Liao W-C, Liu C-H, Chen C-H, Hsu W-M, Liao Y-Y, Chang H-M, Lan C-T, Huang M-C, Shyu M-K
Department of Anatomy, Faculty of Medicine, Chung Shan Medical University, Taichung 402, Taiwan; Department of Pediatrics, Chung Shan Medical University Hospital, Taichung 402, Taiwan.
Research and Development Center for Immunology, China Medical University, Taichung 404, Taiwan.
Placenta. 2015 Apr;36(4):357-64. doi: 10.1016/j.placenta.2015.01.008. Epub 2015 Jan 24.
Glycosylation controls diverse protein functions and regulates various cellular phenotypes. Trophoblast invasion is essential for normal placental development. However, the role of glycosylation in human placenta throughout pregnancy is still unclear. The β-1,4-galactosyltransferase III (B4GALT3) has been found to regulate cancer cell invasion. We therefore investigated the expression of B4GALT3 in placenta and its roles in trophoblast.
B4GALT3 protein expression was examined by quantitative Western blotting analysis in human placentas. For identification of B4GALT3-positive cells in normal human placenta, immunohistochemistry and immunofluorescence methods were used. To investigate effects of B4GALT3 on extravillous trophoblast (EVT)-like cell and primary EVT cells, we analyzed cell growth, adhesion, migration, and invasion in mock and B4GALT3-transfected cell.
B4GALT3 expression significantly increased in third trimester human placenta. Immunostaining revealed that B4GALT3 expressed in placental villous cytotrophoblast, syncytiotrophoblast, and a subpopulation of EVT cells throughout pregnancy. Interestingly, we found increases in the expression level and percentage of B4GALT3-positive cells in third trimester EVT, but not in syncytiotrophoblasts and cytotrophoblasts of placental villi. Overexpression of B4GALT3 in HTR8/SVneo cells and primary trophoblast cells significantly suppressed cell migration. In addition, B4GALT3 suppressed cell invasion, and enhanced cell adhesion to laminin in HTR8/SVneo cells. Notably, we found that B4GALT3 modified glycans on β1-integrin, suppressed focal adhesion kinase (FAK) signaling, and enhanced β1-integrin degradation.
We propose that B4GALT3-mediated glycosylation change not only enhances β1-integrin binding to laminin, but also attenuates β1-integrin stability. Our findings suggest that B4GALT3 is a critical regulator for suppressing EVT invasion in the late stages of pregnancy.
糖基化控制着多种蛋白质功能并调节各种细胞表型。滋养层细胞侵袭对正常胎盘发育至关重要。然而，糖基化在整个孕期人胎盘中的作用仍不清楚。已发现β-1,4-半乳糖基转移酶III（B4GALT3）可调节癌细胞侵袭。因此，我们研究了B4GALT3在胎盘中的表达及其在滋养层细胞中的作用。
通过定量蛋白质免疫印迹分析检测人胎盘中B4GALT3蛋白表达。为鉴定正常人胎盘中B4GALT3阳性细胞，采用免疫组织化学和免疫荧光方法。为研究B4GALT3对绒毛外滋养层（EVT）样细胞和原代EVT细胞的影响，我们分析了mock转染细胞和B4GALT3转染细胞的细胞生长、黏附、迁移和侵袭情况。
在孕晚期人胎盘中，B4GALT3表达显著增加。免疫染色显示，在整个孕期胎盘绒毛的细胞滋养层、合体滋养层和一部分EVT细胞中均有B4GALT3表达。有趣的是，我们发现孕晚期EVT中B4GALT3阳性细胞的表达水平和百分比增加，但胎盘绒毛的合体滋养层细胞和细胞滋养层细胞中未增加。HTR8/SVneo细胞和原代滋养层细胞中B4GALT3的过表达显著抑制细胞迁移。此外，B4GALT3抑制细胞侵袭，并增强HTR8/SVneo细胞对层粘连蛋白的黏附。值得注意的是，我们发现B4GALT3修饰β1整合素上的聚糖，抑制黏着斑激酶（FAK）信号传导，并增强β1整合素降解。
我们提出B4GALT3介导的糖基化变化不仅增强β1整合素与层粘连蛋白的结合，还减弱β1整合素的稳定性。我们的研究结果表明，B4GALT3是孕期晚期抑制EVT侵袭的关键调节因子。
