In neuroblastoma specimens, HIF-2alpha but not HIF-1alpha is strongly expressed in well-vascularized areas. In vitro, HIF-2alpha protein was stabilized at 5% O2 (resembling end capillary oxygen conditions) and, in contrast to the low HIF-1alpha activity at this oxygen level, actively transcribed genes like VEGF. Under hypoxia (1% O2), HIF-1alpha was transiently stabilized and primarily mediated acute responses, whereas HIF-2alpha protein gradually accumulated and governed prolonged hypoxic gene activation. Knockdown of HIF-2alpha reduced growth of neuroblastoma tumors in athymic mice. Furthermore, high HIF-2alpha protein levels were correlated with advanced clinical stage and high VEGF expression and predicted poor prognosis in a clinical neuroblastoma material. Our results demonstrate the relevance of HIF-2alpha in neuroblastoma progression and have general tumor biological implications.

Highly malignant tumors, such as glioblastomas, are characterized by hypoxia, endothelial cell (EC) hyperplasia, and hypercoagulation. However, how these phenomena of the tumor microenvironment may be linked at the molecular level during tumor development remains ill-defined. Here, we provide evidence that hypoxia up-regulates protease-activated receptor 2 (PAR-2), i.e., a G-protein–coupled receptor of coagulation-dependent signaling, in ECs. Hypoxic induction of PAR-2 was found to elicit an angiogenic EC phenotype and to specifically up-regulate heparin-binding EGF-like growth factor (HB-EGF). Inhibition of HB-EGF by antibody neutralization or heparin treatment efficiently counteracted PAR-2–mediated activation of hypoxic ECs. We show that PAR-2–dependent HB-EGF induction was associated with increased phosphorylation of ERK1/2, and inhibition of ERK1/2 phosphorylation attenuated PAR-2–dependent HB-EGF induction as well as EC activation. Tissue factor (TF), i.e., the major initiator of coagulation-dependent PAR signaling, was substantially induced by hypoxia in several types of cancer cells, including glioblastoma; however, TF was undetectable in ECs even at prolonged hypoxia, which precludes cell-autonomous PAR-2 activation through TF. Interestingly, hypoxic cancer cells were shown to release substantial amounts of TF that was mainly associated with secreted microvesicles with exosome-like characteristics. Vesicles derived from glioblastoma cells were found to trigger TF/VIIa–dependent activation of hypoxic ECs in a paracrine manner. We provide evidence of a hypoxia-induced signaling axis that links coagulation activation in cancer cells to PAR-2–mediated activation of ECs. The identified pathway may constitute an interesting target for the development of additional strategies to treat aggressive brain tumors.

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We isolated a tumor B-cell-targeting antibody, BI-505, from a highly diversified human phage-antibody library, using a pioneering "function-first" approach involving screening for (1) specificity for a tumor B cell surface receptor, (2) induction of tumor programmed cell death, and (3) enhanced in vivo antitumor activity compared to currently used treatments. BI-505 bound to intercellular adhesion molecule-1, identifying a previously unrecognized role for this receptor as a therapeutic target in cancer. The BI-505 epitope was strongly expressed on the surface of multiple myeloma cells from both newly diagnosed and relapsed patients. BI-505 had potent macrophage-dependent antimyeloma activity and conferred enhanced survival compared to currently used treatments in advanced experimental models of multiple myeloma.

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ID (inhibitor of differentiation/DNA binding) proteins, frequently deregulated in advanced human malignancies, can participate in multiple fundamental traits of cancer, such as block of differentiation, increased proliferation, tissue invasiveness, and angiogenesis. We have previously demonstrated that hypoxia decreases expression of neuronal marker genes in neuroblastoma, but induces genes expressed in the neural crest, such as ID2. Because of its involvement in normal neural crest development and its ability to inhibit proneuronal bHLH proteins, the hypoxic induction of ID2 was of particular interest. Here we report fast induction kinetics of ID2 expression in hypoxic neuroblastoma cells. The up-regulation of ID2 was abolished by addition of actinomycin D, implicating a hypoxia-driven transcriptional mechanism. Analyzing the ID2 promoter revealed several potential binding sites for hypoxia-inducible factors. Subsequent electrophoretic mobility shift and chromatin immunoprecipitation assays demonstrated two functional HIF-1 binding sites within ID2 gene regulatory sequences located at ؊725 and ؊1893 relative to the transcriptional initiation point. In transfection assays, DNA constructs of the ID2 promoter, including the functional HIF-1 binding sites, induced luciferase reporter activity in a HIF-1-specific manner. These observations demonstrate that ID2 is actively engaged by hypoxia and represents a novel HIF-1 target. Hypoxiainduced ID2 expression could play a significant role in the previously observed dedifferentiation of hypoxic neuroblastoma cells, which in a clinical setting could lead to less mature and more aggressive tumors.In solid tumors the supply of oxygen and nutrients to some areas is often deprived because of a high rate of cellular proliferation that outpaces the rate of angiogenesis, and structurally abnormal vascularization leading to inadequate intratumoral blood circulation (1). In the resulting hypoxic microenvironment, cancer cells undergo adaptive changes that allow them to survive and even proliferate under hypoxic conditions (2). Mammalian cells, including cancer cells, adapt to hypoxia primarily through a transcriptional response pathway mediated by the hypoxia-inducible factors HIF 1 -1 and HIF-2, which consist of an ␣-subunit (HIF-1␣ or HIF-2␣) and the constitutively expressed transcription factor ARNT/HIF-1␤ (3). At normoxia the ␣-subunit is hydroxylated at critical proline residues by Fe(II)-and O 2 -dependent prolyl hydroxylases (4, 5) and proteasomally degraded via interaction with the von Hippel-Lindau tumor suppressor protein, pVHL (6, 7). In addition to regulation of stability, hydroxylation of an asparagine residue within the ␣-subunit negatively interferes with the function of the transactivation region of HIF under normoxic conditions (8). Hypoxia abrogates both proline and asparagine hydroxylation (4, 8), leading to stable and functional HIFs that can bind regulatory HIF binding sites (HBSs) of target genes involved in maintaining homeostasis, for instance erythropoiet...

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