title: Binding of heat shock protein 70 to extracellular phosphatidylserine promotes killing of normoxic and hypoxic tumor cells.
abstract: Hypoxia is well known to limit curability of tumors by ionizing radiation. Here, we show that hypoxia treatment of tumor cells causes coexpression of heat shock protein 70 (Hsp70) and phosphatidylserine (PS) on the cell surface. Colocalization of Hsp70 and PS, as determined by confocal microscopy, also occurs when exogenous FITC-labeled Hsp70 protein is added to normoxic and hypoxic tumor cells. Moreover, the interaction of Hsp70 with PS was demonstrated in artificial unilamellar phosphatidylcholine/ phosphatidylserine (PC/PS) liposomes at the physiological ratio of 8/2. Indeed, the Hsp70-liposome interaction gradually increased with elevating PS molar ratios (8/2 > or = 7/3 < 5/5 < 4/6 < 3/7 < 2/8). In contrast, only a weak Hsp70 interaction was detected in phosphatidylcholine/phosphatidylglycerol (PC/PG) liposomes, thus demonstrating that the interaction was not a charge-related effect. The interaction of Hsp70 with surface PS significantly reduces clonogenic cell survival in normoxic (EC(50) of Hsp70=85 microg/ml) and hypoxic (EC(50) of Hsp70=55 microg/ml) tumor cells. The radiation-induced tumor cell killing was significantly enhanced by the addition of Hsp70 protein (50 microg/ml). Since apoptosis was not significantly enhanced in normoxic and hypoxic tumor cells by the addition of Hsp70, we hypothesize that the Hsp70 protein-induced reduction in clonogenic cell survival might be through necrosis rather than apoptosis.
authors.affiliation: Department of Radiation Oncology, Klinikum rechts der Isar, Technische Universität München, Ismaningerstrasse 22, 81675 Munich, Germany.
authors.forename: Daniela
authors.initials: D
authors.lastname: Schilling
authors.forename: Mathias
authors.initials: M
authors.lastname: Gehrmann
authors.forename: Claudia
authors.initials: C
authors.lastname: Steinem
authors.forename: Antonio
authors.initials: A
authors.lastname: De Maio
authors.forename: Alan G
authors.initials: AG
authors.lastname: Pockley
authors.forename: Michael
authors.initials: M
authors.lastname: Abend
authors.forename: Michael
authors.initials: M
authors.lastname: Molls
authors.forename: Gabriele
authors.initials: G
authors.lastname: Multhoff
mesh_terms: D017209:Apoptosis; D016923:Cell Death / Q000502:physiology* / Q000528:radiation effects; D015687:Cell Hypoxia / Q000502:physiology*; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D005110:Extracellular Space / Q000378:metabolism; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D054709:Lecithins / Q000378:metabolism; D009336:Necrosis; D009369:Neoplasms / Q000378:metabolism* / Q000473:pathology* / Q000532:radiotherapy; D010718:Phosphatidylserines / Q000378:metabolism*; D011485:Protein Binding
chemical_list: D018840:HSP70 Heat-Shock Proteins; D054709:Lecithins; D010718:Phosphatidylserines