Interactions of mammalian Basigin is reviewed in the following article, which is freely available online:
CD147, also known as extracellular matrix metalloproteinase inducer, is a regulator of matrix metalloproteinase production and also serves as a signaling receptor for extracellular cyclophilins. Cell surface expression of CD147 is sensitive to cyclophilin-binding drug cyclosporin A, suggesting involvement of a cyclophilin in the regulation of intracellular transport of CD147. This report identifies this cyclophilin as cyclophilin 60 (Cyp60), a distinct member of the cyclophilin family of proteins. CD147 co-immunoprecipitates with Cyp60, and confocal immunofluorescent microscopy revealed intracellular co-localization of Cyp60 and CD147. This interaction with Cyp60 involves proline 211 of CD147, which was shown previously to be critical for interaction between CD147 and another cyclophilin, cyclophilin A, in solution. Mutation of this proline residue abrogates co-immunoprecipitation of CD147 and Cyp60 and reduces surface expression of CD147 on the plasma membrane. Suppression of Cyp60 expression using RNA interference had an effect similar to that of cyclosporin A: reduction of cell surface expression of CD147. These results suggest that Cyp60 plays an important role in the translocation of CD147 to the cell surface. Therefore, Cyp60 may present a novel target for therapeutic interventions in diseases where CD147 functions as a pathogenic factor, such as cancer, human immunodeficiency virus infection, or rheumatoid arthritis (Pushkarsky, 2005).
CD147, also known as extracellular matrix metalloproteinase inducer, is a regulator of matrix metalloproteinase production and serves as a signaling receptor for extracellular cyclophilins. The cell surface expression of CD147 is regulated by cyclophilins via the transmembrane domain of CD147. Solution binding experiments demonstrated that the transmembrane domain was both necessary and sufficient for CD147 binding to cyclophilin A (CypA). Treatment with cyclosporin A significantly reduces surface expression of CD147 and of CD8-CD147 fusion protein carrying the extracellular domain of CD8 fused to the transmembrane and cytoplasmic domains of CD147, but does not affect expression of CD8. Peptide binding studies demonstrated specific interaction between CypA and the proline-containing peptide from the CD147 transmembrane domain. Mutation of this proline residue reduces binding of CD147-derived peptides to CypA and also diminishes transport of CD147 to the plasma membrane without reducing the total level of CD147 expression. These results suggest involvement of a cyclophilin-related protein in CD147 cell surface expression and provide molecular details for regulation of CD147 trafficking by cyclophilins (Yurchenko, 2005).
CD147, a type I integral membrane protein of the immunoglobulin superfamily, exhibits reversed polarity in retinal pigment epithelium (RPE). CD147 is apical in RPE in contrast to its basolateral localization in extraocular epithelia. This stimulated an interest in understanding the basolateral sorting signals of CD147 in prototypic Madin-Darby canine kidney (MDCK) cells. The cytoplasmic domain of CD147 has basolateral sorting information but is devoid of well-characterized basolateral signals, such as tyrosine and di-leucine motifs. Hence, systematic site-directed mutagenesis was carried out to delineate basolateral targeting information in CD147. This detailed analysis identified a single leucine (252) as the basolateral targeting motif in the cytoplasmic tail of CD147. Four amino acids (243-246) N-terminal to leucine 252 are also critical basolateral determinants of CD147, because deletion of these amino acids leads to mistargeting of CD147 to the apical membranes. The involvement of adaptor complex 1B (AP1B) in the basolateral trafficking of CD147 was ruled out, because LLC-PK1 cells lacking AP1B, target CD147 basolaterally. At variance with MDCK cells, the human RPE cell line ARPE-19 does not distinguish between CD147 (WT) and CD147 with leucine 252 mutated to alanine and targets both proteins apically. Thus, this study identifies an atypical basolateral motif of CD147, which comprises a single leucine and is not recognized by RPE cells. This unusual basolateral sorting signal will be useful in unraveling the specialized sorting machinery of RPE cells (Deora, 2004).
Proton-coupled monocarboxylate transporters (MCT) MCT1, MCT3, and MCT4 form heterodimeric complexes with the cell surface glycoprotein CD147 and exhibit tissue-specific polarized distributions that are essential for maintaining lactate and pH homeostasis. In the parenchymal epithelia of kidney, thyroid, and liver, MCT/CD147 heterocomplexes are localized in the basolateral membrane where they transport lactate out of or into the cell depending on metabolic conditions. A unique distribution of lactate transporters is found in the retinal pigment epithelium (RPE), which regulates lactate levels of the outer retina. In RPE, MCT1/CD147 is polarized to the apical membrane and MCT3/CD147 to the basolateral membrane. The mechanisms responsible for tissue-specific polarized distribution of MCTs are unknown. This study demonstrates that CD147 carries sorting information for polarized targeting of the MCT1/CD147 hetero-complexes in kidney and RPE cells. In contrast, MCT3 and MCT4 harbor dominant sorting information that cotargets CD147 to the basolateral membrane in both epithelia. RNA interference experiments show that MCT1 promotes CD147 maturation. These results open a unique paradigm to study the molecular basis of tissue-specific polarity (Deora, 2005).
