Study On Interaction Mechanisms Between Mycobacterial PPE38 Protein And The Host

Tuberculosis caused by Mycobacterium tuberculosis. At present, approximately one third of the world’s population is infected by Mycobacterium tuberculosis. Tuberculosis is an ancient disease, but so far we still do not understand its pathogenesis, and lack effective treatments and vaccines.In the Mycobacterium tuberculosis genome, two distinctive protein families have been described, PE/PPE families, which occupy about the 10% of the gene coding capacity of the genome. The PE/PPE families contain a large number of repeat units, and have been considered as restructuring and mutation hotspots. As such, researchers have speculated that Mycobacterium tuberculosis may undergo antigenic variation within these regions, thereby escaping the immune response of the host cells.In our prior study, mutant strains of ppe38 (05B1) were found by screening a MycoMarT7 mariner transposon mutagenesis library. Further study found:the cord structure of 05B1 was disappeared. PPE38 was localized in the cell wall, and disruption of PPE38 resulted in reduced secretion of TNF-a and IL-6 and a decreased ability to invade macrophages. Adult zebrafish infected with the 05B1 survived longer and exhibited reduced pathology. Based on these observations, it appears that PPE38 plays an important role in the virulence of Mycobacteria, and have complex interaction with the host. However, the interaction of PPE38 protein with the host and its pathogenic mechanism are still not well understood.To further elucidate the mechanism of interaction of PPE38 protein with macrophages, in this current study, we used SILAC/AACT to label macrophages, labeled and unlabeled macrophages were infected by wild type (WT) and 05B1 Mycobacterium marinum strains, respectively. We then studied the differences in downstream pathways using subcellular quantitative proteomics. We found that the PPE38 protein can trigger downstream signaling from NF-KB、ERK、JNK and PI3K pathways by combining with TLR2. Furthermore, transcription factors and transcription factors-associated proteins were studied using bioinformatics methods, and the links between TFs and related biological processes were determined. The proteins of MHC-1 and its associated pathways were reduced in our results, so we believe the PPE38 protein of Mycobacterium marinum was implicated in antigen processing and presentation, and ultimately resisted the adaptive immune response of the host.To further study the interaction between PPE38 protein and the host immune system, we studied the function of PPE38 protein in cell and the overall level of host. In cell model, we found PPE38 protein was involved in invasion, and reduced the MHC-1 expression of macrophage, but not participated in cell death. In zebrafish larva model, we found that WT and 05B1 were no difference in the proliferation. In animal model, C57BL/6 mice were infected by Mycobacterium smegmatis which expressed PPE38 (MS-PPE38), from CFU counts, immunohistochemistry and flow cytometry, we found that PPE38 was an important virulence factor of Mycobacteria and able to reduce the activation of CD8+ T cell.Overall, this study helps to further our understanding of the biological function of the PE/PPE proteins, in particular how to escape the host immune by mycobacterial PPE protein, and has important significance for study interaction between other cell wall proteins and the host.