Abstract
The E3 ligase RNF8 activates TWIST via K63-linked ubiquitination to promote EMT and CSC self-renewal.
Major finding: The E3 ligase RNF8 activates TWIST via K63-linked ubiquitination to promote EMT and CSC self-renewal.
Clinical relevance: RNF8 overexpression is associated with poor outcomes in patients with breast cancer.
Impact: Targeting RNF8 may be a potential strategy for indirect targeting of TWIST and EMT.
Triple negative breast cancer (TNBC) is an aggressive subtype characterized by an enrichment of cancer stem cells (CSC) and an epithelial-to-mesenchymal transition (EMT) gene signature including upregulation of the EMT transcription factor TWIST. Targeting EMT via TWIST is a potential therapeutic strategy in TNBC, but direct pharmacologic TWIST inhibition has proven difficult. Lee and colleagues performed an E3 ligase shRNA screen to identify potentially targetable post-translational regulators of TWIST and found that knockdown of RNF8 reduced TWIST transcriptional activity by over 50%. Data from The Cancer Genome Atlas revealed that basal-like breast cancers, which largely overlap with TNBCs, frequently exhibit RNF8 amplification or upregulation, consistent with a role for RNF8 in promoting TNBC. Mechanistically, RNF8-mediated K63-linked ubiquitination of TWIST promoted its nuclear localization and stabilization. RNF8 depletion disrupted EMT as evidenced by the reduced expression of TWIST and mesenchymal markers, and increased expression of epithelial markers. Further, RNF8 depletion reduced the ability of TNBC cell lines to grow in mammospheres, suggesting a reduced self-renewing capacity of CSCs that could be rescued by TWIST, but not a ubiquitination-deficient TWIST mutant. RNF8 depletion also enhanced CSC sensitivity to chemotherapy, leading to their near-complete elimination in mammosphere cultures. In patients with unresectable breast tumors treated with doxorubicin chemotherapy, high expression of RNF8 was associated with recurrent or metastatic tumors, as well as upregulation of TWIST and downregulation of the epithelial marker E-cadherin, further indicating that RNF8 is involved in chemoresistance as well as EMT. Moreover, RNF8 expression was elevated in patients with advanced breast cancer and was correlated with reduced metastasis-free survival. Collectively, these results indicate that RNF8 activates TWIST to promote EMT and chemoresistance and suggest the potential for therapeutic targeting of RNF8 to indirectly target TWIST.
RSS Feeds