Melanoma is one of the most aggressive solid tumors and includes a stromal microenvironment that regulates cancer growth and progression.,The components of stromal microenvironment such as fibroblasts, fibroblast aggregates and cancer-associated fibroblasts (CAFs) can differently influence the melanoma growth during its distinct stages.,In this work, we have developed and studied a stromal microenvironment model, represented by fibroblasts, proto-myofibroblasts, myofibroblasts and aggregates of inactivated myofibroblasts, such as spheroids.,In particular, we have generated proto-myofibroblasts from primary cutaneous myofibroblasts.,The phenotype of proto-myofibroblasts is characterized by a dramatic reduction of α-smooth muscle actin (α-SMA) and cyclooxygenase-2 (COX-2) protein levels, as well as an enhancement of cell viability and migratory capability compared with myofibroblasts.,Furthermore, proto-myofibroblasts display the mesenchymal marker vimentin and less developed stress fibers, with respect to myofibroblasts.,The analysis of crosstalk between the stromal microenvironment and A375 or A2058 melanoma cells has shown that the conditioned medium of proto-myofibroblasts is cytotoxic, mainly for A2058 cells, and dramatically reduces the migratory capability of both cell lines compared with the melanoma-control conditioned medium.,An array analysis of proto-myofibroblast and melanoma cell-conditioned media suggests that lower levels of some cytokines and growth factors in the conditioned medium of proto-myofibroblasts could be associated with their anti-tumor activity.,Conversely, the conditioned media of melanoma cells do not influence the cell viability, outgrowth, and migration of proto-myofibroblasts from spheroids.,Interestingly, the conditioned medium of proto-myofibroblasts does not alter the cell viability of both BJ-5ta fibroblast cells and myofibroblasts.,Hence, proto-myofibroblasts could be useful in the study of new therapeutic strategies targeting melanoma.
Novel targeted and immunotherapeutic approaches have revolutionized the treatment of metastatic melanoma.,A better understanding of the melanoma-microenvironment, in particular the interaction of cells with extracellular matrix molecules, may help to further improve these new therapeutic strategies.,We observed that the extracellular matrix molecule biglycan (Bgn) was expressed in certain human melanoma cells and primary fibroblasts when evaluated by microarray-based gene expression analysis.,Bgn expression in the melanoma tissues correlated with low overall-survival and low progression-free-survival in patients.,To understand the functional role of Bgn we used gene-targeted mice lacking functional Bgn.,Here we observed that melanoma growth, metastasis-formation and tumor-related death were reduced in Bgn−/− mice compared to Bgn+/+ mice.,In vitro invasion of melanoma cells into organotypic-matrices derived from Bgn−/− fibroblasts was reduced compared to melanoma invasion into Bgn-proficient matrices.,Tissue stiffness as determined by atomic-force-microscopy was reduced in Bgn−/− matrices.,Isolation of melanoma cells and fibroblasts from the stiffer Bgn+/+ matrices revealed an increase in integrin-β1 expression compared to the Bgn−/− fibroblast matrices.,Overexpression of integrin-β1 in B16-melanoma cells abolished the survival benefit seen in Bgn−/− mice.,Consistent with the studies performed in mice, the abundance of Bgn-expression in human melanoma samples positively correlated with the expression of integrin-β1, which is in agreement with results from the organotypic invasion-assay and the in vivo mouse studies.,This study describes a novel role for Bgn-related tissue stiffness in the melanoma-microenvironment via regulation of integrin-β1 expression by melanoma cells in both mice and humans.