Decreased expression of glutathione S-transferase M1 in HPV16-transfected human cervical keratinocytes in culture

Glutathione S-transferase (GST) M1 is a member of the GST mu family of cyto solic enzymes that have been hypothesized to catalyze the conjugation of gl utathione to a large number of hydrophobic substances, including carcinogen s such as polynuclear aromatic hydrocarbons present in tobacco smoke, leadi ng to their excretion, Epidemiologic and experimental evidence suggests tha t the risk of cervical cancer is related to both human papillomavirus (HPV) infection and cigarette smoking. We compared the enzymatic activities and mRNA levels of GSTs in GSTM1-positive human cervical keratinocytes (HCKs) t hat had been transfected with HPV16 with those in the parental cells. The G STM1 activity toward the substrate trans-stilbene oxide was 5- to 7-fold lo wer than in the parental cells. The relative mRNA level in HCK transfected with HPV16 E6/E7, as quantified by reverse transcriptase-polymerase chain r eaction (RT-PCR) with normalization against endogenous glyceraldehyde-3-pho sphate dehydrogenase (GAPDH) expression, was 6% that of the parental cells. It was 16 and 82%, respectively, in cells that were transfected with HPV16 E6 alone or HPV16 E7 alone. When quantified by competitive RT-PCR using an exogenous nuclease-resistant synthetic cyclophilin RNA transcript as contr ol, the mRNA level in HCK transfected with HPV16 E6 was similar to 10-fold lower that that in the parental cells, It was similar to 5- to 7-fold lower in the HPV16 E7 or HPV16 E6/E7 cells, Our results suggest that viral infec tions, through the modulation of cellular xenobiotic-metabolizing enzymes, may play a role in the ability of cells to handle environmental carcinogens .