Data from The Proto-oncogene PKCι Regulates the Alternative Splicing of Bcl-x Pre-mRNA

<div>Abstract<p>Two splice variants derived from the <i>Bcl-x</i> gene via alternative 5′ splice site selection (5′SS) are proapoptotic Bcl-x(s) and antiapoptotic Bcl-x(L). Previously, our laboratory showed that apoptotic signaling pathways regulated the alternative 5′SS selection via protein phosphatase-1 and <i>de novo</i> ceramide. In this study, we examined the elusive prosurvival signaling pathways that regulate the 5′SS selection of Bcl-x pre-mRNA in cancer cells. Taking a broad-based approach by using a number of small-molecule inhibitors of various mitogenic/survival pathways, we found that only treatment of non–small cell lung cancer (NSCLC) cell lines with the phosphoinositide 3-kinase (PI3K) inhibitor LY294002 (50 μmol/L) or the pan-protein kinase C (PKC) inhibitor Gö6983 (25 μmol/L) decreased the Bcl-x(L)/(s) mRNA ratio. Pan-PKC inhibitors that did not target the atypical PKCs, PKCι and PKCζ, had no effect on the Bcl-x(L)/(s) mRNA ratio. Additional studies showed that downregulation of the proto-oncogene, PKCι, in contrast to PKCζ, also resulted in a decrease in the Bcl-x(L)/(s) mRNA ratio. Furthermore, downregulation of PKCι correlated with a dramatic decrease in the expression of SAP155, an RNA <i>trans</i>-acting factor that regulates the 5′SS selection of Bcl-x pre-mRNA. Inhibition of the PI3K or atypical PKC pathway induced a dramatic loss of SAP155 complex formation at ceramide-responsive RNA <i>cis</i>-element 1. Finally, forced expression of Bcl-x(L) “rescued” the loss of cell survival induced by PKCι siRNA. In summary, the PI3K/PKCι regulates the alternative splicing of Bcl-x pre-mRNA with implications in the cell survival of NSCLC cells. <i>Mol Cancer Res; 10(5); 660–9. ©2012 AACR</i>.</p></div>