Characterization of the IkappaB-like gene family in polydnaviruses associated with wasps belonging to different Braconid subfamilies.
Polydnaviruses (PDVs) are obligate symbionts of hymenopteran parasitoids of lepidopteran larvae that induce host immunosuppression and physiological redirection. PDVs include bracoviruses (BVs) and ichnoviruses (IVs), which are associated with braconid and ichneumonid wasps, respectively. In this study, the gene family encoding IkappaB-like proteins in the BVs associated with Cotesia congregata (CcBV) and Toxoneuron nigriceps (TnBV) was analysed. PDV-encoded IkappaB-like proteins (ANK) are similar to insect and mammalian IkappaB, an inhibitor of the transcription factor nuclear factor kappaB (NF-kappaB), but display shorter ankyrin domains and lack the regulatory domains for signal-mediated degradation and turnover. Phylogenetic analysis of ANK proteins indicates that those of IVs and BVs are closely related, even though these two taxa are believed to lack a common ancestor. Starting from a few hours after parasitization, the transcripts of BV ank genes were detected, at different levels, in several host tissues. The structure of the predicted proteins suggests that they may stably bind NF-kappaB/Rel transcription factors of the tumour necrosis factor (TNF)/Toll immune pathway. Accordingly, after bacterial challenge of Heliothis virescens host larvae parasitized by T. nigriceps, NF-kappaB immunoreactive material failed to enter the nucleus of host haemocytes and fat body cells. Moreover, transfection experiments in human HeLa cells demonstrated that a TnBV ank1 gene product reduced the efficiency of the TNF-alpha-induced expression of a reporter gene under NF-kappaB transcriptional control. Altogether, these results suggest strongly that TnBV ANK proteins cause retention of NF-kappaB/Rel factors in the cytoplasm and may thus contribute to suppression of the immune response in parasitized host larvae.
Falabella
Patrizia
P
Dipartimento di Biologia, Difesa e Biotecnologie Agro-Forestali, Università della Basilicata, Potenza, Italy.
Varricchio
Paola
P
Istituto di Genetica e Biofisica, CNR, Napoli, Italy.
Provost
Bertille
B
Institut de Recherche sur la Biologie de l'Insecte, CNRS, Université de Tours, Faculté des Sciences, Tours, France.
Espagne
Eric
E
Institut de Recherche sur la Biologie de l'Insecte, CNRS, Université de Tours, Faculté des Sciences, Tours, France.
Ferrarese
Roberto
R
Dipartimento di Biologia Strutturale e Funzionale, Università dell'Insubria, Varese, Italy.
Grimaldi
Annalisa
A
Dipartimento di Biologia Strutturale e Funzionale, Università dell'Insubria, Varese, Italy.
de Eguileor
Magda
M
Dipartimento di Biologia Strutturale e Funzionale, Università dell'Insubria, Varese, Italy.
Fimiani
Giorgia
G
Istituto di Genetica e Biofisica, CNR, Napoli, Italy.
Ursini
Matilde Valeria
MV
Istituto di Genetica e Biofisica, CNR, Napoli, Italy.
Malva
Carla
C
Istituto di Genetica e Biofisica, CNR, Napoli, Italy.
Drezen
Jean-Michel
JM
Institut de Recherche sur la Biologie de l'Insecte, CNRS, Université de Tours, Faculté des Sciences, Tours, France.
Pennacchio
Francesco
F
Dipartimento di Entomologia e Zoologia Agraria 'F. Silvestri', Università di Napoli 'Federico II', Via Università 100, 80055 Portici (NA), Italy.
D000818:Animals; D015967:Gene Expression Regulation, Viral; D016679:Genome, Viral; D020672:I-kappa B Proteins / Q000737:chemistry / Q000235:genetics*; D018071:Polydnaviridae / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D017422:Sequence Analysis, DNA; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D014863:Wasps / Q000821:virology*
D020672:I-kappa B Proteins; D014764:Viral Proteins