The role of Helicobacter pylori CagA in regulation of Bcl-2, Bcl-xL and Bcl-6

• Main Authors: Li-Pu Huang, 黃立普
• Other Authors: Ping-Ning Hsu
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/33467328348766330372

碩士 === 國立臺灣大學 === 免疫學研究所 === 98 === Helicobacter pylori is a Gram-negative bacteria. Infection with Helicobacter pylori leads to chronic gastrits, peptic ulcer disease, adenocarcinoma and gastric MALT lymphoma. CagA, a virulent factor of Helicobacter pylori, is an 120~145 kD bacteria protein. CagA could be translocated into the host cell via type IV secretion system. Within host cells, CagA is phosphorylated by protein kinase, and the phospho-CagA could bind to SHP-2, and to activate intracellular MAPK kinase signaling pathway. In cagA transgenic mice, gastric cancer and adenocarcinomas, as well as hematological malignancies were observed to develop in the CagA transgenic mice, but not in transgenic mice expressing phosphorylation-resistant CagA, suggesting that phosphorylation of CagA plays an important role in transformation of B cell. To study the mechanism of Helicobacter pylori CagA in B cell transformation, we proposed that Helicobacter pylori CagA could directly translocated into B cell, and increase the potential of B cell transformation. First, we found that H. pylori translocates CagA directly into B cell and undergoes phosphoralytion in H. pylori and BJAB cell co-culture system in a dose- and time-dependent manner. To further examine whether H. pylori CagA could promote B cell survival via CagA, we investigate the effect of CagA on antiapoptotic molecules Bcl-2 and Bcl-xL. We demonstrated that H. pylori induced higher Bcl-2 and Bcl-XL expression, not in cagA knock-out H. pylori strain in human B cell lines, indicating H. pylori CagA may increase B cell survival. Next we investigated the effects of CagA on expression of Bcl-6. We found that H. pylori could repress Bcl-6 expression, but not in cagA knock-out H. pylori strain. Expression of Bcl-2 and Bcl-xL mRNA is up-regulated while expression of Bcl-6 mRNA is inhibited in wild type but not in cagA knock-out H. pylori strain in real-time PCR analysis. To further investigate the role of SHP-2 in the regulation of Bcl-2 Bcl-xL and Bcl-6 expression, we used SHP-2 inhibitor NSC-87877 to inhibit SHP-2 activity and SHP-2 siRNA to knockdown SHP-2 expression. Our results demonstrated the effects on Bcl-2, Bcl-xL and Bcl-6 is not affected by knocking down SHP-2. To further confirm whether CagA may directly regulate Bcl-2, Bcl-xL and Bcl-6, we transfected WT-CagA or PR-CagA into B cell. The expression of Bcl-2 and Bcl-xL are induced in B cell transfected with either WT-CagA or PR-CagA, indicating that the expression of Bcl-2 and Bcl-xL are phospho-CagA independent. In order to examine whether H. pylori promote B cell survival, we treated B cell with etoposide after co-culture with H. pylori. The results showed that the survival of B cell after co-cultured with cagA knock-out strain was significantly decreased; in contrast, B cell transfected with WT-CagA or PR-CagA showed increased survival rate compare to vector control, suggesting CagA can promote B cell survival. Thus anti-apoptotic molecules induced by CagA might play an important role in transformation of B cell, and in the development of MALT lymphoma.