title: Hypoxia triggers a proangiogenic pathway involving cancer cell microvesicles and PAR-2-mediated heparin-binding EGF signaling in endothelial cells.
abstract: 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.
authors.affiliation: Department of Clinical Sciences, Section of Oncology, Lund University, SE-221 85 Lund, Sweden.
authors.forename: Katrin J
authors.initials: KJ
authors.lastname: Svensson
authors.forename: Paulina
authors.initials: P
authors.lastname: Kucharzewska
authors.forename: Helena C
authors.initials: HC
authors.lastname: Christianson
authors.forename: Stefan
authors.initials: S
authors.lastname: Sköld
authors.forename: Tobias
authors.initials: T
authors.lastname: Löfstedt
authors.forename: Maria C
authors.initials: MC
authors.lastname: Johansson
authors.forename: Matthias
authors.initials: M
authors.lastname: Mörgelin
authors.forename: Johan
authors.initials: J
authors.lastname: Bengzon
authors.forename: Wolfram
authors.initials: W
authors.lastname: Ruf
authors.forename: Mattias
authors.initials: M
authors.lastname: Belting
mesh_terms: D015687:Cell Hypoxia; D045744:Cell Line, Tumor; D042783:Endothelial Cells / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology* / Q000648:ultrastructure; D055354:Exosomes / Q000378:metabolism* / Q000648:ultrastructure; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D066257:Heparin-binding EGF-like Growth Factor; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism*; D009389:Neovascularization, Pathologic / Q000378:metabolism* / Q000473:pathology; D021381:Protein Transport; D044464:Receptor, PAR-2 / Q000378:metabolism*; D015398:Signal Transduction; D013925:Thromboplastin / Q000378:metabolism; D014471:Umbilical Veins / Q000166:cytology
chemical_list: C587883:HBEGF protein, human; D066257:Heparin-binding EGF-like Growth Factor; D036341:Intercellular Signaling Peptides and Proteins; D044464:Receptor, PAR-2; D013925:Thromboplastin; D048049:Extracellular Signal-Regulated MAP Kinases