ERV-derived dsRNAs induce stress granules that drive neural crest fate to initiate melanoma

Melanoma arises when melanocytes are oncogenically reprogrammed into neural crest-like cells, but what initiates this switch is unknown. Here we show that endogenous retrovirus (ERV)-derived double stranded RNAs (dsRNAs) induce stress granules (SGs) that drive this fate change. In zebrafish, melanoma progresses through a stage-specific ERV switch: zferv marks precursor cells before crestin activates in tumor cells. Both elements generate dsRNA that triggers eif2ak2-dependent SGs within precursor lesions and through transformation. SGs are tumorigenic as G3BP1 overexpression accelerates melanoma onset, whereas mosaic, melanocyte-specific g3bp1/2 knockout delays it. Small molecule-mediated inhibition of G3BP1/2 eliminates precursor lesions and reduces tumor burden. Similarly, blocking dsRNA sensing prevents SG formation and lowers melanoma incidence. Human nevi and melanomas show analogous, stage-specific ERV programs and SG assembly. In human melanoma cells, SGs sequester and translationally repress SOX10-regulating mRNAs, including the tumor suppressor KMT2D. Mosaic knockout of kmt2d in vivo enhances SOX10-driven neural crest reactivation. Thus, an ERV-SG axis establishes an oncogenic translatome that enables melanoma fate, with diagnostic and therapeutic potential.