Impaired nucleotide excision repair in UV-irradiated human oral keratinocytes immortalized with type 16 human papillomavirus genome

We previously reported that 'high risk' human papillomaviruses (HPV) induce genetic instability in human oral keratinocytes. To understand the mechani sms of HPV-induced genetic instability, we determined the nucleotide excisi on repair (NER) capacity of normal (NHOK) and human papillomavirus type-16 immortalized oral keratinocytes HOK-16B) by strand-specific removal of UV-i nduced cyclobutane pyrimidine diners (CPDs) from a 16 Kb fragment of the p5 3 gene. In NHOK the NER activity was initiated in both DNA strands immediat ely, although the process in the non-transcribed strand was notably slower than that of the transcribed strand. In HOK-16B cells the initiation of CPD s removal was delayed for at least 8h in both DNA strands, and the process was significantly slower than that in NHOK. UV-irradiation enhanced the p53 protein level more than 30-fold in NHOK(, but it did not significantly alt er the protein level in the HOK-16B cells. UV-irradiation also increased th e p21(WAF1/CIP1) protein level only in NHOK. These data indicate that 'high risk' HPV induces genetic instability by impairing NER capacity of cells. Impaired NER activity of HOK-16B cells may be implicated with their inabili ty to enhance active p53 when challenged by genotoxic stress.