Abstract 10885: Integrin β 3 Directly Inhibits Galpha 13 -p115rhogef Interaction and Its Role in Regulating Platelet Exocytosis

Abstract

G protein-coupled receptors (GPCRs) and adhesion receptor integrins are fundamental to a cell’s response to extracellular stimuli. GPCRs, through Gα q and Gα i , activate integrins and, through the Gα 13 -p115RhoGEF-RhoA pathway, stimulate contractility and integrin-independent exocytosis (granule secretion). Gα 13 also interacts with integrins and mediates outside-in signaling, cell spreading and integrin-dependent exocytosis. However, it was unknown whether there was crosstalk between integrins and the Gα 13 /p115RhoGEF-mediated RhoA signaling pathway. It was also unclear with the role of Gα 13 -integrin interaction in regulating GPCR- and integrin- mediated platelet exocytosis. In this study, we demonstrate that binding of the integrin β 3 cytoplasmic domain to Gα 13 through its ExE motif, directly disrupts the interaction between p115RhoGEF and Gα 13 , thus inhibiting Gα 13 -p115RhoGEF-mediated RhoA activation and signaling. In platelets, this inhibitory effect of integrins greatly reduces GPCR-mediated integrin-independent granule secretion. On the other hand, the Gα 13 -integrin interaction stimulates integrin outside-in signaling and integrin-dependent granule secretion. Furthermore, we demonstrate that the inhibitor peptide derived from the Gα 13 -binding β 3 ExE motif disrupts the β 3 -Gα 13 interaction to inhibit GPCR-induced integrin-independent granule secretion and also inhibits outside-in signaling and integrin-dependent granule secretion. This dual effect results in robust inhibition of granule secretion without affecting primary platelet aggregation, suggesting a new therapeutic approach for the development of selective inhibitors of platelet granule secretion. In conclusion, we have discovered a mechanism underlying direct integrin-GPCR crosstalk that regulates the Gα 13 -p115RhoGEF-RhoA signaling pathway. Our data also demonstrate an approach to potently inhibit platelet granule secretion without impairing primary platelet adhesion/aggregation and hemostasis.