Calnexin (CNX), a membrane-bound molecular chaperone, is involved in protein folding and quality control of nascent glycoproteins in the endoplasmic reticulum. We previously suggested critical roles of calreticulin, a functional paralogue of CNX, in placentation, including invasion of extravillous trophoblasts and syncytialization of cytotrophoblasts. However, the roles of CNX in placentation are unclear. In human choriocarcinoma BeWo cells, which serve as an experimental model of syncytialization, CNX knockdown suppressed forskolin-induced cell fusion and β-human chorionic gonadotropin (β-hCG) induction. Cell-surface luteinizing hormone/chorionic gonadotropin receptor, a β-hCG receptor, was significantly down-regulated in CNX-knockdown cells, which suggested the presence of a dysfunctional autocrine loop of β-hCG up-regulation. In this study, we also found abundant CNX expression in normal human placentas. Collectively, our results revealed the critical role of CNX in the syncytialization-related signaling in a villous trophoblast model and suggest a link between CNX expression and placenta development.
Keywords: calnexin; chaperone; placenta; syncytialization; trophoblast; β-hCG.