胃幽門螺旋桿菌CagA調控Bcl-6、Blimp-1以及抗細胞凋亡分子Bcl-2 和 Bcl-XL之研究

Abstract

Helicobacter pylori is a gram-negative bacteria. Human who infected Helicobacter pylori causes chronic gastrits, peptic ulcer and gastric adenocarcinoma. CagA, Helicobacter pylori virulent factor, is 120~148 kD. It is translocated into the cell by type IV secretion system. In host cells, CagA is phosphorylated by protein kinase. Phospho-CagA binds SHP-2 to activate ERK signal pathway. cagA+ H. pylori strains have been reported to affect the cell cycle by stimulating cyclin D1 expression and host cell survival. In previous studies, CagA activates STAT3 pathway in gastric epithelium cell. In B cell activation and differentiation, STAT3 also plays an important role. To study the mechanism of Helicobacter pylori-dependent regulation of B cell transformation, we suggest that Helicobacter pylori CagA may play an important role. First, we found that H. pylori translocates CagA into B cell in H. pylori and BJAB cell co-culture system. To further examine whether H. pylori directly regulates B cell activation via CagA, we investigate the phosphorylation of B cell activation molecule STAT3 and P38. Our results show that H. pylori activates STAT3 and P38 pathway, but the expression of phospho-STAT3 and phospho-P38 decrease when BJAB cell co-cultures with cagA knock-out strain. Therefore, CagA increases STAT3 and P38 activation in B cell activation. Next, we explore whether CagA in B cells regulates B cell survival. We found that H. pylori induces Bcl-2 and Bcl-XL expression, but Bcl-2 and Bcl-XL expression is not up-regulated when BJAB cell co-cultures with cagA knock-out H. pylori strain. We transfected CagA into B cell and found that Bcl-2 and Bcl-XL expression is up-regulated. The results indicate that H. pylori CagA can increase B cell survival. Moreover, in B cell differentiation, we also found that H. pylori decreases Bcl-6 protein expression, but Bcl-6 does not decrease when BJAB cell co-cultures with cagA knock-out strain. We used real-time PCR to investigate Bcl-6 mRNA expression. The results show that expression of Bcl-6 mRNA is inhibited, but we do not found the same result when BJAB cell co-cultures with cagA knock-out strain. We used real-time PCR to explore whether H. pylori can affect the expression of plasma cell differentiation associated molecule Blimp-1. Our results show that the H. pylori increases expression of Blimp-1 mRNA. To investigate the role of activated STAT3 in the mechanism of induction of Bcl-2 and Bcl-XL expression, we used Jak inhibitor AG490 to inhibit STAT3 pathway and STAT3 siRNA to inhibit STAT3 expression. Our results show that Bcl-2 and Bcl-XL expression is inhibited. However, inhibition of STAT3 expression does not regulate Bcl-6 and Blimp-1 expression. These results demonstrate that H. pylori translocate CagA into B cells to induce Bcl-2 and Bcl-XL expression via STAT3 pathway and to modulate Bcl-6 and Blimp-1 expression. These anti-apoptotic molecules induced by CagA might be one of the mechanisms that Helicobacter pylori controls B cell transformation, and that indicate that inhibition of translocating CagA into B cell or inhibition of CagA activity in B cell might be new way to cure the MALTlymphoma.