The present study investigates the response of the marine fish cobia, Rachycentron canadum, to stressors as measured by phosphorylation of the α-subunit of the translational initiation factor, eIF2. eIF2α is the target of phosphorylation by a family of kinases that respond to a range of physiological stressors. Phosphorylation of eIF2α not only inhibits overall protein synthesis, but allows cells to reprogram gene expression to adapt to, and recover from, stress. The deduced coding sequence of cobia eIF2α has 94 % identity to both zebrafish (Danio rerio) and human eIF2α sequences with identical phosphorylation and kinase docking sites. The present study uses a cobia cell line, Cm cells, derived from muscle, as well as cobia larvae to investigate the response of cobia eIF2α to various stressors. In Cm cells, phosphorylation of eIF2α is increased by nutrient deficiency, leucinol, and ER stress, consistent with the activation of the eIF2 kinases, GCN2, and PERK. In cobia juveniles, diet and water temperature affect the phosphorylation state of eIF2α. We conclude that evaluation of eIF2α phosphorylation could function as an early marker to evaluate diet, aquaculture stressors and disease in cobia and may be of particular use in the optimization of conditions for raising cobia larvae and juveniles.

The integrated stress response (ISR) is an adaptational signaling pathway that is induced in response to different stimuli, such as accumulation of unfolded and misfolded protein, hypoxia, amino acid deprivation, viral infection and ultraviolet light. It has been known that viral infection can activate ISR, but the role of ISR during viral infection is still unclear. In some cases, ISR is a protective mechanism of host cell against infection with virus whilst ISR may be hijacked by viruses for facilitating its replication. In this review, we highlighted recent advances on induction of ISR upon viral infection and the downstream responses involved such as autophagy, apoptosis, formation of stress granules and innate immunity response. We then discussed the molecular mechanism of ISR regulating viral replication and how viruses antagonize this cellular stress response resulting from ISR.