Role of Brf1 interaction with ER, and significance of its overexpression, in human breast cancer

TFIIB-related factor 1 (Brf1) modulates the transcription of RNA Pol III genes (polymerase-dependent genes). Upregulation of Pol III genes enhances tRNA and 5S RNA production and increases the translational capacity of cells to promote cell transformation and tumor development. However, the significance of Brf1 overexpression in human breast cancer (HBC) remains to be investigated. Here, we investigate whether Brf1 expression is increased in the samples of HBC, and we explore its molecular mechanism and the significance of Brf1 expression in HBC. Two hundred and eighteen samples of HBC were collected to determine Brf1 expression by cytological and molecular biological approaches. We utilized colocalization, coimmunoprecipitation, and chromatin immunoprecipitation methods to explore the interaction of Brf1 with estrogen receptor alpha (ER). We determined how Brf1 and ER modulate Pol III genes. The results indicated that Brf1 is overexpressed in most cases of HBC, which is associated with an ER-positive status. The survival period of the cases with high Brf1 expression is significantly longer than those with low levels of Brf1 after hormone treatment. ER mediates Brf1 expression. Brf1 and ER are colocalized in the nucleus. These results indicate an interaction between Brf1 and ER, which synergistically regulates the transcription of Pol III genes. Inhibition of ER by its siRNA or tamoxifen reduces cellular levels of Brf1 and Pol III gene expression and decreases the rate of colony formation of breast cancer cells. Together, these studies demonstrate that Brf1 is a good biomarker for the diagnosis and prognosis of HBC. This interaction of Brf1 with ER and Brf1 itself are potential therapeutic targets for this disease.