Abstract 2217: Stress-induced NQO1 controls stability of C/EBPα against 20S proteasomal degradation to regulate p63 expression with implications in protection against chemical-induced skin cancer

Abstract

Abstract In previous studies we have illustrated a role of cytosolic NAD(P)H:quinone oxidoreductase 1 (NQO1) in stabilization of tumor suppressor transcription factor p63 against 20S proteasomal degradation, resulting in thinning of epithelium and chemical-induced skin cancer [Oncogene (2011) 30, 1098-1107]. Current studies demonstrate that an intermediate pathway involving NQO1 control of C/EBPα against 20S proteasomal degradation also contributes to the upregulation of p63 expression and protection. Western and immunohistochemistry analysis revealed that disruption of NQO1 gene in mice and mouse keratinocytes led to degradation of C/EBPα and profound decrease of p63 gene expression. p63 promoter mutagenesis, transfection and ChIP assays identified C/EBPα binding site between nucleotide position −185 to −174 that allows C/EBPα to enhance p63 gene expression. Coimmunoprecipitation and immunoblot analysis demonstrated that 20S proteasomes directly interacted and degraded C/EBPβ. NQO1 direct interaction with C/EBPα led to stabilization of C/EBPα against ubiquitin-independent 20S proteasomal degradation and NQO1 protection of C/EBPα required binding of cofactor NADH. Exposure of skin and keratinocytes to stress agents benzo(a)pyrene, UVB, antioxidant t-BHQ and ionizing radiation led to induction of NQO1 and stabilization of C/EBPα protein resulting in an increase in p63 RNA and protein in wild type but not in NQO1-null mice. Collectively, the current data combined with previous suggest that stress-mediated induction of NQO1 acts both through stabilization of p63-transactivating C/EBPα and through direct stabilization of p63 to control keratinocyte differentiation leading to normal skin development and possibly contribute to protection against chemical/radiation-induced skin carcinogenesis. The studies are significant in light of the knowledge that 2-4% human individuals are homozygous and 23% are heterozygous for NQO1P187S mutation and might be susceptible to stress-induced skin diseases. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2217. doi:1538-7445.AM2012-2217