Cell surface CD147 shows remarkable variations in size (31-65 kDa) because of heterogeneous N-glycosylation, with the most highly glycosylated forms functioning to induce matrix metalloproteinase (MMP) production. All three CD147 N-glycosylation sites make similar contributions to both high and low glycoforms (HG- and LG-CD147). l-Phytohemagglutinin lectin binding and swainsonine inhibition experiments indicated that HG-CD147 contains N-acetylglucosaminyltransferase V-catalyzed, beta1,6-branched, polylactosamine-type sugars, which account for its excess size. Therefore, CD147, which is itself elevated on invasive tumor cells, may make a major contribution to the abundance of beta1,6-branched polylactosamine sugars that appear on invasive tumor cells. Caveolin-1 associates with CD147, thus inhibiting CD147 self-aggregation and MMP induction. This study shows that caveolin-1 associates with LG-CD147 and restricts the biosynthetic conversion of LG-CD147 to HG-CD147. In addition, HG-CD147 (but not LG-CD147) was preferentially captured as a multimer after treatment of cells with a homobifunctional cross-linking agent and was exclusively recognized by monoclonal antibody AAA6, a reagent that selectively recognizes self-associated CD147 and inhibits CD147-mediated MMP induction. In conclusion, this study has (1) determined the biochemical basis for the unusual size variation in CD147, (2) established that CD147 is a major carrier of beta1,6-branched polylactosamine sugars on tumor cells, and (3) determined that caveolin-1 can inhibit the conversion of LG-CD147 to HG-CD147. Because it is HG-CD147 that self-aggregates and stimulates MMP induction, a mechanism has been found to explain how caveolin-1 inhibits these processes. These results help explain the previously established tumor suppressor functions of caveolin-1 (Tang, 2004).
Matrix metalloproteinases (MMPs) are endopeptidases that play pivotal roles in promoting tumor disease progression, including tumor angiogenesis. In many solid tumors, MMP expression can be attributed to tumor stromal cells and is partially regulated by tumor-stroma interactions via tumor cell-associated extracellular matrix metalloproteinase inducer (EMMPRIN). The role of EMMPRIN during tumor angiogenesis and growth was explored by modulating EMMPRIN expression and activity using recombinant DNA engineering and neutralizing antibodies. In human breast cancer cells, changes in EMMPRIN expression influences vascular endothelial growth factor (VEGF) production at both RNA and protein levels. In coculture of tumor cells and fibroblasts mimicking tumor-stroma interactions, VEGF expression is induced in an EMMPRIN- and MMP-dependent fashion, and is further enhanced by overexpressing EMMPRIN. Conversely, VEGF expression is inhibited by suppressing EMMPRIN expression in tumor cells, by neutralizing EMMPRIN activity, or by inhibiting MMPs. In vivo, EMMPRIN overexpression stimulates tumor angiogenesis and growth; both are significantly inhibited by antisense suppression of EMMPRIN. Expression of both human and mouse VEGF and MMP, derived from tumor and host cells, respectively, is regulated by EMMPRIN. These results suggest a novel tumor angiogenesis mechanism in which tumor-associated EMMPRIN functionally mediates tumor-stroma interactions and directly contributes to tumor angiogenesis and growth by stimulating VEGF and MMP expression (Tang, 2005; full text of article).
Proteolytic shedding is an important step in the functional down-regulation and turnover of most membrane proteins at the cell surface. Extracellular matrix metalloproteinase inducer (EMMPRIN) is a multifunctional glycoprotein that has two Ig-like domains in its extracellular portion and functions in cell adhesion as an inducer of matrix metalloproteinase (MMP) expression in surrounding cells. Although the shedding of EMMPRIN is reportedly because of cleavage by metalloproteinases, the responsible proteases, cleavage sites, and stimulants are not yet known. In this study, it was found that human tumor HT1080 and A431 cells shed a 22-kDa EMMPRIN fragment into the culture medium. The shedding is enhanced by phorbol 12-myristate 13-acetate and inhibited by TIMP-2 but not by TIMP-1, suggesting the involvement of membrane-type MMPs (MT-MMPs). Indeed, down-regulation of the MT1-MMP expression in A431 cells using small interfering RNA inhibits the shedding. The 22-kDa fragment was purified, and the C-terminal amino acid was determined. A synthetic peptide spanning the cutting site was cleaved by MT1-MMP in vitro. The cleavage site is located in the linker region connecting the two Ig-like domains. The N-terminal Ig-like domain is important for the MMP inducing activity of EMMPRIN and for cell-cell interactions, presumably through its ability to engage in homophilic interactions, and the 22-kDa fragment retained the ability to augment MMP-2 expression in human fibroblasts. Thus, the MT1-MMP-dependent cleavage eliminates the functional N-terminal domain of EMMPRIN from the cell surface, which is expected to down-regulate its function. At the same time, the released 22-kDa fragment may mediate the expression of MMPs in tumor tissues (Egawa, 2006).
