The Viral Proteins, PTP109, Vank86 And Vank92 From Microplitis Bicoloratus Bracovirus, Suppress The Host Immune Response

We found a large number of protein tyrosine phosphatases (PTPs) and viral ankyrin repeats (Vanks) genes in Microplitis bicoloratus bracovirus (MbBV) genome. Moreover, ptp and vank genes in the MbBV genome has a high proportion. As a kind of dephosphorylase, PTPs and protein tyrosine kinases(PTKs) co-regulate the phosphorylation levels which determine the switch of signaling pathways in cellular processes. In bracovirus, PTPs regulate the process of cell growth, apoptosis, immune and so on. However, there are few studies on the specific fuction of PTPs in MbBV so the function still remains unknown. This vank genes in bracoviruses is similar to the genes of IkB-like, which could suppress immune response via NF-κB signal transduction pathways to control the production of antimicrobial peptide genes in certain bracoviruses. But it is still unclear whether the Vanks in MbBV involved in the immune suppression. The aim of this thesis is to investigate whether MbBV-PTPs and MbBV-Vanks involves in host immune suppression. Through the analysis of the data of Spodoptera litura larvas hemocytes transcriptome sequencing, our finds out that some ptps and vanks exsists in Spodoptera litura larvas hemocytes post-parasitization. The ptps transcriptome sequencing result 1-7 day post-parasitization is confirmed by RT-PCR. This thesis chooses ptp 109、vank86 and vank92 to do further study for their transcriptome sequencing level obviously rises in post-parasitization and then clone them to construct an eukaryotic expression vector(pIZT/V5-His).We find that the PTP109, Vank86 and Vank92 localize in cytoplasm and nucleus by immunofluorescence.Besides, the Vank86 and Vank92 can affect the morphology of the Spli221 cells and PTP 109 can induce apoptosis of Spli221 cells. At the same time, Vank86 can lead to the paramorphia of High Five cells. This thesis further confirms through western blot that PTP109 can induce Spli221 cells to produce activited Caspase-3 which proves that PTP 109 can induce apoptosis of Spli221 cells. Moreover, PTP 109 can reduce Akt (Thr308) and Akt(Ser473) phosphorylation level. According to the data of qRT-PCR, Vank86、Vank92 and PTP109 largely suppress the genes participating in immunoreaction stimulated by LPS, including attacin, defensin and ppA3 which is important in cellular immunity and humoral immunity. Above all, our data suggests that PTP109, Vank86 and Vank92 can inhibit immune response of host cells by suppressing up-regulation of amps and inducing apoptosis. Moreover, this study lays the foundation for further understanding for the supression of MbBV in the host immune response.