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Hypoxia is a common feature of the tumor microenvironment that results from an imbalance in oxygen supply and consumption leading to oxygen deprivation. As a result, hypoxia, which is often accompanied by low pH, is perceived as a stress by cells. Previously, it has been reported that repair of a UV-damaged reporter gene was diminished in the RKO colorectal carcinoma cell line (Rcneo) and a transformed mouse cell line (3340) when cells were incubated under conditions of hypoxic and low pH compared to normoxic conditions. These results suggested inhibition of repair by the nucleotide excision repair (NER) pathway in cells exposed to hypoxic conditions. In the present work we have examined the effects of hypoxia on NER in human cells using host cell reactivation (HCR) of a recombinant adenovirus encoded reporter gene that expresses lacZ. We observed reduced HCR for expression of the UV-damaged reporter gene in the same tumor (Rcneo) and mouse (3340) cell lines under hypoxic and low pH conditions compared to normoxic conditions, in agreement with the previous report. In contrast, hypoxia and low pH resulted in enhanced HCR of the UV-damaged reporter construct in normal NER-proficient primary human fibroblasts. NER is divided into two sub-pathways: global genomic repair (GGR) and transcription-coupled repair (TCR). We examined also the effects of hypoxia alone on HCR of the UV-damaged reporter gene in NER-deficient human cells from a Cockayne syndrome patient of complementation group B (GGR-proficient and TCR-deficient) and a xeroderma pigmentosum patient from complementation group A (GGR- and TCR-deficient). We detected increased HCR of the UV-damaged reporter in primary and SV40-transformed CS-B fibroblasts, but not in primary and SV40-transformed XP-A fibroblasts for cells incubated under hypoxic conditions compared to normoxic conditions. These results indicate that NER is differentially affected by hypoxia and low pH depending on cell type and that hypoxia can upregulate the GGR pathway in human fibroblasts. Since the response of tumor cells to several treatment therapies, including cisplatin treatment, is dependent on NER these results suggest that a tumor microenvironment of hypoxia could influence the clinical outcome through a modulation of NER.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA