RESUMO
Objective To explore the molecular mechanism underlying the anti-apoptotic activity of pORF5 plasmid protein of Chlamydia trachomatis,so as to provide an experimental basis for further clarifying the pathogenesis of Chlamydia trachomatis.Methods HeLa cells were divided into two groups:carbonyl cyanide m-chlorophenyl hydrazone (CCCP,an apoptosis inducer) group was stimulated by CCCP for 30 minutes,and pORF5 + CCCP group was pretreated with pORF5 plasmid protein for 18 hours followed by CCCP for 30 minutes.Then,Western blot analysis was performed to determine the expression of apoptosisrelated proteins Bcl-2,Bax and caspase-3,JC-1 fluorescent probe was used to detect changes in the mitochondrial membrane potential in HeLa cells,and cytochrome c release from mitochondria was analyzed by indirect immunofluorescence assay.To analyze whether high-mobility group box 1 (HMGB1) protein participated in the anti-apoptotic role of pORF5 plasmid protein,HMGB 1 shRNA and control RNA were separately transfected into the HeLa cells,which were then stimulated by pORF5 plasmid protein and CCCP.Then,the protein expression of Bcl-2,Bax,activated caspase-3 was determined,and cytochrome c release was analyzed.Data were compared between two groups by using paired t test.Results pORF5 plasmid protein could antagonize the CCCP-induced decrease of mitochondrial membrane potential,and the red/green fluorescence intensity ratio was significantly lower in the CCCP group (0.4 ± 0.1) than in the pORF5 + CCCP group (1.7 ± 0.3;t =6.95,P ＜ 0.01).The protein expression of Bcl-2 in the HeLa cells in the pORF5 + CCCP group was 5.3 ± 0.6 times more than that in the CCCP group (t =8.62,P ＜ 0.01),while the protein expression of Bax and activated caspase-3 in the pORF5 + CCCP group significantly decreased by 79％ ± 10％ (t =9.23,P ＜ 0.01) and 75％ ± 8％ (t =4.26,P ＜ 0.05) respectively compared with the CCCP group.Compared with the control RNA transfection group,the HMGB1 shRNA transfection group showed significantly decreased mitochondrial membrane potential in the HeLa cells (t =11.23,P ＜ 0.01),increased cytochrome c release,decreased Bcl-2 expresson (t =7.19,P ＜ 0.05) and increased Bax expression (t =13.06,P ＜ 0.01) after stimulation with pORF5 and CCCP.Conclusion Chlamydia trachomatis plasmid protein pORF5 plays an anti-apoptosis role by blocking the mitochondrial apoptotic pathway through HMGB1 protein.
RESUMO
Objective:To investigate the immunogenicity of pORF5 plasmid protein,and further to screen and identify its im-munodominant domian.Methods: 10 different fragments of pORF5 gene including full length were amplified from the DNA of Chlamydia trachomatis serovar D by PCR and cloned into appropriate site of pGEX-6p vector to construct recombinant vectors after digested with BamHⅠand NotⅠrestriction endonucleases.After identification by PCR and sequencing,the recombinant plasmids were transformed into XL1 Blue E.coli to express the GST fusion proteins.ELISA and Western blot were carried out to identify the immunogenicity and immunoreaction of pORF5 plasmid protein.10 different fragments were reacted with sera from patients urogenitally infected with Chlamydia trachomatis, mouse polyclonal antibodies and mouse monoclonal antibodies of pORF5 plasmid protein with ELISA method.Results: pORF5 plasmid protein displayed strong immunogenicity and could induce a strong antibody response in human.The reactivity of human antibodies almost completely disappeared,when the native structure of pORF5 plasmid protein was de-stroyed.F6 that only lacked the N-terminal 66 amino acids was recognized by antibodies in ELISA as strongly as the whole pORF5 plasmid protein was.However,no other fragments were significantly recognized although there was a minimal reactivity of F2 and F3 with antibodies.Conclusion:pORF5 plasmid protein was an immunodominant antigen containing conformation-dependent epitope,and the C-terminal three quarters of pORF5 amino acid sequence was required for maintaining its immune dominance and conformation.The significance of the above findings lay a foundation for the further study on pORF5 protein function and vaccine development.