hnRNP U enhances caspase-9 splicing and is modulated by AKT-dependent phosphorylation of hnRNP L.

J Biol Chem

Department of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, Virginia 23298; Research and Development, Hunter Holmes McGuire Veterans Affairs Medical Center, Richmond, Virginia 23249; The Massey Cancer Center, Virginia Commonwealth University, Richmond, Virginia 2329

Published: March 2013


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Article Abstract

Caspase-9 has two splice variants, pro-apoptotic caspase-9a and anti-apoptotic caspase-9b, which are regulated by RNA trans-factors associated with exon 3 of caspase-9 pre-mRNA (C9/E3). In this study, we identified hnRNP U as an RNA trans-factor associated with C9/E3. Down-regulation of hnRNP U led to a decrease in the caspase-9a/9b mRNA ratio, demonstrating a novel enhancing function. Importantly, hnRNP U bound specifically to C9/E3 at an RNA cis-element previously reported as the binding site for the splicing repressor, hnRNP L. Phosphorylated hnRNP L interfered with hnRNP U binding to C9/E3, and our results demonstrate the importance of the phosphoinositide 3-kinase/AKT pathway in modulating the association of hnRNP U to C9/E3. Taken together, these findings show that hnRNP U competes with hnRNP L for binding to C9/E3 to enhance the inclusion of the four-exon cassette, and this splice-enhancing function is blocked by the AKT pathway via phosphorylation of hnRNP L.

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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3605676PMC
http://dx.doi.org/10.1074/jbc.M112.443333DOI Listing

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