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Loss of full-length hnRNP R isoform impairs DNA damage response in motoneurons by inhibiting Yb1 recruitment to Chromatin

ABSTRACT: Neurons critically rely on the functions of RNA-binding proteins to maintain their polarity and resistance to neurotoxic stresses. HnRNP R has a diverse range of post-transcriptional regulatory functions and is important for neuronal development by regulating axon growth. Hnrnpr pre-mRNA undergoes alternative splicing to produce transcripts encoding two protein isoforms: a full-length protein and a shorter form lacking the N-terminal acidic domain. While the neuronal defects produced by total hnRNP R depletion have been investigated before, the individual functions of each hnRNP R isoforms are unknown. We generated a Hnrnpr knockout mouse (Hnrnprtm1a/tm1a) showing selective loss of the full-length hnRNP R isoform. Motoneurons cultured from Hnrnprtm1a/tm1a mice did not show any axonal growth defects. However, they show an accumulation of double-strand breaks and an impaired DNA damage response. Proteomic analysis of the hnRNP R interactome revealed the multifunctional Y-box binding protein 1 (Yb1) as a top interactor. Yb1 depleted motoneurons also exhibit defects in DNA ´damage repair. We show that Yb1 is recruited to chromatin upon DNA damage, a mechanism that is dependent on full length hnRNP R. Our findings thus suggest a novel role of hnRNP R in maintaining genomic integrity and highlight the function of its N-terminal acidic domain in this context.

INSTRUMENT(S): Q Exactive

ORGANISM(S): Mus Musculus (mouse)

TISSUE(S): Motoneuron

SUBMITTER: Mario Oroshi

LAB HEAD: Felix Meissner

PROVIDER: PXD022467 | Pride | 2021-11-01

REPOSITORIES: Pride

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Project description:Regulation of gene expression at the post-transcriptional level plays an indispensable role during TGFbeta-induced EMT and metastasis. This regulation involves a transcript-selective translational regulatory pathway in which a ribonucleoprotein (mRNP) complex, consisting of heterogeneous nuclear ribonucleoprotein E1 (hnRNP E1) and eukaryotic elongation factor 1A1 (eEF1A1), binds to a 3M-bM-^@M-^Y-UTR regulatory BAT (TGFM-NM-2 activated translation) element and silences translation of Dab2 and ILEI mRNAs, two transcripts which are involved in mediating EMT. TGFbeta activates a kinase cascade terminating in the phosphorylation of hnRNP E1, by isoform-specific stimulation of protein kinase B/Akt2, inducing the release of the mRNP complex from the 3M-bM-^@M-^Y-UTR element, resulting in the reversal of translational silencing and increased expression of Dab2 and ILEI transcripts. We adopted a combinatorial approach involving polysome profiling and RIP-Chip analyses using hnRNP E1 and filtered the array data based on the regulatory mechanism of Dab2 and ILEI. This led to the identification and validation of a cohort of target mRNAs that follow the same pattern of regulation as Dab2 and ILEI. To identify potential target mRNA transcripts that are translationally regulated by hnRNP E1 in a TGF-beta-dependent manner, we adopted a combinatorial approach involving expression profiling analyses and RNA immunoprecipitation analysis (RIP-Chip). We performed a screen using: 1) total mRNA and 2) RNA isolated from monosomal (non-translating) versus polysomal (translating) fractions from TGF-beta-treated (24 h) and non-treated NMuMG cells and from the hnRNP E1 knockdown derivative (E1KD), that undergo constitutive EMT even in the absence of TGF-beta. In addition, we screened for transcripts that selectively interact with hnRNP E1 in NMuMG cells under unstimulated conditions and subsequently lose their temporal association following TGF-beta stimulation. The samples were individually hybridized to Affymetrix GeneChipM-BM-. Mouse Genome 430 2.0 arrays.

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Loss of full-length hnRNP R isoform impairs DNA damage response in motoneurons by inhibiting Yb1 recruitment to Chromatin

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