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

Previously, we have shown a role of cytosolic NAD(P)H:quinone oxidoreductase 1 (NQO1) in stabilization of p63 against 20S proteasomal degradation resulting in thinning of epithelium and chemical-induced skin cancer [Oncogene (2011) 30,1098–1107]. Current studies demonstrate that NQO1 control of C/EBPα against20S proteasomal degradation also contributes to the up regulation of p63 expression and protection. Western and immunohistochemistry analysis revealed that disruption of NQO1 gene in mice and mouse keratinocytes led todegradation of C/EBPα and loss of p63 gene expression. p63 promoter mutagenesis, transfection and ChIP assays identified C/EBPα binding site between nucleotide position −185 to −174 that bound to C/EBPα and up regulated p63 gene expression. Coimmunoprecipitation and immunoblot analysis demonstrated that 20S proteasomes directly interacted and degraded C/EBPα. NQO1 direct interaction with C/EBPα led to stabilization of C/EBPα against 20S proteasomal degradation. NQO1 protection of C/EBPα required binding of NADH with NQO1. Exposure of skin and keratinocytes to chemical stress agent benzo(a)pyrene 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−/− mice. Collectively, the current data combined with previous suggest that stress-induction of NQO1 through both stabilization of C/EBPα and increase in p63 and direct stabilization of p63 controls keratinocyte differentiation leading to protection against chemical-induced skin carcinogenesis. The studies are significant since 2–4% human individuals are homozygous and 23% are heterozygous for NQO1P187S mutation and might be susceptible to stress-induced skin diseases.