Properties of estrogen and hydroxysteroid sulphotransferases in human mammary cancer

Partial purification (~ χ 140-fold) of estrogen sulphotransferase (EC 2.8.2.4) in human mammary estrogen receptor positive cancer tissue was achieved by affinity chromatography on adenosine-3',5'-diphosphate-agarose. It had a M_r, of approximately 70,000 by gel filtration and upon electrophoresis on concave gradient polyacrylamide gels, showed a major (M_r 70,000) and a minor (M_r 200,000) peak of activity. Kinetics of this preparation (estradiol-17β and estrone as substrates), and also that of hydroxysteroid sulphotransferase (EC 2.8.2.2) contained in the cytosol of human mammary cancer MCF-7 cells (5-androstene-3β,17β-diol and dehydroepiandrosterone as substrates), were compared. The enzymes showed very similar behaviour, characterized by high affinity for their steroid substrates (low nM range) and co-operativity in their binding. For hydroxysteroid sulphotransferase, the adrenal-derived estrogen 5-androstene-3β,17β-diol was the preferred substrate compared to dehydro-epiandrosterone in the 0–40 nM concentration range. Such properties of the enzymes might be designed to limit the exposure of nuclear receptor to free ligand. Alternatively, a defined subcellular location would perhaps involve the enzymes in the elimination of estrogen after processing of the ligand-bound receptor.