Analysis of differential protein expression profile of HeLa cells stably transfected with Chlamydia trachomatis pORF5 gene
Objective 
To analyze the protein expression profile of HeLa cells transfected with pORF5 gene of Chlamydia trachomatis. 
 
 
Methods 
A lentiviral expression vector containing pORF5 gene was constructed. The lentiviral expression vector and helper plasmids were co-transfected into 293T cells to construct the recombinant lentivirus, which was used to infect HeLa cells. HeLa cells transfected with pORF5 gene and control HeLa cells were sorted out by flow cytometry. The isobaric tags for relative and absolute quantitation (iTRAQ) approach combined with nano-liquid chromatography-tandem mass spectrometry (NanoLC-MS/MS) analysis was performed to understand protein expression profiles and to identify and quantify the differentially expressed proteins in the pORF5-transfected HeLa cells (pORF5-Hela) and the control HeLa cells. Quantitative real-time PCR (qRT-PCR) and Western blot analysis were performed to detect the expression of some proteins at mRNA and protein levels, respectively. 
 
 
Results 
HeLa cell line stably transfected with pORF5 gene and control HeLa cell line were constructed successfully. Totally 314 proteins were differentially expressed between the pORF5-HeLa and control HeLa cells, 159 of which showed increased expression and the other 155 showed decreased expression in pORF5-HeLa cells. The differentially expressed proteins were involved in many processes, such as metabolic process, immune response, biological adhesion and so on. Results of qRT-PCR showed that the expression of HIST1H1C(histone H1.2C), HBA1(hemoglobin subunit alpha), PARK7(parkinson disease protein 7), HMGB1(high mobility group protein B1) and HMGB2 at mRNA level in pORF5-HeLa cells were up-regulated, while the expression of CLIC1(chloride intracellular channel protein 1), KRT7(typeⅡ cytoskeletal 7), SFN(14-3-3 protein sigma) and CDKN2A(cyclin-dependent kinase inhibitor 2A) were down-regulated. Western blot analysis confirmed the enhanced expression of HMGB1 and PRAK7 at protein level. The results of qRT-PCR and Western blot analysis were consistent with proteomic data. 
 
 
Conclusion 
Expression profiles for differentially expressed proteins between pORF5-HeLa and control HeLa cells were established successfully. The differentially expressed proteins regulated by pORF5 gene were found to be related to cell metabolism, proliferation, adhesion and so on, suggesting that pORF5 might promote the growth and proliferation of Ct by regulating protein expression and biological behavior of host cells. 
 
 
Key words: 
Chlamydia trachomatis; pORF5 gene; Isobaric tags for relative and absolute quantitation (iTRAQ); Proteomic technology; Differentially expressed protein