Tissue sections from aggressive human intraocular (uveal) and metastatic cutaneous melanomas generally lack evidence of significant necrosis and contain patterned networks of interconnected loops of extracellular matrix. The matrix that forms these loops or networks may be solid or hollow. Red blood cells have been detected within the hollow channel components of this patterned matrix histologically, and these vascular channel networks have been detected in human tumors angiographically. Endothelial cells were not identified within these matrix-embedded channels by light microscopy , by transmission electron microscopy , or by using an immunohistochemical panel of endothelial cell markers (Factor VIIIrelated antigen , Ulex , CD31 , CD34 , and KDR[Flk-1]). Highly invasive primary and metastatic human melanoma cells formed patterned solid and hollow matrix channels (seen in tissue sections of aggressive primary and metastatic human melanomas) in threedimensional cultures containing Matrigel or dilute Type I collagen , without endothelial cells or fibroblasts. These tumor cell-generated patterned channels conducted dye , highlighting looping patterns visualized angiographically in human tumors. Neither normal melanocytes nor poorly invasive melanoma cells generated these patterned channels in vitro under identical culture conditions , even after the addition of conditioned medium from metastatic pattern- It is generally assumed that tumors require a blood supply for growth and metastasis. 1 The development of the tumor microcirculation compartment includes both the production of new blood vessels (angiogenesis) and their remodeling. 2 In fact, the number of vessels 3 and the patterning of the microcirculation 4 by remodeling events are used as histological markers of tumor progression. Although attention has been focused on factors that stimulate and suppress tumor angiogenesis, the molecular mechanisms underlying tumor remodeling remain enigmatic. It is therefore critical to investigate remodeling of the intratumoral microvasculature in various tumor models.Melanoma is among the better characterized tumor models with respect to prognostic staging of disease progression. The rising incidence of cutaneous melanoma makes this tumor an important public health problem. Melanoma of the interior of the eye, uveal melanoma, although much less common than cutaneous melanoma, poses a threat to vision and significant morbidity; nearly 50% of patients with uveal melanoma die from metastatic melanoma. 5 Cutaneous melanoma may disseminate through lymphatics or blood vessels. In contrast, the interior of the eye lacks lymphatics, and uveal melanoma, which develops in one of the most capillary-rich tissues of the body, is a paradigm for pure hematogeneous dissemination of cancer. 6 Therefore, the development of a tumor microcirculation in uveal melanoma is a rate-limiting step for hematological metastasis and serves as an important model for study of the cellular and molecular infrastruc-

We report here that living cells and nuclei are hard-wired such that a mechanical tug on cell surface receptors can immediately change the organization of molecular assemblies in the cytoplasm and nucleus. When integrins were pulled by micromanipulating bound microbeads or micropipettes, cytoskeletal filaments reoriented, nuclei distorted, and nucleoli redistributed along the axis of the applied tension field. These effects were specific for integrins, independent of cortical membrane distortion, and were mediated by direct linkages between the cytoskeleton and nucleus. Actin microfilaments mediated force transfer to the nucleus at low strain; however, tearing of the actin gel resulted with greater distortion. In contrast, intermediate filaments effectively mediated force transfer to the nucleus under both conditions. These filament systems also acted as molecular guy wires to mechanically stiffen the nucleus and anchor it in place, whereas microtubules acted to hold open the intermediate filament lattice and to stabilize the nucleus against lateral compression. Molecular connections between integrins, cytoskeletal filaments, and nuclear scaffolds may therefore provide a discrete path for mechanical signal transfer through cells as well as a mechanism for producing integrated changes in cell and nuclear structure in response to changes in extracellular matrix adhesivity or mechanics.Cells generate mechanical tension in their actin cytoskeleton (CSK) and exert tractional forces on their adhesions to extracellular matrix (ECM) (1). Changes in the balance of forces between cells and ECM, induced by altering matrix flexibility or adhesivity, can change cell shape and switch cells between growth and differentiation (1-5). The precise mechanism by which cell shape changes influence gene expression and cell cycle progression remains unclear. However, these regulatory effects appear to be mediated, at least in part, by associated changes in CSK and nuclear structure (1, 6-10). Thus, it is critical to understand how mechanical stresses applied to the surface membrane can promote coordinated alterations in cell, CSK, and nuclear form. Understanding this mechanism also could provide insight into mechanotransduction, the process by which cells sense and respond to external mechanical stimuli.One explanation for integrated cell shape control is that transmembrane ECM receptors, CSK filaments, and nuclear scaffolds are ''hard-wired'' together such that a mechanical pull on the surface membrane results in coordinated realignment of structural elements throughout this interconnected molecular network (11,12). This model is in direct contrast to many current models of cell mechanics, which envision the viscous fluid-like cytoplasm and surrounding elastic membrane to be the major load-bearing elements in living cells (13)(14)(15). On the other hand, microscopic studies demonstrate structural continuity between ECM molecules, transmembrane proteins, CSK filaments, and nuclear scaffolds in detergent-extracted cells (16)(17)...

