The mRNA encoding the JUND tumor suppressor detains nuclear RNA-binding proteins to assemble polysomes that are unaffected by mTOR

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Abstract

One long-standing knowledge gap is the role of nuclear proteins in mRNA translation. Nuclear RNA helicase A (DHX9/ RHA) is necessary for the translation of the mRNAs of JUND (JunD proto-oncogene AP-1 transcription factor subunit) and HIV-1 genes, and nuclear cap-binding protein 1 (NCBP1)/ CBP80 is a component of HIV-1 polysomes. The protein kinase mTOR activates canonical messenger ribonucleoproteins by post-translationally down-regulating the eIF4E inhibitory protein 4E-BP1. We posited here that NCBP1 and DHX9/RHA (RHA) support a translation pathway of JUND RNA that is independent of mTOR. We present evidence from reciprocal immunoprecipitation experiments indicating that NCBP1 and RHA both are components of messenger ribonucleoproteins in several cell types. Moreover, tandem affinity and RT– quantitative PCR results revealed that JUND mRNA is a component of a previously unknown ribonucleoprotein complex. Results from the tandem IP indicated that another component of the JUND-containing ribonucleoprotein complex is NCBP3, a recently identified ortholog of NCBP2/CBP20. We also found that NCBP1, NCBP3, and RHA, but not NCBP2, are components of JUNDcontaining polysomes. Mutational analysis uncovered two dsRNA-binding domains of RHA that are necessary to tether JUND–NCBP1/NCBP3 to polysomes. We also found that JUND translation is unaffected by inhibition of mTOR, unless RHA was down-regulated by siRNA. These findings uncover a noncanonical cap-binding complex consisting of NCBP1/NCBP3 and RHA substitutes for the eukaryotic translation initiation factors 4E and 4G and activates mTOR-independent translation of the mRNA encoding the tumor suppressor JUND.

Original languageEnglish (US)
Pages (from-to)7763-7773
Number of pages11
JournalJournal of Biological Chemistry
Volume295
Issue number22
DOIs
StatePublished - May 28 2020

Bibliographical note

Funding Information:
This work was supported by National Institutes of Health Grants P50 NIGMS0103297, T32GM068412, and U54AI50470. The authors declare that they have no conflicts of interest with the contents of this article. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

Publisher Copyright:
© 2020 Singh et al. Published under exclusive license by The American Society for Biochemistry and Molecular Biology, Inc.

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