gamma-Secretase is a membrane protein complex that cleaves the beta-amyloid precursor protein (APP) within the transmembrane region, after prior processing by beta-secretase, producing amyloid beta-peptides Abeta(40) and Abeta(42). Errant production of Abeta-peptides that substantially increases Abeta(42) production has been associated with the formation of amyloid plaques in Alzheimer's disease patients. Biophysical and genetic studies indicate that presenilin-1, which contains the proteolytic active site, and three other membrane proteins [nicastrin, anterior pharynx defective-1 (APH-1), and presenilin enhancer-2 (PEN-2)] are required to form the core of the active gamma-secretase complex. This study reports the purification of the native gamma-secretase complexes from HeLa cell membranes and the identification of an additional gamma-secretase complex subunit, CD147, a transmembrane glycoprotein with two Ig-like domains. The presence of this subunit as an integral part of the complex itself was confirmed through coimmunoprecipitation studies of the purified protein from HeLa cells and of solubilized complexes from other cell lines such as neural cell HCN-1A and HEK293. Depletion of CD147 by RNA interference was found to increase the production of Abeta peptides without changing the expression level of the other gamma-secretase components or APP substrates whereas CD147 overexpression has no statistically significant effect on Abeta-peptide production, other gamma-secretase components or APP substrates, indicating that the presence of the CD147 subunit within the gamma-secretase complex down-modulates the production of Abeta-peptides (Zhou, 2005; full text of article).
Translocation of monocarboxylate transporters MCT1 and MCT4 to the plasma membrane requires CD147 (basigin) with which they remain tightly associated. However, the importance of CD147 for MCT activity is unclear. MCT1 and MCT4 are both inhibited by the cell-impermeant organomercurial reagent p-chloromercuribenzene sulfonate (pCMBS). This study demonstrates by site-directed mutagenesis that removal of all accessible cysteine residues on MCT4 does not prevent this inhibition. pCMBS treatment of cells abolishes co-immunoprecipitation of MCT1 and MCT4 with CD147 and enhances labeling of CD147 with a biotinylated-thiol reagent. This suggested that CD147 might be the target of pCMBS, and further evidence for this was obtained by treatment of cells with the bifunctional organomercurial reagent fluorescein dimercury acetate that caused oligomerization of CD147. Site-directed mutagenesis of CD147 implicated the disulfide bridge in the Ig-like C2 domain of CD147 as the target of pCMBS attack. MCT2, which is pCMBS-insensitive, co-immunoprecipitates with gp70 rather than CD147. The interaction between gp70 and MCT2 was confirmed using fluorescence resonance energy transfer between the cyan fluorescent protein- and yellow fluorescent protein-tagged MCT2 and gp70. pCMBS strongly inhibits lactate transport into rabbit erythrocytes, where MCT1 interacts with CD147, but not into rat erythrocytes where it interacts with gp70. These data imply that inhibition of MCT1 and MCT4 activity by pCMBS is mediated through its binding to CD147, whereas MCT2, which associates with gp70, is insensitive to pCMBS. It is concluded that ancillary proteins are required to maintain the catalytic activity of MCTs as well as for their translocation to the plasma membrane (Wilson, 2005; full text of article).
