Depletion of Ric-8B leads to reduced mTORC2 activity.

Maíra H Nagai,Bettina Malnic,Alice H Reis,Cleiton F Machado,Victor P S Xavier,Jose G Abreu,Pedro A F Galante,William T Festuccia,Luciana M Gutiyama,Elisa R Donnard,J Silvio Gutkind

doi:10.1371/journal.pgen.1008255

Abstract

mTOR, a serine/threonine protein kinase that is involved in a series of critical cellular processes, can be found in two functionally distinct complexes, mTORC1 and mTORC2. In contrast to mTORC1, little is known about the mechanisms that regulate mTORC2. Here we show that mTORC2 activity is reduced in mice with a hypomorphic mutation of the Ric-8B gene. Ric-8B is a highly conserved protein that acts as a non-canonical guanine nucleotide exchange factor (GEF) for heterotrimeric Gαs/olf type subunits. We found that Ric-8B hypomorph embryos are smaller than their wild type littermates, fail to close the neural tube in the cephalic region and die during mid-embryogenesis. Comparative transcriptome analysis revealed that signaling pathways involving GPCRs and G proteins are dysregulated in the Ric-8B mutant embryos. Interestingly, this analysis also revealed an unexpected impairment of the mTOR signaling pathway. Phosphorylation of Akt at Ser473 is downregulated in the Ric-8B mutant embryos, indicating a decreased activity of mTORC2. Knockdown of the endogenous Ric-8B gene in cultured cell lines leads to reduced phosphorylation levels of Akt (Ser473), further supporting the involvement of Ric-8B in mTORC2 activity. Our results reveal a crucial role for Ric-8B in development and provide novel insights into the signals that regulate mTORC2.

Highlights

IntroductionRic-8B (resistant to inhibitors of cholinesterase 8B) is a highly conserved protein which interacts with Gαs class subunits from heterotrimeric G proteins [1,2]
Ric-8B is a highly conserved protein which interacts with Gαs class subunits from heterotrimeric G proteins [1,2]
Gene inactivation in mice can be used to identify genes that are involved in important biological processes and that may contribute to disease

Summary

Introduction

Ric-8B (resistant to inhibitors of cholinesterase 8B) is a highly conserved protein which interacts with Gαs class subunits from heterotrimeric G proteins [1,2]. Ric-8B can work as a guanine nucleotide exchange factor (GEF) for both Gαs and Gαolf [1,3]. Ric-8B expression in adult mice is highly predominant in the same tissues where Gαolf is expressed indicating that these two proteins are functional partners in vivo [2]. Consistent with the role of a GEF, Ric-8B is able to amplify odorant receptor signaling or dopamine receptor signaling through Gαolf in cultured cells [2,7,8,9]. A series of studies indicate that Ric-8B regulates Gα protein abundance in the cells, and suggest that Ric-8B may serve as a chaperone that promotes Gα protein stability and the formation of functional G protein complexes [7,8,10,11,12,13]

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Results

Discussion

Conclusion