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 Ca(2+)-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.
Hellman
P
P
Department of Surgery, University of Uppsala, Sweden.
Hellman
B
B
Juhlin
C
C
Jüppner
H
H
Rastad
J
J
Ridefelt
P
P
Akerström
G
G
D002118:Calcium / Q000502:physiology*; D002455:Cell Division / Q000502:physiology*; D000242:Cyclic AMP / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D008562:Membrane Glycoproteins / Q000378:metabolism / Q000502:physiology*; D010281:Parathyroid Hormone / Q000378:metabolism / Q000502:physiology*; D044162:Parathyroid Hormone-Related Protein; D011506:Proteins / Q000378:metabolism / Q000502:physiology*; D015398:Signal Transduction; D014327:Trophoblasts / Q000166:cytology* / Q000378:metabolism; D014407:Tumor Cells, Cultured
D008562:Membrane Glycoproteins; C470121:PTHLH protein, human; D010281:Parathyroid Hormone; D044162:Parathyroid Hormone-Related Protein; D011506:Proteins; D000242:Cyclic AMP; D002118:Calcium