Methods: Expressions of UCH-L1 and ER alpha were examined in breast cancer cells and patient specimens. The associations between UCH-L1 and ER alpha, therapeutic response and prognosis in breast cancer patients were analyzed using multiple databases. The molecular pathways by which UCH-L1 regulates ER alpha were analyzed using immunoblotting, qRT-PCR, immunoprecipitation, ubiquitination, luciferase and ChIP assays. The effects of UCH-L1 inhibition on the efficacy of tamoxifen in ER alpha (-) breast cancer cells were tested both in vivo and in vitro.  

Results: UCH-L1 expression was conversely correlated with ER alpha status in breast cancer, and the negative regulatory effect of UCH-L1 on ER alpha was mediated by the deubiquitinase-mediated stability of EGFR, which suppresses ER alpha transcription. High expression of UCH-L1 was associated with poor therapeutic response and prognosis in patients with breast cancer. Up-regulation of ER alpha caused by UCH-L1 inhibition could significantly enhance the efficacy of tamoxifen and fulvestrant in ER alpha (-) breast cancer both in vivo and in vitro.  

Conclusions: Our results reveal an important role of UCH-L1 in modulating ER alpha status and demonstrate the involvement of UCH-L1-EGFR signaling pathway, suggesting that UCH-L1 may serve as a novel adjuvant target for treatment of hormone therapy-insensitive breast cancers. Targeting UCH-L1 to sensitize ER negative breast cancer to anti-estrogen therapy might represent a new therapeutic strategy that warrants further exploration.