Hypoxia-inducible factor-1 alpha regulates the expression of nucleotide excision repair proteins in keratinocytes

The regulation of DNA repair enzymes is crucial for cancer prevention, initiation, and therapy. We have studied the effect of ultraviolet B (UVB) radiation on the expression of the two nucleotide excision repair factors (XPC and XPD) in human keratinocytes. We show that hypoxia-inducible factor-1 alpha (HIF-1 alpha) is involved in the regulation of XPC and XPD. Early UVB-induced downregulation of HIF-1 alpha increased XPC mRNA expression due to competition between HIF-1 alpha and Sp1 for their overlapping binding sites. Late UVB-induced enhanced phosphorylation of HIF-1 alpha protein upregulated XPC mRNA expression by direct binding to a separate hypoxia response element (HRE) in the XPC promoter region. HIF-1 alpha also regulated XPD expression by binding to a region of seven overlapping HREs in its promoter. Quantitative chromatin immunoprecipitation assays further revealed putative HREs in the genes encoding other DNA repair proteins (XPB, XPG, CSA and CSB), suggesting that HIF-1 alpha is a key regulator of the DNA repair machinery. Analysis of the repair kinetics of 6-4 photoproducts and cyclobutane pyrimidine dimers also revealed that HIF-1 alpha downregulation led to an increased rate of immediate removal of both photolesions but attenuated their late removal following UVB irradiation, indicating the functional effects of HIF-1 alpha in the repair of UVB-induced DNA damage.