胎盤融合性蛋白質 syncytin 2 的功能探討

Functional characterization of the placental fusion protein, syncytin 2

楊書睿(Shu-Jui Yang)

指導教授 ： 陳宏文

國立臺灣大學/生命科學院/生化科學研究所/碩士(2005年)

https://doi.org/10.6342/NTU.2005.01474

摘要

利用資料分析比對人類基因體序列，可發現有兩個相關於人類內生性反轉錄病毒（human endogenous retrovirus, HERV）家族的膜蛋白質：其中一個是屬於 HERV-W 家族，也稱為 syncytin；另一個則是屬於 HERV-FRD 家族，被命名為 syncytin 2。這兩個基因被發現僅表現在胎盤，特別是胎盤的滋養層細胞，滋養層在囊胚的著床以及發育成為母體與胎兒之間的胎盤，扮演著舉足輕重的角色。我們便想針對其中具有融合功能的蛋白質 syncytin 2 進行研究。
首先，我們製備具有專一性的 syncytin 2 抗體，並且與 syncytin 抗體一起對子癇前症（pre-eclampsia）病人的胎盤組織進行西方墨點法分析，再以相同週數的正常人組織相互比較，發現 syncytin 與 syncytin 2 的蛋白質表現量在子癇前症病人之中明顯少於正常人組織。
為了進一步探討 syncytin 與 syncytin 2 的結構與功能上的關係，我們將兩蛋白質的 SU 以及 TM 次單元互相交換，而後利用 SU1–TM2 鑲嵌蛋白質（chimeric protein）進行分析，發現此鑲嵌蛋白質都可在細胞內進行水解成為 SU 與 TM 次單元，但卻無法促使融合的發生，推測 SU 與 TM 兩部分存在著某種交互作用以維持其正常功能。
我們也發現了在胎盤細胞株：BeWo、JEG3、JAR，三者之中只有 BeWo 與 JEG3 可進行自發性的細胞融合，而 JAR 細胞卻缺失了細胞融合的能力。我們排除了 JAR 細胞中扮演水解 syncytin 與 syncytin 2 的水解酶 furin 或是受器方面上的缺失。並且提出可能在 JAR 細胞中的 syncytin 與 syncytin 2 基因序列發生了突變，導致 JAR 細胞株缺失了促使細胞融合的能力。

關鍵字

滋養層 ； 胎盤 ； 融合

並列摘要

Data mining of the human genome sequence has revealed two human endogenous retrovirus (HERV) envelope proteins: one is HERV-W, also called syncytin and the other is HERV-FRD named syncytin2. These two genes appear to be almost exclusively expressed in placenta, in particular, in trophoblasts that are the specialized cells of the placenta playing a major role in implantation and formation of the maternal-fetal interface. In the current study, we characterize the fusogenic function of syncytin2.
First, we induced syncytin2 antibody and then using this antibody and syncytin antibody to screen pre-eclamptic placenta and gestation age-matched controls. We found that the protein level of syncytin and syncytin2 in pre-eclampsia patient is decreased compared with the controls.
We further performed domain swapping analysis and constructed chimeric protein, SU1-TM2. We found that both SU1-TM2 can be processing into SU and TM domains. On the observation of fusion assay, chimeric protein, SU1-TM2, can not mediated cell-cell fusion and propose that SU1-TM2 lost some kinds of interaction between. SU and TM domains
We also studied cell fusion in three placental cell lines, BeWo, JEG3, and JAR. BeWo and JEG3 cells underwent spontaneous cell fusion, but not JAR cells. We investigated the possible mechanisms underlying the loss of spontaneous cell fusion in JAR. We ruled out the possibilities of furin processing and receptor deficiency in JAR cells and proposed that mutation in syncytin and syncytin2 genes in JAR cell line is a possible reason attributed to the loss of spontaneous cell fusion.

並列關鍵字

syncytin 2 ； placenta ； trophoblast

參考文獻

A.J.G.Po¨tgens, S.Drewlo, M.Kokozidou and P.Kaufmann. (2004) Syncytin: the major regulator of trophoblast fusion? Recent developments and hypotheses on its action. Human Reproduction Update, 10, 487–496.

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