Tumor Cell Plasticity in Uveal Melanoma

Abstract

The histological detection of laminin-rich vasculogenic mimicry patterns in human primary uveal melanomas is associated with death from metastases. We therefore hypothesized that highly invasive uveal melanoma cells forming vasculogenic mimicry patterns after exposure to a laminin-rich three-dimensional microenvironment would differentially express genes associated with invasive and metastatic behavior. However, we discovered that genes associated with differentiation (GDF15 and ATF3) and suppression of proliferation (CDKNa1/p21) were up-regulated in highly invasive uveal melanoma cells forming vasculogenic mimicry patterns, and genes associated with promotion of invasive and metastatic behavior such as CD44, CCNE2 (cyclin E2), THBS1 (thrombospondin 1), and CSPG2 (chondroitin sulfate proteoglycan; versican) were down-regulated. After forming vasculogenic mimicry patterns, uveal melanoma cells invaded only short distances, failed to replicate, and changed morphologically from the invasive epithelioid to the indolent spindle A phenotype. In human tissue samples, uveal melanoma cells within vasculogenic mimicry patterns assumed the spindle A morphology, and the expression of Ki67 was significantly reduced in adjacent melanoma cells. Thus, the generation of vasculogenic mimicry patterns is accompanied by dampening of the invasive and metastatic uveal melanoma genotype and phenotype and underscores the plasticity of these cells in response to cues from the microenvironment. The term vasculogenic mimicry describes the formation of perfusion pathways in tumors by highly invasive, genetically deregulated tumor cells 1,2 : vasculogenic because, although these pathways do not form from preexisting vessels, they distribute plasma and may contain red blood cells and mimicry because the pathways are not blood vessels and merely mimic vascular function. In vasculogenic mimicry of the patterned matrix type, 3 highly invasive tumor cells form looping patterns rich in extracellular matrix (ECM) in three-dimensional (3D) culture conditions. 1 Highly invasive tumor cells do not generate these patterns when grown under monolayer conditions or on thin matrix, and poorly invasive tumor cells do not generate these patterns under any culture condition. 1,4 These looping patterns, termed the "fluid-conducting meshwork," 5 connect to endothelial cell-lined blood vessels 4,6 and conduct fluid in vitro 1,4 and in animal models of melanoma. 5,7,8 Vasculogenic mimicry patterns are composed of laminin, 5,9,10 collagen types IV 11 and VI, 12 fibronectin, 13 Pathology, Vol. 169, No. 4, October 2006 Copyright © American Society for Investigative Pathology DOI: 10.2353/ajpath.2006 1376 focally and weakly for collagen I and are structurally different from stromal host-derived fibrovascular septa. There is a strong association between the histological detection of vasculogenic mimicry patterns in primary uveal [15][16][17][18][19][20][21] and cutaneous 22,23 melanomas and subsequent death from metastasis, consistent with the in vitro observatio...

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