Silencing IFI6 enhances radiation sensitivity of triple-negative breast cancer via ER stress-driven immunogenic cell death

Interferon-γ-inducible protein 6 (IFI6) has been implicated in tumour progression and resistance to ionizing radiation; nevertheless, its functional relevance and mechanistic underpinnings in triple-negative breast cancer (TNBC) radioresistance remain inadequately characterised. Here, we interrogated the contribution of IFI6 to the radiosensitivity of TNBC cells and dissected the associated regulatory circuitry. An isogenic radioresistant MDA-MB-231 sub-line (MDA-MB-231/IR) was generated by fractionated irradiation, and IFI6 expression was quantified by quantitative RT-PCR and immunoblot analyses, revealing pronounced up-regulation in radioresistant cells. Loss-of-function studies employing lentiviral short-hairpin RNA (shRNA)-mediated silencing were conducted to investigate the functional role of IFI6 and underlying molecular mechanisms. It was demonstrated that IFI6 depletion markedly sensitized MDA-MB-231/IR cells to irradiation, as evidenced by enhanced apoptotic index and induction of immunogenic cell death (ICD). Mechanistically, IFI6 knock-down triggered endoplasmic-reticulum stress (ERS) and consequent reactive oxygen species (ROS) accumulation, thereby amplifying the cytotoxic effects of radiation. Rescue experiments with the ERS inhibitor 4-phenylbutyric acid (4-PBA) corroborated this causal axis: 4-PBA attenuated ROS generation and partially reversed the radiosensitising effect elicited by IFI6 silencing. Collectively, our data establish IFI6 as a critical molecular determinant of TNBC radioresistance and unveil that its targeted suppression can overcome radioresistance by converting a sub-lethal stress into a potent ERS-dependent ICD pathway.