Heterotrimeric Gi Proteins Link Hedgehog Signaling to Activation of Rho Small GTPases to Promote Fibroblast Migration

Abstract

Evidence supporting the functionality of Smoothened (SMO), an essential transducer in most pathways engaged by Hedgehog (Hh), as a Gi-coupled receptor contrasts with the lack of an apparently consistent requirement for Gi in Hh signal transduction. In the present study, we sought to evaluate the role of SMO-Gi coupling in fibroblast migration induced by Sonic Hedgehog (Shh). Our results demonstrate an absolute requirement for Gi in Shh-induced fibroblast migration. We found that Shh acutely stimulates the small Rho GTPases Rac1 and RhoA via SMO through a Gi protein- and PI3K-dependent mechanism, and that these are required for cell migration. These responses were independent of transcription by Gli and of the C-terminal domain of SMO, as we show using a combination of molecular and genetic tools. Our findings provide a mechanistic model for fibroblast migration in response to Shh and underscore the role of SMO-Gi coupling in non-canonical Hh signaling.

Sonic hedgehog mediates a novel pathway of PDGF-BB–dependent vessel maturation

“…21,23,[28][29][30] We demonstrated that recombinant Shh is capable of inducing a fast (15-minute) Akt phosphorylation in SMCs. We showed that Shhinduced Akt phosphorylation is entirely inhibited by the pan PI3K inhibitor Wortmannin, the PI3Kg selective inhibitor AS-252424 ( Figure 3A), and competition with the inactive mutant of PI3Kg 25 (supplemental Figure 7A), demonstrating that Shh-induced Akt phosphorylation is mediated via PI3Kg.…”

“…At the cellular level, recombinant Shh was shown to induce SMC and pericyte proliferation and survival [16][17][18][19] and to contribute to PDGF-BB-induced myofibroblast proliferation. 20 Even though Shh was shown to induce the migration of various cell types such as fibroblasts, 21 ECs, 22 endothelial progenitors, 23 and monocytes, 24 its role and mechanism in SMC migration in vitro and in MC recruitment in vivo have never been investigated.…”

Autonomous and nonautonomous roles of Hedgehog signaling in regulating limb muscle formation

“…In cell culture studies, Shh has been shown to be required for cell motility by activating Rho GTPases through a ''noncanonical'' or Gli-independent pathway (Renault et al 2010;Sasaki et al 2010;Polizio et al 2011). In these scenarios, signaling activation is relayed from Smo to the G proteins or Tiam1, a GEF for Rac1 (Sasaki et al 2010;Polizio et al 2011).…”

Gas1 is a receptor for sonic hedgehog to repel enteric axons

“…Shh-mediated Smo-dependent signaling has been implicated in MEF chemotaxis (43) and scratch healing (44), but the surface receptors are also not defined. In both cases, PTX-sensitive Gαi proteins (Gαi 1-3) have been implicated.…”