Death regulator Nedd2-like caspase: Biological Overview | Evolutionary Homologs | Regulation | Developmental Biology | Effects of Mutation | References
Gene name - Death regulator Nedd2-like caspase

Synonyms - Dronc

Cytological map position - 67C4--5

Function - caspase

Keywords - programmed cell death, apoptosis

Symbol - Nc

FlyBase ID: FBgn0026404

Genetic map position -

Classification - p20 and p10 domains, Caspase (ICE-like protease)

Cellular location - cytoplasmic



NCBI links: Precomputed BLAST | Entrez Gene

Recent literature
Orme, M. H., et al. (2016). The unconventional myosin CRINKLED and its mammalian orthologue MYO7A regulate caspases in their signalling roles. Nat Commun 7: 10972. PubMed ID: 26960254
Summary:
Caspases provide vital links in non-apoptotic regulatory networks controlling inflammation, compensatory proliferation, morphology and cell migration. How caspases are activated under non-apoptotic conditions and process a selective set of substrates without killing the cell remain enigmatic. This study found that the Drosophila unconventional myosin Crinkled (Ck) selectively interacts with the initiator caspase DRONC and regulates some of its non-apoptotic functions. Loss of CK in the arista, border cells or proneural clusters of the wing imaginal discs affects DRONC-dependent patterning. The data indicate that CK acts as substrate adaptor, recruiting Shaggy46/GSK3-β to DRONC, thereby facilitating caspase-mediated cleavage and localized modulation of kinase activity. Similarly, the mammalian CK counterpart, MYO7A, binds to and impinges on CASPASE-8, revealing a new regulatory axis affecting receptor interacting protein kinase-1 (RIPK1)>CASPASE-8 signalling. Together, these results expose a conserved role for unconventional myosins in transducing caspase-dependent regulation of kinases, allowing them to take part in specific signalling events.

