DIFFERENTIAL RESPONSE OF NORMAL AND HPV IMMORTALIZED ECTOCERVICAL EPITHELIAL-CELLS TO B[ALPHA]P

Cigarette smoking has been established as a risk factor for the develo pment of cervical cancer. Polycyclic aromatic hydrocarbons such as ben zo[a]pyrene (B[a]P), which are present in cigarette smoke, might accou nt for this increased risk. The effects of B[a]P on cell growth, aryl hydrocarbon hydroxylase, DNA adducts and p53 levels was measured in ce rvical cells. Since 90% of cervical preneoplastic lesions are positive for the human papillomavirus (HPV) we compared the effects of these c hemicals in normal ectocervical epithelial cells (ECE) and human papil lomavirus 16 (HPV16) immortalized ectocervical epithelial cells (ECE16 -1). Exposure of normal ECE and HPV immortalized ECE16-1 cells to B[a] P inhibited cell proliferation. Inhibition occurred at 20-fold lower c oncentrations in the normal ECE cells compared to ECE16-1 cells. The p roliferation of cervical cells which express mutated p53 was unaffecte d by B[a]P. Neither cervical stromal cells nor endometrial stromal cel ls were affected by these compounds. The effects of B[a]P on normal EC E cell proliferation correlated with increased terminal differentiatio n as measured by increased envelope formation. In contrast, B[a]P expo sure did not induce envelope formation in immortalized ECE16-1 cells o r in cervical tumor cells. Pretreatment of both ECE and ECE16-1 cells with 2,3,7,8-tetrachlorodibenzo-p-dioxin, which induces P450 expressio n and activity, did not alter B[a]P metabolism in either normal or imm ortalized cells. Furthermore, equivalent levels of DNA adducts were fo rmed by B[a]P in ECE and ECE16-1 cells. Neither the extent of adduct f ormation nor the rate of their removal differed in normal and immortal ized cervical cells. Therefore, the diminished growth inhibition of th e ECE16-1 cells as compared to normal ECE cells by B[a]P is not due to changes in cytochrome P450 of the 1A family metabolism or DNA adduct number. Furthermore, analysis of the p53 levels in both normal and ECE 16-1 cells revealed that p53 levels are higher in normal versus immort alized ectocervical cells, and p53 is induced in both cell types follo wing B[a]P treatment. Thus reduced p53 levels in ECE16-1 cells may con tribute to a lack of growth suppression following B[a]P treatment. The se results demonstrate that HPV16 immortalization diminishes ectocervi cal epithelial cell responsiveness to toxicant damage (i.e. decreased cell proliferation and increased terminal differentiation). As a resul t, ECE16-1 cells that sustain genotoxic damage which leads to DNA addu ct formation continue to proliferate and may be at increased risk for mutations and further progression towards a fully transformed phenotyp e.