Insulin-like growth factor 2 mRNA-binding protein 1 (IGF2BP1) is a multifunctional RNA-binding protein with an oncofetal pattern of expression shown to be implicated in the development of a variety of malignancies.,In this study, we explored the role and mechanisms of IGF2BP1 in melanoma development and progression.,In two different in vivo models, we showed that while genetic deletion or shRNA-mediated suppression of IGF2BP1 did not affect primary tumor formation, it drastically suppressed lung metastasis.,Here we demonstrated that extracellular vesicles (EVs) secreted by melanoma cells mediate the effects of IGF2BP1 on metastasis: EVs from the IGF2BP1 knockdown melanoma cells failed to promote metastasis whereas EVs isolated from IGF2BP1-overexpressed melanoma cells further accelerated EV-induced metastasis.,Moreover, the EVs from IGF2BP1 knockdown melanoma cells inhibited fibronectin deposition and accumulation of CD45+ cells in the lungs compared to control EVs, thus blocking the pre-metastatic niche formation potential of EVs.,IGF2BP1 knockdown did not affect size, number, or protein/RNA concentration of secreted EVs or their uptake by recipient cells in vitro or in vivo.,However, RNA-sequencing and proteomics analysis of the EVs revealed differential expression in a number of mRNA, proteins and miRNAs.,This suggested that IGF2BP1 is intimately involved in the regulation of the cargo of EVs, thereby affecting the pro-metastatic function of melanoma-derived EVs.,To the best of our knowledge, this is the first study that demonstrates the role of RNA-binding protein IGF2BP1 in EV-mediated promotion of melanoma metastasis and may provide novel avenues for the development of metastatic inhibitors.
Bone metastases occur rarely in patients suffering from malignant melanoma, although their onset severely worsens both prognosis and quality of life.,Extracellular vesicles (EVs) including exosomes (Exos) are active players in melanoma progression involved in the formation of the pre-metastatic niche.,Trans-well assays explored the basal migratory and invasive potential of four melanoma cell lines and investigated their different propensity to be attracted toward the bone.,Exosomes were purified from cell supernatants by ultracentrifugation and explored in their ability to influence the bone tropism of melanoma cells.,The molecular machinery activated during this process was investigated by RT-PCR, droplet digital-PCR, flow-cytometry and Western blot, while loss of function studies with dedicated siRNAs defined the single contribute of CXCR4 and CXCR7 molecules.,Melanoma cells revealed a variable propensity to be attracted toward bone fragments.,Gene profiling of both osteotropic and not-osteotropic cells did not show a different expression of those genes notoriously correlated to chemotaxis and bone metastasis.,However, bone conditioned medium significantly increased CXCR4, CXCR7 and PTHrP expression solely to osteotropic cells, while their Exos were able to revert the original poor bone tropism of not-osteotropic cells through CXCR7 up-regulation.,Silencing experiments also demonstrated that membrane expression of CXCR7 is required by melanoma cells to promote their chemotaxis toward SDF-1 gradients.,Our data correlated the osteotropism of melanoma cells to the activation of the SDF-1/CXCR4/CXCR7 axis following the exposition of tumor cells to bone-derived soluble factors.,Also, we demonstrated in vitro that tumor-derived Exos can reprogram the innate osteotropism of melanoma cells by up-regulating membrane CXCR7.,These results may have a potential translation to future identification of druggable targets for the treatment of skeletal metastases from malignant melanoma.,The online version of this article (10.1186/s12967-019-1982-4) contains supplementary material, which is available to authorized users.