Extracellular matrix regulation of gene expression and the development of extravascular matrix patterns by aggressive primary and metastatic uveal melanoma cells

Abstract

Abstract: : Purpose: Extravascular matrix patterns (EMPs) are associated with metastasis from uveal and cutaneous melanoma. Non–invasive melanoma cells do not form EMPs. Invasive melanoma cells form EMPs, but only under 3D matrix conditions. To discover the mechanisms of matrix regulation of EMPs, we studied differential gene expression under paired matrix conditions that were non–permissive and permissive of EMP formation. Methods: Two aggressive primary melanoma cell lines (C918, M619), and one metastatic uveal melanoma cell line (MUM–2B) were grown under monolayer and 3D matrix conditions, and cells were harvested for Affymetrix microarray analysis. Expression among six replicates for each paired condition was averaged and differences between the paired conditions were compared with a t–test. Results: As shown in previous experiments, the invasive C918, M619 and MUM2B cell lines formed sheets under monolayer conditions and looping extravascular matrix patterns in thick Matrigel. At a p–value set to 10^–3, 17 genes common to the 3 invasive cell lines were differentially expressed under thick matrix conditions permissive of EMP formation, and 30 genes were differentially expressed in the same cells in conditions non–permissive of EMP formation. Conclusions: We have shown previously that non–invasive uveal melanoma cells are incapable of forming EMPs under any matrix condition. We and others have also shown previously that there are significant differences in gene expression between non–invasive and invasive uveal melanoma cells. In this study, we compared three different invasive uveal melanoma cell lines under paired conditions – non–permissive and permissive of EMP formation. Exposure to thick matrix conditions resulted in changes in gene expression common to all three invasive cell lines and to the generation of EMPs. The formation of EMPs appears to play a critical role in metastasis from uveal melanoma, and the generation of EMPs requires (a) invasive uveal melanoma cells, and (b) exposure of these cells to local matrix conditions that alter gene expression and morphogenetic behavior.

Keywords: melanoma • extracellular matrix • gene microarray