NECTIN1 controls an IGF1-dependent adhesion switch in melanoma spreading

Defects in cell-cell contacts have been proposed to participate in early steps of tumor metastasis1 but little is known about the signals from the cancer cell niche that influence this process. Here, we show that the lack of adherens junctions caused by genetic loss of the adhesion molecule NECTIN1 in melanoma promotes tumor dissemination specifically under growth factor deprivation. We found that NECTIN1 was deleted in 53% of human melanomas and that its loss was enriched in metastases. NECTIN1 inactivation in zebrafish melanomas stimulated cancer cell spreading in vivo, while in human cell lines, it increased cell migration specifically in response to serum starvation. We further identified IGF1 as the serum component responsible for this effect. Serum withdrawal or IGF1 inhibition induced formation of strong adherens junctions between NECTIN1-wild-type melanoma cells. In contrast, NECTIN1-deficient cells were unable to establish adherens junctions and instead activated integrin-mediated motility through a FAK/SRC axis. During melanoma dissemination, NECTIN1 loss thus causes a cellular phenotypic switch from cell-cell adhesion to cell-matrix adhesion triggered by IGF1 signaling. Our study uncovers a mechanism by which cancer cells integrate information from the tumor microenvironment and cell-cell contacts to regulate their migratory behavior during spreading. Overall design: In order to identify secreted factors that may be responsible for the formation of adherens junctions between melanoma cells upon serum depletion, we examined the transcriptional response of human melanoma cells to serum withdrawal by RNA-sequencing. We analyzed gene expression in 4 lines derived from the A375 human melanoma cell line by single-cell cloning and cultured in DMEM in the presence or absence of 10% FBS for 12 hours.