REGULATION BY CALCIUM-ION OF CHORIOCARCINOMA AROMATASE-ACTIVITY

Intratumoral estrogen could function as an autocrine or paracrine grow th factor. We investigated the regulation of estrogen synthetase (arom atase) activity by Ca2+ in choriocarcinoma JAr cell line. Aromatase en zymatic activity was measured in whole intact cells and microsome frac tions 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-max imal inhibition occurred at 1 nM. In membrane fractions, free Ca-2+ in hibited aromatase activity in a noncompetitive manner. Maximal effect (approximately 50%-inhibition) occurred at 1 mM Ca2+ and a half-maxima l inhibition occurred at 10 mu M. These results on both intact cells a nd membrane fractions suggest that the increase in intracellular calci um concentration modulates the estrogen production by JAr cells. Physi ological factors that might have been considered as likely candidates to raise. intracellular Ca2+ level may be applicable to control of cho riocarcinoma proliferation.