Binding of heat shock protein 70 to extracellular phosphatidylserine promotes killing of normoxic and hypoxic tumor cells.
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.
Schilling
Daniela
D
Department of Radiation Oncology, Klinikum rechts der Isar, Technische Universität München, Ismaningerstrasse 22, 81675 Munich, Germany.
Gehrmann
Mathias
M
Steinem
Claudia
C
De Maio
Antonio
A
Pockley
Alan G
AG
Abend
Michael
M
Molls
Michael
M
Multhoff
Gabriele
G
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
D018840:HSP70 Heat-Shock Proteins; D054709:Lecithins; D010718:Phosphatidylserines