title: Functional analysis of placental 57-kDa Ca(2+)-binding protein: overexpression and downregulation in a trophoblastic cell line.
abstract: The placental trophoblastic epithelium functions to transport nutrients needed by the fetus, including calcium, which is required in the greatest amounts during the last third of pregnancy when the majority of fetal skeletal mineralization occurs. The mechanism of placental calcium transport and the developmental changes in the trophoblast that facilitate this process are currently incompletely understood. We have previously identified a 57-kDa, Ca(2+)-binding protein (CaBP) functionally implicated in placental calcium transport and trophoblast differentiation. In this study we have directly examined the role of CaBP in these processes by (1) recombinantly overexpressing CaBP in an inducible manner and (2) downregulating CaBP expression using antisense technology, using the rat choriocarcinoma cell line Rcho-1 as a trophoblastic cell model system. Our results show that overexpression of CaBP stimulates both cellular calcium uptake and vectorial calcium transport activities in Rcho-1 cells. Those cells stably expressing CaBP also exhibit higher levels of steady-state intracellular calcium and enhanced calcium-buffering ability. In addition, prolonged overexpression of CaBP in Rcho-1 cultures promotes trophoblast differentiation. Conversely, downregulation of CaBP expression had a negative effect on calcium uptake, calcium transport, and trophoblast differentiation in Rcho-1 cells. These data indicate that CaBP plays a direct role in placental calcium transport, functioning both as an intracellular calcium buffer and as a shuttle. These results also support a more direct role for CaBP in the trophoblast differentiation pathway.
authors.affiliation: Department of Orthopaedic Surgery, Thomas Jefferson University, Philadelphia, Pennsylvania, 19107, USA.
authors.forename: M E
authors.initials: ME
authors.lastname: Hershberger
authors.forename: R S
authors.initials: RS
authors.lastname: Tuan
mesh_terms: D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D002454:Cell Differentiation; D002460:Cell Line; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects; D007700:Kinetics; D020319:Oligodeoxyribonucleotides, Antisense / Q000494:pharmacology; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D014162:Transfection; D014327:Trophoblasts / Q000166:cytology / Q000378:metabolism*
chemical_list: D002135:Calcium-Binding Proteins; D020319:Oligodeoxyribonucleotides, Antisense; D011994:Recombinant Proteins; C113608:calcium-binding protein, 57-kDa; D002118:Calcium