The Melanoma Vascular Mimicry Phenotype Defined in Gene Expression and Microsome Sequencing Analysis

The phenomenon of vasculogenic mimicry in melanoma has been recently described to be an important factor relating to melanoma progression. Large scale gene expression profiling by real-time quantitative RT-QPCR of a panel of 40 normal tissues and 54 cancer cell lines revealed that two genetically related melanoma cell lines, one derived from a primary lesion Hs.688(A) and one derived from a lymph node metastasis Hs.688(B), displayed a unique expression pattern when compared to other cancer cell lines and tissue samples in the panel. Quantitative-RT-PCR data indicated that these melanoma cells expressed a number of activated endothelial cell-associated genes such as tissue inhibitors of matrix metalloproteinases TIMP-2, matrix metalloproteinase (MMP-1, MMP-2), thrombospondin 1 (TSP1), proto-oncogene c-MET and vascular endothelial growth factor (VEGF). To examine the gene expression profile of these unique melanoma cells in greater depth, cDNA libraries were made from isolated microsome complexes to enrich those transcripts that were destined to be translated into cell surface or secreted proteins. High throughput sequencing analysis revealed that this library contained over 7000 cDNAs and was enriched by over 80% of secreted or membrane-bound proteins. The presence in the cDNA library of genes such as acetyl LDL receptor, tumor endothelial markers-1, 5 and 8 (TEMs), flow-induced endothelial G protein coupled receptor-1 and VEGF-related protein (VRP), all of which are known to be expressed uniquely by endothelial cells, supported the hypothesis that Hs.688(A) and Hs.688(B) cells were mimicking an activated vascular phenotype. Ultimately the goal is to investigate the biological roles of endothelial cell-associated genes in the behavior of Hs.688(A) and Hs.688 (B) melanoma cells.