The multifunctional polydnavirus TnBVANK1 protein: impact on host apoptotic pathway

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 apoptosis-linked 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.

Regulation of the Larval Transcriptome of Diatraea saccharalis (Lepidoptera: Crambidae) by Maternal and Other Factors of the Parasitoid Cotesia flavipes (Hymenoptera: Braconidae)

“…Some caspases and Ca +2 -dependent molecules (caspase activators), such as calpain and calcineurin, were up-regulated in D. saccharalis larvae parasitized and pseudoparasitized by C. flavipes (Mattson and Chan, 2003; Humeau et al, 2017). Apoptosis of High Five cells was induced in the presence of viral protein associated with Microplitis bicoloratus Chen (Hymenptera: Braconidae) and Toxoneuron nigriceps (Viereck) (Hymenoptera: Braconidae), through their interaction with cell proteins that activate caspases (Yu et al, 2016; Salvia et al, 2017). Cotesia flavipes also regulated Ca +2 channels, Ca +2 modulators and Ca +2 -dependent molecules, altering several physiological processes ranging from cell proliferation to apoptosis activation.…”

Novel Factors of Viral Origin Inhibit TOR Pathway Gene Expression

“…Among these were previously identified and, in some cases, functionally characterized Tn BV genes ( Varricchio et al, 1999 ; Falabella et al, 2003 ; Provost et al, 2004 ) such as TnBV1 , TnBV2 , TnBVank1 , ptp1 , ptp4 , ptp6 , and ptp8 . Tn BVank1 displays significant sequence similarity with members of the IkB family ( Silverman and Maniatis, 2001 ; Thoetkiattikul et al, 2005 ; Falabella et al, 2007 ; Bitra et al, 2012 ; Salvia et al, 2017 ). These proteins are generally involved in the control of NF-kB signaling pathways both in insects and vertebrates ( Silverman and Maniatis, 2001 ).…”

“…This multifunctional activity of Tn BVank1 is not surprising. The expression of this gene in H. virescens immune cells was demonstrated to induce apoptosis through the interaction with Alix, besides its irreversible inhibition of NF-kB translocation in cell nuclei, thus blocking the expression of key genes and inducing apoptotic phenomena ( Falabella et al, 2007 ; Salvia et al, 2017 ). The reduced gland size observed in D. melanogaster larvae ( Valzania et al, 2014 ) and the low basal production of ecdysteroids in PGs of H. virescens parasitized larvae were also reported ( Pennacchio et al, 1997 , 1998b ).…”

“…In H. virescens larvae parasitized by T. nigriceps , the main infection target tissues are haemocytes and prothoracic glands (PGs) ( Stoltz and Vinson, 1979 ; Wyder et al, 2003 ), where Tn BV expresses several genes belonging to different families encoding protein tyrosine phosphatases (PTPs), the largest gene family in bracovirus ( Provost et al, 2004 ; Falabella et al, 2006 , 2007 ; Webb et al, 2006 ), ankyrin motif protein (ANK) ( Falabella et al, 2007 ; Salvia et al, 2017 ), UDP dehydrogenase, proteins containing Ben domains ( Park and Kim, 2010 ; Falabella et al, unpublished data). Other viral genes expressed in the host are Tn BV1, implicated in immune suppression ( Varricchio et al, 1999 ; Malva et al, 2004 ) and activating caspase proteins ( Lapointe et al, 2005 ) and Tn BV2 encoding a retroviral aspartyl protease ( Falabella et al, 2003 ).…”

Aphidius ervi Teratocytes Release Enolase and Fatty Acid Binding Protein Through Exosomal Vesicles

“…Ultrathin sections (80–90 nm in thickness) were collected on 200 mesh gold grids. After etching with 3% NaOH in absolute ethanol (Causton, 1984), sections were incubated for 30 min with PBS containing 2% bovine serum albumin (BSA) and then for 1 h at room temperature (RT), with the following primary antibodies (working dilution 1:40): rabbit polyclonal antibodies anti-Ae-ENO (Grossi et al, 2016) and anti-Ae-FABP (Falabella et al, 2005) and mouse monoclonal antibodies anti-Alix (Salvia et al, 2017) and anti-HSP70 (Sigma-Aldrich, St Louis, MO, USA). After several washing in PBS, samples were incubated for 1 h at RT with secondary goat anti-rabbit IgG (H + L)-gold conjugate (working dilution 1:100, particle size 6 nm, GE Healthcare Amersham, Buckinghamshire, UK) to detect Ae-ENO and anti-Ae-FABP, and with goat anti-mouse IgG (H + L)-gold conjugate (working dilution 1:100, particle size 6 nm, GE Healthcare Amersham, Buckinghamshire, UK) to detect Alix and HSP70, or with a protein G gold-conjugated 1:100, particle size 6 nm, GE Healthcare Amersham, Buckinghamshire, UK, to detect the mouse primary antibodies.…”