Consistent with our above findings, nude mice injected with ESCC cells intravenously demonstrated reduced metastatic ability in the Pol ι knockdown group, while the overexpression of HIF-1α and USP7 partially reversed the decreased migratory ability caused by Pol ι knockdown (Fig. 6H and Fig. S3C). This evidence concerns the gene USP7 and esophageal squamous cell carcinoma.