Protein phosphatase 1 binds to the RNA recognition motif of several splicing factors and regulates alternative pre-mRNA processing

Abstract

Alternative splicing emerges as one of the most important mechanisms to generate transcript diversity. It is regulated by the formation of protein complexes on pre-mRNA. We demonstrate that protein phosphatase 1 (PP1) binds to the splicing factor transformer2-beta1 (tra2-beta1) via a phylogenetically conserved RVDF sequence located on the RNA recognition motif (RRM) of tra2-beta1. PP1 binds directly to tra2-beta1 and dephosphorylates it, which regulates the interaction between tra2-beta1 and other proteins. Eight other proteins, including SF2/ASF and SRp30c, contain an evolutionary conserved PP1 docking motif in the beta-4 strand of their RRMs indicating that binding to PP1 is a new function of some RRMs. Reducing PP1 activity promotes usage of numerous alternative exons, demonstrating a role of PP1 activity in splice site selection. PP1 inhibition promotes inclusion of the survival of motoneuron 2 exon 7 in a mouse model expressing the human gene. This suggests that reducing PP1 activity could be a new therapeutic principle to treat spinal muscular atrophy and other diseases caused by missplicing events. Our data indicate that the binding of PP1 to evolutionary conserved motifs in several RRMs is the link between known signal transduction pathways regulating PP1 activity and pre-mRNA processing.

A role for protein phosphatase PP1γ in SMN complex formation and subnuclear localization to Cajal bodies

“…The physiological relevance of our data is that a specific manipulation of PP1c might impact on the SMN complex independently of an increase in SMN levels (Figs 5,8). However, pharmacological ablation of all three PP1 catalytic subunits causes formation of SMN nuclear gems in SMA cells (Novoyatleva et al, 2008;our unpublished data). Because gems are storage sites formed when pre-mRNA splicing is inhibited, more specific molecules will be required.…”

Control of alternative pre-mRNA splicing by Ca++ signals

“…Phosphatases, including PP1 [173][174][175][176][177][178][179][180], PP2C-gamma [181,182], PP2A [178,183], and the pol II CTD phosphatase FCP1 [184], also interact with splicing factors or are known to control splicing. Of these, PP2A binds CaMK IV in a signalling complex [185,186].…”

Intra-domain Cross-talk Regulates Serine-arginine Protein Kinase 1-dependent Phosphorylation and Splicing Function of Transformer 2β1

“…The efficiency of this process is guided by a docking groove in the kinase domain of SRPK1 that feeds Arg-Ser dipeptides to the active site. In this work we address how SRPK1 phosphorylates Tra2␤1, an SRlike protein that contains two RS domains and controls gene splicing in a phosphorylation-dependent manner (10,46). Interestingly, although most SR proteins gain entry into the nucleus through a phosphorylation-dependent process, hyperphosphorylation drives Tra2␤1 into the cytoplasm (30,31), similar to that for the splicing regulator hnRNP1 (47).…”

“…Furthermore, localization of these factors is controlled by phosphorylation-dependent interactions with a specific transportin (TRN-SR) that promotes entry through the nuclear pore and deposition in nuclear speckles (18,49). In the case of the SR-like Tra2␤1, the alternative splicing of several genes has been linked to both hypo-and hyper-phosphorylation levels (29,46,50). Although the details of these processes are not well understood at a molecular level, it is anticipated that large phosphorylationdependent structural changes in these splicing factors may be required for any biological regulatory mechanism.…”