Abstract 186: NER factor XPC enhances DNA damage-induced apoptosis independently of p53 function

Abstract

Abstract Xeroderma Pigmentosum complementation group C (XPC) is a 940-aa protein engaged in the DNA damage recognition during nucleotide excision repair (NER). It was reported that one of the XPC polymorphisms, Lys939Gln, is associated to cancer predisposition, although this variant did not affect NER. Thus, another mechanism must exist to contribute to this cancer susceptibility. In addition, this XPC genetic polymorphism correlates with the failure of imatinib treatment in patients with chronic myeloid leukemia. We reasoned that XPC must be influencing other functions unrelated to DNA repair. Here, we demonstrated that XPC can enhance the apoptosis induced by various DNA damaging agents, including ionizing radiation (IR), ultraviolet light (UV), cisplatin, and etoposide. In addition, XPC-mediated apoptosis is independent of p53, as reflected by the findings that knock-down of XPC expression compromised the UV or IR-induced apoptosis in p53-deficient Li-Fraumeni Syndrome (LFS) MDAH041 and HCT116 cell lines, while having no influence on apoptosis in their p53-proficient counterparts. Also, in response to UV irradiation, XPC deficiency did not affect the mitochondrial cytochrome c release or had only slight effect on the activation of caspase-3. However, XPC deficiency compromised the UV-induced activation of caspase-9. Therefore, XPC seems to function downstream of mitochondrial membrane permeabilization (MMP) and upstream of caspase-9 activation during DNA damage-induced apoptosis. We further demonstrated that XPC deficiency impaired the UV-induced caspase-2 activation, as reflected by reduced cleavage of long isoform of caspase-2 (CASP-2L) in XP-C cells compared to XPC-restored XP-C cells following UV irradiation. Meanwhile, the short isoform of caspase-2 (CASP-2S) was found to be induced in XP-C cells at early times following UV irradiation, while it remained unchanged in XPC-restored XP-C cells. Given that caspase 2 gene generates both proapoptotic (CASP-2L) and antiapoptotic (CASP-2S) isoforms by alternative splicing, our data suggest that XPC enhances DNA damage-induced apoptosis by inhibiting the production of anti-apoptotic CASP-2S via regulation of the alternative splicing of caspase-2. (Supported by NIH grants CA93413, ES2388 and ES12991). Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 186. doi:10.1158/1538-7445.AM2011-186