TRIM21 and neoplasm: Similar results were observed in HT29 s.c. tumors; while TRIM21 KO in HT29 cells significantly promoted tumor growth and clearly increased mutp53 protein levels in tumors, mutp53 KO in HT29 cells significantly inhibited tumor growth and largely abolished the promoting effect of TRIM21 KO on tumor growth (Figure 5, D and E, and Supplemental Figure 4B).