Vargas Amandine, Moreau Julie, Landry Sébastien, LeBellego Frédérique, Toufaily Chirine, Rassart Eric, Lafond Julie, Barbeau Benoit
Département des Sciences Biologiques, Université du Québec à Montréal, Montréal, Québec, Canada.
J Mol Biol. 2009 Sep 18;392(2):301-18. doi: 10.1016/j.jmb.2009.07.025. Epub 2009 Jul 16.
Human endogenous retrovirus (HERV)-encoded Syncytin-1 has been suggested to play a major role in trophoblast cell fusion and thereby placenta development. However, recent studies have strongly suggested that other HERV envelope proteins could also be implicated in this process. Based on this premise, herein we compared the expression and functional implication of Syncytin-1 with the more recently described Syncytin-2 protein in various trophoblast cells. Real-time reverse transcription PCR and Western blot analyses in differentiating primary trophoblast cells first indicated a direct correlation between mRNA and protein levels of Syncytin-2 and cell fusion, while an inverse correlation for Syncytin-1 was noted. Similar reverse transcription PCR experiments and promoter studies showed that cell fusion-inducing agents in the trophoblastic BeWo cell line increased the expression of Syncytin-1 but, more importantly, augmented Syncytin-2 expression. Confocal microscopy experiments further revealed that in BeWo cells and in freshly isolated primary human trophoblast cells, Syncytin-1 was present as a cytoplasmic punctuated structure in proximity to regions of cell-to-cell contact. On the other hand, Syncytin-2 presented an inducible signal, which mainly localized to the cytoplasmic membrane. Experiments with siRNA (small interfering RNA)-transfected BeWo and primary human trophoblast cells demonstrated an important diminution in the number of cell fusion events upon repression of Syncytin-2 expression, whereas transfection experiments with Syncytin-1-specific siRNA resulted in a more modest effect. Overall, these results highlight the importance of Syncytin-2 in BeWo and primary human trophoblast cell fusion.
人类内源性逆转录病毒（HERV）编码的合胞素-1被认为在滋养层细胞融合以及胎盘发育过程中发挥主要作用。然而，最近的研究强烈表明，其他HERV包膜蛋白也可能参与这一过程。基于这一前提，我们在此比较了合胞素-1与最近描述的合胞素-2蛋白在各种滋养层细胞中的表达及功能意义。对分化中的原代滋养层细胞进行实时逆转录PCR和蛋白质印迹分析，结果首先表明合胞素-2的mRNA和蛋白质水平与细胞融合之间存在直接相关性，而合胞素-1则呈负相关。类似的逆转录PCR实验和启动子研究表明，滋养层BeWo细胞系中的细胞融合诱导剂可增加合胞素-1的表达，但更重要的是，可增强合胞素-2的表达。共聚焦显微镜实验进一步显示，在BeWo细胞和新鲜分离的原代人滋养层细胞中，合胞素-1以细胞质点状结构的形式存在于细胞间接触区域附近。另一方面，合胞素-2呈现出一种可诱导信号，主要定位于细胞质膜。用小干扰RNA（siRNA）转染BeWo细胞和原代人滋养层细胞的实验表明，抑制合胞素-2表达后，细胞融合事件的数量显著减少，而用合胞素-1特异性siRNA进行转染实验的效果则较为有限。总体而言，这些结果突出了合胞素-2在BeWo细胞和原代人滋养层细胞融合中的重要性。
