SH3BGRL3 promotes radioresistance and immune evasion in triple-negative breast cancer by regulating Rab27a

This study aims to elucidate the molecular mechanisms by which SH3BGRL3 regulates radiosensitivity and immune evasion in triple-negative breast cancer (TNBC). An orthotopic TNBC model was established by injecting 4T1 cells into the mice. In vitro, BT549 cells were co-cultured with CD8+ T cells isolated to mimic the immune microenvironment. Cell proliferation was assessed by CCK-8 and colony formation assays, while migration was evaluated using Transwell. Key protein expression was analyzed by Western blot, immunofluorescence, and immunohistochemistry. Our study revealed that SH3BGRL3 is upregulated in TNBC, where its knockdown suppresses the proliferation and migration of irradiated BT549 cells in vitro and inhibits tumor growth in vivo. Additionally, SH3BGRL3 depletion downregulated ferroptosis-related proteins GPX4 and SLC7A11, elevated Fe²⁺, MDA, and lipid ROS levels, and reduced GSH-effects that were rescued by the ferroptosis inhibitor Fer-1. Our study further demonstrates that SH3BGRL3 knockdown reduces the expression of exhaustion markers (PD-1, TIM-3, LAG-3, TIGIT) on CD8⁺ T cells while increasing the secretion of effector molecules (IFNg, granzyme B, perforin). Notably, we found that Rab27a expression is also upregulated in TNBC, and SH3BGRL3 can bind to Rab27a and stabilize its protein level. Mechanistic studies revealed that knocking down SH3BGRL3 attenuates its interaction with Rab27a and reduces Rab27a expression, thereby promoting ferroptosis and enhancing radiosensitivity, while also inhibiting the Rab27a-mediated exosome release pathway, which in turn enhances CD8⁺ T cell function and suppresses tumor immune escape. This study demonstrates that SH3BGRL3 promotes radioresistance and immune evasion in triple-negative breast cancer by regulating Rab27a.