Lee, T. V., Kamber Kaya, H. E., Simin, R., Baehrecke, E. H. and Bergmann, A. (2016). The initiator caspase Dronc is subject of enhanced autophagy upon proteasome impairment in Drosophila. Cell Death Differ [Epub ahead of print]. PubMed ID: 27104928
Summary:
A major function of ubiquitylation is to deliver target proteins to the proteasome for degradation. In the apoptotic pathway in Drosophila, the inhibitor of apoptosis protein 1 (Diap1) regulates the activity of the initiator caspase Dronc (death regulator Nedd2-like caspase; caspase-9 ortholog) by ubiquitylation, supposedly targeting Dronc for degradation by the proteasome. Using a genetic approach, this study showed that Dronc protein fails to accumulate in epithelial cells with impaired proteasome function suggesting that it is not degraded by the proteasome, contrary to the expectation. Similarly, decreased autophagy, an alternative catabolic pathway, does not result in increased Dronc protein levels. However, combined impairment of the proteasome and autophagy triggers accumulation of Dronc protein levels suggesting that autophagy compensates for the loss of the proteasome with respect to Dronc turnover. Consistently, it was shown that loss of the proteasome enhances endogenous autophagy in epithelial cells. It is proposed that enhanced autophagy degrades Dronc if proteasome function is impaired.
Koerver, L., Melzer, J., Roca, E. A., Teichert, D., Glatter, T., Arama, E. and Broemer, M. (2016). The de-ubiquitylating enzyme DUBA is essential for spermatogenesis in Drosophila. Cell Death Differ[Epub ahead of print]. PubMed ID: 27518434
Summary:
De-ubiquitylating enzymes (DUBs) reverse protein ubiquitylation and thereby control essential cellular functions. A screen for a DUB that counteracts caspase ubiquitylation to regulate cell survival identified the Drosophila ovarian tumour-type DUB DUBA (CG6091). DUBA physically interact with the initiator caspase Death regulator Nedd2-like caspase (Dronc) and de-ubiquitylates it, thereby contributing to efficient inhibitor of apoptosis-antagonist-induced apoptosis in the fly eye. Searching also for non-apoptotic functions of DUBA, Duba-null mutants were found to be male sterile and display defects in spermatid individualisation, a process that depends on non-apoptotic caspase activity. Spermatids of DUBA-deficient flies showed reduced caspase activity and lack critical structures of the individualisation process. Biochemical characterisation revealed an obligate activation step of DUBA by phosphorylation. With genetic rescue experiments it was demonstrated that DUBA phosphorylation and catalytic activity are crucial in vivo for DUBA function in spermatogenesis. These results demonstrate for the first time the importance of de-ubiquitylation for fly spermatogenesis.
Kamber Kaya, H.E., Ditzel, M., Meier, P. and Bergmann, A. (2017). An inhibitory mono-ubiquitylation of the Drosophila initiator caspase Dronc functions in both apoptotic and non-apoptotic pathways. PLoS Genet 13: e1006438. PubMed ID: 28207763
Summary:
Apoptosis is an evolutionary conserved cell death mechanism, which requires activation of initiator and effector caspases. The Drosophila initiator caspase Dronc, the ortholog of mammalian Caspase-2 and Caspase-9, has an N-terminal CARD domain that recruits Dronc into the apoptosome for activation. In addition to its role in apoptosis, Dronc also has non-apoptotic functions such as compensatory proliferation. One mechanism to control the activation of Dronc is ubiquitylation. However, the mechanistic details of ubiquitylation of Dronc are less clear. For example, monomeric inactive Dronc is subject to non-degradative ubiquitylation in living cells, while ubiquitylation of active apoptosome-bound Dronc triggers its proteolytic degradation in apoptotic cells. This study examined the role of non-degradative ubiquitylation of Dronc in living cells in vivo, i.e. in the context of a multi-cellular organism. In vivo data suggest that in living cells Dronc is mono-ubiquitylated on Lys78 (K78) in its CARD domain. This ubiquitylation prevents activation of Dronc in the apoptosome and protects cells from apoptosis. Furthermore, K78 ubiquitylation plays an inhibitory role for non-apoptotic functions of Dronc. Further, not all of the non-apoptotic functions of Dronc require its catalytic activity. In conclusion, data demonstrate a mechanism whereby Dronc's apoptotic and non-apoptotic activities can be kept silenced in a non-degradative manner through a single ubiquitylation event in living cells.

Jo, J., Im, S. H., Babcock, D. T., Iyer, S. C., Gunawan, F., Cox, D. N. and Galko, M. J. (2017). Drosophila caspase activity is required independently of apoptosis to produce active TNF/Eiger during nociceptive sensitization. Cell Death Dis 8(5): e2786. PubMed ID: 28492538
Summary:
Tumor necrosis factor (TNF) signaling is required for inflammatory nociceptive (pain) sensitization in Drosophila and vertebrates. Nociceptive sensitization in Drosophila larvae following UV-induced tissue damage is accompanied by epidermal apoptosis and requires epidermal-derived TNF/Eiger and the initiator caspase, Dronc. In this study, apoptotic cell death and thermal nociceptive sensitization are genetically and procedurally separable in a Drosophila model of UV-induced nociceptive sensitization. Activation of epidermal Dronc induces TNF-dependent but effector caspase-independent nociceptive sensitization in the absence of UV. In addition, knockdown of Dronc attenuated nociceptive sensitization induced by full-length TNF/Eiger but not by a constitutively soluble form. UV irradiation induced TNF production in both in vitro and in vivo, but TNF secretion into hemolymph was not sufficient to induce thermal nociceptive sensitization. Downstream mediators of TNF-induced sensitization included two TNF receptor-associated factors, a p38 kinase, and the transcription factor nuclear factor kappa B. Finally, sensory neuron-specific microarray analysis revealed downstream TNF target genes induced during thermal nociceptive sensitization. One of these, enhancer of zeste (E(z)), functions downstream of TNF during thermal nociceptive sensitization. These findings suggest that an initiator caspase is involved in TNF processing/secretion during nociceptive sensitization, and that TNF activation leads to a specific downstream signaling cascade and gene transcription required for sensitization. These findings have implications for both the evolution of inflammatory caspase function following tissue damage signals and the action of TNF during sensitization in vertebrates.
Khan, C., Muliyil, S., Ayyub, C. and Rao, B. J. (2017). The initiator caspase Dronc plays a non-apoptotic role in promoting DNA damage signalling in D. melanogaster. J Cell Sci 130(18): 2984-2995. PubMed ID: 28751499
Summary:
The phosphorylation of the variant histone H2Ax (denoted gammaH2Ax; gammaH2Av in flies) constitutes an important signalling event in DNA damage sensing, ensuring effective repair by recruiting DNA repair machinery. In contrast, the gammaH2Av response has also been reported in dying cells, where it requires activation of caspase-activated DNases (CADs). Moreover, caspases are known to be required downstream of DNA damage for cell death execution. This study shows that the Drosophila initiator caspase Dronc acts as an upstream regulator of the DNA damage response (DDR) independently of executioner caspases by facilitating gammaH2Av signalling, possibly through a function that is not related to apoptosis. Such a gammaH2Av response is mediated by ATM rather than ATR, suggesting that Dronc function is required upstream of ATM. In contrast, the role of gammaH2Av in cell death requires effector caspases and is associated with fragmented nuclei. This study uncovers a novel function of Dronc in response to DNA damage aimed at promoting DDR via gammaH2Av signalling in intact nuclei. It is proposed that Dronc plays a dual role that can either initiate DDR or apoptosis depending upon its level and the required threshold of its activation in damaged cells.
BIOLOGICAL OVERVIEW

