Knockdown of NIR Suppresses Breast Cancer Cell Proliferation via Promoting FOXO3

BACKGROUND: Novel inhibitor of histone acetyltransferase repressor (NIR), a corepressor with a novel inhibitor of histone acetyltransferase (INHAT) activity, has been reported to be a negative modulator of p53 and a regulator of the cell cycle in cancer cells. However, the role of NIR in the progression of breast cancer remains elusive. MATERIALS AND METHODS: Oncomine database was used to analyze the mRNA levels and prognosis value of NIR in breast cancer. We performed loss-of-function and gain-of-function studies using lentivirus expressing shRNA targeting NIR, enhancer of zeste homolog 2 (EZH2) and forkhead box O3 (FOXO3) or lentivirus expressing NIR or FOXO3, respectively. Cell proliferation and colony formation assays were performed. Co-immunoprecipitation (Co-IP) and immunoprecipitation (IP) were performed to identify the interaction between NIR and polycomb repressive complex 2 (PRC2) subunits. ChIP assay was used to identify the enrichment of NIR, EZH2, H3K27ac and H3K27me3 at the FOXO3 promoter region and the regulation of H3K27 modification at the FOXO3 promoter by NIR. RESULTS: High levels of NIR expression were correlated with poor prognosis in breast cancer patients. Knockdown of NIR suppressed the proliferation of breast cancer cells. Mechanically, NIR was recruited by EZH2 to the promoter vicinity of FOXO3 via direct protein–protein interaction. Silencing NIR increased H3K27ac and decreased H3K27me3 levels at the FOXO3 promoter, resulting in enhancing FOXO3 expression. In accordance with this, growth inhibition of breast cancer cells caused by silencing of NIR could be reversed by FOXO3 knockdown. CONCLUSION: NIR knockdown inhibited proliferation by switching the H3K27me3 and H3K27ac marks at the FOXO3 promoter to promote FOXO3 transcription, and this effect depends on the physical interaction between NIR and PRC2 in breast cancer cells. Our results suggest that NIR might be a potential target for breast cancer treatment.