title: HnRNPH1/H2, U1 snRNP, and U11 snRNP cooperate to regulate the stability of the U11-48K pre-mRNA.
abstract: Alternative splicing (AS) is a major contributor to proteome diversity, but it also regulates gene expression by introducing premature termination codons (PTCs) that destabilize transcripts, typically via the nonsense-mediated decay (NMD) pathway. Such AS events often take place within long, conserved sequence elements, particularly in genes encoding various RNA binding proteins. AS-NMD is often activated by the protein encoded by the same gene, leading to a self-regulating feedback loop that maintains constant protein levels. However, cross-regulation between different RNA binding proteins is also common, giving rise to finely tuned regulatory networks. Recently, we described a feedback mechanism regulating two protein components of the U12-dependent spliceosome (U11-48K and U11/U12-65K) through a highly conserved sequence element. These elements contain a U11 snRNP-binding splicing enhancer (USSE), which, through the U11 snRNP, activates an upstream U2-type 3'ss, resulting in the degradation of the U11-48K mRNA by AS-NMD. Through phylogenetic analysis, we now identify a G-rich sequence element that is conserved in fishes as well as mammals. We show that this element binds hnRNPF/H proteins in vitro. Knockdown of hnRNPH1/H2 or mutations in the G-run both lead to enhanced activation of the 3'ss in vivo, suggesting that hnRNPH1/H2 proteins counteract the 3'ss activation. Furthermore, we provide evidence that U1 binding immediately downstream from the G-run similarly counteracts the U11-mediated activation of the alternative 3'ss. Thus, our results elucidate the mechanism in which snRNPs from both spliceosomes together with hnRNPH1/H2 proteins regulate the recognition and activation of the highly conserved alternative splice sites within the U11-48K pre-mRNA.
authors: Institute of Biotechnology, PL 56, FIN-00014 University of Helsinki, Helsinki, Finland.
authors: Janne J
authors: JJ
authors: Turunen
authors: Bhupendra
authors: B
authors: Verma
authors: Tuula A
authors: TA
authors: Nyman
authors: Mikko J
authors: MJ
authors: Frilander
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D012322:RNA Precursors / Q000378:metabolism*; D012326:RNA Splicing; D020871:RNA Stability; D012332:RNA, Heterogeneous Nuclear / Q000378:metabolism*; D017412:Ribonucleoprotein, U1 Small Nuclear / Q000737:chemistry / Q000378:metabolism*; D017411:Ribonucleoproteins, Small Nuclear / Q000235:genetics / Q000378:metabolism*; D017381:Spliceosomes / Q000378:metabolism
chemical_list: D012322:RNA Precursors; D012332:RNA, Heterogeneous Nuclear; D017412:Ribonucleoprotein, U1 Small Nuclear; D017411:Ribonucleoproteins, Small Nuclear; C098762:U11 small nuclear ribonucleoprotein, human