Duck enteritis virus activates CaMKKβ-AMPK to trigger autophagy in duck embryo fibroblast cells via increased cytosolic calcium

Background: The results of our previous study showed that impaired cellular energy metabolism contributes to duck enteritis virus-induced autophagy via the 5`-adenosine monophosphate-activated protein kinase (AMPK)/tuberous sclerosis complex 2/mammalian target of rapamycin pathway in duck embryo fibroblast (DEF) cells. However, it remains unknown whether any other underlying mechanisms of AMPK activation are involved in autophagy induction. Methods: The activity of CaMKK beta and AMPK in DEF cells infected with DEV were evaluated. The Effect of inhibitory activity of CaMKK beta on DEV-induced autophagy was investigated. In addtion to, the cytosolic calcium level in DEF cells infected with DEV were evaluated. The Effect of inhibitory cytosolic calcium level on DEV-induced autophagy was investigated. Results: In this study, duck enteritis virus (DEV) infection activated CaMKK beta and its substrate molecule AMPK at 36, 48, and 60 h post-infection (hpi). STO-609, a CaMKK beta inhibitor, or CaMKK beta siRNA significantly inhibited the activation of DEV to AMPK, LC3I to LC3II transformation, and GFP-LC3 puncta distribution. In addition, inhibition of CaMKK beta activity also significantly reduced progeny DEV titer and gB protein expression. Besides, cytosolic calcium (Ca2+) was higher in DEV-infected cells than mock controls at 36, 48, and 60 hpi, respectively. Treatment of DEV-infected cells with 1,2-Bis (2-aminophenoxy) ethane-N, N, N', N-tetraacetic acid (BAPTA-AM) significantly reduced intracellular Ca2+ ion concentrations, as well as CaMKK beta and AMPK activities, and subsequent autophagy, in addition to viral protein synthesis and viral titer. Conclusions: These results showed that elevated [Ca2+] cyto-mediated activation of CaMKK beta managed the activation of AMPK, which then positively regulated autophagy, thereby providing further insight into DEV-host interactions.