DHX15 regulates CMTR1-dependent gene expression and cell proliferation

Francisco Inesta-Vaquera,Simone Weidlich,Viduth K Chaugule,Laurel Chandler,Mark Peggie,Alejandro Rojas-Fernandez,Victoria H Cowling,Alison Galloway

doi:10.26508/lsa.201800092

Francisco Inesta-Vaquera, Simone Weidlich + Show 6 more

Open Access

https://doi.org/10.26508/lsa.201800092

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Abstract

CMTR1 contributes to mRNA cap formation by methylating the first transcribed nucleotide ribose at the O-2 position. mRNA cap O-2 methylation has roles in mRNA stabilisation and translation, and self-RNA tolerance in innate immunity. We report that CMTR1 is recruited to serine-5-phosphorylated RNA Pol II C-terminal domain, early in transcription. We isolated CMTR1 in a complex with DHX15, an RNA helicase functioning in splicing and ribosome biogenesis, and characterised it as a regulator of CMTR1. When DHX15 is bound, CMTR1 activity is repressed and the methyl-transferase does not bind to RNA pol II. Conversely, CMTR1 activates DHX15 helicase activity, which is likely to impact several nuclear functions. In HCC1806 breast carcinoma cell line, the DHX15-CMTR1 interaction controls ribosome loading of a subset of mRNAs and regulates cell proliferation. The impact of the CMTR1-DHX15 interaction is complex and will depend on the relative expression of these enzymes and their interactors, and the cellular dependency on different RNA processing pathways.

Highlights

Formation of the mRNA cap initiates the maturation of RNA pol II transcripts into translation-competent mRNA (Furuichi, 2015)
CMTR1 was biochemically characterised as the O-2 ribose methyltransferase of the first transcribed nucleotide and the catalytic domain was crystalized with S-adenosyl methionine (SAM) and a capped oligonucleotide (Belanger et al, 2010; Smietanski et al, 2014)
DHX15 (O43143), a 95-kD DEAH-box RNA helicase, was the only protein identified with significant mascot scores and coverage in HA-CMTR1 immunoprecipitates (IP) (Fig S1) (Imamura et al, 1997)

Summary

Introduction

Formation of the mRNA cap initiates the maturation of RNA pol II transcripts into translation-competent mRNA (Furuichi, 2015). MRNA cap formation initiates with the addition of an inverted guanosine group, via a tri-phosphate bridge, to the first transcribed nucleotide of nascent RNA pol II transcripts. This guanosine cap is methylated on the N-7 position to create the cap 0 structure, which binds efficiently to CBC, eIF4F, and other complexes involved in RNA processing and translation initiation. RNGTT/capping enzyme catalyses guanosine cap addition and RNA guanine-7 methyltransferase (RNMT)-RNMT-activating miniprotein (RAM) catalyses guanosine cap N-7 methylation. CMTR1 was biochemically characterised as the O-2 ribose methyltransferase of the first transcribed nucleotide and the catalytic domain was crystalized with S-adenosyl methionine (SAM) and a capped oligonucleotide (Belanger et al, 2010; Smietanski et al, 2014)

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