ADAM28

Abstract: A disintegrin and metalloproteinases (ADAMs) are a new gene family of proteins with sequence similarity to the reprolysin family of snake venomases that share the metalloproteinase domain with matrix metalloproteinases (MMPs). They are structurally classified into two groups: the membrane-anchored ADAM and ADAM with thrombospondin motifs (ADAMTS). These molecules are involved in various biological events such as cell adhesion, cell fusion, cell migration, membrane protein shedding and proteolysis. Studies on the biochemical characteristics and biological functions of ADAMs are in progress, and accumulated lines of evidence have shown that some ADAMs are expressed in malignant tumors and participate in the pathology of cancers. The activities of ADAMs are regulated by gene expression, intracytoplasmic and pericellular regulation, activation of the zymogens and inhibition of activities by inhibitors. Many ADAM species, including ADAM8, ADAM9, ADAM10, ADAM12, ADAM15, ADAM17, ADAM19, ADAM28, ADAMTS1, ADAMTS4 and ADAMTS5, are expressed in human malignant tumors. Many of them are involved in the regulation of growth factor activities and integrin functions, leading to promotion of cell growth and invasion, although the precise mechanisms of these are not clear at the present time. In this article, we review recent information about ADAM family members and their implications for cancer cell proliferation and progression.

Abstract: The metalloprotease disintegrins are a family of membrane-anchored glycoproteins with diverse functions in fertilization, myoblast fusion, neurogenesis and protein ectodomain shedding. Here we report a cDNA sequence, encoding a metalloprotease disintegrin, termed ADAM28 ('a disintegrin and metalloprotease 28'), which was cloned from mouse lung. From protein sequence comparisons, ADAM28 is more closely related to snake venom metalloproteases (SVMPs) than to other ADAMs, and hence may cleave similar substrates to SVMPs, perhaps including components of the extracellular matrix. Northern blot analysis of selected mouse tissues revealed that ADAM28 is expressed highly and in alternatively spliced forms in the epididymis, suggesting a possible role in sperm maturation, and at lower levels in lung. The intracellular maturation of ADAM28 expressed in COS-7 cells resembles that of other ADAMs, in that ADAM28 is made as a precursor and processed to a mature form in a late Golgi compartment of the secretory pathway. Most or all of the mature, and thus presumably catalytically active, form of ADAM28 in COS-7 cells is accessible to cell surface trypsinization, suggesting that ADAM28 functions mainly on the cell surface. A mutation converting the catalytic-site glutamate residue into alanine abolishes pro-domain removal, even though this mutant form of ADAM28 can be transported to the cell surface in a manner similar to the wild-type protein. This suggests that pro-domain removal and maturation of ADAM28 may be, at least in part, autocatalytic. This is in contrast with several other ADAMs, for which furin-like proprotein convertases are involved in pro-domain removal, and in which a glutamate-to-alanine mutation in the catalytic site does not alter pro-domain removal.

Abstract: A disintegrin and metalloproteinases (ADAMs) are involved in various biological events including cell adhesion, cell fusion, membrane protein shedding, and proteolysis. In the present study, our reverse transcription-PCR analysis showed that among the 12 different ADAM species with a putative metalloproteinase motif, prototype membrane-anchored ADAM28m and secreted-type ADAM28s are selectively expressed in human breast carcinoma tissues. By real-time quantitative PCR, their expression levels were significantly higher in carcinomas than in nonneoplastic breast tissues. In situ hybridization, immunohistochemistry, and immunoblotting analyses indicated that ADAM28 is predominantly expressed in an active form by carcinoma cells within carcinoma tissues. A direct correlation was observed between mRNA expression levels and proliferative activity of the carcinoma cells. Treatment of ADAM28-expressing breast carcinoma cells (MDA-MB231) with insulin-like growth factor-I (IGF-I) increased cell proliferation, cleavage of IGF binding protein (IGFBP)-3, as well as IGF-I cell signaling; these processes were all significantly inhibited by treatment with ADAM inhibitor or anti-ADAM28 antibody. Down-regulation of ADAM28 expression in MDA-MB231 cells with small interfering RNA significantly reduced cell proliferation, IGFBP-3 cleavage, and growth of xenografts in mice. In addition, cleavage of IGFBP-3 in breast carcinoma tissues was correlated with ADAM28 expression levels and inhibited by treatment with ADAM inhibitor or anti-ADAM28 antibody. These results show that ADAM28 is overexpressed in an activated form in human breast carcinoma cells and suggest that ADAM28 is involved in cell proliferation through enhanced bioavailability of IGF-I released from the IGF-I/IGFBP-3 complex by selective IGFBP-3 cleavage in human breast carcinomas.