Melanoma Differentiation-associated Gene 7/IL-24 Exerts Cytotoxic Effects by Altering the Alternative Splicing of Bcl-x Pre-mRNA via the SRC/PKCδ Signaling Axis

• Published in: The Journal of biological chemistry 2016-10, Vol.291 (41), p.21669-21681
• Main Authors: Shapiro, Brian A., Vu, Ngoc T., Shultz, Michael D., Shultz, Jacqueline C., Mietla, Jennifer A., Gouda, Mazen M., Yacoub, Adly, Dent, Paul, Fisher, Paul B., Park, Margaret A., Chalfant, Charles E.
• Format: Article
• Language: English
• Subjects: A549 Cells; Alternative Splicing; apoptosis; bcl-X Protein - genetics; bcl-X Protein - metabolism; Carcinoma, Non-Small-Cell Lung - genetics; Carcinoma, Non-Small-Cell Lung - metabolism; Carcinoma, Non-Small-Cell Lung - pathology; cell death; cell signaling; Humans; Interleukins - genetics; Interleukins - metabolism; Lung Neoplasms - genetics; Lung Neoplasms - metabolism; Lung Neoplasms - pathology; MDA-7/IL-24, Bcl-x; non-small cell lung cancer; Protein Kinase C-delta - genetics; Protein Kinase C-delta - metabolism; Proto-Oncogene Proteins pp60(c-src) - genetics; Proto-Oncogene Proteins pp60(c-src) - metabolism; RNA splicing; RNA Stability; RNA, Messenger - genetics; RNA, Messenger - metabolism; RNA, Neoplasm - genetics; RNA, Neoplasm - metabolism; Signal Transduction
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M116.737569

Melanoma differentiation-associated gene 7 (MDA-7/IL-24) exhibits cytotoxic effects on tumor cells while sparing untransformed cells, and Bcl-x(L) is reported to efficiently block the induction of cell death by MDA-7/IL-24. The expression of Bcl-x(L) is regulated at the level of RNA splicing via alternative 5′ splice site selection within exon 2 to produce either the pro-apoptotic Bcl-x(s) or the anti-apoptotic Bcl-x(L). Our laboratory previously reported that Bcl-x RNA splicing is dysregulated in a large percentage of human non-small cell lung cancer (NSCLC) tumors. Therefore, we investigated whether the alternative RNA splicing of Bcl-x pre-mRNA was modulated by MDA-7/IL-24, which would suggest that specific NSCLC tumors are valid targets for this cytokine therapy. Adenovirus-delivered MDA-7/IL-24 (Ad.mda-7) reduced the viability of NSCLC cells of varying oncogenotypes, which was preceded by a decrease in the ratio of Bcl-x(L)/Bcl-x(s) mRNA and Bcl-x(L) protein expression. Importantly, both the expression of Bcl-x(L) and the loss of cell viability were “rescued” in Ad.mda-7-treated cells incubated with Bcl-x(s) siRNA. In addition, NSCLC cells ectopically expressing Bcl-x(s) exhibited significantly reduced Bcl-x(L) expression, which was again restored by Bcl-x(s) siRNA, suggesting the existence of a novel mechanism by which Bcl-x(s) mRNA restrains the expression of Bcl-x(L). In additional mechanistic studies, inhibition of SRC and PKCδ completely ablated the ability of MDA-7/IL-24 to reduce the Bcl-x(L)/(s) mRNA ratio and cell viability. These findings show that Bcl-x(s) expression is an important mediator of MDA-7/IL-24-induced cytotoxicity requiring the SRC/PKCδ signaling axis in NSCLC cells.