Bromodomain-containing protein 9 activates proliferation and epithelial-mesenchymal transition of colorectal cancer via the estrogen pathway in vivo and in vitro

BACKGROUND: Bromodomain-containing protein 9 (BRD9) has been reported to be upregulated in multiple malignancies and facilitate cancer progression. However, there is a paucity of data relating to its expression and biological role in colorectal cancer (CRC). Therefore, this current study examined the prognostic role of BRD9 in CRC and the underlying mechanisms involved. METHODS: Real-time polymerase chain reaction (PCR) and Western blotting were used to examine the expression of BRD9 in paired fresh CRC and para-tumor tissues from colectomy patients (n=31). Immunohistochemistry (IHC) was performed to assess BRD9 expression in 524 paraffin-embedded archived CRC samples. The clinical variables are including age, sex, carcinoembryonic antigen (CEA), location of tumor, T stage, N stage, and TNM classification. The effect of BRD9 on the prognosis of CRC patients was explored by Kaplan-Meier and Cox regression analyses. Cell counting kit 8 (CCK-8), clone formation assay, transwell assay, and flow cytometry were used to determine CRC cell proliferation, migration, invasion, and apoptosis, respectively. Xenograft models in nude mice were established to investigate the role of the BRD9 in vivo. RESULTS: BRD9 mRNA and protein expression levels were significantly upregulated in CRC cells compared to normal colorectal epithelial cells (P<0.001). IHC analysis of 524 paraffin-embedded archived CRC tissues showed that high BRD9 expression was significantly associated with TNM classifications, CEA, and lymphatic invasion (P<0.01). Univariate and multivariate analyses indicated that BRD9 [hazard ratio (HR): 3.04, 95% confidence interval (CI): 1.78–5.20; P<0.01] expression and sex (HR: 6.39, 95% CI: 3.94–10.37; P<0.01) were independent prognostic factors for overall survival in the entire cohort. Overexpressing BRD9 promoted CRC cell proliferation, while silencing BRD9 inhibited the proliferation of CRC cells. Furthermore, we showed that BRD9 silencing significantly inhibited epithelial-mesenchymal transition (EMT) via the estrogen pathway. Finally, we demonstrated that silencing BRD9 significantly inhibited the proliferation and tumorigenicity of SW480 and HCT116 cells in vitro and in vivo in nude mice (P<0.05). CONCLUSIONS: This study demonstrated that BRD9 high could be an independent prognostic risk factor for CRC. Furthermore, the BRD9/estrogen pathway may contribute to the proliferation of CRC cells and EMT, suggesting that BRD9 may be a novel molecular target in the therapeutic treatment of CRC.