Suppression of hypoxia-induced HIF-1alpha and of angiogenesis in endothelial cells by myo-inositol trispyrophosphate-treated erythrocytes.
Allosteric regulation of oxygen delivery by RBCs may have significant effects on tumor growth. Indeed, angiogenesis, the formation of new blood vessels, is induced in growing tumors by low oxygen partial pressure. Hypoxia-inducible genes are switched on, among which are the VEGF gene and its receptors. Most important, under hypoxia, hypoxia-inducible factor 1alpha has a significantly prolonged half-life and up-regulates a number of hypoxia genes. Human microvascular endothelial cells (MECs), when subjected in vitro to hypoxia, align to form vessel-like structures as in the angiogenic process. We report here that, when cultured in hypoxic conditions in the presence of human RBCs loaded with a new membrane-permeant allosteric effector of Hb, myo-inositol trispyrophosphate (ITPP), endothelial cells (ECs) do not align, i.e., do not form "vessel"-like structures, because the "loaded" RBCs are capable of releasing under hypoxia more oxygen than their "normal" counterparts. Levels of VEGF and of hypoxia-inducible factor 1alpha, elevated in the human MECs under hypoxia, were dramatically reduced or even suppressed in the presence of the ITPP-loaded RBCs. Treatment of these ECs directly with free ITPP at different concentrations had no effect on their ability to undertake angiogenesis. Incubation with ITPP enhances the capacity of Hb to release bound oxygen, leading to higher oxygen tension in the hypoxic environment, thus inhibiting hypoxia-induced angiogenesis. These observations are suggestive of a potential in vivo role of ITPP-loaded, "low-O2-affinity" RBCs in cancer therapy.
Kieda
Claudine
C
Centre de Biophysique Moléculaire, Centre National de la Recherche Scientifique, Unité Propre de Recherche 4301, 45045 Orléans, France.
Greferath
Ruth
R
Crola da Silva
Claire
C
Fylaktakidou
Konstantina C
KC
Lehn
Jean-Marie
JM
Nicolau
Claude
C
D000494:Allosteric Regulation; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000166:cytology / Q000502:physiology*; D004912:Erythrocytes / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D000860:Hypoxia; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism*; D007295:Inositol Phosphates / Q000494:pharmacology*; D018919:Neovascularization, Physiologic; D010100:Oxygen / Q000378:metabolism; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism
C497442:HIF1A protein, human; D006454:Hemoglobins; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D007295:Inositol Phosphates; D042461:Vascular Endothelial Growth Factor A; C516441:inositol trispyrophosphate; D010100:Oxygen