Ubiquitin-Specific Peptidase 8 Modulates Cell Proliferation and Induces Cell Cycle Arrest and Apoptosis in Breast Cancer by Stabilizing Estrogen Receptor Alpha

Abstract

Breast cancer (BC) is the most common neoplastic and lethal malignancy in women. Although antiendocrine therapy is the main treatment for estrogen receptor alpha (ERα)-positive BC, the development of resistance is a major clinical complication. In this study, we aimed to explore the role of ubiquitin-specific peptidase 8 (USP8) in ERα signaling and identify potential targets for endocrine resistance. Public databases were used to analyze USP8 expression, prognosis, clinical characteristics, and immune cell infiltration. Immunohistochemistry and western blot assays were used to detect protein levels and ERα signaling. Quantitative reverse transcription-PCR was used to measure ERα target gene expression. The cell counting kit-8, wound-healing, clone formation, and Transwell assays were used to investigate the effects of USP8 depletion or inhibition on cell proliferation, migration, and invasion. An immunofluorescence assay was used for localizing USP8 and ERα, and a protein stability assay was performed for detecting the degradation of ERα protein. The cell cycle and apoptosis were assessed using flow cytometry. USP8 was highly expressed in the luminal subtype of BC and was associated with poor prognosis. The infiltration levels of many immune cells were positively correlated with USP8 expression. Depletion of USP8 dramatically decreased the ERα signaling activity and weakened the proliferation, migration, and invasion capabilities of BC cells. USP8 knockdown markedly induced apoptosis and cell cycle arrest ( $G0/G1$ ). Colocalization analysis and protein stability assays indicated a probable mechanism by which USP8 regulates ERα. Our study demonstrates that USP8 might be crucial in BC development and may be considered a potential target for treating ER-positive BC malignancies in vitro.