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1.  SRSF1 (SRp30a) regulates the alternative splicing of caspase 9 via a novel intronic splicing enhancer affecting the chemotherapeutic sensitivity of non-small cell lung cancer cells 
Molecular cancer research : MCR  2011;9(7):889-900.
Increasing evidence points to the functional importance of alternative splice variations in cancer pathophysiology with the alternative pre-mRNA processing of caspase 9 as one example. In this study, we delve into the underlying molecular mechanisms that regulate the alternative splicing of caspase 9. Specifically, the pre-mRNA sequence of caspase 9 was analyzed for RNA cis-elements known to interact with SRSF1, a required enhancer for caspase 9 RNA splicing. This analysis revealed thirteen possible RNA cis-elements for interaction with SRSF1 with mutagenesis of these RNA cis-elements identifying a strong intronic splicing enhancer located in intron 6 (C9-I6/ISE). SRSF1 specifically interacted with this sequence, which was required for SRSF1 to act as a splicing enhancer of the inclusion of the four exon cassette. To further determine the biological importance of this mechanism, we employed RNA oligonucleotides to redirect caspase 9 pre-mRNA splicing in favor of caspase 9b expression, which resulted in an increase in the IC50 of non-small cell lung cancer (NSCLC) cells to daunorubicin, cisplatinum, and paclitaxel. In contrast, downregulation of caspase 9b induced a decrease in the the IC50 of these chemotherapeutic drugs. Lastly, these studies demonstrated that caspase 9 RNA splicing was a major mechanism for the synergistic effects of combination therapy with daunorubicin and erlotinib. Overall, we have identified a novel intronic splicing enhancer that regulates caspase 9 RNA splicing and specifically interacts with SRSF1. Furthermore, we demonstrate that the alternative splicing of caspase 9 is an important molecular mechanism with therapeutic relevance to NSCLCs.
PMCID: PMC3140550  PMID: 21622622
ceramide; non-small cell lung cancer; RNA trans-factor; tumor repressor; oncogene; ASF/SF2; SRp30a; SRSF1; chemotherapy; erlotinib; daunorubicin; cisplatinum; paclitaxel
2.  The RNA-binding protein Sam68 modulates the alternative splicing of Bcl-x 
The Journal of Cell Biology  2007;176(7):929-939.
The RNA-binding protein Sam68 is involved in apoptosis, but its cellular mRNA targets and its mechanism of action remain unknown. We demonstrate that Sam68 binds the mRNA for Bcl-x and affects its alternative splicing. Depletion of Sam68 by RNA interference caused accumulation of antiapoptotic Bcl-x(L), whereas its up-regulation increased the levels of proapoptotic Bcl-x(s). Tyrosine phosphorylation of Sam68 by Fyn inverted this effect and favored the Bcl-x(L) splice site selection. A point mutation in the RNA-binding domain of Sam68 influenced its splicing activity and subnuclear localization. Moreover, coexpression of ASF/SF2 with Sam68, or fusion with an RS domain, counteracted Sam68 splicing activity toward Bcl-x. Finally, Sam68 interacted with heterogenous nuclear RNP (hnRNP) A1, and depletion of hnRNP A1 or mutations that impair this interaction attenuated Bcl-x(s) splicing. Our results indicate that Sam68 plays a role in the regulation of Bcl-x alternative splicing and that tyrosine phosphorylation of Sam68 by Src-like kinases can switch its role from proapoptotic to antiapoptotic in live cells.
PMCID: PMC2064079  PMID: 17371836

Results 1-2 (2)