DHX15 regulates CMTR1-dependent gene expression and cell proliferation

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.

The mRNA cap 2’O methyltransferase CMTR1 regulates the expression of certain interferon-stimulated genes

“…Surprisingly, we also found no difference in the polysome association of the CMTR1-regulated ISG transcripts ( ISG15, MX1 , and IFITM1 ) following CMTR1 depletion ( Figure 3D) . Collectively, these results suggest that loss of CMTR1 does not globally alter cellular translation in response to IFN-β, similar to results described by others (41), nor does it alter the nuclear export, transcript stability, or polysome association of the CMTR1-regulated ISGs.…”

“…Alternatively, the non-CMTR1 regulated ISG IFIT3 may only have low levels of Cap 1, and so it may not be as sensitive to changes in CMTR1 and resulting decrease in Cap 1 levels that would enable IFIT1 sensing and translational inhibition. Indeed, CMTR1 has reduced activity on mRNAs with highly structured 5’ UTRs and as such these structured 5’ UTRs require unwinding by the helicase DHX15 helicase for efficient Cap 1 formation (41, 48). Finally, it is possible that CMTR1 depletion preferentially affects the levels of Cap 1 in ISGs with highly structured 5’ UTRs which are not efficiently 2’O methylated, thereby specifically resulting in reduced translation of these transcripts following CMTR1 depletion.…”

Interactome analysis of the human Cap‐specific mRNA (nucleoside‐2′‐O‐)‐methyltransferase 1 (hMTr1) protein

“…A recent paper has reported that the interaction between hMTr1 and DHX15 is also maintained after RNase treatment and mediated by hMTr1 G-patch domain. 8 Other studies are needed to further characterize the hMTr1 interactions found in this study. Importantly, our data also confirmed the interaction between hMTr1 and DHX15, which was considered a high probable interaction based on our analysis ( Table 1 and Figure 1H).…”

“…Importantly, a recent article described that the DHX15-CMTR1 interaction controls ribosome loading of a subset of mRNAs and impacts on cell proliferation. 8 Synthesis of mRNA requires the participation of a large set of proteins and ribonucleoprotein complexes that act cotranscriptionally to catalyze synthesis of the 5′-end cap, excision of introns, and polyadenylation of the 3′ terminus. 9 Because hMTr1 acts on the maturation of the 5′-end, which is believed to take place early in pre-mRNA processing, by determining the composition of the complexes formed by hMTr1, we expect to obtain information on the factors involved in the initiation of mRNA synthesis.…”

Interplay of mRNA capping and transcription machineries

“…This modification has a role in translation initiation and identification of transcripts as 'self' in innate immunity [4]. CMTR1 is recruited to Ser 5 -phosphorylated Pol II CTD early in transcription [65].…”