RAPID AND LONG-TERM EFFECTS OF 17-BETA-ESTRADIOL ON PIP2-PHOSPHOLIPASE C-SPECIFIC ACTIVITY OF MCF-7 CELLS

Activity of the enzyme phosphatidylinositol 4,5-bisphosphate phospholipase C (PIP2-PLC) was demonstrated in MCF-7 human breast cancer cell homogenate. The addition of 10(-9)M 17beta-estradiol to the culture medium elicited in the cells two types of responses depending on the period of exposure. Enzyme activity was rapidly activated at 15 s of incubation. After 5 min, PIP2-PLC activity was inhibited, and this effect continued at least until 24 h of exposure to the hormone. When 17beta-estradiol was added in vitro to the total homogenate of untreated cells, enzyme activity was stimulated in a dose-dependent manner. These findings indicate that 17beta-estradiol induces early and long-term modifications of the phosphoinositide signal pathway in intact MCF-7 cells as well as in vitro. The rapidity of the early effect suggests a non-genomic action of estradiol.