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

Ariel H Polizio,Pilar Chinchilla,Xiaole Chen,Sangbumn Kim,David R Manning,Natalia A Riobo

doi:10.1074/jbc.m110.197111

Ariel H Polizio, Pilar Chinchilla + Show 4 more

Open Access

https://doi.org/10.1074/jbc.m110.197111

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Abstract

Evidence supporting the functionality of Smoothened (SMO), an essential transducer in most pathways engaged by Hedgehog (Hh), as a G(i)-coupled receptor contrasts with the lack of an apparently consistent requirement for G(i) in Hh signal transduction. In the present study, we sought to evaluate the role of SMO-G(i) coupling in fibroblast migration induced by Sonic Hedgehog (Shh). Our results demonstrate an absolute requirement for G(i) in Shh-induced fibroblast migration. We found that Shh acutely stimulates the small Rho GTPases Rac1 and RhoA via SMO through a G(i) 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-G(i) coupling in non-canonical Hh signaling.

Highlights

The Hh family of secreted proteins, Sonic (Shh), Indian (Ihh), and Desert Hedgehog (Dhh), exerts its functions by binding to the 12-transmembrane (12-TM)3 receptor Patched1 (Ptc1)
Whether Gi is required in all cell types for activation of Gli transcription factors, is unlikely given the paucity of data regarding pertussis toxin (PTX) in this context
Our results reveal a strict requirement for Gi and PI3K in Sonic Hedgehog (Shh)-induced fibroblast migration, which is mediated by the rapid stimulation of Rac1 and RhoA small GTPases

Summary

Introduction

The Hh family of secreted proteins, Sonic (Shh), Indian (Ihh), and Desert Hedgehog (Dhh), exerts its functions by binding to the 12-transmembrane (12-TM)3 receptor Patched1 (Ptc1). Pretreatment of cells with an inverse agonist specific for SMO, KAAD-cyclopamine, which prevents activation of Gli-dependent transcription as well as stimulation of Gi proteins by SMO [14], completely blocked cell migration in response to both agonists (Fig. 1, A and B, and supplemental Fig. S1, white bars).

Results

Conclusion