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Expression of Calbindin-D28k (CaBP28k) in Trophoblasts from Human Term Placenta¹

Laboratoire de Physiologie Materno-foetale,³ Département des Sciences Biologiques, Université du Québec à Montréal, Montreal, Quebec, Canada Service de pathologie,⁴ Pavillon St. Luc, CHUM, Montreal, Quebec, Canada Polypeptide Hormone Laboratory,⁵ Strathcona Anatomy Building, Montreal, Quebec, Canada

Calbindin-D28k (CaBP28k) belongs to a large class of eucaryotic proteins that bind calcium (Ca²⁺) to a specific helix-loop-helix structure. To date, this protein was mainly linked to brain, kidneys, and pancreas. Here, we demonstrate for the first time the existence of CaBP8k in the human placental trophoblasts of the human term placenta. Placental Ca²⁺ transfer from maternal to fetus is crucial for fetal development, although the biochemical mechanisms responsible for this process are largely unknown. In the current study, we have investigated the ⁴⁵Ca²⁺ uptake by human trophoblast cells in correlation with the expression CaBP28k. The expression of CaBP28k was determined by Northern blot analysis, reverse transcriptase polymerase chain reaction (RT-PCR), immunochemistry, and Western blot analysis. Indeed, Northern blot analysis revealed the presence of a CaBP28k transcript in syncytiotrophoblasts, cytotrophoblast cells, and HEK-293 cells. This was further confirmed by RT-PCR analysis followed by sequencing. In addition, anti-CaBP28k labeling was associated with cytotrophoblast and syncytiotrophoblast tissues in placental tissue sections and in vitro cultured cells. The presence of CaBP28k protein in these cells was confirmed by Western blotting. Cytotrophoblast cells isolated from human term placenta showed differentiation into syncytiotrophoblasts in culture according to the increase in hCG secretion. Both Ca²⁺ uptake and hCG secretion by trophoblasts increased gradually and were high at Day 4. Taken together, these data suggest that CaBP28k may play a role in Ca²⁺ transport or cell development in human trophoblast possibly trough Ca²⁺ buffering.

¹ This work is funded by a grant from March of Dimes Foundation Saving Babies Together, USA.

² Correspondence: Julie Lafond, Laboratoire de Physiologie Materno-ftale, Département des Sciences Biologiques, Université du Québec à Montréal, C.P. 8888, Succursale "Centre-Ville", Montréal, QC, Canada H3C 3P8. FAX: 514 987 4647; lafond.julie{at}uqam.ca

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