Drosophila Nedd2-like caspase, referred to here and in the literature as Dronc (Drosophila Nedd2-like caspase, not to be confused with Death related ced-3/Nedd2-like protein), is a caspase recruitment domain-containing Drosophila caspase that is expressed in a temporally and spatially restricted fashion during development. Dronc is the only fly caspase known to be regulated by the hormone ecdysone. Ectopic expression of dronc in the developing fly eye leads to increased cell death and an ablated eye phenotype that can be suppressed by halving the dosage of the genes in the H99 complex (reaper, hid, and grim) and enhanced by mutations in diap1 (thread). The dronc eye ablation phenotype can be suppressed by coexpression of the baculoviral caspase inhibitor p35. Dronc also interacts, both genetically and biochemically, with the CED-4/Apaf-1 fly homolog, Ark. Furthermore, extracts made from Ark homozygous mutant flies have reduced ability to process Dronc, showing that Ark is required for Dronc processing. Using the RNA interference technique, it has been shown that loss of Dronc function in early Drosophila embryos results in a dramatic decrease in cell death, indicating that Dronc is important for programmed cell death during embryogenesis. These results suggest that Dronc is a key caspase mediating programmed cell death in Drosophila (Quinn, 2000).

Caspases are cysteine proteases that act as central effectors of programmed cell death. These proteases are synthesized as precursor molecules that are processed in cells undergoing apoptosis to generate two subunits that fold into a tetrameric active enzyme conformation. In mammals, 14 caspases have been described thus far, which can be grouped into two classes based upon the length of their prodomain. Caspases containing a long prodomain, such as caspase-2, -8, -9, and -10, appear to be activated first by a proximity-induced autoprocessing mechanism involving clustering of procaspase molecules, often assisted by specific adaptor molecules. These caspases contain specific protein-protein interaction domains in the prodomain region that mediate their interaction with their respective adaptors or mediate dimerization of procaspase molecules. For example, caspase-2 and caspase-9 contain caspase recruitment domains (CARDs) in their prodomain, whereas caspase-8 and caspase-10 contain two copies of death effector domains (DEDs). The CARD in caspase-2 is required for homodimerization, whereas the CARD in caspase-9 interacts with the mammalian CED-4-like adaptor Apaf-1 (Drosophila homolog, Apaf-1-related-killer). Cytochrome c- and dATP-dependent oligomerization of Apaf-1, followed by interaction of oligomerized Apaf-1 with procaspase-9, results in proximity-induced activation of caspase-9. One of the DEDs in caspase-8 interacts with the DED in the adaptor FADD, a molecule that helps recruit procaspase-8 to activated death receptors of the tumor necrosis factor receptor family. Again, this adaptor-mediated recruitment of the procaspase molecules is believed to be sufficient for caspase activation. Once the caspases containing long prodomains are activated, they are believed to activate downstream caspases that lack specific protein-protein interaction domains, thereby initiating a cascade of caspase activation (Quinn, 2000 and references therein).

