MDA5 attenuate autophagy in chicken embryo fibroblasts infected with IBDV

1. The role of melanoma differentiation-associated protein 5 (MDA5) in infectious bursal disease virus (IBDV)-induced autophagy was studied in chicken embryos.2. Chicken embryo fibroblasts (CEF) were used as the research model and small interfering RNA (siRNA), western blot, indirect enzyme-linked immunosorbent assay (ELISA), real-time fluorescence quantitative polymerase chain reaction (PCR) and transmission electron microscopy were used to detect autophagy, IBDV replication, CEF damage, and activation of both MDA5 and its signalling pathway.3. The results showed that CEF infected with IBDV activated the intracellular MDA5 signalling pathway and caused autophagy via inactivation of the AKT/mTOR pathway. While autophagy promotes IBDV proliferation, MDA5 weakens IBDV-induced CEF autophagy thus inhibiting IBDV replication and protecting CEF cells.4. The results indicated that chMDA5 can be activated by IBDV and attenuate CEF autophagy caused by IBDV infection, thereby inhibiting IBDV replication. This study provided a foundation for further exploring the relationship between viruses, autophagy and the pathogenic mechanism of the MDA5 pathway involved in IBDV.

Potential Role of Macrophage Migration Inhibitory Factor in the Pathogenesis of Marek's Disease

Introduction

Marek’s disease virus (MDV) can cause malignant T-cell lymphomas and immunosuppression in chickens. Macrophage migration inhibitory factor (MIF) not only plays a critical role in inhibiting T-cell responses, but also contributes to multiple aspects of tumour progression. The aim of this study was to reveal the potential role of MIF in the pathogenesis of MDV infection.

Material and Methods

MIF gene expression levels were measured by using real-time PCR. Expression was assayed at different times in chicken embryo fibroblast (CEF) cells and tissue samples of SPF chickens infected with different MDV strains and fold change was calculated by the 2^–△△CT method.

Results

The expression of MIF was significantly downregulated (p < 0.05 and FC > 2) in CEF cells infected with the very virulent MDV RB1B strain at 48 h post infection (hpi) and in the skin and spleen at 14 days post infection (dpi). The reduction of MIF expression was also found in CEF cells infected by reticuloendotheliosis virus (REV), avian leukosis virus subgroup J (ALV-J), and MDV vaccine strain CVI988 or in HD11 cells stimulated with TLR2, 3, 4, and 7 ligands. Interestingly, MIF expression decreased continuously from 7 to 28 dpi in the thymus after RB1B virus infection while it increased after CVI988 virus infection. Upregulated expression of MIF was found in CEF infected with RB1B at 96 hpi and in the spleen and skin at 21 and 28 dpi.

Conclusion

The present study revealed the different expression pattern of MIF in response to MDV infection and indicated that MIF level may be associated with MDV pathogenesis.

Specific binding of phorbol ester tumor promoters

[20-(3)H]Phorbol 12,13-dibutyrate bound to particulate preparations from chicken embryo fibroblasts in a specific, saturable, reversible fashion. Equilibrium binding occurred with a K(d) of 25 nM; this value is very close to the 50% effective dose (ED(50)), 50 nM, previously determined for the biological response (induction of fibronectin loss) in growing chicken embryo fibroblasts. At saturation, 1.4 pmol of [20-(3)H]phorbol 12,13-dibutyrate was bound per mg of protein (approximately 7 x 10(4) molecules per cell). Binding was inhibited by phorbol 12-myristate 13-acetate (K(i) = 2 nM), mezerein (K(i) = 180 nM), phorbol 12,13-dibenzoate (K(i) = 180 nM), phorbol 12,13-diacetate (K(i) = 1.7 muM), phorbol 12,13,20-triacetate (K(i) = 39 muM), and phorbol 13-acetate (K(i) = 120 muM). The measured K(i) values are all within a factor of 3.5 of the ED(50) values of these derivatives for inducing loss of fibronectin in intact cells. Binding was not inhibited by the inactive compounds phorbol (10 mug/ml) and 4alpha-phorbol 12,13-didecanoate (10 mug/ml) or by the inflammatory but nonpromoting phorbol-related diterpene esters resiniferatoxin (100 ng/ml) and 12-deoxyphorbol 13-isobutyrate 20-acetate (100 ng/ml). These data suggest that biological responses to the phorbol esters in chicken embryo fibroblasts are mediated by this binding activity and that the binding activity corresponds to the phorbol ester target in mouse skin involved in tumor promotion. Binding was not inhibited by the nonphorbol promoters anthralin (1 muM), phenol (1 mM), iodoacetic acid (1.7 muM), and cantharidin (75 muM), or by epidermal growth factor (100 ng/ml), dexamethasone acetate (2 muM), retinoic acid (10 muM), or prostaglandin E(2) (1 muM). These agents thus appear to act at a target distinct from that of the phorbol esters.