Insulin-like Growth Factor-I Receptor Mediates the Prosurvival Effect of Fibronectin

We recently showed that extracellular matrix (ECM) proteins, which are abundant in desmoplastic pancreatic tumor, are as potent as growth factors in inhibiting apoptosis in pancreatic cancer (PaCa) cells. Here we show that fibronectin, a major ECM component, engages insulin-like growth factor-I receptor (IGF-IR) to inhibit PaCa cell death. We found that fibronectin-induced protection from apoptosis is fully mediated by IGF-IR and is independent of IGF-I. Pharmacologic and molecular inhibitions of IGF-IR stimulated apoptosis and prevented the prosurvival effect of fibronectin in PaCa cells. Our data indicate that fibronectin protects from apoptosis through trans-activation of IGF-IR. We showed that fibronectin stimulated complex formation between its receptor β3 integrin and protein-tyrosine phosphatase SHP-2. This process of complex formation, in turn, prevents SHP-2 from dephosphorylating IGF-IR resulting in sustained phosphorylation of IGF-IR and leading to the downstream activation of Akt kinase, up-regulation of antiapoptotic BclxL, and inhibition of apoptosis. Among ECM proteins tested only fibronectin and laminin but not vitronectin and collagen I stimulated trans-activation of IGF-IR. Interaction of fibronectin with β3 but not β1 integrin receptors mediates the survival pathway. In contrast, fibronectin-induced adhesion is mediated through β1 integrin receptor and is IGF-IR-independent. Thus, our results indicate that the prosurvival effect of fibronectin in PaCa cells is mediated by trans-activation of IGF-IR induced by the β3 integrin receptor. The data suggest IGF-IR as a key target for prevention of the prosurvival effects of ECM proteins and growth factors in pancreatic cancer.