Extracellular matrix regulates endothelial functions through interaction of VEGFR-3 and integrin alpha(5)beta(1)

Endothelium extracellular matrix (ECM) interactions can provide distinct spatial and molecular signals which control cellular proliferation, migration, and differentiation. Here, we investigated the role of fibronectin (FN), a major ECM protein, on the functions of lymphatic endothelial cells (LEC). We observed that FN, the ligand for integrin alpha(5)beta(1), selectively promoted the growth of LEC as compared with vitronectin VN) in the presence of the ligand for vascular endothelial growth factor receptor 3 [VEGFR-3 (VEGF-C] 56S)]. Upon investigating the mechanisms whereby ECM components regulate VEGFR-3 signaling, we found that FN transactivated VEGFR-3 and significantly enhanced the phosphorylation of VEGFR-3 induced by VFGF-C156S as compared to VN. An enhanced association of the integrin subunit alpha(5) or, with VEGFR-3, after stimulation with VEGF-Cl 56S, was observed by co-irnmunoprecipitation. While blockade of integrin alpha(5)beta(1) inhibited the VEGF-Cl 56S-induced phosphorylation of VEGFR-3, no similar effect was obtained by blocking integrin alpha(v)beta(3) FN also protected the endothelial cells from serum deprivation-induced apoptosis. Moreover, while the specific PI3 kinase inhibitor, LY294002, abolished this FN-mediated cell Survival, the MAPK kinase inhibitor, PD98059, had no significant effect. Furthermore, a dominant-negative mutant of VEGFR-3 (G857R) reduced VEGF-Cl 56S or FN-mediated cell survival, as well as the activities of P13 kinase/Akt. Our results indicate that integrin alpha(5)beta(1) 1 participates in the activation of both VEGFR-3 and its downstream P13 kinase/Akt signaling pathway, which is essential for FN-rnecliated lymphatic endothelial cell survival and proliferation. J. Cell. Physiol. 202: 205-214, 2005. (C) 2004 Wiley-Liss, Inc.