REGULATION OF PROLIFERATION IN JEG-3 CELLS BY A 500-KDA CA2+ SENSOR AND PARATHYROID HORMONE-RELATED PROTEIN

JEG-3 cells are derived from human trophoblasts and demonstrated to express a 500-kDa Ca2+ sensing protein, which elicits biphasic elevations of cytoplasmic Ca2+ concentrations ([Ca2+]i) and mediates Ca2+ regulation of parathyroid hormone-related protein (PTHrP) release from placental cytotrophoblasts. Cytocentrifuged JEG-3 cells were immunostained by monoclonal and polyclonal antiserum toward PTHrP(1-34) and (38-64). Elevation of external Ca2+ from 0.5 to 3.0 mM induced only a sluggish rise in [Ca2+]i and no stimulation of cAMP production despite a more than twofold elevation of PTHrP(1-34) release. Monoclonal antibodies recognizing functionally discrepant epitopes of the Ca2+ sensor protein substantiated uncoupling of this sensor in the Ca2+-regulated PTHrP release. Exogenous activation of protein kinase C by a phorbol ester strongly augmented the secretion of PTHrP(1-34), whereby uncoupling of the Ca2+ sensor was partially reversed. This functional differentiation was associated with reduced [3H]thymidine incorporation in JEG-3 cells. Proliferation of these cells was inhibited by 71% upon rise of extracellular Ca2+ from 0.5 to 3.0 mM, and this inhibition was abolished by antibody-mediated interference with the Ca2+ sensor function. PTHrP(1-86) and PTH(1-34) at concentrations up to 10-7 M decreased proliferation and stimulated the cAMP content of JEG-3 cells. The findings support concomitant Ca2+ sensor and PTH/PTHrP receptor expression in JEG-3 cells, and that Ca2+ inhibits proliferation by actions on the Ca2+ sensor as well as by stimulation of PTHrP release possibly mediating autocrine growth inhibition. © 1993 Academic Press, Inc.