T3SS通过ERK/ROS信号通路促进铜绿假单胞菌侵袭肺上皮细胞的作用

Role of T3SS in promoting Pseudomonas aeruginosa internalization in pulmonary epithelial cells via ERK/ROS signaling pathway

目的探究Ⅲ型分泌型系统(type three secretion system,T3SS)在调控铜绿假单胞菌(Pseudomonas aeruginosa,PA)侵袭肺上皮细胞中的作用及具体机制。方法采用PA菌株感染人非小细胞肺癌A549细胞,分为未处理组、PAO1(PA实验室标准菌株)组、△exsA(缺失与T3SS转录激活相关的基因exsA)组、△pscJ(缺失与T3SS蛋白分泌相关基因pscJ)组和PAO1-E(经EGTA诱导后高表达T3SS基因)感染组。采用U0126抑制A549细胞ERK活性或通过apocynin(APO)/N-acetyl-L-cysteine(NAC)抑制A549细胞活性氧(reactive oxygen species,ROS)产生并随后感染PAO1或PAO1-E菌株,分为未处理组、PAO1或PAO1-E感染组、抑制剂处理组,以及抑制剂联合PAO1或PAO1-E感染组。选用庆大霉素杀伤胞外细菌并将细胞裂解液倍比稀释后涂布PA筛选平板,通过计数菌落形成单位(CFUs),明确PA感染后细胞内的细菌量;通过荧光探针标记以及流式细胞术检测感染后细胞内ROS水平;通过Western blot检测感染后ERK通路的活化情况。结果与PAO1感染组相比,△exsA和△pscJ感染组的细胞内细菌量减少(P<0.05,P<0.01),且伴随ROS产生减少(P<0.01),而PAO1-E感染组则呈现相反趋势(P<0.01)。PAO1或PAO1-E感染联合APO/NAC处理组的细胞内细菌量明显低于PAO1或PAO1-E感染组(P<0.01)。相较PAO1感染组,△exsA和△pscJ感染组的ERK磷酸化水平增加(P<0.01),而PAO1-E感染组的ERK磷酸化降低(P<0.01)。与PAO1感染组相比,PAO1联合U0126处理组的细胞ERK磷酸化水平降低,伴随ROS产生以及细胞内细菌量增加(P<0.01)。结论T3SS介导ERK通路抑制可通过促进肺上皮细胞ROS产生,增加PA对肺上皮细胞侵袭。

Objective To explore the role and underlying mechanism of typeⅢsecretion system(T3SS)in regulating the internalization of Pseudomonas aeruginosa(PA)into pulmonary epithelial cells.Methods The human non-small cell lung cancer A549 cells were infected with or without PA strains,including wild-type PAO1(a standard experimental PA strain),△exs A(knockout of the critical activator for T3SS genes),△psc J(T3SS secretion-defective strain)and PAO1-E(EGTA-induced high expression of T3SS genes).The A549 cells pretreated with ERK inhibitor U0126 or reactive oxygen species(ROS)inhibitor apocynin(APO)/N-acetyl-L-cysteine(NAC)were infected with PAO1 or PAO1-E strain.Thus,the experiment was grouped as follows:the mock-treated group,PAO1-or PAO1-E-infected group,inhibitor-treated group,and PAO1/PAO1-E plus inhibitor-treated group.Extracellular bacteria were killed by gentamicin,and the cell lysates were diluted and then plated on PA screening plates.Bacterial amounts were detected by counting colony-forming units(CFUs).The production of ROS was analyzed using fluorescent probe labeling and flow cytometry.The activation of the ERK pathway was detected by Western blotting.Results Compared with the PAO1-infected group,the intracellular bacteria and ROS level in△exs A-or△psc J-infected cells were lower(P<0.05,P<0.01),so was the generation of ROS(P<0.01);In contrast,those of the PAO1-E strain-infected cells displayed an opposite trend(P<0.01).Compared with the PAO1-or PAO1-E-infected group,the cells pretreated with APO/NAC followed by PAO1 or PAO1-E infection showed reduced intracellular bacterial amounts(P<0.01).Compared to the PAO1-infected A549 cells,the phosphorylation level of ERK was increased in the△exs A-or△psc J-infected cells(P<0.01),while that level was suppressed in the PAO1-E-treated cells(P<0.01).Compared with the PAO1-infected group,the PAO1-infected cells pretreated with U0126 displayed reduced ERK activation,elevated ROS production,and increased intracellular counts of PAO1(P<0.01).Conclusion T3SS-mediated inhibition of the ERK pathway promotes the production of ROS and the internalization of PA in lung epithelial cells.