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Abstract:
Toxoneuron nigriceps (Hymenoptera, Braconidae) is an endophagous parasitoid of the larval stages of
the tobacco budworm, Heliothis virescens (Lepidoptera, Noctuidae). The bracovirus associated with this
wasp (TnBV) is currently being studied. Several genes expressed in parasitised host larvae have been
isolated and their possible roles partly elucidated. TnBVank1 encodes an ankyrin motif protein similar
to insect and mammalian IκB, an inhibitor of the transcription nuclear factor κB (NF-κB). Here we show
that, when TnBVank1 was stably expressed in polyclonal Drosophila S2 cells, apoptosis is induced.
Furthermore, we observed the same effects in haemocytes of H. virescens larvae, after TnBVank1 in vivo
transient transfection, and in haemocytes of parasitised larvae. Coimmunoprecipitation experiments
showed that TnBVANK1 binds to ALG-2 interacting protein X (Alix/AIP1), an interactor of apoptosislinked
gene protein 2 (ALG-2). Using double-immunofluorescence labeling, we observed the potential
colocalization of TnBVANK1 and Alix proteins in the cytoplasm of polyclonal S2 cells. When Alix was
silenced by RNA interference, TnBVANK1 was no longer able to cause apoptosis in both S2 cells and
H. virescens haemocytes. Collectively, these results indicate that TnBVANK1 induces apoptosis by
interacting with Alix, suggesting a role of TnBVANK1 in the suppression of host immune response
observed after parasitisation by T. nigriceps.
