TRIM21 and esophageal squamous cell carcinoma: To further elucidate TRIM21's impact on ID1 protein levels in ESCC, we overexpressed TRIM21 in KYSE150 and KYSE510 cells which have low endogenous TRIM21, and deleted TRIM21 in KYSE30 and KYSE450 cells which exhibit high endogenous TRIM21 (Figure S1C, Supporting Information).