Expression of dominant-negative PERK, but not dominant-negative PKR, inhibits phosphorylation of eIF2α induced by LMP1 expression. (A) The EBV-negative B cell, BJAB, constructed to express LMP1 inducible by tetracycline, BJAB/HA-LMP1, was untreated or treated with 1 ng/mL or 10 ng/mL tetracycline for 48 hours. The cells were harvested and analyzed by Western blotting using anti–phosphorylated eIF2α, anti–total eIF2α, and anti-LMP1 antibodies. (B) BJAB/HA-LMP1 cells were infected with a control retrovirus and either dominant-negative PERK or dominant-negative PKR. After 48 hours of infection, the cells were sorted for the highest levels of expression of GFP encoded by the retroviruses. Each population was either left untreated, treated with 10 ng/mL tetracycline for 48 hours to induce LMP1, or treated with 2.5 μg/mL tunicamycin for 4 hours to activate PERK. The cells were harvested and analyzed as described in panel A. The ratios of phosphorylated eIF2α to total eIF2α were calculated. The numbers represent the percentage of phosphorylation of eIF2α relative to cells infected with control retrovirus. *P (2-sided) <.05, Wilcoxon signed rank test. A representative example of 4 independent experiments is shown.