Profilin-1 Deficiency Activates STING to Drive T Cell-Mediated Anti-Tumor Immunity in Breast Cancer.

Dysregulation of actin-binding protein Profilin1 (Pfn1) in tumor cells has prominent impacts on the tumor-intrinsic aspects of tumor progression. However, whether and how modulation of Pfn1 expression in tumor cells influences immune surveillance in cancer is not known. We utilized an inducible CRISPR/Cas9 knockout (KO) model to first demonstrate that triggering Pfn1 depletion in breast cancer cells leads to features of genomic instability (polyploidy, micronuclei, and DNA damage) and intrinsic defects in both homologous-recombination- and non-homologous end-joining-mediated double-stranded DNA repair. Pfn1-deficient breast cancer cells exhibit nuclear envelope abnormality and the accumulation of cytosolic DNA. This leads to activation of the nucleic acid-sensing cGAS-STING pathway and the type-I interferon (IFN) response including STING-mediated upregulation of pro-inflammatory chemokines. In an immunocompetent mouse model of breast cancer, triggering Pfn1 loss selectively in tumor cells promotes an immunogenic tumor microenvironment marked by a striking increase in intratumoral presence of CD8⁺ T cells, leading to a robust tumor regression. Pfn1 knockout-induced tumor regression requires an intact immune system and can also be reversed by CD8 + T cell depletion. Based on these findings, we conclude that Pfn1 loss in tumor cells leverages a type I IFN response to drive a T-cell-mediated anti-tumor response in breast cancer. These findings for the first time reveal promising therapeutic opportunities in targeting Pfn1-driven pathways to enhance immunotherapeutic outcomes in breast cancer. Expression of actin-binding protein Profilin-1 is frequently altered in cancer; yet how these changes impact the immune response against tumors is unclear. Here we show that triggering Profilin-1 depletion in breast cancer cells promotes features of genomic instability, defects in DNA repair, and cytosolic release of DNA. This activates the cGAS-STING pathway, triggering a type I interferon response and immune-cell-attracting signals that drive a CD8+ T cell-mediated anti-tumor immune response and tumor regression in vivo . Therefore, Profilin-1 could be a novel actionable target for achieving immunological benefit in breast cancer. On a broader level, our studies establish a conceptual framework of how dysregulation of actin cytoskeletal proteins can harness nuclear damage-sensing signaling to augment anti-tumor immune response in cancer.