A Role for Rac3 GTPase in the Regulation of Autophagy

Patrick J. Casey,Dian Yan Guo,Mohammed S. Hossain,Sen Liu,Wan Long Zhu,Atefeh Khakpoor,Honglian Tong,Mei Wang

doi:10.1074/jbc.m111.280990

Patrick J. Casey, Dian Yan Guo + Show 6 more

Open Access

https://doi.org/10.1074/jbc.m111.280990

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Abstract

The process of autophagy is situated at the intersection of multiple cell signaling pathways, including cell metabolism, growth, and death, and hence is subject to multiple forms of regulation. We previously reported that inhibition of isoprenylcysteine carboxylmethyltransferase (Icmt), which catalyzes the final step in the post-translational prenylation of so-called CAAX proteins, results in the induction of autophagy which enhances cell death in some cancer cells. In this study, using siRNA-mediated knockdown of a group of small GTPases that are predicted Icmt substrates, we identify Rac3 GTPase as a negative regulator of the process of autophagy. Knockdown of Rac3, but not the closely related isoforms Rac1 and Rac2, results in induction of autophagy. Ectopic expression of Rac3, significantly rescues cells from autophagy and cell death induced by Icmt inhibition, strengthening the notion of an isoform-specific autophagy regulatory function of Rac3. This role of Rac3 was observed in multiple cell lines with varying Rac subtype expression profiles, suggesting its broad involvement in the process. The identification of this less-studied Rac member as a novel regulator provides new insight into autophagy and opens opportunities in identifying additional regulatory inputs of the process.

Highlights

Given its role in performing important homeostatic functions, it is not surprising that autophagy is subjected to multiple modes of regulation in response to intra- and extracellular
The Ras-centric view has given way to the understanding that many other CAAX proteins are important signaling molecules involved in cell survival, proliferation, migration, and other processes associated with tumorigenesis and tumor progression, and functions of these proteins can be affected by C-terminal methylation [22]
Because cancer cells may have several different CAAX proteins involved in aberrant signaling, targeting either FTase or GGTase-I may only cover a subpopulation of CAAX proteins involved in the aberrancies of signaling

Summary

The abbreviations used are

Isoprenylcysteine carboxylmethyltransferase; FTase, protein farnesyltransferase, GGTase-I, protein geranylgeranyltransferase-I. Rac Regulates Autophagy ators in Icmt inhibitor-induced autophagy. We report the identification of a specific Ras family member, Rac, as a negative regulator of autophagy and present evidence for the impact of Rac function on cancer cell survival through its modulation of autophagy

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION