A non-proteolytic role for ubiquitin in deadenylation of MHC-I mRNA by the RNA-binding E3-ligase MEX-3C.

Florencia Cano,Radu Rapiteanu,G Sebastiaan Winkler,Paul J Lehner

doi:10.1038/ncomms9670

Florencia Cano, Radu Rapiteanu + Show 2 more

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https://doi.org/10.1038/ncomms9670

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Abstract

The regulation of protein and mRNA turnover is essential for many cellular processes. We recently showed that ubiquitin—traditionally linked to protein degradation—directly regulates the degradation of mRNAs through the action of a newly identified family of RNA-binding E3 ubiquitin ligases. How ubiquitin regulates mRNA decay remains unclear. Here, we identify a new role for ubiquitin in regulating deadenylation, the initial and often rate-limiting step in mRNA degradation. MEX-3C, a canonical member of this family of RNA-binding ubiquitin ligases, associates with the cytoplasmic deadenylation complexes and ubiquitinates CNOT7(Caf1), the main catalytic subunit of the CCR4-NOT deadenylation machinery. We establish a new role for ubiquitin in regulating MHC-I mRNA deadenylation as ubiquitination of CNOT7 by MEX-3C regulates its deadenylation activity and is required for MHC-I mRNA degradation. Since neither proteasome nor lysosome inhibitors rescued MEX-3C-mediated MHC-I mRNA degradation, our findings suggest a new non-proteolytic function for ubiquitin in the regulation of mRNA decay.

Highlights

The regulation of protein and Messenger RNA (mRNA) turnover is essential for many cellular processes
In a small interfering RNA ubiquitome screen, we identified MEX-3C, a canonical member of this novel family of RNA-binding ubiquitin E3-ligases, which regulates the cell surface expression of major histocompatibility complex (MHC) class I proteins, via the post-transcriptional regulation of MHC-I mRNA
This HLA-A2 mRNA substrate bound to MEX-3C cannot be translated into protein, a function conserved with its C. elegans MEX-3 ancestor that binds mRNA but lacks the RING domain[6]

Summary

Introduction

The regulation of protein and mRNA turnover is essential for many cellular processes. MEX-3C, a canonical member of this family of RNA-binding ubiquitin ligases, associates with the cytoplasmic deadenylation complexes and ubiquitinates CNOT7(Caf1), the main catalytic subunit of the CCR4-NOT deadenylation machinery. We show that MEX-3C associates with different members of the cytoplasmic deadenylation complexes and ubiquitinates CNOT7, the main catalytic subunit of the CCR4-NOT deadenylation machinery Ubiquitination of this subunit (CNOT7) by MEX-3C regulates its deadenylation activity and is required for HLA-A2 mRNA degradation. Since neither proteasome nor lysosome inhibitors, nor the use of ubiquitin mutants that prevent the formation of protein degradation signalling K11- and K48-linked chains, rescued MEX-3Cmediated mRNA degradation, our findings point to a new non-proteolytic function for ubiquitin in the regulation of mRNA decay

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