Alterations in phosphoinositide metabolism associated with 17 β-estradiol and growth factor treatment of MCF-7 breast cancer cells

Steady-state levels of phosphatidyl inositol (Ptdlns) turnover are examined in MCF-7 human breast cancer cells in response to estradiol treatment. Elevated levels of Ptdlns are observed 12-24 h after estradiol treatment, occur at estradiol concentrations as low as 10^-12 m, and are competitively blocked by the antiestrogen LY117018. MCF-7 cells secrete a transforming growth factor (TGF) α-like material which can partly replace estradiol in conferring tumorgen-icity in nude mice. We show that acute or chronic treatment of MCF-7 cells with TGFα results in elevated Ptdlns turnover and that chronic treatment increases growth rate. In contrast TGFβ is growth inhibitory and blocks estradiol-induced increases in Ptdlns turnover. A phosphatidyl inositol 4, 5-bisphos-phate specific phospholipase-C activity has been identified and is elevated in association with estradiol treatment. These data are consistent with estradiol-induced autocrine growth factors, including TGFα, acting through the Ptdlns turnover pathway as part of their mechanism of action.