In vitro study of placental trophoblast calcium uptake using JEG-3 human choriocarcinoma cells.
During human fetal development, placental syncytiotrophoblasts actively transport calcium from the maternal to the fetal circulation. Two functional components, a cytosolic Ca2(+)-binding protein (CaBP) and a Ca2(+)-ATPase have been identified in the syncytiotrophoblasts of the chorionic villi. We report here the calcium uptake properties of a human choriocarcinoma cell line, JEG-3, which was used as an in vitro model cell system for the syncytiotrophoblasts. In culture, JEG-3 proliferated as large syncytial aggregates expressing typical syncytiotrophoblast markers. 45Ca uptake by JEG-3 was a substrate- and temperature-dependent, membrane-mediated active process that exhibited linear kinetics for up to 7 min. Both the CaBP and the Ca2(+)-ATPase were expressed by JEG-3, on the basis of biochemical, histochemical, immunochemical and or mRNA assays. Immunohistochemistry and in situ hybridization revealed that JEG-3 cells were heterogeneous with respect to the expression of the CaBP. The Ca2(+)-ATPase activity of JEG-3 was similar to the placental enzyme in terms of sensitivity to specific inhibitors, and was detected histochemically along the cell membrane. Fura-2 Ca2+ imaging revealed that calcium uptake by JEG-3 was not accompanied by a concomitant increase in cytosolic [Ca2+], suggesting a specific Ca2+ sequestration mechanism. The involvement of calciotropic hormonal regulation was evaluated by studying the response of JEG-3 to 1,25-dihydroxy vitamin D3. Calcium uptake was significantly stimulated in a dose-dependent manner by a 24-h treatment of the cells with 1,25-dihydroxy vitamin D3 (optimal dose approximately 0.5 nM); the CaBP level doubled whereas steady-state CaBP mRNA did not, suggesting that CaBP expression was regulated by 1,25-dihydroxy vitamin D3. These observations strongly suggest that the JEG-3 human choriocarcinoma cells should serve as a convenient in vitro model system for studying the cellular mechanism and regulation of transplacental calcium transport.
Tuan
R S
RS
Department of Orthopaedic Surgery, Thomas Jefferson University, Philadelphia, PA 19107.
Moore
C J
CJ
Brittingham
J W
JW
Kirwin
J J
JJ
Akins
R E
RE
Wong
M
M
D001693:Biological Transport, Active; D015152:Blotting, Northern; D002117:Calcitriol / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002822:Choriocarcinoma; D003593:Cytoplasm / Q000378:metabolism; D015870:Gene Expression; D006801:Humans; D007150:Immunohistochemistry; D007700:Kinetics; D014327:Trophoblasts / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D002135:Calcium-Binding Proteins; D000252:Calcium-Transporting ATPases; D002117:Calcitriol; D002118:Calcium