G Protein Subunit Gα ₁₃ Binds to Integrin α _IIb β ₃ and Mediates Integrin “Outside-In” Signaling

Abstract

Integrins mediate cell adhesion to the extracellular matrix and transmit signals within the cell that stimulate cell spreading, retraction, migration, and proliferation. The mechanism of integrin outside-in signaling has been unclear. We found that the heterotrimeric guanine nucleotide-binding protein (G protein), Gα13, directly bound to the integrin β3 cytoplasmic domain, and that Gα13-integrin interaction was promoted by ligand binding to the integrin αIIbβ3 and by guanosine triphosphate (GTP)-loading of Gα13. Interference of Gα13 expression or a myristoylated fragment of Gα13 that inhibited interaction of αIIbβ3 with Gα13 diminished activation of protein kinase c-Src and stimulated the small GTPase RhoA, consequently inhibiting cell spreading and accelerating cell retraction. We conclude that integrins are non-canonical Gα13-coupled receptors that provide a mechanism for dynamic regulation of RhoA.

Integrin αIIbβ3

“…By generating mice in which the platelets were depleted of Gα 13 using siRNA 5 The confocal images very clearly showed that, in the absence of Gα 13 , platelets spread poorly on Fg, which was rescued by pretreatment with the Rho-kinase inhibitor Y27632, confirming previous findings that RhoA activated downstream of integrin α IIb β 3 inhibits platelet spreading. Interestingly, Gα 13 -depleted platelets failed to activate c-Src but accelerated RhoA activation.…”

“…From these observations, the authors infer that Gα 13 is important for integrin-mediated c-Src activation and RhoA inhibition, leading to increased cell spreading. 5 Since Gα 13 regulates integrin-mediated cell spreading and c-Src activation, Gong et al examined the interaction of Gα 13 with α IIb β 3 using co-immunoprecipitation and GST pull-down assays. 5 They found that the GTP-bound form of Gα 13 shows enhanced interaction with the integrin β 3 subunit.…”

“…5 Since Gα 13 regulates integrin-mediated cell spreading and c-Src activation, Gong et al examined the interaction of Gα 13 with α IIb β 3 using co-immunoprecipitation and GST pull-down assays. 5 They found that the GTP-bound form of Gα 13 shows enhanced interaction with the integrin β 3 subunit. This interaction is required for the activation of c-Src and the inhibition of RhoA.…”

HIF2α signaling inhibits adherens junctional disruption in acute lung injury

“…The Co-IP assay was performed as previously reported (53). Cell lysates from HLMVECs exposed to 1% O 2 or Fg4497 were incubated with either a mouse anti-tyrosine phosphorylation antibody, an anti-VE-cadherin antibody, or an equal amount of normal mouse or goat IgG, and then subsequently with protein A-or protein G-conjugated Sepharose beads, followed by Western blot (WB) analysis.…”

Solute carrier family 3 member 2 (Slc3a2) controls yolk syncytial layer (YSL) formation by regulating microtubule networks in the zebrafish embryo

“…Mammalian SLC3a2/4F2hc/CD98hc contributes to integrin outside-in signaling to regulate various integrin-mediated cell functions, including cell adhesion and cell-cell fusion (19,(21)(22)(23)(24). A downstream effector of integrin outside-in signaling is c-Src, which is phosphorylated at tyrosine 416 upon integrin-ligand binding (34). Because activation of c-Src transiently inhibits RhoA activity via p190RhoGAP (35), we hypothesized that zebrafish Slc3a2 might inhibit RhoA via c-Src activation.…”