FOS‐Mediated PLCB1 Induces Radioresistance and Weakens the Antitumor Effects of CD8⁺ T Cells in Triple‐Negative Breast Cancer

Radioresistance and immune evasion are interactive and crucial events leading to treatment failure and progression of human malignancies. This research studies the role of phospholipase C beta 1 (PLCB1) in these events in triple-negative breast cancer (TNBC) and the regulatory mechanism. PLCB1 was bioinformatically predicted as a dysregulated gene potentially linked to radioresistance in TNBC. Parental TNBC cell lines were exposed to fractionated radiation for 6 weeks. PLCB1 expression was decreased in the first 2 weeks but gradually increased from Week 3. PLCB1 knockdown increased the radiosensitivity of the cells, as manifested by a decreased half-inhibitory dose of irradiation, reduced cell proliferation, apoptosis resistance, mobility, and tumorigenesis in mice. The FOS transcription factor promoted PLCB1 transcription and activated the PI3K/AKT signaling. Knockdown of FOS similarly reduced radioresistance and T cells-mediated immune evasion. However, the radiosensitivity of TNBC cells and the antitumor effects of CD8⁺ T cells could be affected by a PI3K/AKT activator or by the PLCB1 upregulation. The PLCB1 or FOS knockdown also suppressed radioresistance and tumorigenesis of the TNBC cells in mice. In conclusion, FOS-mediated PLCB1 induces radioresistance and weakens the antitumor effects of CD8⁺ T cells in TNBC by activating the PI3K/AKT signaling pathway.