Non‐Canonical Function of ORC1 : Regulating Notch‐ VEGFR2 ‐Mediated Angiogenesis in Melanoma Progression

ABSTRACT Melanoma is an aggressive skin cancer characterized by high metastatic potential and substantial genetic heterogeneity. Although genome‐wide association studies (GWAS) have identified numerous susceptibility loci, the functional roles of risk variants, most of which reside in non‐coding regions, remain poorly understood. This study aimed to identify genetic susceptibility genes involved in melanoma progression and investigate their non‐canonical roles in the tumor microenvironment. GWAS summary statistics from the GWAS Catalog, FinnGen, and UK Biobank were integrated using MAGMA and FUSION to prioritize candidate genes, which were subsequently evaluated using TCGA‐SKCM transcriptomic and survival data. ORC1 emerged as a key susceptibility gene that was significantly upregulated in metastatic melanoma and associated with poor overall survival. Bioinformatic analyses further showed that ORC1 expression was positively correlated with Notch signaling activity and alterations in the immune microenvironment. The functional effects of ORC1 were examined using in vitro co‐culture systems in which human umbilical vein endothelial cells were exposed to melanoma‐derived conditioned medium. ORC1 overexpression in melanoma cells promoted endothelial prol iferation, migration, tube formation, and vascular permeability in a paracrine manner. Dual‐luciferase reporter assays, quantitative reverse‐transcription polymerase chain reaction, and Western blotting indicated that ORC1 was associated with enhanced NOTCH1 promoter‐reporter activity, activation of Notch‐related signaling, and induction of downstream angiogenic programs. In xenograft models, ORC1 overexpression was associated with increased tumor growth and microvascular density, whereas pharmacological inhibition of Notch pathway activity with the γ‐secretase inhibitor DAPT attenuated ORC1‐overexpression‐associated tumor growth and vascular changes. Collectively, these findings identify a non‐canonical pro‐angiogenic role for ORC1 in melanoma progression that is mediated, at least in part, through Notch–VEGFR2 signaling. The ORC1–Notch–VEGFR2 axis may therefore represent a potential therapeutic target for modulating the melanoma microenvironment and limiting disease progression.