Surprisingly, cellular OXPHOS was significantly inhibited by the addition of PD98059 (MEK/ERK signaling pathway inhibitor), evidenced by a decrease in mitochondrial complex I enzyme activity (Fig. 7B) and total ATP production level (Fig. 7C), suggesting that there might be a reciprocal regulatory relationship between OXPHOS and the MEK/ERK pathway in ESCC cells. This evidence concerns the gene MAP2K7 and esophageal squamous cell carcinoma.