Abstract: |
Glioblastoma (GBM) is among the most aggressive of human cancers. A key feature of GBMs is the extensive network of abnormal vasculature characterized by glomeruloid structures and endothelial hyperplasia. Yet the mechanisms of angiogenesis and the origin of tumour endothelial cells remain poorly defined. Here we demonstrate that a subpopulation of endothelial cells within glioblastomas harbour the same somatic mutations identified within tumour cells, such as amplification of EGFR and chromosome 7. We additionally demonstrate that the stem-cell-like CD133+ fraction includes a subset of vascular endothelial-cadherin (CD144)-expressing cells that show characteristics of endothelial progenitors capable of maturation into endothelial cells. Extensive in vitro and in vivo lineage analyses, including single cell clonal studies, further show that a subpopulation of the CD133+ stem-like cell fraction is multipotent and capable of differentiation along tumour and endothelial lineages, possibly via an intermediate CD133+/CD144 + progenitor cell. The findings are supported by genetic studies of specific exons selected from The Cancer Genome Atlas, quantitative FISH and comparative genomic hybridization data that demonstrate identical genomic profiles in the CD133+ tumour cells, their endothelial progenitor derivatives and mature endothelium. Exposure to the clinical anti-angiogenesis agent bevacizumab or to a γ-secretase inhibitor as well as knockdown shRNA studies demonstrate that blocking VEGF or silencing VEGFR2 inhibits the maturation of tumour endothelial progenitors into endothelium but not the differentiation of CD133+ cells into endothelial progenitors, whereas γ-secretase inhibition or NOTCH1 silencing blocks the transition into endothelial progenitors. These data may provide new perspectives on the mechanisms of failure of anti-angiogenesis inhibitors currently in use. The lineage plasticity and capacity to generate tumour vasculature of the putative cancer stem cells within glioblastoma are novel findings that provide new insight into the biology of gliomas and the definition of cancer stemness, as well as the mechanisms of tumour neo-angiogenesis. © 2010 Macmillan Publishers Limited. All rights reserved. |
Keywords: |
controlled study; protein expression; vascular endothelial growth factor a; somatic mutation; exon; mutation; angiogenesis inhibitor; bevacizumab; nonhuman; chromosome; mouse; animals; mice; in situ hybridization, fluorescence; enzyme inhibition; gene amplification; gene expression profiling; cell maturation; epidermal growth factor receptor; animal experiment; animal model; in vivo study; cell differentiation; receptor, notch1; in vitro study; mice, scid; cell line, tumor; inhibitor; vasculotropin receptor 2; neovascularization, pathologic; cell lineage; endothelium cell; endothelial cells; molecular cloning; antibodies, monoclonal; fluorescence in situ hybridization; quantitative analysis; glioblastoma; amplification; cancer stem cell; cell subpopulation; tumor cell; peptides; cell fractionation; cd133 antigen; antigens, cd; chromosome aberrations; tumor; mice, inbred nod; tumor vascularization; cadherins; comparative genomic hybridization; neural stem cells; glycoproteins; short hairpin rna; cell organelle; gamma secretase inhibitor; amyloid precursor protein secretases; gamma secretase; integrin beta4; chromosome 7; coculture techniques; hybridization; vascular endothelial cadherin; subpopulation
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