Department of Surgery, Vanderbilt University Medical Center, Nashville, Tennessee, USA.
Gastroenterology. 2010 Oct;139(4):1333-43. doi: 10.1053/j.gastro.2010.06.018. Epub 2010 Jun 12.
BACKGROUND & AIMS: Infection with the gastric mucosal pathogen Helicobacter pylori is the strongest identified risk factor for distal gastric cancer. These bacteria colonize a significant part of the world's population. We investigated the molecular mechanisms of p53 regulation in H pylori-infected cells.
Mongolian gerbils were challenged with H pylori and their gastric tissues were analyzed by immunohistochemistry and immunoblotting with p53 antibodies. Gastric epithelial cells were co-cultured with H pylori and the regulation of p53 was assessed by real-time polymerase chain reaction, immunoblotting, immunofluorescence, and cell survival assays. Short hairpin RNA and dominant-negative mutants were used to inhibit activities of Human Double Minute 2 (HDM2) and AKT1 proteins.
We found that in addition to previously reported up-regulation of p53, H pylori can also negatively regulate p53 by increasing ubiquitination and proteasomal degradation via activation of the serine/threonine kinase AKT1, which phosphorylates and activates the ubiquitin ligase HDM2. These effects were mediated by the bacterial virulence factor CagA; ectopic expression of CagA in gastric epithelial cells increased phosphorylation of HDM2 along with the ubiquitination and proteasomal degradation of p53. The decrease in p53 levels increased survival of gastric epithelial cells that had sustained DNA damage.
H pylori is able to inhibit the tumor suppressor p53. H pylori activates AKT1, resulting in phosphorylation and activation of HDM2 and subsequent degradation of p53 in gastric epithelial cells. H pylori-induced dysregulation of p53 is a potential mechanism by which the microorganism increases the risk of gastric cancer in infected individuals.
胃黏膜病原体幽门螺杆菌（H. pylori）感染是远端胃癌最强的确定风险因素。这些细菌在世界上很大一部分人口中定植。我们研究了 H. pylori 感染细胞中 p53 调节的分子机制。
用 H. pylori 感染蒙古沙土鼠，用 p53 抗体进行免疫组化和免疫印迹分析其胃组织。将胃上皮细胞与 H. pylori 共培养，通过实时聚合酶链反应、免疫印迹、免疫荧光和细胞存活测定评估 p53 的调节。使用短发夹 RNA 和显性负突变体抑制 Human Double Minute 2（HDM2）和 AKT1 蛋白的活性。
我们发现，除了先前报道的 p53 上调外，H. pylori 还可以通过激活丝氨酸/苏氨酸激酶 AKT1 增加泛素化和蛋白酶体降解来负调控 p53，AKT1 磷酸化并激活泛素连接酶 HDM2。这些作用是由细菌毒力因子 CagA 介导的；胃上皮细胞中 CagA 的异位表达增加了 HDM2 的磷酸化以及 p53 的泛素化和蛋白酶体降解。p53 水平的降低增加了持续 DNA 损伤的胃上皮细胞的存活。
H. pylori 能够抑制肿瘤抑制因子 p53。H. pylori 激活 AKT1，导致胃上皮细胞中 HDM2 的磷酸化和激活以及随后 p53 的降解。H. pylori 诱导的 p53 失调是该微生物增加感染个体胃癌风险的潜在机制。
