SRSF2 regulation of MDM2 reveals splicing as a therapeutic vulnerability of the p53 pathway

Abstract

MDM2 is an oncogene and critical negative regulator of tumor suppressor p53. Genotoxic stress causes alternative splicing of MDM2 transcripts, which leads to alterations in p53 activity and contributes to tumorigenesis. MDM2-ALT1 is one of transcripts predominantly produced in response to genotoxic stress and is comprised of terminal coding exons 3 and 12. Previously, we found that SRSF1 induces MDM2-ALT1 by promoting MDM2 exon 11 skipping. Here we report that splicing regulator SRSF2 antagonizes the regulation of SRSF1 by facilitating the inclusion of exon 11 through binding at two conserved exonic splicing enhancers. Overexpression of SRSF2 reduced the generation of MDM2-ALT1 in genotoxic stress condition, whereas knockdown induces the expression of MDM2-ALT1 in absence of genotoxic stress. Consistently, blocking the exon 11 SRSF2 binding sites using oligonucleotides promotes MDM2-ALT1. The regulation of MDM2 splicing by SRSF2 is also conserved in mouse as mutation of one SRSF2 binding site in Mdm2 exon 11, using CRISPR-Cas9, increases the expression MDM2-ALT1 homolog Mdm2-MS2 and proliferation of NIH 3T3 cells. Taken together, these findings underscore the relevance of MDM2 alternative splicing in cancer and suggest that p53 levels can be modulated by artificially regulating MDM2 splicing.