Protein tyrosine phosphatase-H2 from a polydnavirus induces apoptosis of insect cells.
The family Polydnaviridae is a large group of immunosuppressive insect viruses that are symbiotically associated with parasitoid wasps. The polydnavirus Microplitis demolitor bracovirus (MdBV) causes several alterations that disable the cellular and humoral immune defences of host insects, including apoptosis of the primary phagocytic population of circulating immune cells (haemocytes), called granulocytes. Here, we show that MdBV infection causes granulocytes in the lepidopteran Spodoptera frugiperda to apoptose. An expression screen conducted in the S. frugiperda 21 cell line identified the MdBV gene ptp-H2 as an apoptosis inducer, as indicated by cell fragmentation, annexin V binding, mitochondrial membrane depolarization and caspase activation. PTP-H2 is a classical protein tyrosine phosphatase that has been shown previously to function as an inhibitor of phagocytosis. PTP-H2-mediated death of Sf-21 cells was blocked by the pan-caspase inhibitor benzyloxycarbonyl-Val-Ala-(O-methyl) Asp-fluoromethylketone (Z-VAD-FMK), but cells maintained in this inhibitor still exhibited a suppressed phagocytic response. Mutagenesis experiments indicated that the essential catalytic cysteine residue required for the phosphatase activity of PTP-H2 was required for apoptotic activity in Sf-21 cells. Loss of adhesion was insufficient to stimulate apoptosis of Sf-21 cells. PTP-H2 expression, however, did significantly reduce proliferation of Sf-21 cells, which could contribute to the apoptotic activity of this viral gene. Overall, our results indicate that specific genes expressed by MdBV induce apoptosis of certain insect cells and that this activity contributes to immunosuppression of hosts.
Suderman
Richard J
RJ
Department of Entomology and Center for Tropical and Emerging Global Diseases, University of Georgia, Athens, GA 30602, USA.
Pruijssers
Andrea J
AJ
Department of Entomology and Center for Tropical and Emerging Global Diseases, University of Georgia, Athens, GA 30602, USA.
Strand
Michael R
MR
Department of Entomology and Center for Tropical and Emerging Global Diseases, University of Georgia, Athens, GA 30602, USA.
D000818:Animals; D017209:Apoptosis; D002460:Cell Line; D006434:Hemocytes / Q000473:pathology; D007165:Immunosuppression Therapy; D051336:Mitochondrial Membranes / Q000378:metabolism; D018071:Polydnaviridae / Q000201:enzymology*; D017027:Protein Tyrosine Phosphatases / Q000502:physiology*; D015398:Signal Transduction; D018411:Spodoptera / Q000502:physiology / Q000821:virology*
D017027:Protein Tyrosine Phosphatases