Tumors require a blood supply for growth and hematogenous dissemination. Much attention has been focused on the role of angiogenesis-the recruitment of new vessels into a tumor from pre-existing vessels. However, angiogenesis may not be the only mechanism by which tumors acquire a microcirculation. Highly aggressive and metastatic melanoma cells are capable of forming highly patterned vascular channels in vitro that are composed of a basement membrane that stains positive with the periodic acid-Schiff (PAS) reagent in the absence of endothelial cells and fibroblasts. These channels formed in vitro are identical morphologically to PAS-positive channels in histological preparations from highly aggressive primary uveal melanomas, in the vertical growth phase of cutaneous melanomas, and in metastatic uveal and cutaneous melanoma. The generation of microvascular channels by genetically deregulated, aggressive tumor cells was termed "vasculogenic mimicry" to emphasize their de novo generation without participation by endothelial cells and independent of angiogenesis. Techniques designed to identify the tumor microcirculation by the staining of endothelial cells may not be applicable to tumors that express vasculogenic mimicry. Although it is not known if therapeutic strategies targeting endothelial cells will be effective in tumors whose blood supply is formed by tumor cells in the absence of angiogenesis, the biomechanical and molecular events that regulate vasculogenic mimicry provide opportunities for the development of novel forms of tumor-targeted treatments. The unique patterning characteristic of vasculogenic mimicry provides an opportunity to design noninvasive imaging techniques to detect highly aggressive neoplasms and their metastases. Tumors require a blood supply to sustain growth. The tumor microcirculation plays a central role in the hematogenous dissemination of cancers. Considerable attention has been focused on the mechanisms by which tumors acquire their blood supply. It is a well-accepted paradigm that tumors recruit new blood vessels from the existing circulation 1 -angiogenesis-either from factors secreted by the tumor cells, as Folkman 2,3 has emphasized, or from surrounding stromal cells. 4 There are two variations on the theme of tumor angiogenesis: augmentation of the angiogenic response by progenitor endothelial cells, and vessel cooption. Asahara and associates 5 described the incorporation of endothelial cell progenitors (or angioblasts) from circulating peripheral blood into sites of ischemic-driven angiogenesis. Holash and associates 6 described a process of "vessel cooption" in which tumors coopt the existing vasculature, which regresses leading to massive necrosis, and the tumor is then vascularized at the periphery by tumor angiogenesis as described above.We 7 recently described a novel process by which tumors develop a highly patterned microcirculation that is independent of angiogenesis: in aggressive primary and metastatic melanomas, the tumor cells generate acellular microcirculat...

Glioblastoma is one of the most angiogenic human tumours and endothelial proliferation is a hallmark of the disease. A better understanding of glioblastoma vasculature is needed to optimize anti-angiogenic therapy that has shown a high but transient efficacy. We analysed human glioblastoma tissues and found non-endothelial cell-lined blood vessels that were formed by tumour cells (vasculogenic mimicry of the tubular type). We hypothesized that CD133+ glioblastoma cells presenting stem-cell properties may express pro-vascular molecules allowing them to form blood vessels de novo. We demonstrated in vitro that glioblastoma stem-like cells were capable of vasculogenesis and endothelium-associated genes expression. Moreover, a fraction of these glioblastoma stem-like cells could transdifferentiate into vascular smooth muscle-like cells. We describe here a new mechanism of alternative glioblastoma vascularization and open a new perspective for the antivascular treatment strategy.