Metabolic fate of estradiol in human mammary cancer cells in culture: estrogen sulfate formation and cooperativity exhibited by estrogen sulfotransferase

Abstract

The metabolism of 17β-estradiol in both estrogen receptor positive and negative human breast cancer cell lines has been compared. Initial experiments in which confluent cells were exposed to 1 nM [ 3H]17β-estradiol for 24 h, revealed that the main metabolites formed by estrogen receptor positive MCF-7 and ZR-75-1 cells were 17β-estradiol-3-sulfate (together with lesser amounts of estrone sulfate) and estrone. In estrogen receptor negative cell lines, production of estrogen sulfates was either significantly lower (MDA-MB-231 cells) than receptor positive cells, or failed to be produced at all (MDA-MB-330 cells). In both these receptor negative cell lines, production of estrone was significantly higher than in receptor positive cells. Accumulation of estrogen sulfates resulted from attainment of a steady state between synthesis catalysed by estrogen sulfotransferase and degradation catalysed by estrogen sulfatase. The former was present in the cytosol and showed a very high affinity for 17β-estradiol and estrone (low nM range). Complex initial velocity versus estrogen substrate curves were obtained with enzyme purified 106-fold by affinity chromatography. Such curves were consistent with a rate equation of degree 3 or 4 and suggest the presence of cooperatively linked dependent binding sites.