Functional characterization of the 9q34.13 locus identifies RAPGEF1 as a candidate gene modulating risk for melanoma and nevi via RAS activation.

RAPGEF1

Cis-regulatory variants at the 9q34.13 locus modulating RAPGEF1 expression, which activates RAP1 and RAS and promotes melanocyte growth

Genome-wide association studies had identified a melanoma and nevus count susceptibility locus at 9q34.13 without naming a causal gene. Fine-mapping and melanocyte expression data point to two candidate genes with opposite effects: higher RAPGEF1 levels and lower UCK1 levels. Melanocyte capture-HiC and CRISPR inhibition demonstrated regulatory interactions between the fine-mapped variants and the RAPGEF1 and UCK1 promoters. RAPGEF1 expression promotes growth and colony formation of human immortalised melanocytes, and its overexpression activated both RAP1 and RAS after epidermal growth factor treatment. This expression is significantly enriched in melanomas lacking strongly activating RAS-MAPK pathway mutations, with preliminary evidence of prognostic relevance in that subgroup.

Synthesis written by Geno'X. For the full original abstract, please refer to the source publication.

The work is methodologically clean — fine-mapping, capture-HiC, CRISPRi, then functional demonstration of RAS activation — and it fills the usual missing link between a GWAS signal and a mechanism. Clinically it changes nothing today: this is a common susceptibility factor without Mendelian penetrance, and no surveillance scheme or genetic counselling can follow from it. The most interesting medium-term observation is the enrichment of RAPGEF1 in melanomas lacking RAS or BRAF mutations, but it is explicitly presented as preliminary and needs validation in an independent cohort before any prognostic reading.

Analysis by Dr Thibaut Benquey