Antiapoptotic Effects of Estrogen in Normal and Cancer Human Cervical Epithelial Cells

The present study investigated the antiapoptotic effects of estrogen in normal and cancer human cervical cells and the mechanisms involved. Baseline apoptosis in human cervical epithelial cells is mediated predominantly by P2X7-receptor-induced, Ca2+-dependent activation of the mitochondrial (caspase-9) pathway. Treatment with 10 nm 17β-estradiol blocked apoptosis induced by the P2X7-receptor ligands ATP and 2′,3′-0-(4-benzoylbenzoyl)-ATP in normal human cervical epithelial cells (hECEs) and attenuated the effect in hECEs immortalized with human papillomavirus-16 (ECE16–1) and the cancer cervical cells HT3 and CaSki. Diethylstilbestrol and to a lesser degree estrone could mimic the effects of 17β-estradiol, whereas actinomycin-D and cycloheximide attenuated the response. The antiapoptotic effect of estrogen did not depend on cell cycle phase, and in both normal and cancer cervical cells, it involved attenuation of activation of caspase-9 and the terminal caspase-3. However, involvement of cascades upstream to the caspase-9 differed in normal vs. cancer cervical cells. In the normal hECEs estrogen blocked P2X7-receptor-induced calcium influx. In contrast, in the cancer CaSki cells, estrogen up-regulated expression of Bcl-2 and attenuated Ca2+-induced mitochondrial swelling (i.e. formation of mitochondrial permeability transition pores). Estrogen had no effect on P2X7-receptor-induced apoptosis in the anaplastic SiHa and Hela cells. These results point to a novel antiapoptotic effect of estrogen in the cervix that is independent of its mitogenic function. The results also suggest that cancer cervical cells evolved antiapoptotic mechanisms that enable the cells to evade apoptosis and could therefore promote tumor progression.