Decreased tyrosine phosphorylation of focal adhesion kinase after estradiol treatment of MCF-7 human breast carcinoma cells

MCF-7 human breast carcinoma cultures grown in the presence of 17-beta estr adiol form solid, multicellular nodules, a process that reflects changes in cell-substrate adhesions and loss of growth inhibition. We examined the ef fects of estradiol on the status of tyrosine phosphorylation in focal adhes ion kinase (FAK) and the association of FAK with paxillin using immunopreci pitations and then probing western blots for FAK, phosphotyrosine, and paxi llin. Culture of MCF-7 cells for seven days in the presence of 1 nM E-2 res ulted in decreased tyrosine phosphorylation of FAK compared to controls. Th e estradiol-induced effect was blocked by 100 nM of the estrogen receptor a ntagonist 4-hydroxytamoxifen, indicating dephosphorylation of FAK is an est rogen receptor-mediated event. FAK immunoprecipitated from either estradiol or DMSO-treated cells phosphorylated the exogenous substrate poly(Glu,Tyr) , suggesting that the potential kinase activity of FAK was not changed by e stradiol. Estradiol treatment also resulted in a reduced association betwee n FAK and paxillin. The decreased phosphorylation levels and reduced associ ation between FAK and paxillin may be important steps leading to the loss o f stable focal contacts and loss of growth inhibition during MCF-7 nodulati on. (C) 1998 Elsevier Science Ltd. All rights reserved.