PYCR1 and esophageal squamous cell carcinoma: Moreover, the key region where 1-Pyrroline-5-carboxylate and l-erythro-4-Hydroxyglutamate are converted by pyrroline-5-carboxylate reductase (PYCR, 1.5.1.2) to proline (red arrow region in Figure 1) was closely related to ROS production in ESCC [13].