Breast cancer stem cells (BCSCs) are the main cause of breast cancer recurrence and metastasis. While the ubiquitin-proteasome system contributes to the regulation of BCSC stemness, the underlying mechanisms remain unclear. Here, we identified ubiquitin-conjugating enzyme E2T (UBE2T) as a pivotal ubiquitin enzyme regulating BCSC stemness through systemic screening assays, including single-cell RNA sequencing (scRNA-seq) and stemness-index analysis. We found that patients with high UBE2T expression exhibited worse prognosis than those with low expression (10-year PFS: 55.95% vs. 85.08%), which are consistent across various subtypes of breast cancers. Genetic ablation of UBE2T suppresses BCSC stemness and tumor progression in organoids and spontaneous MMTV-PyMT mice, dependent on the transcriptional inactivation of pluripotency genes SOX2 and NANOG. Mechanically, UBE2T collaborates with the E3 ligase TRIM25 to perform K48-linked polyubiquitination and degradation of CBX6 at K214, which deficiency helps to promote the transcription of SOX2 and NANOG and enhances BCSC stemness. The pharmacological inhibitor of UBE2T significantly reduced the expression of NANOG and SOX2, suppressed tumor progression, and demonstrated synergistic effects when combined with chemotherapeutics, but not with other treatments. Collectively, our study revealed that the UBE2T-TRIM25-CBX6 axis can regulate BCSC stemness and offers a potentially therapeutic strategy to combat breast cancer in a clinical translation setting.
Keywords: Breast cancer; CBX6; UBE2T; stemness; ubiquitination.
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