<scp>RIPK</scp> 4 function interferes with melanoma cell adhesion and metastasis

Receptor-interacting protein kinase 4 (RIPK4) has been implicated in the progression of numerous tumours. In nonmelanoma skin cancer, RIPK4 plays a suppressor role, whereas in melanoma, it functions as an oncogene that modulates key signalling pathways involved in melanoma cell survival and expansion. Increased RIPK4 levels in metastatic melanoma biopsies prompted us to investigate the consequences of RIPK4 loss for the invasive and metastatic phenotype of melanoma cells. Using an integrated approach involving clinical samples, in vivo xenograft models, transcriptomic analysis and 3D functional assays, we show that RIPK4 deletion significantly reduces pulmonary metastasis formation. This reflects its role in late-stage metastatic events, such as extravasation and colonization, particularly since this phenotype correlates with extensive transcriptional reprogramming of adhesion- and motility-related genes in melanoma cells, as evidenced by next-generation sequencing and functional validation in spheroid and collagen-based models. Despite exhibiting features of a partial shift towards an amoeboid phenotype such as membrane blebbing and increased MLC2 phosphorylation, RIPK4 knockout cells display impaired motility and invasion. Re-expression of RIPK4 restores mesenchymal morphology and migratory capacity. Together, our results establish RIPK4 as a critical regulator of melanoma invasion and metastasis. Nonetheless, they also demonstrate that the loss of RIPK4 function activates compensatory phenotypic shifts in melanoma cells that fail to fully rescue their invasive potential.