Immune checkpoint inhibitors (ICIs) can re-active the immune response and induce a complete response in mismatch repair-deficient and microsatellite instability-high (dMMR/MSI-H) colorectal cancer (CRC). However, most CRCs exhibit proficient mismatch repair and microsatellite stable (pMMR/MSS) phenotypes with limited immunotherapy response because of sparse intratumoral CD8T-lymphocyte infiltration. Cellular senescence has been reported to involve immune cell infiltration through a senescence-associated secretory phenotype (SASP). However, the relationship between CRC cellular senescence and CD8T-lymphocyte infiltration remains unclear. Through integrated analysis of clinical cohorts and transcriptomic data across mismatch repair (MMR) subtypes, we identified cellular senescence as a hallmark of dMMR tumors, accompanied by elevated expression of KDM4A (lysine demethylase 4A). Clinically, KDM4ACDKN2A/p16expression correlated with improved CRC patient prognosis. Mechanistically, KDM4A upregulated AGT (angiotensinogen) expression through H3K9me3 demethylation and promoted CRC cellular senescence. Meanwhile, KDM4A-driven senescence suppressed tumor growth and enhanced intratumoral CD8T-lymphocyte infiltration via enhancing SASP-associated secretion. Furthermore, AGT disrupted PHB1 (prohibitin 1)-mediated basal mitophagy, triggering cytoplasmic mitochondrial DNA (mtDNA) accumulation that activated CGAS-STING1 signaling and enhanced SASP secretion. Crucially, KDM4A overexpression potentiated anti-PDCD1/PD1 efficacy in MSI-H CRC and reversed therapy resistance in MSS CRC. Conclusively, we established a KDM4A-AGT-PHB1 (KAP) grade system that robustly predicts immunotherapy responsiveness in pMMR CRC patients.: AGT: angiotensinogen; BafA: bafilomycin A; CCCP: carbonyl cyanide 3-chlorophenylhydrazone; CRC: colorectal cancer; CDKN1A/p21: cyclin dependent kinase inhibitor 1A; CDKN2A/p16: cyclin dependent kinase inhibitor 2A; CHX: cycloheximide; Co-IP: co-immunoprecipitation; dMMR: deficient mismatch repair; EdU: 5-ethynyl-2'-deoxyuridine; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; IL6: interleukin 6; IL8: interleukin 8; IHC: immunohistochemical; KDM4A: lysine demethylase 4A; mtDNA: mitochondrial DNA; MS: mass spectrometry; NFKB/NF-κB: nuclear factor kappa B; PHB1: prohibitin 1; PHB2: prohibitin 2; PINK1: PTEN induced kinase 1; pMMR: proficient mismatch repair; PRKN/parkin: parkin RBR E3 ubiquitin protein ligase; SASP: senescence-associated secretory phenotype; SA-GLB1/β-gal: senescence-associated galactosidase beta 1; TIMM23: translocase of inner mitochondrial membrane 23; TOMM20: translocase of outer mitochondrial membrane 20; TRIM21: tripartite motif containing 21; TUBB/beta-tubulin: tubulin beta class I. + + high high + Abbreviation1
