Angiogenesis is the propelling force for tumor growth and metastasis, and antiangiogenic therapy represents one of the most promising modalities for cancer treatment. CD105 (endoglin) is a proliferation-associated and hypoxia-inducible protein abundantly expressed in angiogenic endothelial cells (EC). It is a receptor for transforming growth factor (TGF) -beta1 and -beta3 and modulates TGF-beta signaling by interacting with TGF-beta receptors I and/or II. Immunohistochemistry studies have revealed that CD105 is strongly expressed in blood vessels of tumor tissues. Intratumoral microvessel density (MVD) determined using antibodies to CD105 has been found to be an independent prognostic indicator, wherein increased MVD correlates with shorter survival. CD105 is able to be shed into the circulation, with elevated levels detected in patients with various types of cancer and positively correlated with tumor metastasis. Tangible evidence of its proangiogenic role comes from knockout studies in which CD105 null mice die in utero as a result of impaired angiogenesis in the yolk sac and heart defects. The potential usefulness of CD105 for tumor imaging has been evaluated in tumor-bearing mice and dogs that have shown the rapid accumulation of radiolabeled anti-CD105 monoclonal antibody in the tumors with a high tumor-to-background ratio. The anti-CD105 antibody conjugated with immunotoxins and immunoradioisotopes efficiently suppressed/abrogated tumor growth in murine models bearing breast and colon carcinoma without any significant systemic side effects. Immunoscintigraphy in patients with renal cell carcinomas has shown specific localization of 99Tcm-labeled CD105 mab in tumor endothelial cells. Thus, CD105 is a promising vascular target that can be used for tumor imaging, prognosis, and bears therapeutic potential in patients with solid tumors and other angiogenic diseases.

Cell lines have been produced from long-term cultures of mouse bone marrow that require a factor, present in WEHI-3 conditioned medium (CM) or in spleen CM, for their sustained growth. The cell lines were obtained from nonvirus-treated cultures, are nonleukemic, maintain a normal karyotype, and form colonies showing granulocyte maturation when plated in soft agar. Granulocyte/macrophage (GM) colony-stimulating factor is not the inductive moiety involved in the maintenance of proliferation of these cells. It is suggested that the cell lines represent a self-renewing population of cells ancestral to GM colony-forming cells, which may be responding to a hitherto unrecognized regulator.

A myelomonocytic leukaemia cell line, WEHI-3, releases into its growth medium factors which stimulate the development of pluripotential cells, granulocyte/macrophage progenitor cells, megakaryocytic and erythroid progenitor cells. Also present is a factor which is essential for the continued proliferation in vitro of a variety of haemopoietic precursor cell lines of a granulocytic nature (FDC-P cells). Characterization of this growth factor has demonstrated that it is a glycoprotein of apparent Mr 25 800, in which the carbohydrate component appears to be important for activity. After several purification steps, there is an increase in specific activity of approx. 4000-fold over the starting material. At each stage of purification, the factor necessary for the proliferation of FDC-P cells 'co-purifies' with activity which stimulates the proliferation and development of normal multipotential haemopoietic cells as well as megakaryocytic, erythroid and granulocytic committed progenitor cells. This 'co-purification' occurs to the extent that the multilineage stimulating factor and the FDC-P growth factor can be eluted from the same region of sodium dodecyl sulphate/polyacrylamide gels. Thus, evidence so far, using different starting methods and purification regimes, suggests that one molecule may have multiple activities on diverse cell types.

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We have investigated cell metabolism during apoptosis in the murine interleukin-3 (IL-3)-dependent cell line Bo and two derivative clones (B14 and B15) overexpressing human bcl-2a. On removal of IL-3, Bo cells underwent apoptosis within 8 h, whereas B14 and B15 cells were resistant for at least 24 h. Metabolically, Bo, B14, and B15 cells were indistinguishable from each other. All were insensitive to mitochondrial poisons, derived ATP entirely by glycolysis, and maintained similar mitochondrial membrane potentials measured by rhodamine-123 fluorescence with or without IL-3. All virtually ceased glycolysis and production of lactic acid on IL-3 withdrawal but maintained intracellular [ATP] until in Bo cultures the cells began to apoptose. B14 and B15 cells became glycolytically arrested but maintained stable ATP levels during protection from apoptosis. Depletion of intracellular ATP by uncoupling the mitochondrial ATPase with 2,4-dinitrophenol or carbonyl cyanide p-trifluoromethoxyphenylhydrazone induced apoptosis in Bo cells with or without IL-3, but not in B14 or B15 cells. bcl-2-overexpressing cells were recoverable with high plating efficiency even after prolonged exposure to 2,4-dinitrophenol. We conclude that IL-3 withdrawal leads to arrest of energy metabolism in which ATP levels are maintained. In Bo cells this is followed by apoptosis, whereas in bcl-2-overexpressing cells this state is stably prolonged. ATP depletion is a strong apoptotic signal which overrides IL-3 signaling in normal cells but is ineffective in bcl-2-overexpressing cells. Prolonged metabolic arrest and resistance to ATP depletion facilitated by bcl-2 are both reversible. Persistent reversible metabolic dormancy would provide cells with a survival advantage in nonsustainable environments (e.g. hypoxia or substrate lack) and suggests a mechanism for the survival advantage displayed by cells overexpressing bcl-2.

Background: TGF-β1 is an important angiogenic factor involved in the different aspects of angiogenesis and vessel maintenance. TGF-β signalling is mediated by the TβRII/ALK5 receptor complex activating the Smad2/Smad3 pathway. In endothelial cells TGF-β utilizes a second type I receptor, ALK1, activating the Smad1/Smad5 pathway. Consequently, a perturbance of ALK1, ALK5 or TβRII activity leads to vascular defects. Mutations in ALK1 cause the vascular disorder hereditary hemorrhagic telangiectasia (HHT).

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