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

UNLABELLED: 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 antitumor immunity. In this study, we conducted integrated multiomics 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 noncanonical NF-κB signaling-dependent cGAS-STING activation, which in turn drove immune suppression via MDSC 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 antitumor 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.

SIGNIFICANCE: Pathogenic LINE-1 retrotransposon-derived L1-ORF1p forms condensates to scaffold cGAS-HMGN2 complexes that activate cGAS-STING and drive immunosuppression in lung squamous cell carcinoma, which can be overcome by combined targeting of LINE-1 and cGAS.