ADHESION OF HUMAN UMBILICAL VEIN ENDOTHELIAL-CELLS TO THE IMMEDIATE-EARLY GENE-PRODUCT CYR61 IS MEDIATED THROUGH INTEGRIN ALPHA(V)BETA(3)

Cyr61 is a member of a family of growth factor-inducible immediate-ear ly gene products thought to act cooperatively with the activities of g rowth factors, Upon synthesis, Cyr61 is secreted and is predominantly incorporated into the extracellular matrix, Recently, we demonstrated that Cyr61 promotes cell adhesion and migration and augments growth fa ctor-induced DNA synthesis (Kireeva, M, L., Mo, F.-E,, Yang, G, P., an d Lau, L, F. (1996) Mol, Cell. Biol. 16, 1326-1334), In the present st udy, we investigated possible candidate receptor(s) on human umbilical vein endothelial cells (HUVECs) mediating adhesion to Cyr61. Under bo th serum-containing and serum-free conditions, adhesion of HUVECs to C yr61 was dose-dependent, saturable, and abolished by affinity-purified anti-Cyr61 antibodies, Cell adhesion to Cyr61 was divalent cation-dep endent and specifically inhibited by the peptide RGDS and LM609, a mon oclonal antibody against integrin alpha(v) beta(3) Furthermore, purifi ed alpha(v) beta(3) bound directly to an affinity matrix of Cyr61-coup led Sepharose 4B, and this interaction was specifically blocked by ant i-Cyr61 antibodies, Additionally, in a solid phase binding assay, solu ble Cyr61 bound to immobilized gp, in a dose-dependent manner, and hal f-saturation binding occurred at approximately 5 nM Cyr61, As expected , the interaction of Cyr61 with immobilized alpha(v) beta(3) was block ed by RGDS and LM609. In sum, these results identified Cyr61 as a nove l ligand for alpha(v) beta(3) and indicate that the adhesion of HUVECs to Cyr61 is mediated through interaction with this integrin, The poss ibility that integrin alpha(v) eta(3) functions as a signaling recepto r for Cyr61 accounts for most if not all activities that can be ascrib ed to Cyr61 to date and suggests a mechanism of action discussed herei n.