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Abstract Background Parathyroid hormone (PTH) gene expression is regulated post-transcriptionally through the binding of the trans-acting proteins AU rich binding factor 1 (AUF1), Upstream of N-ras (Unr) and KH-type splicing regulatory protein (KSRP) to an AU rich element (ARE) in PTH mRNA 3'-UTR. AUF1 and Unr stabilize PTH mRNA while KSRP, recruiting the exoribonucleolytic complex exosome, promotes PTH mRNA decay. Results PTH mRNA is cleaved by the endoribonuclease polysomal ribonuclease 1 (PMR1) in an ARE-dependent manner. Moreover, PMR1 co-immunoprecipitates with PTH mRNA, the exosome and KSRP. Knock-down of either exosome components or KSRP by siRNAs prevents PMR1-mediated cleavage of PTH mRNA. Conclusion PTH mRNA is a target for the endonuclease PMR1. The PMR1 mediated decrease in PTH mRNA levels involves the PTH mRNA 3'-UTR ARE, KSRP and the exosome. This represents an unanticipated mechanism by which the decay of an ARE-containing mRNA is facilitated by KSRP and is dependent on both the exosome and an endoribonuclease.

Most mutations that truncate the reading frame of the DMD gene cause loss of dystrophin expression and lead to Duchenne muscular dystrophy. However, amelioration of disease severity has been shown to result from alternative translation initiation beginning in DMD exon 6 that leads to expression of a highly functional N-truncated dystrophin. Here we demonstrate that this isoform results from usage of an internal ribosome entry site (IRES) within exon 5 that is glucocorticoid inducible. We confirmed IRES activity by both peptide sequencing and ribosome profiling in muscle from individuals with minimal symptoms despite the presence of truncating mutations. We generated a truncated reading frame upstream of the IRES by exon skipping, which led to synthesis of a functional N-truncated isoform in both human subject-derived cell lines and in a new DMD mouse model, where expression of the truncated isoform protected muscle from contraction-induced injury and corrected muscle force to the same level as that observed in control mice. These results support a potential therapeutic approach for patients with mutations within the 5' exons of DMD., Mutations in the DMD gene result in either the more severe Duchenne muscular dystrophy (DMD) or the milder Becker muscular dystrophy (BMD). The phenotype generally depends on whether the mutation [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.tibs.2009.05.003 Byline: Daniel R. Schoenberg (1), Lynne E. Maquat (2) Abstract: The 5'-cap structure that typifies all polymerase II-transcribed RNAs plays important roles in pre-mRNA processing and mRNA export, translation and quality control. Removal of the cap is a regulated process that is considered to be the first irreversible step in mRNA decay. An emerging view challenges this idea: mRNAs have been identified in mammalian cells that lack sequences from their 5' ends but nevertheless appear to be modified with a cap or cap-like structure. Furthermore, a cytoplasmic form of capping enzyme was recently identified that, together with a novel kinase, generates capped ends from cleaved RNAs. These and other findings provide evidence for re-capping and its possible functions. Author Affiliation: (1) Department of Molecular and Cellular Biochemistry and Center for RNA Biology, The Ohio State University, Columbus, OH 43210, USA (2) Department of Biochemistry and Biophysics and Center for RNA Biology, University of Rochester, Rochester, NY 14642, USA

Previous work showed that human [beta]-globin mRNAs harboring a premature termination codon are degraded in the erythroid tissues of mice to products that lack sequences from the mRNA 5' end but contain a 5' cap-like structure. Whether these decay products are the consequence of endonucleolytic or 5'-to-3' exonucleolytic activity is unclear. We report that this [beta]-globin mRNA decay pathway is recapitulated in cultured mouse erythroleukemia (MEL) cells and targets nonsense-free mRNA to a lesser extent than nonsense-containing mRNA. S1 nuclease mapping and primer extension demonstrated that 70-80% of decay product 5' ends contain a UG dinucleotide. Detection of upstream counterparts of these decay products indicates that they are generated by endonucleolytic activity. Both crude and partially purified polysome extracts prepared from MEL cells contain an endonucleolytic activity that generates decay products comparable to those observed in vivo. These data suggest that an endonuclease with preference for UG dinucleotides is involved in the degradation of nonsense-containing and, to a lesser extent, nonsense-free human [beta]-globin mRNAs in mouse erythroid cells. nonsense codon | UG dinucleotides | mRNA endonuclease | polysomes

Abstract Background Parathyroid hormone (PTH) gene expression is regulated post-transcriptionally through the binding of the trans-acting proteins AU rich binding factor 1 (AUF1), Upstream of N-ras (Unr) and KH-type splicing regulatory protein (KSRP) to an AU rich element (ARE) in PTH mRNA 3'-UTR. AUF1 and Unr stabilize PTH mRNA while KSRP, recruiting the exoribonucleolytic complex exosome, promotes PTH mRNA decay. Results PTH mRNA is cleaved by the endoribonuclease polysomal ribonuclease 1 (PMR1) in an ARE-dependent manner. Moreover, PMR1 co-immunoprecipitates with PTH mRNA, the exosome and KSRP. Knock-down of either exosome components or KSRP by siRNAs prevents PMR1-mediated cleavage of PTH mRNA. Conclusion PTH mRNA is a target for the endonuclease PMR1. The PMR1 mediated decrease in PTH mRNA levels involves the PTH mRNA 3'-UTR ARE, KSRP and the exosome. This represents an unanticipated mechanism by which the decay of an ARE-containing mRNA is facilitated by KSRP and is dependent on both the exosome and an endoribonuclease.

In the version of this article initially published online, the nucleotide numbering of the AS (-3 to + 16), B (+17 to +40) and C (+49 to -10) targeted sequences [...]

In the version ofthis article initially published online, the nucleotide numbering of the AS (-3 to + 16), B (+17 to +40) and C (+49 to -10) targeted sequences in [...]