MAPK3 and esophageal squamous cell carcinoma: In addition, the mitochondrial respiratory chain complex I activity as well as ATP levels and mitochondrial ATP/glycolysis, were obviously reduced after the addition of the p-MEK1/2/p-ERK1/2 inhibitor PD98059, suggesting that CST1 might have a reciprocal regulatory relationship existed between OXPHOS and the MEK/ERK pathway in ESCC cells.