Targeting YES1 Disrupts Mitotic Fidelity and Potentiates the Response to Taxanes in Triple-Negative Breast Cancer.

Clinical trials examining broad-spectrum Src family kinase (SFK) inhibitors revealed significant dose-limiting toxicities, preventing advancement for solid tumors. SFKs are functionally heterogeneous, thus targeting individual members is a potential strategy to elicit anti-tumor efficacy while avoiding toxicity. Here, we identified that YES1 is the most highly overexpressed SFK in triple negative breast cancer (TNBC) and is associated with poor patient outcomes. Disrupting YES1, genetically or pharmacologically, induced aberrant mitosis, centrosome amplification, multi-polar spindles, and chromosomal instability (CIN). Mechanistically, YES1 sustained FOXM1 protein levels and elevated expression of FOXM1 target genes that control centrosome function and are essential for effective and accurate mitotic progression. In both in vitro and in vivo TNBC models, YES1 suppression potentiated the efficacy of taxanes, cornerstone drugs for TNBC that require elevated CIN for efficacy. Clinically, elevated expression of YES1 was associated with worse overall survival of TNBC patients treated with taxane and anthracycline combination regimens. Together, this study demonstrates that YES1 is an essential regulator of genome stability in TNBC that can be leveraged to improve taxane efficacy.

TLE3 Sustains Luminal Breast Cancer Lineage Fidelity to Suppress Metastasis.

Breast cancer subtypes and their phenotypes parallel different stages of the mammary epithelial cell developmental hierarchy. Discovering mechanisms that control lineage identity could provide novel avenues for mitigating disease progression. Here we report that the transcriptional corepressor TLE3 is a guardian of luminal cell fate in breast cancer and operates independently of the estrogen receptor. In luminal breast cancer, TLE3 actively repressed the gene-expression signature associated with highly aggressive basal-like breast cancers (BLBC). Moreover, maintenance of the luminal lineage depended on the appropriate localization of TLE3 to its transcriptional targets, a process mediated by interactions with FOXA1. By repressing genes that drive BLBC phenotypes, including SOX9 and TGFß2, TLE3 prevented the acquisition of a hybrid epithelial-mesenchymal state and reduced metastatic capacity and aggressive cellular behaviors. These results establish TLE3 as an essential transcriptional repressor that sustains the more differentiated and less metastatic nature of luminal breast cancers. Approaches to induce TLE3 expression could promote the acquisition of less aggressive, more treatable disease states to extend patient survival. SIGNIFICANCE: Transcriptional corepressor TLE3 actively suppresses SOX9 and TGFß transcriptional programs to sustain the luminal lineage identity of breast cancer cells and to inhibit metastatic progression.