Global assessment of melanoma-endothelial cell communication identifies neuropilin-2 as a mediator of melanoma cell proliferation

Metastasis of melanoma is a significant clinical issue because lesions as thin as one millimeter can spread to other parts of the body, and patients with metastatic disease have a life expectancy of less than eight months. Metastasis is challenging to study in the laboratory because the process is highly complex and difficult to model. We wished to develop a simple in vitro model of melanoma metastasis to better understand the cell-cell communication which occurs during this process, and identify and explore the role of a specific gene in melanoma proliferation, migration, and interaction with endothelial cells. Utilizing a two-dimensional co-culture model and gene expression profiling of melanoma and endothelial cells, we observed morphological and gene expression changes induced by heterotypic cell-cell communication. The results from these studies suggest that our model can accurately describe some of the molecular changes associated with tumor-endothelial cell communication during the processes of metastasis and angiogenesis. We identified neuropilin-2 (NRP2), a member of the neuropilin family of transmembrane glycoproteins, as a transcript that is upregulated in melanoma cells during communication with endothelial cells. NRP2 is implicated in metastasis and angiogenesis through its involvement in the VEGF signaling pathways, although its mechanism of action is poorly characterized. Inhibition of NRP2 signaling in melanoma cells using antibodies resulted in a significant and irreversible reduction of proliferation of melanoma cells. Immunohistochemical staining revealed that NRP2 is highly expressed in human metastatic melanomas. Staining of tissue microarrays revealed that all melanoma subtypes except desmoplastic melanomas express NRP2 at very high levels, while the expression of NRP2 in other tumor types except renal clear cell carcinomas was low. We conclude that NRP2 may be a viable diagnostic marker or therapeutic target for melanoma due to its high expression in human disease and its role in tumor growth. We expect that this model will provide insight into the molecular determinants of melanoma metastasis and lead to the identification of potential therapeutic targets for this aggressive form of skin cancer.