The hnRNP C tetramer binds to CBC on mRNA and impedes PHAX recruitment for the classification of RNA polymerase II transcripts

Abstract

In eukaryotic cells, various classes of RNAs are exported to the cytoplasm by class-specific factors. Accumulating evidence has shown that export factors affect the fate of RNA, demonstrating the importance of proper RNA classification upon export. We previously reported that RNA polymerase II transcripts were classified after synthesis depending on their length, and identified heterogeneous nuclear ribonucleoprotein (hnRNP) C as the key classification factor. HnRNP C inhibits the recruitment of PHAX, an adapter protein for spliceosomal U snRNA export, to long transcripts, navigating these RNAs to the mRNA export pathway. However, the mechanisms by which hnRNP C inhibits PHAX recruitment to mRNA remain unknown. We showed that the cap-binding complex, a bridging factor between m7G-capped RNA and PHAX, directly interacted with hnRNP C on mRNA. Additionally, we revealed that the tetramer-forming activity of hnRNP C and its strong RNA-binding activity were crucial for the inhibition of PHAX binding to longer RNAs. These results suggest that mRNA is wrapped around the hnRNP C tetramer without a gap from the cap, thereby impeding the recruitment of PHAX. The results obtained on the mode of length-specific RNA classification by the hnRNP C tetramer will provide mechanistic insights into hnRNP C-mediated RNA biogenesis.

Structural basis for competitive binding of productive and degradative co-transcriptional effectors to the nuclear cap-binding complex

“…A minimal region, PHAX 103-327 , is required for full binding (Schulze et al, 2018), which includes the PHAX non-specific RNA-binding domain (Mourao et al, 2010; Segref et al, 2001). PHAX may initially bind to a wide-range of transcripts (Giacometti et al, 2017) but is thought to be displaced by hnRNP-C on RNAs, such as mRNAs, with long enough (> 200 nts) unstructured 5’ regions (Dantsuji et al, 2023; McCloskey et al, 2012). It has been shown that PHAX binding to CBC is incompatible with the binding of NELF-E (Schulze and Cusack, 2017) and ZC3H18 (Giacometti et al, 2017).…”

Upregulation of Long Noncoding RNA MAGOH-DT Mediates TNF-<i><b>α</b></i> and High Glucose-Induced Endothelial-Mesenchymal Transition in Arteriosclerosis Obliterans

“…Mammalian TGF-β consists of three isoforms: TGF-β1, TGF-β2 and TGF-β3, and all of them have been reported to induce EndMT in human endothelial cells (Ciavarella et al, 2021;Hong et al, 2020;Nasim et al, 2023). HNRPC is a nuclear-restricted RNA-binding protein involved in mRNA stability, splicing, export and translation (Dantsuji et al, 2023;L. Mo et al, 2022).…”

Virus Infection and mRNA Nuclear Export

“…Thus, the tetramer sorts the transcripts into two RNA categories: mRNA or uridine-rich small nuclear RNA (U snRNA). Further mechanistic studies proved that the hnRNP-C tetramer binds the cap-binding complex (CBC) on mRNA and blocks PHAX (an adaptor protein for splicosomal U snRNA output) recruitment for the classification of RNA polymerase II transcripts, so as to direct these RNAs to the mRNA nuclear export pathway [ 59 ]. This discovery of the hnRNP C tetramer for length-specific RNA classification contributes to a deeper understanding of RNA biogenesis and provides potential strategies for future disease treatments.…”