Avian infectious bronchitis virus disrupts the melanoma differentiation associated gene 5 (MDA5) signaling pathway by cleavage of the adaptor protein MAVS

Yu, Liping; Zhang, Xiaorong; Wu, Tianqi; Su, Jin; Wang, Yuyang; Wang, Yuexin; Ruan, Baoyang; Niu, Xiaosai; Wu, Yantao

To determine the relationship between the antiviral immune response and virus titer, CEK cells were infected with IBV at 10 −2 , 10 −1 , 10 0 , 10 1 and 10 2 MOI for 36 h. As shown in Fig. 4 , IBV induced chMDA5 (Fig. 4b) , chIFN-β (Fig. 4c), chIFN-λ (Fig. 4d) and chMx (Fig. 4e ) transcription in CEK cells at different infectious doses. We also found that IBV induced chMDA5, chIFN-β, chIFN-λ and chMx transcription in CEK cells to a greater extent than in mockinfected cells at infectious doses of 10 1 and 10 2 MOI (P ≤ 0.01). Overall, IBV significantly induced the activation of chMDA5, chIFN-β, chIFN-λ and chMx in a dose-dependent manner. The PRRs RIG-I and MDA5 are critical regulators of the host antiviral response and share a similar homology in their overall primary structure. This similarity prompted us to investigate whether dgRIG-I has the same role as chMDA5 in the IBV-induced IFN response in chicken cells. The expression of chMDA5 in DF1 cells enhanced chIFN-β transcription after the cells were infected with IBV compared with the control group transfected with vector and primed by IBV infection (P ≤ 0.05) (Fig. 5a) . We also found that infection with IBV induced higher chIFN-β transcription in dgRIG-I-expressing cells to a greater extent than the control group (P ≤ 0.01), and dgRIG-I induced chIFN-β expression after IBV infection to a greater extent than chMDA5. Expression of chTLR3 did not enhance chIFN-β transcription after being infected with IBV. These results appear to indicate that IBV stimulates chIFN-β transcription via MDA5. Similarly, the IBV-induced chIFN-β transcription was further increased by the overexpression of dgRIG-I. These data show that chMDA5 and dgRIG-I act as positive regulators of the IBV-induced chIFN-β signaling pathway (Fig. 5a) .