CARCINOPLACENTAL ALKALINE-PHOSPHATASE - BASE LEVEL AND HORMONE-INDUCED ACTIVITY ASSOCIATED WITH EVENTS IN CELL-CYCLE

Using HeLa TCRC-1, human cervical cancer cell line which is monophenotypic with respect to the Regan isoenzyme of alkaline phosphatase, the factors which influence its expression in relation to events of the cell cycle were examined. DNA synthesis is not required for hormone induction of the Regan isoenzyme. As in the presence of hydroxyurea, a specific inhibitor of DNA synthesis, induction occurred. When partially synchronized cells were allowed to leave the S period prior to hormone treatment, and hydroxyurea was added to prevent cells from entering the next S period, hormone induction of the Regan isoenzyme was still observed. This indicates that initiation of expression of hormone-induced carcinoplacental alkaline phosphatase occurs prior to the DNA synthetic phase of the cell cycle. A hypothetical 2 step mechanism of hormone induction was proposed to interpret the present findings in relation to previous results.