LINE-1 Retrotransposon Protein ORF1p Forms Condensates that Drive cGAS-Induced Immune Evasion in Lung Squamous Cell Carcinoma

Abstract Lung squamous cell carcinoma (LUSC) is a lethal malignancy with limited treatment options, driven by an immunosuppressive tumor microenvironment (TME) and a paucity of actionable targets. Pathogenic LINE-1 (pL1HS) retrotransposons promote LUSC progression by fostering immune evasion. Elucidation of the mechanistic link between retrotransposon activity and TME reprogramming could help identify strategies to stimulate anti-tumor immunity. Here, we conducted integrated multi-omics analyses, including bulk and single-cell RNA-sequencing combined with proteomics, that revealed hyperactivated cGAS-STING signaling and a myeloid-derived suppressor cell (MDSC)-rich TME in pL1HS+ LUSC. Mechanistically, LINE-1 open reading frame 1 protein (L1-ORF1p) underwent liquid-liquid phase separation (LLPS) via its intrinsically disordered region, forming cytosolic condensates that scaffolded pL1HS nucleic acid, HMGN2, and cGAS into a ternary complex. This complex sustained chronic non-canonical NF-κB signaling-dependent cGAS-STING activation, which in turn drove immune suppression via MDSCs recruitment and activation. The coiled-coil domain of L1-ORF1p stabilized these condensates by binding HMGN2, perpetuating this immunosuppressive cascade. Dual targeting of pL1HS and cGAS restored anti-tumor immunity and suppressed tumor growth in preclinical models. Together, this work reveals a therapeutically actionable LLPS-driven axis that can be targeted with a combinatorial strategy to overcome immune evasion in LUSC, thereby addressing a critical unmet clinical need.