In Drosophila, three proteins, Reaper, Hid, and Grim, play critical roles in apoptosis. These proteins act upstream of caspase activation and appear to be required to counteract the caspase inhibitors Diap1 and Diap2, which are Drosophila homologs of the baculovirus inhibitor of apoptosis, IAP. In Drosophila, specific mutations in diap1 (thread) show increased cell death in the embryo, and Diap1 has been shown to bind to and inhibit the activity of Drosophila effector caspases. The Drosophila Apaf-1-related-killer (Ark) and a proapoptotic CED-9/Bcl-2 homolog, Debcl/Drob-1/dBorg-1, have been described. There are seven known caspases in Drosophila, including five published ones (Dcp-1, Dredd, Drice, Dronc, and Decay, and two unpublished ones (Damm and Strica; GenBankTM accession numbers AF240763 and AF242734, respectively). Dredd and Dronc contain long prodomains carrying DEDs and a CARD, respectively, suggesting that these two caspases may act as upstream caspases. Strica also contains a long prodomain, but it lacks any CARD/DED sequences. However, Dcp-1, Drice, Decay, and Damm lack long prodomains and are thus similar to downstream effector caspases in mammals. A dcp-1 mutation results in larval lethality and melanotic tumors. Additionally, dcp-1 mutants show a defect in transfer of nurse cell cytoplasmic contents to developing oocytes, suggesting that dcp-1 may also be required for Drosophila oogenesis. Because no mutants for other Drosophila caspases are currently available, their precise functions remain unknown. However, a number of indirect observations point to a role for other Drosophila caspases in apoptosis in vivo. For example, dredd mRNA accumulates in embryonic cells undergoing programmed cell death; in nurse cells in the ovary at a time that coincides with nurse cell death, dronc mRNA, although widely expressed during development, is up-regulated by ecdysone in larval salivary glands and midgut before histolysis of these tissues. jAntibody depletion experiments suggest that Drice is required for apoptotic activity in the S2 Drosophila cell line. Furthermore, a deficiency uncovering dredd dominantly suppresses the ablated eye phenotype due to ectopic expression of rpr, hid, or grim, and a mini-gene of dredd reverses this suppression, showing that dredd is important for PCD in vivo (Quinn, 2000 and references therein).

Overexpression of Dronc induces cell death in mammalian cells (Dorstyn, 1999). In two recent studies (Meier, 2000 and Hawkins, 2000), it has been shown that ectopic expression of dronc promotes apoptosis in the developing Drosophila eye that can be suppressed by co-expression of diap1. Furthermore, in yeast, Diap1 inhibits Dronc activity, and this inhibition is abrogated by co-expression of Hid or Grim (Hawkins, 2000). Diap1 binds to the prodomain of Dronc, and, consistent with this, expression of a truncated version of Dronc lacking the prodomain results in a more severely ablated eye phenotype that can not be rescued by co-expression of Diap1 (Meier, 2000). These studies also show that a mutated version of dronc (containing a mutation in the caspase active site) acts in a dominant negative manner to suppress rpr- and hid-induced cell death (Meier, 2000). Likewise, a deficiency removing the dronc gene is able to dominantly suppress rpr- and hid-induced cell death in the eye (Meier, 2000), showing that Dronc mediates cell death by Rpr and Hid. In addition, these studies showed that Dronc associates with the effector caspase Drice and is able to process Drice to the active form (Meier, 2000 and Hawkins, 2000). Ectopic expression of dronc at various developmental stages results in apoptosis. The dronc eye ablation phenotype can also be blocked by co-expression of the baculoviral caspase inhibitor p35. Confirming these genetic interactions, Dronc can form complexes with Diap1, Grim, Ark, and P35; however, the interaction between Dronc and Grim or P35 is indirect. Because a direct binding between Dronc and P35 could not be demonstrated in vitro, it is likely that P35 interacts with and inhibits a downstream caspase rather than Dronc itself. One possible candidate is Drice, which has been shown to interact with both P35 (19) and Dronc (Meier, 2000), or Dcp-1, which can cleave P35. Ark is required for Dronc activation because Dronc is poorly processed in extracts from Ark homozygous mutant flies. Because specific dronc mutants are currently unavailable, the technique of RNA interference (RNAi) was used to ablate dronc mRNA in embryos. Dronc is shown to be essential for cell death during embryogenesis and these results suggest a central function for Dronc in the cell death effector machinery in Drosophila (Quinn, 2000 and references therein).

