IRAK2 Downregulation Reverses 5-FU Resistance and Reduces Stemness-Associated Drug-Transporter Expression in TNBC-Derived Breast Cancer Stem Cells

Triple-negative breast cancer (TNBC) remains a major therapeutic challenge, largely due to the persistence of drug-tolerant breast cancer stem cell (BCSC) populations that can with-stand cytotoxic stress and drive disease relapse. Although interleukin-1 recep-tor-associated kinase 2 (IRAK2) has been implicated in inflammatory signaling and en-do-plasmic reticulum stress responses, its functional role in the development of acquired chemotherapy resistance in BCSCs has not been fully elucidated. In this study, we inves-tigated whether IRAK2 contributes to the maintenance of a drug-tolerant phenotype in BCSC1, MDA-MB-231, and MDA-MB-468 cells. Exposure to chemotherapeutic agents in-duced IRAK2 mRNA expression in most drug-cell line combinations, while BCSC1 cells exhibited a functionally resistant phenotype following 5-fluorouracil (5-FU) treatment. Stable or doxycycline-inducible IRAK2 knockdown significantly impaired cell prolifera-tion, prevented post-treatment recovery after 5-FU exposure, reduced sphere-forming ca-pacity, and attenuated the 5-FU-induced expression of the drug transporters ABCC3 and ABCC4. Collectively, these findings identify IRAK2 as a key mediator of stress-adaptive signaling that promotes chemotherapy tolerance and stemness-associated survival mech-anisms in TNBC-derived BCSCs. IRAK2 therefore represents both a potential biomarker of emerging chemoresistance and a promising therapeutic target for combination strategies aimed at eradicating drug-tolerant cancer stem cell populations.