There is a poor prognosis of metastasis in hormone receptor negative breast cancer (HRNBC), including triple-negative breast cancer (TNBC) and HER-2 overexpression breast cancer. Recent studies have indicated that BTB/POZ domain-containing protein 7 (BTBD7) regulates SLUG which is a key EMT (epithelial-mesenchymal transformation)-associated protein. The role of BTBD7 in HRNBC, however, has not been identified. In this study, The Cancer Genome Atlas (TCGA) was used to identify BTBD7 mRNA expression in breast cancer. In addition, GO and Metascape were used to identify differentially expressed genes. Immunohistochemical staining were applied to determine the protein expression of Btbd7 and Slug in paraffin-embedded samples from 144 HRNBC patients and 30 benign lesion patients. In cancer tissue, 64.9% in TNBC and 70.0% in HER-2+ overexpression breast cancer of Btbd7 protein was expressed when compared with a 20% expression in benign lesion tissues. Increased Btbd7 expression was further associated with larger tumor volume and poor TNM stages in HRNBC patients. Higher BTBD7 mRNA expression level was associated with shorter disease free survival (DFS) time from TCGA data. Higher Btbd7 protein expression in HRNBC tissue was associated with shorter DFS and OS time. Btbd7 protein expression significantly correlated with Slug expression in HRNBC tissue. Combining Btbd7 and Slug expression had a high predictive value for 3-year and 5-year DFS. As such, the positive expression of Btbd7 may contribute towards the development of breast cancer, specifically HRNBC via the up-regulation of Slug expression. Btbd7 was concluded to be an important predictor for the diagnosis of HRNBC patients.

BACKGROUND: Hormone receptor-negative breast cancer (HRNBC), including triple-negative breast cancer (TNBC) and human epidermal growth factor receptor 2 (HER-2) overexpressing breast cancer, is prone to metastasis and has a poor prognosis. BTB/POZ domain-containing protein 7 (Btbd7) is considered to regulate Slug and the epithelial-mesenchymal transition (EMT) process. However, the role of Btbd7 in HRNBC is unclear. This study aimed to investigate the localization and function of Btbd7 in HRNBC as well as its relationship with Slug and the EMT process.METHODS: Bioinformatics analysis was performed to evaluate the effect of the BTBD7 and SLUG genes expression on the prognosis in HRNBC patients. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) were used to identify differentially expressed genes (DEGs) and possible mechanism in breast cancer. Expression of Btbd7 and Slug in 144 HRNBC and 30 benign lesion tissues obtained from the patients was evaluated using immunohistochemistry and immunofluorescence staining. MDA-MB-231 cells were transfected with BTBD7 siRNA and the expression levels of Btbd7, Slug, and key EMT proteins were analyzed. CCK-8 and cell invasion assays were performed to evaluate cell proliferation and invasion in response to BTBD7 silencing.RESULTS: The total positive rate of Btbd7 expression in HRNBC tumor tissue was 66.7% (96/144), which was higher than that in normal adjacent tissue (NAT) (52.1% 75/144 P=0.001) and benign breast lesion tissues (20%, 6/30 P<0.001). TCGA and immunohistochemistry staining both indicated that higher Btbd7 and Slug expression in HRNBC was associated with poor clinicopathologic features and prognosis. Co-expression of Slug and Btbd7 proteins could be found in HRNBC tissue and MDA-MA-231 cells. BTBD7 silencing significantly up-regulated the epithelial marker E-cadherin (P<0.05), down-regulated the mesenchymal markers α-SMA and Slug (P<0.05), and suppressed the proliferation and invasion abilities of cells. GO and KEGG analyses based on 322 DEGs showed that BTBD7 may be associated with generic transcription in breast cancer.CONCLUSION: Higher expression of BTBD7 was a poor prognostic factor in HRNBC patients and BTBD7 silencing inhibited EMT through regulation of Slug expression. BTBD7 might act as a potential molecular target for gene therapy in HRNBC patients.