CST1 and esophageal squamous cell carcinoma: The results showed that CST1 expression significantly upregulated the activity of mitochondrial respiratory chain complex I in ESCC cells (Fig. 5A), while not changing the activities of complexes II, III, IV, and V (Fig. 5B–E), suggesting that CST1 expression might elevate the OXPHOS levels by upregulating the activity of mitochondrial respiratory chain complex I in ESCC cells.