MyD88 sustains a metastasis-competent cell state by promoting integrin-mediated adhesion in melanoma

Abstract Background Metastatic dissemination remains a major challenge in melanoma, as environmental cues can reshape tumor cell plasticity and promote transient states that enable invasion and colonization of distant organs. However, the tumor cell-intrinsic mechanisms that integrate these external signals and sustain metastatic competence remain incompletely understood. Methods To identify tumor cell-intrinsic regulators of melanoma dissemination, we performed functional drop-out screens in NRAS-mutant melanoma patient-derived xenograft (PDX) models. The role of MyD88 was investigated through genetic silencing and overexpression approaches combined with transcriptomic profiling and functional assays of invasion, adhesion, and interaction with endothelial cells and the extracellular matrix. Moreover, we carried out in vivo metastatic studies, including extensive isolation and single-cell analyses of circulating tumor cells (CTCs). We also evaluated the impact of environmental stimuli on MyD88 expression and downstream signaling pathways. Results Functional drop-out screens identify the adaptor protein MyD88 as a tumor cell-intrinsic dependency selectively required for metastatic progression. MyD88 silencing profoundly impairs metastatic dissemination, without affecting primary tumor growth. At the molecular level, MyD88 depletion rewires melanoma cell transcriptional programs, suppressing mesenchymal-like invasive features and reducing metastatic competence. In particular, MyD88 sustains an integrin-mediated adhesion program that enhances tumor cell interactions with the extracellular matrix and endothelium, thereby supporting local invasion, intravasation, extravasation, and ultimately dissemination to distant sites. Multiple environmental stimuli, including genotoxic stress, growth factors, and nutrient deprivation, increase MyD88 expression and activate STAT3 signaling, which emerges as a central pathway driving integrin-associated adhesive programs. Within primary tumors, MyD88 identifies a metastasis-competent subpopulation, characterized by pro-adhesive and pro-metastatic features. Consistently, circulating tumor cells are enriched for MyD88 expression and display motility- and adhesion-associated states. Conversely, MyD88 interference reduces CTC release and significantly impairs metastatic seeding to distant organs. Conclusions These findings establish MyD88 as an environmentally responsive regulator of melanoma cell-state plasticity that links adaptive responses to the acquisition of adhesion-dependent metastatic traits. By coordinating integrin-mediated interactions required for dissemination, MyD88 supports multiple steps of the metastatic cascade.