Regulated Intron Retention and Nuclear Pre-mRNA Decay Contribute to PABPN1 Autoregulation

Abstract

The poly(A)-binding protein nuclear 1 is encoded by the PABPN1 gene, whose mutations result in oculopharyngeal muscular dystrophy, a late-onset disorder for which the molecular basis remains unknown. Despite recent studies investigating the functional roles of PABPN1, little is known about its regulation. Here, we show that PABPN1 negatively controls its own expression to maintain homeostatic levels in human cells. Transcription from the PABPN1 gene results in the accumulation of two major isoforms: an unspliced nuclear transcript that retains the 3′-terminal intron and a fully spliced cytoplasmic mRNA. Increased dosage of PABPN1 protein causes a significant decrease in the spliced/unspliced ratio, reducing the levels of endogenous PABPN1 protein. We also show that PABPN1 autoregulation requires inefficient splicing of its 3′-terminal intron. Our data suggest that autoregulation occurs via the binding of PABPN1 to an adenosine (A)-rich region in its 3′ untranslated region, which promotes retention of the 3′-terminal intron and clearance of intron-retained pre-mRNAs by the nuclear exosome. Our findings unveil a mechanism of regulated intron retention coupled to nuclear pre-mRNA decay that functions in the homeostatic control of PABPN1 expression.

Supplemental material for this article may be found at http://dx.doi.org/10.1128/MCB.00070-15.

ACKNOWLEDGMENTS

We thank Bin Tian (Rutgers New Jersey Medical School) for PABPN1 3′ READS data and Roscoe Klinck for critical reading of the manuscript. We thank Anne-Marie Landry-Voyer for generating the cell lines that conditionally express normal and alanine-expanded versions of PABPN1.

This work was supported by the Canadian Institutes of Health Research grant MOP-106595 to F.B. F.B. is a Canada Research Chair in the Quality Control of Gene Expression.