Characterization of dMLF in the present study provides the molecular basis for analysis of its significance in Drosophila (Ohno, 2000).
Search PubMed for articles about Drosophila Mlf
Bras, S., Martin-Lanneree, S., Gobert, V., Auge, B., Breig, O., Sanial, M., Yamaguchi, M., Haenlin, M., Plessis, A. and Waltzer, L. (2012). Myeloid leukemia factor is a conserved regulator of RUNX transcription factor activity involved in hematopoiesis. Proc Natl Acad Sci U S A 109: 4986-4991. PubMed ID:22411814
Dyer, J. O., Dutta, A., Gogol, M., Weake, V. M., Dialynas, G., Wu, X., Seidel, C., Zhang, Y., Florens, L., Washburn, M. P., Abmayr, S. M. and Workman, J. L. (2017). Myeloid Leukemia Factor acts in a chaperone complex to regulate transcription factor stability and gene expression. J Mol Biol 429(13): 2093-2107. PubMed ID: 27984043
Fouix, S., Martin-Lanneree, S., Sanial, M., Morla, L., Lamour-Isnard, C. and Plessis, A. (2003). Over-expression of a novel nuclear interactor of Suppressor of fused, the Drosophila myelodysplasia/myeloid leukaemia factor, induces abnormal morphogenesis associated with increased apoptosis and DNA synthesis. Genes Cells 8: 897-911. PubMed ID:14622141
Jasper, H., et al. (2002). A genomic switch at the transition from cell proliferation to terminal differentiation in the Drosophila eye. Dev. Cell 3(4): 511-21. PubMed ID: 12408803
Kazemi-Esfarjani, P. and Benzer, S. (2002). Suppression of polyglutamine toxicity by a Drosophila homolog of myeloid leukemia factor 1. Hum Mol Genet 11: 2657-2672. PubMed ID:12354791
Kim, W. Y., Fayazi, Z., Bao, X., Higgins, D. and Kazemi-Esfarjani, P. (2005). Evidence for sequestration of polyglutamine inclusions by Drosophila myeloid leukemia factor. Mol Cell Neurosci 29: 536-544. PubMed ID:15936212
Martin-Lanneree, S., Lasbleiz, C., Sanial, M., Fouix, S., Besse, F., Tricoire, H. and Plessis, A. (2006). Characterization of the Drosophila myeloid leukemia factor. Genes Cells 11: 1317-1335. PubMed ID:17121541
Miller, M., Chen, A., Gobert, V., Auge, B., Beau, M., Burlet-Schiltz, O., Haenlin, M. and Waltzer, L. (2017). Control of RUNX-induced repression of Notch signaling by MLF and its partner DnaJ-1 during Drosophila hematopoiesis. PLoS Genet 13(7): e1006932. PubMed ID: 28742844
Ohno, K., Takahashi, Y., Hirose, F., Inoue, Y. H., Taguchi, O., Nishida, Y., Matsukage, A. and Yamaguchi, M. (2000). Characterization of a Drosophila homologue of the human myelodysplasia/myeloid leukemia factor (MLF). Gene 260: 133-143. PubMed ID:11137299
Rau, R. and Brown, P. (2009). Nucleophosmin (NPM1) mutations in adult and childhood acute myeloid leukaemia: towards definition of a new leukaemia entity. Hematol Oncol 27: 171-181. PubMed ID:19569254
Sugano, W. and Yamaguchi, M. (2007). Identification of novel nuclear localization signals of Drosophila myeloid leukemia factor. Cell Struct Funct 32: 163-169. PubMed ID:18159124
Sugano, W., Ohno, K., Yoneda-Kato, N., Kato, J. Y. and Yamaguchi, M. (2008). The myeloid leukemia factor interacts with COP9 signalosome subunit 3 in Drosophila melanogaster. FEBS J 275: 588-600. PubMed ID:18199288
Williams, J. H., Daly, L. N., Ingley, E., Beaumont, J. G., Tilbrook, P. A., Lalonde, J. P., Stillitano, J. P. and Klinken, S. P. (1999). HLS7, a hemopoietic lineage switch gene homologous to the leukemia-inducing gene MLF1. EMBO J 18: 5559-5566. PubMed ID:10523300
Winteringham, L. N., Kobelke, S., Williams, J. H., Ingley, E. and Klinken, S. P. (2004). Myeloid Leukemia Factor 1 inhibits erythropoietin-induced differentiation, cell cycle exit and p27Kip1 accumulation. Oncogene 23: 5105-5109. PubMed ID:15122318
Yoneda-Kato, N., Tomoda, K., Umehara, M., Arata, Y. and Kato, J. Y. (2005). Myeloid leukemia factor 1 regulates p53 by suppressing COP1 via COP9 signalosome subunit 3. EMBO J 24: 1739-1749. PubMed ID:15861129
date revised: 22 December 2017
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