ZEB1 directly activates IL-6 to promote triple-negative breast cancer stemness in an epigenetically constrained context.

ZEB1 is a key driver of breast cancer pathogenesis and therapy resistance, largely through its ability to promote cancer stem cells (CSCs). Although tumor-secreted cytokines such as IL-6 are known to support tumor progression, how their expression is regulated by upstream transcriptional factors such as ZEB1 remains incompletely understood. Here, we identify IL-6 as a direct transcriptional target of ZEB1 and reveal an epigenetic dimension associated with this regulation. Mechanistically, ZEB1 binds to specific E2-box elements within the IL-6 promoter and activates its transcription. The IL-6 promoter exhibits local DNA methylation, and ZEB1-dependent IL-6 expression was further enhanced by DNA methyltransferase and histone deacetylase inhibitors, suggesting that the local epigenetic context constrains IL-6 transcription. ZEB1 overexpression was also accompanied by enrichment of the active histone marks H3K27ac and H3K4me3 at the IL-6 promoter, consistent with a more transcriptionally permissive local chromatin state. Functionally, the ZEB1-induced IL-6 expression enhanced CSC-associated properties in vitro and tumor-initiating capacity in vivo. Conversely, IL-6 knockdown attenuated ZEB1-induced CSC-associated phenotypes, whereas pharmacological IL-6 neutralization reduced xenograft burden and CSC-associated populations in vivo. Collectively, our findings establish the ZEB1-IL-6 axis as an important regulator of triple-negative breast cancer (TNBC) stemness and indicate that ZEB1-dependent IL-6 activation is influenced by the local epigenetic context. These findings support further investigation of the ZEB1-IL-6 axis as a potential therapeutic target in ZEB1-high TNBC.