Extracellular matrix metalloproteinase (MMP) inducer (EMMPRIN) is a cell surface glycoprotein overexpressed in many solid tumors. In addition to its ability to stimulate stromal MMP expression, tumor-associated EMMPRIN also induces vascular endothelial growth factor (VEGF) expression. To explore the underlying signaling pathways used by EMMPRIN, the involvement of phosphoinositide 3-kinase (PI3K)-Akt, mitogen-activated protein kinase (MAPK), JUN, and p38 kinases in EMMPRIN-mediated VEGF regulation, was studied. Overexpression of EMMPRIN in MDA-MB-231 breast cancer cells stimulates the phosphorylation of only Akt and MAPKs but not that of JUN and p38 kinases. Conversely, inhibition of EMMPRIN expression results in suppressed Akt and MAPK phosphorylation. Furthermore, the PI3K-specific inhibitor LY294002 inhibits VEGF production by EMMPRIN-overexpressing cells in a dose- and time-dependent manner. In contrast, the MAPK inhibitor U0126 does not affect VEGF production. In vivo, EMMPRIN-overexpressing tumors with elevated VEGF expression have a high level of phosphorylation of Akt and MAPK. Finally, when fibroblast cells are treated with recombinant EMMPRIN, Akt kinase but not MAPK is phosphorylated concomitant with an increase in VEGF production. Both the activation of Akt kinase and the induction of VEGF are specifically inhibited with a neutralizing antibody to EMMPRIN. These results show that in both tumor and fibroblast cells EMMPRIN regulates VEGF production via the PI3K-Akt pathway but not via the MAPK, JUN, or p38 kinase pathways (Tang, 2006; full text of article).
Cell surface CD147 protein promotes production of matrix metalloproteinases and hyaluronan, associates with monocarboxylate transporters and integrins, and is involved in reproductive, neural, inflammatory, and tumor functions. This study combined covalent cross-linking, mass spectrometric protein identification, and co-immunoprecipitation to show selective CD147 association with three major types of transporters (CD98 heavy chain (CD98hc)-L-type amino acid transporter, ASCT2, and monocarboxylate transporters) as well as a regulator of cell proliferation (epithelial cell adhesion molecule). In the assembly of these multicomponent complexes, CD147 and CD98hc play a central organizing role. RNA interference knock-down experiments established a strong connection between CD147 and CD98hc expression and a strong positive association of CD147 (and CD98hc) with cell proliferation. As the CD147-CD98hc complex and proliferation diminished, AMP-activated protein kinase (a cellular 'fuel gauge') became activated, indicating a disturbance of cellular energy metabolism. These data point to a CD147-CD98 cell surface supercomplex that plays a critical role in energy metabolism, likely by coordinating transport of lactate and amino acids. Furthermore this study showed how covalent cross-linking, together with mass spectrometry, can be used to identify closely associated transmembrane proteins. This approach should also be applicable to many other types of transmembrane proteins besides those associated with CD98hc and CD147 (Xu, 2005; full text of article).
Shrew-1 was isolated from an endometriotic cell line in a search for invasion-associated genes. It is a membrane protein that targets to the basolateral membrane of polarized epithelial cells, interacting with E-cadherin-catenin complexes of adherens junctions. Paradoxically, the existence of adherens junctions is incompatible with invasion. To investigate whether shrew-1 can indeed influence cellular invasion, it was overexpressed in HT1080 fibrosarcoma cells. This resulted in enhanced invasiveness, accompanied by an increased matrix metalloprotease (MMP)-9 level in the supernatant, raising the question about the role of shrew-1 in this process. Interaction with CD147, a known promoter of invasiveness and MMP activity, was tested. Indeed, genetics-based, biochemical, and microscopy experiments revealed shrew-1- and CD147-containing complexes in invasive endometriotic cells and an interaction in epithelial cells, which was stronger in MCF7 tumor cells, but weaker in Madin-Darby canine kidney cells. In contrast to the effect mediated by overexpression, small interfering RNA-mediated down-regulation of either shrew-1 or CD147 in HeLa cells decreased invasiveness without affecting the proliferation behavior of HeLa cells, but the knockdown cells displayed decreased motility. Altogether, these results imply that shrew-1 has a function in the regulation of cellular invasion, which may involve its interaction with CD147 (Schreiner, 2007).
To identify the function of CD147 in invasion of host cells by severe acute respiratory syndrome (SARS) coronavirus (CoV), the protein-protein interaction among HAb18G/CD147, cyclophilin A (CyPA), and SARS-CoV structural proteins were analyzed by coimmunoprecipitation and surface plasmon resonance analysis. Although none of the SARS-CoV proteins was found to directly bind CD147, the nucleocapsid (N) protein of SARS-CoV is bound to CyPA, which interacts with CD147. Further research showed that CD147 is highly expressed on 293 cells and that CyPA is integrated with SARS-CoV. CD147-antagonistic peptide (AP)-9, an AP of CD147, had a high rate of binding to 293 cells and an inhibitory effect on SARS-CoV. These results show that CD147, mediated by CyPA bound to SARS-CoV N protein, plays a functional role in facilitating invasion of host cells by SARS-CoV. These findings provide some evidence for the cytologic mechanism of invasion by SARS-CoV and provide a molecular basis for screening anti-SARS drugs (Chen, 2005; full text of article).
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