BMI‐1 promotes breast cancer proliferation and metastasis through different mechanisms in different subtypes

Breast cancer is among the most common malignant cancers in women. B‐cell‐specific Moloney murine leukemia virus integration site 1 (BMI‐1) is a transcriptional repressor that has been shown to be involved in tumorigenesis, the cell cycle, and stem cell maintenance. In our study, increased expression of BMI‐1 was found in both human triple negative breast cancer and luminal A‐type breast cancer tissues compared with adjacent tissues. We also found that knockdown of BMI‐1 significantly suppressed cell proliferation and migration in vitro and in vivo. Further mechanistic research demonstrated that BMI‐1 directly bound to the promoter region of CDKN2D/BRCA1 and inhibited its transcription in MCF‐7/MDA‐MB‐231. More importantly, we discovered that knockdown of CDKN2D/BRCA1 could promote cell proliferation and migration after repression by PTC‐209. Our results reveal that BMI‐1 transcriptionally suppressed BRCA1 in TNBC cell lines whereas, in luminal A cell lines, CDKN2D was the target gene. This provides a reference for the precise treatment of different types of breast cancer in clinical practice.