EZH2 Regulates the Proliferation-Senescence Balance and Tumor–Stromal Signaling in Lung Adenocarcinoma

Enhancer of zeste homolog 2 (EZH2), the catalytic component of the polycomb repressive complex 2, is frequently overexpressed in lung adenocarcinoma and contributes to transcriptional programs that support tumor proliferation and cellular plasticity. However, its role in regulating senescence-associated signaling and tumor–stromal interactions in lung cancer remains incompletely understood. In this study, we combined transcriptomic analysis of The Cancer Genome Atlas lung adenocarcinoma cohort with functional characterization of EZH2 targeting in A549 cells using the catalytic inhibitor EPZ6438 and the EZH2 degrader MS1943. Elevated EZH2 expression was associated with enrichment of cell cycle-related transcriptional pathways. Pharmacological targeting of EZH2 reduced proliferation, migration, stemness-associated features, and sphere-forming capacity, with more pronounced effects observed following EZH2 degradation. Both compounds promoted features consistent with senescence-associated phenotypic remodeling characterized by increased expression of p16 and p21, enhanced β-galactosidase activity, G0/G1 cell cycle arrest, and increased expression of cytokines commonly associated with senescence-related secretory signaling, including IL-6, CCL2, and CXCL8. Conditioned medium from treated tumor cells promoted activation of primary lung fibroblasts, indicating functional paracrine microenvironmental remodeling. Importantly, EZH2 targeting elicited cytostatic responses without induction of apoptosis. Collectively, these findings suggest that EZH2 contributes to regulation of proliferation-associated and senescence-associated phenotypic programs together with stromal signaling in lung adenocarcinoma.