ATF4 and atrial fibrillation: In addition, we found that pretreatment with the antioxidant NAC completely blocked the expression of p-eIF2α, ATF4 and CHOP in AF-treated BGC-823 and SGC-7901 cells (Figure 5E and 5F), and totally inhibited apoptosis of gastric cancer cells, as shown above in Figure 4A.