The double-stranded RNA (dsRNA)-dependent protein kinase (PKR) inhibits protein synthesis by phosphorylating eukaryotic translation initiation factor 2 alpha (eIF2 alpha). In fish species, in addition to PKR, there exists a PKR-like protein kinase containing Z-DNA binding domains (PKZ). However, the antiviral role of fish PKZ and the functional relationship between fish PKZ and PKR remain unknown. Here we confirmed the coexpression of fish PKZ and PKR proteins in Carassius auratus blastula embryonic (CAB) cells and identified them as two typical interferon (IFN)-inducible eIF2 alpha kinases, both of which displayed an ability to inhibit virus replication. Strikingly, fish IFN or all kinds of IFN stimuli activated PKZ and PKR to phosphorylated eIF2 alpha. Overexpression of both fish kinases together conferred much more significant inhibition of virus replication than overexpression of either protein, whereas morpholino knockdown of both made fish cells more vulnerable to virus infection than knockdown of either. The antiviral ability of fish PKZ was weaker than fish PKR, which correlated with its lower ability to phosphorylate eIF2 alpha than PKR. Moreover, the independent association of fish PKZ or PKR reveals that each of them formed homodimers and that fish PKZ phosphorylated eIF2 alpha independently on fish PKR and vice versa. These results suggest that fish PKZ and PKR play a nonredundant but cooperative role in IFN antiviral response.
Liu, Ting-Kai; Zhang, Yi-Bing; Liu, Ying; Sun, Fan; Gui, Jian-Fang.Cooperative Roles of Fish Protein Kinase Containing Z-DNA Binding Domains and Double-Stranded RNA-Dependent Protein Kinase in Interferon-Mediated Antiviral Response,JOURNAL OF VIROLOGY,2011,85(23):12769-12780