Based on homology and the ability of Dronc to form a complex with Ark, Dronc is expected to be a functional homolog of CED-3/caspase-9. Therefore, Dronc is expected to be downstream of Ark and the proteins of the H99 complex, which are known to induce PCD by activating caspases. Consistent with this, a dronc deficiency or expression of the dominant negative dronc mutant is able to suppress the ablated eye phenotype of GMR-hid and GMR-rpr (Meier, 2000; Hawkins, 2000 and Quinn, 2000). Because overexpression of upstream caspases generally results in autoactivation, ectopic expression of dronc was expected to be epistatic to (downstream of) the H99 genes and Ark. However, halving the dosage of the H99 genes or Ark suppresses the GMR-dronc eye phenotype, suggesting that the H99 genes and Ark are rate-limiting for dronc function (Quinn, 2000). This may be explained by the possibility that Dronc, when overexpressed as a zymogen, is not able to self-activate very efficiently and may therefore be dependent on the dosage of upstream activating genes. Another possibility is that the suppression of GMR-dronc by halving the dosage of the H99 genes may be a result of a feedback amplification loop between active caspases and Rpr, Hid, and Grim (Quinn, 2000 and references therein).

Consistent with the genetic interaction, Dronc forms a complex with the H99 gene product Grim when co-expressed in cells. However, this interaction is not direct and may occur through Diap1, which can bind to Dronc and to Grim (Meier, 2000; Hawkins, 2000 and Quinn, 2000). The significance of the in vivo interaction between Grim and Dronc is unclear and requires further investigation. As a CED-3/caspase-9 homolog, activation of Dronc is expected to require Ark, and, consistent with this, Dronc and Ark form a complex in SL2 cells. A complex of Ark and Dronc has also been observed in 293T cells that results in generation of the cleaved, active form of Dronc. Ark mutant extracts are defective in their ability to generate the cleaved active form of Dronc and have lower levels of active caspases. These results, together with genetic data, suggest that Dronc is likely to be a functional homolog of CED-3/caspase-9 because it is activated by Ark, the CED-4/Apaf-1 homolog. Furthermore, the amino-terminal region of Ark containing the CARD and CED-4 homology domain is sufficient for Dronc binding (Quinn, 2000).

The Drosophila apoptosis inhibitor Diap1 inhibits the activity of Drice and Dcp-1 and is antagonized by Rpr, Hid, or Grim. The data showing a dose-dependent enhancement of GMR-Dronc by diap1 mutations and that Dronc and Diap1 form a complex, are consistent with Diap1 also acting as an inhibitor of Dronc. Diap1 and Dronc interact genetically and biochemically and the prodomain of Dronc is required for the Diap1 interaction (Meier, 2000). Expression of diap1 or diap2 (to a lesser extent) is able to suppress the GMR-dronc phenotype, indicating that Diap2 as well as Diap1 can prevent Dronc-mediated cell killing. However, because a diap2 deficiency does not show a dominant enhancement of GMR-dronc, and Diap2 does not form a complex with Dronc, it is likely that the suppression of GMR-Dronc by GMR-Diap2 is indirect, perhaps via the inhibition of downstream caspases. The genetic and biochemical observations for a role for Diap1, but not Diap2, in suppressing Dronc function are consistent with previous studies showing that diap1 and diap2 function differently in inhibiting cell death. Halving the dosage of diap1, but not diap2, enhances rpr-, hid-, or grim-induced cell death, whereas overexpression of diap1 or diap2 can inhibit rpr- or hid-induced death, but only overexpression of diap1 can inhibit grim-induced cell death. Additional studies are required to further explore the precise roles of Diap1 and Diap2 in the Drosophila cell death pathway (Quinn, 2000).

