We have previously shown that endogenous Insulin-like growth factor-I (IGF-I) regulates growth of human intestinal smooth muscle cells by stimulating proliferation and inhibiting apoptosis. In active Crohn's disease, expression of IGF-I and the V3 integrin receptor ligands, fibronectin and vitronectin are increased. The aim of the present study was to determine whether occupation of the V3 receptor influences IGF-I receptor tyrosine kinase activation and function in human intestinal smooth muscle cells. In untreated cells, IGF-I elicited time-dependent tyrosine phosphorylation of its cognate receptor that was maximal within 2 min and sustained for 30 min. In the presence of the V3 ligand, fibronectin, IGF-I stimulated IGF-I receptor activation was augmented. Conversely, in the presence of the V3 specific disintegrin, echistatin, IGF-I-stimulated IGF-I receptor tyrosine kinase phosphorylation was inhibited. IGF-I-stimulated IGF-I receptor activation was accompanied by recruitment of the adapter protein, IRS-1, activation of Erk1/2, p70S6 kinase and proliferation. These effects were augmented by fibronectin and attenuated by echistatin. IGF-I also elicited time-dependent recruitment of protein tyrosine phosphatase SHP-2 that coincided with dephosphorylation of the tyrosine phosphorylated IGF-I receptor tyrosine kinase. The V3 disintegrin, echistatin, accelerated the rate of SHP-2 recruitment and deactivation of the IGF-I receptor tyrosine kinase. The results show that occupancy of the V3 integrin receptor modulates IGF-I-induced IGF-I receptor activation and function in human intestinal muscle cells. We hypothesis that the concomitant increases in the expression of V3 ligands and of IGF-I in active Crohn's disease may contribute to muscle hyperplasia and stricture formation by acting in concert to augment IGF-I stimulated IGF-I receptor tyrosine kinase activity and IGF-I mediated muscle cell growth.