Because overAbMole Riociguat BAY 63-2521 expression of Par-4 did not affect GRP78 expression, but affected its cell surface expression, it was suggested that Par-4 availability affects the cell surface expression of GRP78. To confirm this hypothesis, we next evaluated the role of endogenous Par-4 in GRP78 expression and localisation in HIPEC 65 cells. Transfection of these cells with Par-4 siRNA led to a significant decrease of both Par-4 expression and membrane GRP78 expression evaluated by western blot. We next examined the role of endogenous Par-4 in membrane GRP78 expression in primary evCTB. As shown in figure 4, decreased expression of Par-4 led to a slight but significant decrease in GRP78 membrane expression. Par-4 is a multi-domain protein of 340 amino acids. The key domains are highly conserved among AbMole Sibutramine HCl different species and are leucine zipper domain 
at the C-terminal part, two nuclear localization sequences at the N-terminal part, a nuclear export sequence and the SAC domain. In addition, Par-4 contains a number of conserved consensus sites for phosphorylation by kinases suggesting that Par4 may be tightly regulated by post-translational modification, localization and interactions with proteins of biological consequence. The main biological role of Par-4 described in literature is pro-apoptotic and depends on interactions with other proteins such as PKCf, WT-1, ZIP kinase, THAP-1. More generally, functions of Par-4 are dependent on its partners. Secreted Par-4 could also induce apoptosis and this would be rendered possible by its interaction with cell surface GRP78 in cancer cells. In this last study, Par-4 knock-down does not alter total GRP78 levels in whole-cell lysates, but decreases the cell surface GRP78 expression in prostate cancer cells, suggesting that endogenous Par-4 is involved in the cell surface expression of GRP78. Here, we have reported for the first time the presence of Par-4 in both villous and extravillous trophoblastic cells. Its expression in these cells is significantly correlated with the presence of membrane GRP78 but not with total GRP78 expression, suggesting a role for Par-4 in the GRP78 transport from the ER to the cell surface in trophoblastic cells. Upregulation or downregulation of Par-4 expression in HIPEC 65 cells and evCTB respectively leads to a change in membrane expression of GRP78, confirming the hypothesis that Par-4 plays a role in the transport of GRP78 from the ER to the cell surface in trophoblastic cells. Consistent with previous works suggesting that membrane GRP78 is involved in the regulation of evCTB invasion, downregulation or upregulation of cell surface GRP78 induced by down regulation or upregulation of Par-4 respectively, influences the invasive property of evCTB.