YC-1 inhibits proliferation of breast cancer cells by down-regulating EZH2 expression via activation of c-Cbl and ERK

Background and purpose: YC-1 exhibits potent Anticancer activity via numerous actions in many Cancer cell lines. Hence, we investigated the in vivo antitumour efficacy of YC-1 in an MDA-MB-468 xenograft model and elucidated the mechanism of down-regulation of enhancer of zeste homology 2 (EZH2) by YC-1 in breast Cancer cells.

Experimental approach: In YC-1-treated breast Cancer cells and tumour specimens from YC-1-treated MDA-MB-468 xenografts, EZH2 expression was analysed by Western blotting. Pharmacological inhibitors and short hairpin RNA-mediated knockdown were applied to identify possible signalling pathways involved in EZH2 down-regulation by YC-1.

Key results: YC-1 reduced the viability of breast Cancer cells and tumour growth in MDA-MB-468 xenografts. In breast Cancer cells, YC-1 down-regulated EZH2 expression in a concentration- and time-dependent manner. Depletion of EZH2 reduced the proliferation and susceptibility of breast Cancer cells to YC-1-induced Apoptosis. EZH2 expression was suppressed in tumour specimens from YC-1-treated MDA-MB-468 xenograft mice. YC-1 enhanced both the degradation rate and ubiquitination of EZH2. The down-regulation of EZH2 by YC-1 was associated with activation of PKA and Src-Raf-ERK-mediated signalling pathways. Furthermore, depletion of Casitas B-lineage lymphoma (c-Cbl), an E3 ubiquitin ligase, abolished YC-1-induced Apoptosis and suppression of EZH2. YC-1 rapidly activated c-Cbl to induce signalling associated with ERK and EZH2.

Conclusion and implications: We discovered that YC-1 induces Apoptosis and inhibits tumour growth of breast Cancer cells via down-regulation of EZH2 by activating c-Cbl and ERK. These data suggest that YC-1 is a potential Anticancer drug candidate for triple-negative breast Cancer.