Department of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, Virginia 23298; Vietnam Education Foundation, Arlington, Virginia 22201.
Department of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, Virginia 23298.
J Biol Chem. 2013 Mar 22;288(12):8575-8584. doi: 10.1074/jbc.M112.443333. Epub 2013 Feb 8.
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.
Caspase-9 有两种剪接变异体，促凋亡的 caspase-9a 和抗凋亡的 caspase-9b，它们受与 caspase-9 前体 mRNA（C9/E3）外显子 3 相关的 RNA 转录因子调控。在这项研究中，我们鉴定出 hnRNP U 是与 C9/E3 相关的 RNA 转录因子。hnRNP U 的下调导致 caspase-9a/9b mRNA 比率降低，表明其具有新的增强功能。重要的是，hnRNP U 特异性地结合到 C9/E3 上，该 RNA 顺式元件先前被报道为剪接抑制因子 hnRNP L 的结合位点。磷酸化的 hnRNP L 干扰 hnRNP U 与 C9/E3 的结合，我们的结果表明磷酸肌醇 3-激酶/AKT 途径在调节 hnRNP U 与 C9/E3 的结合中起重要作用。综上所述，这些发现表明 hnRNP U 与 hnRNP L 竞争结合 C9/E3 以增强四外显子盒的包含，并且该剪接增强功能被 AKT 途径通过磷酸化 hnRNP L 所阻断。
