ABSTRACT: Small cell lung cancer (SCLC) is an aggressive neuroendocrine carcinoma characterized by early metastasis, immune evasion, and limited therapeutic progress. While its genomic landscape is well defined, the epigenetic programs sustaining its lineage fidelity, metastatic potential, and immune evasion remain incompletely understood. We used inducible CRISPR-Cas9 knockout models, transcriptomic and epigenetic profiling, immune-competent allografts, and genetically engineered mouse models (GEMMs) to investigate the role of the chromatin regulator UHRF1 in SCLC progression. We identify the chromatin remodeler UHRF1 as a subtype-independent oncogenic driver in SCLC, with high expression correlating with poor survival. UHRF1 loss impaired proliferation, invasion, and metastasis across ASCL1-, NEUROD1-, and POU2F3-driven subtypes. Mechanistically, UHRF1 maintained neuroendocrine lineage identity and suppressed immune gene expression via DNA methylation and interaction with PRC2. UHRF1-deficient tumors displayed increased infiltration of CD8⁺ T cells, monocytes, neutrophils, and dendritic cells, along with a higher CD8⁺/Treg ratio. Secretome profiling revealed upregulation of chemokines, linking UHRF1 loss to active recruitment of immune effector cells. In parallel, UHRF1 regulated the pro-metastatic sialyltransferase ST6GALNAC5 via the transcription factor GATA2. UHRF1 loss downregulated GATA2 and ST6GALNAC5, impairing tumor dissemination. Lastly, UHRF1 depletion increased expression of cancer/testis antigens such as MAGE-A4, without altering DLL3 levels, suggesting compatibility with both antigen-specific and DLL3-targeted immunotherapies. In conclusion, UHRF1 is a master regulator of tumor progression in SCLC, promoting lineage stability, immune evasion, and metastatic spread. Its inhibition reprograms tumors toward an inflamed, less metastatic, and more immunogenic state. These findings establish UHRF1 as a compelling therapeutic target for overcoming the epigenetic and immune resistance barriers in small cell lung cancer.
