BACKGROUND The role of the
ubiquitin-specific peptidase 9 X-linked (USP9X) gene in
breast cancer remains poorly understood. This study aimed to investigate the role of USP9X in
breast cancer tissue and cell lines. MATERIAL AND METHODS Immunohistochemistry was used to examine the expression levels of USP9X in 102
breast cancer tissue samples and 41 normal breast tissue samples. Overexpression of USP9X in MCF-7 and MDA-MB-231
breast cancer cell lines were studied by USP9X lentivirus vector transfection. Clustered regularly interspaced short palindromic repeats (CRISPR)/
caspase-9 USP9X gene knockout was performed. Cell proliferation, growth, and survival were examined using the cell counting kit-8 (CCK-8) assay, the colony formation assay, flow cytometry assays, and a
tumor xenograft study. RESULTS Immunohistochemistry showed that USP9X was significantly overexpressed in 93 of 102 (91.1%)
breast cancer tissue samples compared with 41 normal breast tissue samples and was associated with
tumor size ≥5.0 cm (P<0.05). USP9X overexpression in MCF-7 and MDA-MB-231
breast cancer increased cell proliferation and survival, significantly reduced the number of cells in the G1-phase cells and increased the number of cells in the S-phase cells, which were reversed by CRISPR/
caspase-9 USP9X gene knockout. Overexpression of USP9X upregulated the CCND1 gene encoding
cyclin D1 and downregulated
cyclin-dependent inhibitor
kinase 1A (CDKN1A) gene in
breast cancer cells, which were reversed by USP9X knockout. CONCLUSIONS Overexpression of USP9X was associated with upregulation of the CCND1 gene and downregulation of the CDKN1A gene in
breast cancer tissue and cell lines.