Autoregulation of Polypyrimidine Tract Binding Protein by Alternative Splicing Leading to Nonsense-Mediated Decay

Abstract

Polypyrimdine tract binding protein (PTB) is a regulator of alternative splicing, mRNA 3' end formation, mRNA stability and localization, and IRES-mediated translation. Transient overexpression of PTB can influence alternative splicing, sometimes resulting in nonphysiological splicing patterns. Here, we show that alternative skipping of PTB exon 11 leads to an mRNA that is removed by NMD and that this pathway consumes at least 20% of the PTB mRNA in HeLa cells. We also show that exon 11 skipping is itself promoted by PTB in a negative feedback loop. This autoregulation may serve both to prevent disruptively high levels of PTB expression and to restore nuclear levels when PTB is mobilized to the cytoplasm. Our findings suggest that alternative splicing can act not only to generate protein isoform diversity but also to quantitatively control gene expression and complement recent bioinformatic analyses, indicating a high prevalence of human alternative splicing leading to NMD.

Caspases shutdown nonsense-mediated mRNA decay during apoptosis

“…[8][9][10] In addition to its role in quality control, NMD also regulates gene expression of so-called natural substrates of NMD. [11][12][13][14][15] Proteins that have a central role in NMD, such as UPF1, UPF2, UPF3/UPF3a and UPF3X/UPF3b are highly conserved from yeast to human. The requirement for these UPF proteins in NMD is illustrated by the fact that the downregulation of any one of them results in an inhibition of NMD.…”

Protein kinase clk/STY is differentially regulated during erythroleukemia cell differentiation: a bias toward the skipped splice variant characterizes postcommitment stages

“…Autoregulation via alternative splicing and NMD has been described for other members of the splicing machinery such as PTB [47], SC35 [48], TIA and TIAR [49], Srp20 [50], ADAR2 [51] and hnRNPA1 [52]. These observations led Wollerton and co-workers to propose a common mechanism for gene expression control [47]. Exon 4 in clk/STY is flanked by introns containing several cisacting sequences optimal for the PTB protein binding (data not shown).…”

The importance of RNA binding proteins in preproinsulin mRNA stability

“…For the remaining part of this review we will focuse on PTBP1, and abbreviate it as PTB. PTB levels are controlled by an auto-regulatory feed back loop involving alternative splicing and the nonsense-mediated decay pathway (Wollerton et al, 2004). It appears that overexpression of PTB promotes a splicing pathway that results in exclusion of exon 11 and a generation of a targeting signal to the nonsense-mediated decay pathway.…”

“…This pathway is responsible for the destruction of mRNAs that have either been transcribed from genes with nonsense mutations or that are incorrectly spliced. This auto-regulation may serve to prevent high levels of PTB or to restore nuclear levels during nucleocytoplasmic shuttling (Wollerton et al, 2004).…”

“…Surprisingly, we observed an increase in both PTB mRNA and PTB protein levels in response to the siRNA treatment. Possible explanations for this could be that the siRNA molecule, by binding to a critical region of the PTB mRNA molecule, protects, rather than promotes, against degradation, or that the siRNA molecule modulates PTB mRNA Page 9 of 14 A c c e p t e d M a n u s c r i p t 9 splicing so that a more stable mRNA is generated (Wollerton et al, 2004). In this context it is noteworthy that expression of nPTB is silenced during muscle development by a specific miRNA (miR-133) (Boutz et al, 2007).…”