PSMB9 and breast cancer: To validate the expression of MDC1, PARP3, POLR2K, PSMB1, PSMB9, PSMD2, PSMD7, PSMD14, RFC3, and UBE2T in breast cancer cells, we achieved real-time quantitative polymerase chain reaction (RT-qPCR) to identify the mRNA levels of these 10 genes in T-47D, MCF-7, and MDA-MB-231 human breast cancer cells and MCF-10A mammary epithelial cells (normal cells) (Figure 5D).