Integrin-associated protein stimulates alpha 2 beta 1-dependent chemotaxisvia Gi-mediated inhibition of adenylate cyclase and extracellular-regulated kinases

Integrin-associated protein (IAP/CD47) augments the function of alpha 2 bet a 1 integrin in smooth muscle cells (SMC), resulting in enhanced chemotaxis toward soluble collagen (Wang, X-Q., and W.A. Frazier. 1998. Mel. Biol. Ce ll. 9:865). IAP-deficient SMC derived from IAP(-/-) animals did not migrate in response to 4N1K (KRFYVVMWKK), a peptide agonist of IAP derived from th e COOH-terminal domain of thrombospondin-1 (TSP1). When normal SMC were pre incubated with 4N1K or an anti-alpha 2 beta 1 function-stimulating antibody , cell migration to soluble collagen was significantly enhanced. 4N1K-induc ed chemotaxis was blocked by treatment of SMC with pertussis toxin indicati ng that IAP acts through Gi. In agreement with this, 4N1K evoked a rapid de crease in cAMP levels which was intensified in the presence of collagen, an d forskolin and 8-Br-cAMP both inhibited SMC migration stimulated via IAP. 4N1K strongly inhibited extracellular regulated kinase (ERK) activation in SMC attaching to collagen and reduced basal ERK activity in suspended SMC. Pertussis toxin treatment of SMC significantly activated ERK, suggesting th at an inhibitory input was alleviated. Inhibition of ERK activity by (a) th e MAP kinase kinase (MEK) inhibitor, PD98059, (b) antisense oligonucleotide depletion of ERK, and (c) expression of mitogen-activated protein (MAP) ki nase phosphatase-1 in SMC all led to increased migration to collagen, 4N1K, or 4N1K plus collagen. Thus, IAP stimulates alpha 2 beta 1 integrin-mediat ed SMC migration via Gi-mediated inhibition of ERK activity and suppression of cyclic AMP levels. Both of these signaling pathways could directly modu late the state of the integrin as well as impact downstream components of t he cell motility apparatus.