MAPK3 and gastric cancer: Zhang et al.33 and Song et al.34 indicated that activation of ERK by ER stress such as chronic hypoxia is necessary for the induction of GRP78, which protects gastric cancer cells against apoptosis.33, 34 As shown in Figures 6a and b, phosphorylation of ERK1/2 and expression of GRP78 were attenuated by K5 treatment and a specific inhibitor of ERK1/2.