Aggressive human brain tumours (gliomas) often express a truncated and oncogenic form of the epidermal growth factor receptor, known as EGFRvIII. Within each tumour only a small percentage of glioma cells may actually express EGFRvIII; however, most of the cells exhibit a transformed phenotype. Here we show that EGFRvIII can be 'shared' between glioma cells by intercellular transfer of membrane-derived microvesicles ('oncosomes'). EGFRvIII expression in indolent glioma cells stimulates formation of lipid-raft related microvesicles containing EGFRvIII. Microvesicles containing this receptor are then released to cellular surroundings and blood of tumour-bearing mice, and can merge with the plasma membranes of cancer cells lacking EGFRvIII. This event leads to the transfer of oncogenic activity, including activation of transforming signalling pathways (MAPK and Akt), changes in expression of EGFRvIII-regulated genes (VEGF, Bcl-x(L), p27), morphological transformation and increase in anchorage-independent growth capacity. Thus, membrane microvesicles of cancer cells can contribute to a horizontal propagation of oncogenes and their associated transforming phenotype among subsets of cancer cells.

Tissue factor (TF) is the primary cellular initiator of blood coagulation and a modulator of angiogenesis and metastasis in cancer. Indeed, systemic hypercoagulability in patients with cancer and TF overexpression by cancer cells are both closely associated with tumor progression, but their causes have been elusive. We now report that in human colorectal cancer cells, TF expression is under control of 2 major transforming events driving disease progression (activation of K-ras oncogene and inactivation of the p53 tumor suppressor), in a manner dependent on MEK/mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K). Furthermore, the levels of cell-associated as well as circulating (microvesicle-associated) TF activity are linked to the genetic status of cancer cells. Finally, RNA interference experiments suggest that TF expression is an important effector of the K-ras-dependent tumorigenic and angiogenic phenotype in vivo. Thus, this study establishes a causal link between cancer coagulopathy, angiogenesis, and genetic tumor progression. ( IntroductionCancer is believed to arise and progress toward increasing malignancy as a result of cumulative genetic "hits" sustained by the tumor cell genome. Paradigmatic in this regard is the development of colorectal carcinoma (CRC), where sequential transition through clinical stages of the disease is paralleled by a series of well-characterized alterations in proto-oncogenes and tumor suppressor genes. 1 In this tumor type, activation of mutant K-ras and subsequent inactivation/loss of p53 are key changes, which drive many interrelated aspects of the malignant phenotype including aberrant mitogenesis and survival. 2 Moreover, both of these genetic alterations are thought to contribute to proangiogenic properties of affected cancer cells, 3,4 and thereby enable them to exploit the host vascular system to advance malignant growth and metastasize in vivo. 5 The involvement of the vascular system in malignancy encompasses not only angiogenesis but also systemic hypercoagulability. Blood clotting abnormalities are detected in up to 90% of patients with metastatic disease, and thrombosis represents the second most frequent cause of cancer-related mortality. 6 Cancer coagulopathy is often linked to up-regulation of tissue factor (TF), the primary cellular initiator of the blood coagulation cascade. 7,8 Interaction of coagulation factor VIIa with TF on the cell surface leads to activation of factor X and generation of thrombin, with subsequent involvement of platelets and formation of a fibrin clot. 9 Remarkably, as a member of the class II cytokine receptor family, TF is also capable of transducing intracellular signals and regulating gene expression. 10,11 Interestingly, elements of the coagulation/fibrinolytic system in general, 12 and TF in particular, have been implicated in regulation of angiogenesis, 13,14 as well as tumor growth 15 and metastasis 16 in various experimental settings. This is consistent with the observed up-regulation of TF in huma...

Tissue factor (TF), the primary cellular initiator of blood coagulation, is also involved in cancer-related processes such as hypercoagulability (Trousseau syndrome), tumor growth, angiogenesis, and metastasis. Indeed, elevated TF expression by cancer cells and their associated endothelial cells has been reported frequently. Oncogenic events in cancer cells (e.g., expression of mutant K- ras, EGFR, PTEN or p53) lead to an increase in TF levels and activity, and thereby promote tumor aggressiveness, angiogenesis, and hypercoagulability. Like TF, thrombin receptor (protease-activated receptor-1) is also upregulated in cancer cells expressing oncogenic K -ras. Pharmacological antagonists of some of these transforming genes (e.g., epidermal growth factor receptor inhibitors) could diminish TF expression, both locally and systemically, and hence these targeted agents could be viewed as potential indirect and cancer-specific anticoagulants, in addition to their direct antitumor effects. We postulate that levels of circulating TF may be useful in monitoring the biological activity of these agents. Although TF is essential for vascular development, its expression by tumor-associated endothelium appears to play a subtle and seemingly dispensable role. Thus, TF is a pivotal element of the tumor-vascular interface, is involved in many cancer-related processes, and may well constitute a promising new target for anticancer combination therapies in some disease settings.