BUB1 as a novel marker for predicting the immunotherapy efficacy and prognosis of breast cancer

Budding uninhibited by benzimidazole 1 (BUB1) is a highly conserved serine/threonine kinase, showing prominent importance for proper function during mitosis. However, little is known about mRNA expression in breast cancer (BRCA) and its correlation with prognosis and immune infiltration. Hence, we aimed to unveil its potential as groundbreaking biomarkers for immunotherapy efficacy and the prognosis of BRCA. Database for Annotation, Visualization, and Integrated Discovery (DAVID) is a potent tool for identifying significant clusters of genes and pathways in the resulting dataset. In this study, gene set enrichment analysis of BUB1 was conducted using DAVID. The clinical characteristics of patients with or without altered mRNA expression were compared using cBioPortal. Tumor Immune Estimation Resource (TIMER) is a known as database for comprehensive analysis of tumor-infiltrating immune cells in various cancers. In the present study, the relationship between BUB1 expression and the abundance of immune infiltrates was explored using TIMER in BRCA. Immunohistochemistry staining was performed to analyze the protein expression of BUB1 in tumor tissue specimens. We used PrognoScan and Kaplan-Meier Plotter to evaluate the prognosis of patients with different BUB1 expression levels. The expression of BUB1 in various tumor tissues was higher than that in adjacent normal tissues. BUB1 was mainly localized to the nucleoplasm and additionally localized to the cytosol. Functional enrichment analyses revealed that the cell cycle was the most significant pathway. Abnormal mRNA expression was more frequently detected in invasive ductal carcinoma with higher histological grades and BRCAs with estrogen receptor (ER)-negative, human epidermal growth receptor 2 (HER2)-negative, and basal-like phenotypes. The BUB1 expression was correlated positively with tumor purity, B cells, CD8 T cells, CD4 T cells, neutrophils, and dendritic cells, while BUB1 had no significant correlation with macrophages. The results of immunohistochemical staining from clinical samples further confirmed that BUB1 was overexpressed in BRCA compared to benign tumor (fibroadenoma of breast) (P