Estrogen-induced membrane alterations and growth associated with proteinase activity in endometrial cells.

Abstract

Endometrial cells isolated from uteri of ovariectomized rats were treated in vitro with 1 .apprx. 10-9 M estradiol-17.beta. (E2.beta.) to analyze early changes in membrane properties during hormone-induced growth. After 30 min exposure to E2.beta. at 22.degree. C, cells exhibited an enhanced capacity to bind erythrocytes (hemadsorption) in the presence of concanavalin (Con) A to 237% of the level in paired controls. Fluorescence microscopy revealed that .apprx. 25% of cells exposed to E2.beta., but not estradiol-17.alpha. (E2.alpha.), showed a redistribution into polar clusters of Con A-binding sites that were dispersed in random patches at the external surfaces of control cells. These hormone-induced membrane alterations were abolished by prior treatment of cells with inhibitors of thiol proteinase activity of the cathepsin B1 (CB1) type, such as leupeptin and iodoacetate. Leupeptin at 4.5 .times. 10-7 M also reduced the affinity of [3H]E2.beta. binding to intact cells but did not influence specific binding of the hormone to macromolecular components of cytosol. A pronounced increase in the availability of endogenous CB1, but not of alkaline phosphatase, succinate or lactate dehydrogenase, in the extracellular media was elicited within 30 min after E2.beta. treatment. In cells cultured in chemically defined medium for up to 48 h, E2.beta., but not E2.alpha., enhanced cell proliferation and stimulated [3H]thymidine incorporation into macromolecular form. These E2.beta.-induced effects were abolished by prior treatment of cells with liposome-entrapped leupeptin at a final concentration of 7 .times. 10-8 M. The net rate of intercellular adhesion among endometrial cells was also enhanced by E2.beta.. This hormonal response was diminished by prior exposure to leupeptin. Fractionation of cells by selection for adhesiveness due to E2.beta. exposure for 30 min yielded a subpopulation of rapidly dividing cells which surpassed their less adhesive counterparts in cathepsin secretion and in Con A-mediated hemadsorption. Leupeptin-sensitive proteinase activity may contribute to membrane and growth modifications elicited by E2.beta. treatment in endometrial cells.