In summary, Dronc is essential for cell death in early embryos and ectopic expression of Dronc can induce cell death in flies. Furthermore, Dronc is likely to be a functional homolog of CED-3/caspase-9 in flies. The data showing genetic and physical interactions between Dronc and P35, Grim, Ark, and Diap1 provide a framework for further investigation of the PCD pathway in flies (Quinn, 2000).

Extracellular reactive oxygen species drive apoptosis-induced proliferation via Drosophila macrophages

Apoptosis-induced proliferation (AiP) is a compensatory mechanism to maintain tissue size and morphology following unexpected cell loss during normal development, and may also be a contributing factor to cancer and drug resistance. In apoptotic cells, caspase-initiated signaling cascades lead to the downstream production of mitogenic factors and the proliferation of neighboring surviving cells. In epithelial cells of Drosophila imaginal discs, the Caspase-9 ortholog Dronc drives AiP via activation of Jun N-terminal kinase (JNK); however, the specific mechanisms of JNK activation remain unknown. This study shows that caspase-induced activation of JNK during AiP depends on an inflammatory response. This is mediated by extracellular reactive oxygen species (ROSs) generated by the NADPH oxidase Duox in epithelial disc cells. Extracellular ROSs activate Drosophila macrophages (hemocytes), which in turn trigger JNK activity in epithelial cells by signaling through the tumor necrosis factor (TNF) ortholog Eiger. It is proposed that in an immortalized ('undead') model of AiP, in which the activity of the effector caspases is blocked, signaling back and forth between epithelial disc cells and hemocytes by extracellular ROSs and TNF/Eiger drives overgrowth of the disc epithelium. These data illustrate a bidirectional cell-cell communication pathway with implication for tissue repair, regeneration, and cancer (Fogarty, 2016).

The role of ROSs as a regulated form of redox signaling in damage detection and damage response is becoming increasingly clear. This study has shown that in Drosophila, extracellular ROSs generated by the NADPH oxidase Duox drive compensatory proliferation and overgrowth following hid-induced activation of the initiator caspase Dronc in developing epithelial tissues. At least one consequence of ROS production is the activation of hemocytes at undead epithelial disc tissue. Furthermore, the work implies that extracellular ROS and hemocytes are part of the feedback amplification loop between Hid, Dronc, and JNK that occurs during stress-induced apoptosis. Finally, hemocytes release the TNF ligand Eiger, which promotes JNK activation in epithelial disc cells (Fogarty, 2016).

This work helps to understand why JNK activation occurs mostly in apoptotic/undead cells but occasionally also in neighboring surviving cells. Because the data indicate that hemocytes trigger JNK activation in epithelial cells, the location of hemocytes on the imaginal discs determines which epithelial cells receive the signal for JNK activation. Nevertheless, the possibility is not excluded that there is also an autonomous manner of Dronc-induced JNK activation in undead/apoptotic cells (Fogarty, 2016).

