Abstract 2690: The role of PCNA tyrosine phosphorylation in evading innate immune surveillance

Abstract Cancer cells are continually exposed to intrinsic and extrinsic proliferative stresses that can send the genome stability awry. The aberrant DNA metabolism, evolving through deregulated replicative growth in cancer cells, is increasingly recognized as a major mechanism bridging the crosstalk between the immune microenvironment and tumor tissue, thereby either promoting or suppressing tumor progression. However, the triggering and regulation of these mechanisms remain largely unknown. Proliferating cell nuclear antigen (PCNA) and its homologs are the evolutionarily conserved central components of the DNA replication machinery. In eukaryotic cells, PCNA forms homotrimeric rings encircling the DNA double helix to coordinate the complex processes of DNA replication and damage repair, directed at least in part by differential post-translational modifications of the PCNA protein. In cancer cells, growth signal-stimulated phosphorylation at tyrosine 211 of PCNA (pY211-PCNA) is known to play an important function for active proliferation. Here, we demonstrate that inhibition of pY211 disrupts the processivity of replication forks. This disruption triggers single-stranded DNA (ssDNA) production catalyzed by the MRE11 nuclease, activating the cGAS-STING axis to launch an anti-tumor immune response by natural killer (NK) cells. We further show that the pY211 regulates site-specific post-translational modifications of MRE11, and loss of pY211 promotes the endonuclease mode of MRE11. This causes ssDNA generation in the cytosol, subsequently inducing type I interferon-activated cytotoxicity by NK cells and fostering an anti-tumor immunity that abrogates distant metastasis. Mechanistically, the pY211 determines the recruitment of the writer or eraser of the modification on MRE11, thus tuning the nucleolytic modes of MRE11 and, consequently, ssDNA generation. Therapeutic measures promoting MRE11-dependent ssDNA enhance the response of triple-negative breast cancer to cytotoxic killing mediated by endogenous or allogenic NK cells in mice. In breast cancer patients, the level of cytosolic ssDNA is inversely correlated with the expression of the eraser and pY211-PCNA, which is associated with poor overall survival in cancer patients. Our studies shed new light on the shaping of the tumor immune microenvironment and demonstrate the potential to develop therapeutic approaches that proactively leverage genomic instability and immune activation to target malignant tumors. Citation Format: Chuan-Chun Lee, Wan-Rong Wu, Yi-Chun Shen, Feng-Chi Chung, Yuan-Liang Wang, You-Zhe Lin, Chih-Hao Lu, Wei-Chung Cheng, Han Chang, Liang-Chih Liu, Ji-An Liang, Chang- Fang Chiu, Mien-Chie Hung, Shao-Chun Wang. The role of PCNA tyrosine phosphorylation in evading innate immune surveillance abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 2690.