EIF2AK4 and viral infectious disease: Later research has demonstrated that GCN2 can also be activated by glucose deprivation, purine starvation, and a high-salt environment, as well as by stressors unrelated to nutrients, including UV irradiation, osmotic stress, high levels of urea, oxidative stress (H2O2), high salinity (NaCl), tryptophanol and other anticancer drugs that inhibit proteasomes or histone deacetylases, and viral infections [4,8,21,22,23,24,25,26] (Figure 1).