In the context of apoptosis, hemocytes engulf and degrade dying cells. However, there is no evidence that hemocytes have this role in the undead AiP model. No Caspase-3 (CC3) material is observed in hemocytes attached to undead tissue. Therefore, the role of hemocytes in driving proliferation is less clear and likely context dependent. In Drosophila embryos, hemocytes are required for epidermal wound healing, but this is a nonproliferative process. With respect to tumor models in Drosophila, much of the research to date has focused on the tumor-suppressing role of hemocytes and the innate immune response. However, a few reports have implicated hemocytes as tumor promoters in a neoplastic tumor model. Consistently, in the undead model of AiP, this study found that hemocytes have an overgrowth- and tumor-promoting role. Therefore, the state of the damaged tissue and the signals produced by the epithelium may have differential effects on hemocyte response (Fogarty, 2016).

In a recent study, ROSs were found to be required for tissue repair of wing imaginal discs in a regenerative (p35-independent) model of AiP, consistent with the current work. Although a role of hemocytes was not investigated in this study, it should be noted that p35-independent AiP models do not cause overgrowth, whereas undead ones such as the ey>hid-p35 AiP model do. It is therefore possible that ROSs in p35-independent AiP models are necessary for tissue repair independent of hemocytes, whereas ROSs in conjunction with ROS-activated hemocytes in undead models mediate the overgrowth of the affected tissue. Future work will clarify the overgrowth-promoting function of hemocytes. These considerations are reminiscent of mammalian systems, where many solid tumors are known to host alternatively activated (M2) tumor-associated macrophages, which promote tumor growth and are associated with a poor prognosis (Fogarty, 2016).

Because tumors are considered 'wounds that do not heal', the undead model of AiP is seen as a tool to probe the dynamic interactions and intercellular signaling events that occur in the chronic wound microenvironment. Future studies will investigate the specific mechanisms of hemocyte-induced growth and the tumor-promoting role of inflammation in Drosophila as well as roles of additional tissue types, such as the fat body, on modulating tumorous growth (Fogarty, 2016).


GENE STRUCTURE

cDNA clone length - 2096 bases

Bases in 5' UTR - 368

Exons - 2

Bases in 3' UTR - 374


PROTEIN STRUCTURE

Amino Acids - 450

Structural Domains

To identify CARD-containing molecules, the GenBank database was searched by using the prodomain of Nedd2 (mouse caspase-2). By using the TBLASTN program, a Drosophila EST was identified with a small ORF that shares 29% sequence identity with the caspase-2 prodomain over a 88-aa stretch. This EST belongs to a cluster of 11 ESTs in the Berkeley Fly Database. Sequencing of two independent cDNA clones revealed the presence of a complete ORF for a caspase-like molecule that was named DRONC (for Drosophila Nedd2-like caspase). In vitro translation of mRNA generated from dronc cDNA produced a 50-kDa protein consistent with the expected size. Over the entire length of the protein, DRONC shares 25% identity (40% similarity) with caspase-2. The region downstream of the prodomain, which encodes the two subunits of DRONC, shares highest homology (27%-28% identity, 44%-48% similarity) with all CPP32-like caspases, including caspase-3, -7, -8, -9, -10, and CED-3. Interestingly, DRONC shares <20% identity with the three known Drosophila caspases. The putative prodomain of DRONC contains a CARD that is similar to the CARDs of caspase-1, -2, -9, and CED-3. A unique feature of DRONC is the sequence PFCRG that encompasses the catalytic Cys (Cys-318) residue, which is distinct from the QAC(R/Q/G)(G/E) sequence found in all other known caspases (Dorstyn, 1999).

DRONC does not contain a typical caspase active site pentapeptide QAC(R/Q/G) (G/E) but instead has the novel sequence PFCRG. Based on the X-ray crystal structure of human caspase-1, the glutamine at position 1 of the pentapeptide forms part of the substrate-binding pocket. A change at this position may therefore indicate that DRONC has a different substrate specificity from that of classical caspases. Although the physiological cellular substrate(s) for DRONC have yet to be determined, it may be of note that DRONC cleaves three ascribed caspase substrates, drICE, lamin DmO and DREP-1, in an in vitro assay (Meier, 2000).


Death regulator Nedd2-like caspase: Evolutionary Homologs | Regulation | Developmental Biology | Effects of Mutation | References

date revised: 20 October 2001

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