ADAM15 suppresses cell motility by driving integrin alpha 5 beta 1 cell surface expression via Erk inactivation

Human ADAM15 is unique among the A disintegrin and metalloprotease domain (ADAM) family because of the integrin binding motif Arg-Gly-Asp (RGD) within its disintegrin domain. Integrin alpha 5 beta 1 has been reported to bind to ADAM15 in an RGD-dependent manner, but the biological significance of the interaction between ADAM15 and alpha 5 beta 1 is unknown. To characterize the effects of ADAM15 on alpha 5 beta 1-mediated cell adhesion and migration and elucidate the potential mechanism, CHO cells which express endogenous integrin alpha 5 beta 1 were transfected with human ADAM15 cDNA. ADAM15 overexpression led to enhanced cell adhesion and decreased migration on fibronectin, which were suppressed by down-regulation of integrin alpha 5. Overexpression of ADAM15 not only increased the cell surface expression of integrin alpha 5 but also resulted in a more clustered staining of alpha 5 on cell surface, while the beta 1 subunit remained unchanged. Unexpectedly, results from immunoprecipitation and immunofluorescence indicated that ADAM15 and alpha 5 beta 1 integrin did not interact directly in CHO cells. We found that ADAM15 expression decreased the phosphorylation of Erk1/2. Consistently, down-regulation of Erk1/2 phosphorylation by MEK inhibitor PD98059 or siRNA against Erk1/2 enhanced the expression of alpha 5 on cell surface. By using a B16F10 pulmonary metastasis model, we revealed that overexpression of ADAM15 significantly reduced the number of metastatic nodules on the lung. Taken together, this study reveals for the first time that ADAM15 could drive alpha 5 integrin expression on cell surface via down-regulation of phosphorylated Erk1/2. This presents a novel mechanism by which ADAM15 regulates cell-matrix adhesion and migration. (C) 2008 Elsevier Ltd. All rights reserved.