Intratumoral estrogen could function as an autocrine or paracrine growth factor. We investigated the regulation of estrogen synthetase (aromatase) activity by Ca2+ in choriocarcinoma JAr cell line. Aromatase enzymatic activity was measured in whole intact cells and microsome fractions by quantitating (H2O)-H-3 released from [1-H-3]-androstenedione and [H-3]estrone converted from [1,2,6,7-H-3]androstenedione. Exposure of JAr cells to calcium ionophore A23187 brought about dose-dependent decreases in the cellular aromatization rate by up to 75%; a half-maximal inhibition occurred at 1 nM. In membrane fractions, free Ca-2+ inhibited aromatase activity in a noncompetitive manner. Maximal effect (approximately 50%-inhibition) occurred at 1 mM Ca2+ and a half-maximal inhibition occurred at 10 mu M. These results on both intact cells and membrane fractions suggest that the increase in intracellular calcium concentration modulates the estrogen production by JAr cells. Physiological factors that might have been considered as likely candidates to raise. intracellular Ca2+ level may be applicable to control of choriocarcinoma proliferation.

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