Ei24, a novel E2F target gene, affects p53-independent cell death upon ultraviolet C irradiation

Abstract

The deficiency of retinoblastoma (Rb) gene deregulates E2F transcription factors and thus induces E2F target genes directly or p53 target genes indirectly via mouse p19Arf (or p14ARF in humans), an E2F target gene. Here, we identified that etoposideinduced 2.4 mRNA (Ei24)/p53-induced gene 8 (Pig8), a p53 target gene involved in apoptosis and autophagy, was up-regulated in Rb-/- mouse embryonic fibroblasts (MEFs). The Ei24 promoter was activated by E2F1 via multiple E2F-responsive elements, independently of the previously reported p53-responsive element. Chromatin immunoprecipitation assays revealed that E2F1 directly acts on the mouse Ei24 promoter. We observed that Ei24 expression was suppressed inp53 -/- MEFs upon UVC irradiation, which was exacerbated inp53 -/- E2f1-/- MEFs, supporting the positive role of E2F1 on Ei24 transcription. Furthermore, Ei24 knockdown sensitized p53-/- MEFs against UVC irradiation. Together, our data indicate that Ei24 is a novel E2F target gene contributing to the survival of p53-deficient cells upon UVC irradiation and thus may have a potential significance as a therapeutic target of certain chemotherapy for treating p53-deficient tumors. © 2013 by The American Society for Biochemistry and Molecular Biology, Inc Published in the U.S.A.