沙眼衣原体pORF5 蛋白通过激活PI3K / Akt 信号通路抑制细胞凋亡

目的:探讨沙眼衣原体(Chlamydia trachomatis,Ct)pORF5 蛋白对细胞凋亡的影响,并进一步分析其分子机制,为阐明Ct 致病机制提供实验依据。方法:pGEX-6p/ pORF5 重组质粒转化XL1-blue 大肠杆菌,IPTG 诱导表达GST-pORF5融合蛋白,融合蛋白经谷胱甘肽琼脂糖凝胶4B 纯化及蛋白酶切除GST 标签后得到pORF5 蛋白。用不同浓度的pORF5 蛋白刺激HeLa 细胞,Western blot 检测不同时间Bax 和Bcl-2 的表达水平以及PI3K/ Akt 磷酸化水平,Hoechst 33342 及流式细胞技术分析细胞凋亡情况;HeLa 细胞经PI3K/ Akt 特异性抑制剂LY294002 预处理1 h 后,再用pORF5 蛋白刺激24 h,测定细胞凋亡率,并进一步分析凋亡相关蛋白Bax 和Bcl-2 的表达水平及PI3K/ Akt 磷酸化水平。结果:凋亡相关蛋白Bax 和Bcl-2 的表达变化与pORF5 蛋白浓度呈现一定的浓度和时间依赖性,当pORF5 蛋白浓度达10 μg/ ml 时,Bax 表达下调,Bcl-2 的表达上调,当升高至15 μg/ ml 时,Bax 和Bcl-2 的表达量变化最明显;15 μg/ ml 的pORF5 蛋白刺激HeLa 细胞24 h,Bax 和Bcl-2 表达变化最明显;流式细胞检测结果显示:pORF5 蛋白刺激组较TNF鄄琢处理组和未处理组细胞凋亡率分别降低了27.3% (P<0.01)和8.4% (P<0.05);Akt 在pORF5 蛋白刺激15 min 后发生磷酸化,30 min 后磷酸化水平达到峰值,用PI3K 抑制剂LY294002 预处理Hela 细胞后,发现Akt 的磷酸化显著减少,Bax 蛋白表达明显上调,Bcl-2 表达明显下调;LY294002 处理组细胞凋亡率相比于对照组增加了13.0% (P<0.01)。结论:pORF5 蛋白通过激活PI3K/ Akt 信号通路调节Bcl-2 和Bax 蛋白的表达抑制细胞凋亡。

Chlamydia trachomatis pORF5 protein inhibits apoptosis through activating PI3K-Akt pathway

Objective:To study the relationship between apoptosis and the pORF5 protein of Chlamydia trachomatis,and further to explore its molecular mechanisms,which could lay a foundation for chlamydial pathogenic mechanisms.Methods:pGEX-6p/ pORF5 recombinant expression vector was transformed to XL1-blue E.Coli to express GST-pORF5 fusion protein,and GST-pORF5 fusion protein was purified with Glutathione Sepharose 4B Beads, and cleaved to get pORF5 protein without GST tag by PreScission protease.The pORF5 protein was used to stimulate HeLa cells at different concentrations,then Western blot was used to evaluate the expression of Bax,Bcl-2 and phosphorylation of PI3K/ Akt at different time points,Hoechst staining and Flow cytometry were applied to measure the apoptosis of HeLa cells.Before treated with pORF5 protein for 24 h,HeLa cells were pretreated with PI3K inhibitor LY294002 for 1 h,the expression of Bax,Bcl-2 and the phosphorylation of Akt were evaluated by Western blot,apoptosis rates were also determined.Results:The pORF5 protein changed the expression of Bax and Bcl-2 in dose-and time-dependent manners, pORF5 increased the expression of Bcl-2 and decreased the expression of Bax at the concentration of 10 μg/ ml,and there was obvious change at concentration of 15 μg/ ml for 24 h.The apoptosis rates of pORF5 treated group were reduced by 27.3% and 8.4% respectively when compared with TNF-βtreated group(P<0.01) and untreated group (P<0.05).Akt was phosphorylated after stimulated with pORF5 protein for 15 min, and reached its peak at 30 min.PI3K/ Akt inhibitor led to the decrease of the expression of Bcl-2 and phosphorylation of Akt and increase of the expression of Bax,furthermore,PI3K/ Akt inhibitor reversed pORF5-mediated anti-apoptosis, the apoptosis rate in LY294002 treated group was increased by 13.0%,when compared with the control group (P<0.01).Conclusion:pORF5 protein could inhibit apoptosis through activating PI3K/ Akt signal pathway by induction of Bcl-2 and suppression of Bax.