Integrated bioinformatics investigation and experimental validation reveals the clinical and biological significance of chromobox family in breast cancer

Abstract

Abstract Background Chromobox (CBX) proteins are essential components of the Polycomb group and play critical roles in tumor onset, development, and metastasis. However, the prognostic significance and functions of CBXs in breast cancer (BC) progression have not been sufficiently investigated. Methods The expression and prognostic significance of CBX1-8 in BC were comprehensively analyzed using The Cancer Genome Atlas (TCGA) and multiple databases, including cBioPortal, Human Protein Atlas (HPA), Kaplan-Meier plotter, and TIMER. In vitro validation included conducting cell proliferation and EdU assays to confirm the oncogenic role of BC cells after CBX2 silencing. Additionally, FACS and western blotting were used to elucidate the mechanism of CBX2 in BC. Results The expression levels of CBX1, CBX2, CBX3, CBX4, and CBX8 were significantly elevated in BC tissues compared to normal tissues. High mRNA expression of CBX2, CBX3, and CBX5 in BC patients was significantly associated with shorter overall survival (OS). Univariate and multivariate Cox regression analysis results revealed that the mRNA expression level of CBX2 in BC patients served as an independent prognostic factor. In Luminal A and Luminal B BC subtypes, high expression of CBX2 was associated with poor prognosis. Subsequent Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses revealed a close association between CBX2 and the cell cycle as well as DNA replication. CCK-8 and EdU assays demonstrated that silencing CBX2 inhibited the proliferation of T47D and MCF7 cell lines. Moreover, the cell cycle assay indicated that CBX2 silencing led to cell cycle arrest, accompanied by a marked reduction in the levels of CDK4 and CyclinD1. High CBX2 expression significantly correlated with the infiltration of T cells, B cells, macrophages, and dendritic cells in BC. Conclusions Our findings could provide new insights into identifying potential prognostic markers within the CBX family in BC. Targeting CBX2 may present a promising strategy to tackle endocrine resistance in BC therapy.