Molecular analysis of selected cell cycle regulatory proteins during aerobic and hypoxic maintenance of human ovarian carcinoma cells

We have previously reported on the development of an in vitro model system for studying the effect of hypoxia on ovarian carcinoma cell proliferation and invasion (Krtolica and Ludlow, 1996). These data indicate that the cell division cycle is reversibly arrested during the G1 phase. Here, we have c ontinued this study to include the proliferation properties of both aerobic and hypoxic human ovarian carcinoma cells at the molecular level. The grow th suppressor product of the retinoblastoma susceptibility gene, pRB, appea rs to be functional in these cells as determined by SV40 T-antigen binding studies. Additional G1-to-S cell cycle regulatory proteins, cyclins D and E , cyclin-dependent kinases (cdks) 4 and 2, and cdk inhibitors p27 and p18, also appear to be intact based on their apparent molecular weights and cell cycle stage-specific abundance. During hypoxia, there is a decrease in abu ndance of cyclins D and E lambda with an increase in p27 abundance. cdk4 ac tivity towards pRB and cdk2 activity towards histone H1 are also decreased. Go-precipitation studies revealed an increased amount of p27 complexing wi th cyclin E-cdk2 during hypoxia than during aerobic cell growth. In additio n, pRB-directed phosphatase activity was found to be greater in hypoxic tha n aerobic cells. Taken together, a model is suggested to explain hypoxia-in duced cell cycle arrest in SKA human ovarian carcinoma cells.