Inhibition of IRE1α kinase increases ferroptosis resistance in triple‑negative breast cancer cells

Ferroptosis is a regulated form of cell death that serves a pivotal role in tumor suppression. Whilst the ribonuclease activity of inositol‑requiring enzyme 1α (IRE1α) is associated with the regulation of ferroptosis, the potential involvement of its kinase domain in this process remains elusive. Thus, the present study aimed to investigate the specific role of the IRE1α kinase domain in regulating ferroptosis in breast cancer, particularly in the triple‑negative breast cancer (TNBC) subtype. To this end, it employed a combination of bioinformatic analysis of clinical datasets, pharmacological inhibition of IRE1α kinase and genetic overexpression models in TNBC cell lines. The present study demonstrated that endoplasmic reticulum to nucleus signaling 1 (ERN1; the gene encoding IRE1α) was significantly downregulated in breast cancer compared with that in normal tissues, and that lower ERN1 levels were associated with a worse prognosis of patients with breast cancer. This association persisted in human epidermal growth factor receptor 2‑positive and TNBC subtypes. In TNBC, IRE1α kinase inhibitors (APY29 and sunitinib) markedly inhibited ferroptosis induced by system Xc‑ inhibition. Moreover, by constructing overexpression models of wild‑type IRE1α (IRE1α‑WT) and a kinase‑dead mutant (IRE1α‑K599A), it was demonstrated that IRE1α‑WT overexpression significantly enhanced sensitivity to ferroptosis, whereas the kinase‑dead mutant had no significant effect. Mechanistically, IRE1α kinase inhibition upregulated solute carrier family 7 member 11 (also known as xCT) expression and promoted glutathione (GSH) synthesis, thereby suppressing ferroptosis. Collectively, the present study reveals a new function of IRE1α kinase in the regulation of ferroptosis, highlighting the critical regulatory role of the IRE1α kinase‑xCT‑GSH axis in ferroptosis in TNBC. Thus, IRE1α kinase may have potential as a therapeutic target.