TP53 and breast cancer: Next, we treated MDA-MB-231, HCC1937, MCF-7, and DU4475 cells ectopically expressing SNORD50A/B with 25 μM proteasome inhibitor MG132 for 3 h to block the ubiquitin-proteasome pathway, and found that ectopic expression of SNORD50A/B selectively inhibited protein expression of p53 and p21 in p53wt breast cancer cell lines MCF-7 and DU4475, while this effect could be reversed by MG132 treatment (Fig. 3e).