幽門螺旋桿菌熱緊迫蛋白60活化β1轉化生長因子訊息傳遞之機制

Abstract

幽門螺旋桿菌為普遍存在人體的致病菌。根據統計，全球約有一半左右的人口感染此菌。該菌會在胃部造成持續性的慢性感染，進而增加十二指腸潰瘍、胃癌或淋巴腫瘤之罹患率。在病原慢性感染的機制中，抑制宿主的免疫反應扮演了極為重要的角色；而在幽門螺旋桿菌的免疫抑制效應方面，目前雖然有若干的研究進行探討，然而其機制仍尚未完全被釐清。幽門螺旋桿菌熱緊迫蛋白60為該菌的黏附因子之一；而由於其能引發許多炎症細胞激素的產生，故該蛋白也常作為幽門螺旋桿菌疫苗研發的主要抗原。然而，近來相關的研究顯示，熱緊迫蛋白60具有調控免疫反應的功能。本研究的目的在探討幽門螺旋桿菌熱緊迫蛋白60的結構及其在免疫反應中所扮演的角色。首先，由氨基酸序列比對、圓二色光譜、以及蛋白質膠體電泳的結果顯示：該蛋白質可形成雙體或是四聚體，而這與目前已知的大腸桿菌熱緊迫蛋白60的結構極為不同。而在免疫功能的探討方面，我們發現幽門螺旋桿菌熱緊迫蛋白60和人類β1轉化生長因子的蛋白質結構有部分的相似性，其中有一段相似區已知為β1轉化生長因子與其第二型受器之結合位。後續的結果顯示：在ELISA與細胞的實驗中均可證實熱緊迫蛋白60可與β1轉化生長因子受器結合。此種結合會啟動β1轉化生長因子所調控的SMAD訊息傳遞路徑，開啟下游基因表現，並抑制周邊血球細胞與單核球細胞株THP-1的免疫活性。綜合以上的實驗數據，我們認為幽門螺旋桿菌熱緊迫蛋白60會藉由模仿β1轉化生長因子的生物活性來抑制宿主的免疫系統，以利於該菌的持續性感染。

Helicobacter pylori have explored multiple mechanisms to evade host immune surveillance for chronic infection. But either of them is restricted by certain bacterial strains containing potential virulent factors, or those immune-restrained functions only limit to some specific immunocytes. However, the long-term persistence of H. pylori suggests a more comprehensive and powerful factor(s) hinds behind to regulate host immune system. Helicobacter pylori heat shock protein 60 (HpHsp60) was previous identified as an adhesion molecule or a potent immunogen. This study aims to study the structure of HpHsp60s and evaluates their functions on host immune responses. Analyzing the structure of HpHsp60 via amino acid blast, circular dichroism and electrophoresis indicated most recombinant HpHsp60s form dimers or tetramers that are quite different than E. coli Hsp60 protein structure. Moreover, a novel property of HpHsp60 was found, which is, by mimicking TGF-β1, HpHsp60 could exert immune regulatory effects. With structural homology to the receptor binding site of TGF-β1, HpHsp60 could interact with TGF-β receptor II, trigger SMAD pathway, and inhibiting the immune functions of THP-1 monocytic cells and peripheral mononuclear cells (PBMCs). Our study provides a new hint that H. pylori may employ Hsp60 to surrender host immunity.