RioK1, a New Interactor of Protein Arginine Methyltransferase 5 (PRMT5), Competes with pICln for Binding and Modulates PRMT5 Complex Composition and Substrate Specificity

Gernot Guderian,Christoph Peter,Julia Wiesner,Albert Sickmann,Klaus Schulze-Osthoff,Utz Fischer,Matthias Grimmler

doi:10.1074/jbc.m110.148486

Gernot Guderian, Christoph Peter + Show 5 more

Open Access

https://doi.org/10.1074/jbc.m110.148486

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Abstract

Protein arginine methylation plays a critical role in differential gene expression through modulating protein-protein and protein-DNA/RNA interactions. Although numerous proteins undergo arginine methylation, only limited information is available on how protein arginine methyltransferases (PRMTs) identify their substrates. The human PRMT5 complex consists of PRMT5, WD45/MEP50 (WD repeat domain 45/methylosome protein 50), and pICln and catalyzes the symmetrical arginine dimethylation of its substrate proteins. pICln recruits the spliceosomal Sm proteins to the PRMT5 complex for methylation, which allows their subsequent loading onto snRNA to form small nuclear ribonucleoproteins. To understand how the PRMT5 complex is regulated, we investigated its biochemical composition and identified RioK1 as a novel, stoichiometric component of the PRMT5 complex. We show that RioK1 and pICln bind to PRMT5 in a mutually exclusive fashion. This results in a PRMT5-WD45/MEP50 core structure that either associates with pICln or RioK1 in distinct complexes. Furthermore, we show that RioK1 functions in analogy to pICln as an adapter protein by recruiting the RNA-binding protein nucleolin to the PRMT5 complex for its symmetrical methylation. The exclusive interaction of PRMT5 with either pICln or RioK1 thus provides the first mechanistic insight into how a methyltransferase can distinguish between its substrate proteins.

Highlights

Tional modification, protein arginine methyltransferases (PRMTs),4 have been implicated in the regulation of diverse processes ranging from DNA damage repair and transcriptional regulation to RNA splicing [2, 3]
Among the well characterized components of the PRMT5 complex, pICln, WD45/MEP50, and PRMT5 itself, we identified a novel protein, RioK1, of ϳ90 kDa in size via mass spectrometry
PRMT5 and WD45/MEP50 were always present in stoichiometric amounts in all immunoprecipitations, pICln and RioK1 were only clearly enriched in the corresponding immunoprecipitations (Fig. 1B)

Summary

Introduction

Tional modification, protein arginine methyltransferases (PRMTs),4 have been implicated in the regulation of diverse processes ranging from DNA damage repair and transcriptional regulation to RNA splicing [2, 3]. PICln recruits Sm proteins, RioK1 recruits nucleolin for its symmetrical methylation to the PRMT5 complex. In Vitro Methylation Assay—Purified recombinant substrate proteins were incubated with the PRMT5 complex (immunoprecipitated by anti-WD45/MEP50 antibody from HeLa extract) in 30 ␮l PBS and 2 ␮l [3H]S-adenosyl methionine for 2 h at 37 °C.

Results

Conclusion