Splicing factor SRSF1 negatively regulates alternative splicing of MDM2 under damage. Nucleic Acids Res

Genotoxic stress induces alternative splicing of the oncogene MDM2 generating MDM2-ALT1, an isoform attributed with tumorigenic properties. However, the mechanisms underlying this event remain unclear. Here we explore MDM2 splicing regulation by utiliz-ing a novel minigene that mimics endogenous MDM2 splicing in response to UV and cisplatinum-induced DNA damage. We report that exon 11 is necessary and sufficient for the damage-specific alternative splicing of the MDM2 minigene and that the splicing factor SRSF1 binds exon 11 at evolutionarily con-served sites. Interestingly, mutations disrupting this interaction proved sufficient to abolish the stress-induced alternative splicing of the MDM2 minigene. Furthermore, SRSF1 overexpression promoted ex-clusion of exon 11, while its siRNA-mediated knock-down prevented the stress-induced alternative splic-ing of endogenous MDM2. Additionally, we observed elevated SRSF1 levels under stress and in tumors correlating with the expression of MDM2-ALT1. No-tably, we demonstrate that MDM2-ALT1 splicing can be blocked by targeting SRSF1 sites on exon 11 using antisense oligonucleotides. These results present conclusive evidence supporting a negative role for SRSF1 in MDM2 alternative splicing. Importantly, we define for the first time, a clear-cut mechanism for the regulation of damage-induced MDM2 splicing and present potential strategies for manipulating MDM2 expression via splicing modulation