Induction of heat shock protein 70 protects thymocytes against radiation-induced apoptosis.
OBJECTIVE
To determine if induction of heat shock protein 70 (HSP 70), a stress protein that plays a cytoprotective role and inhibits cell death in response to various stimuli, will protect thymocytes and T-cell clones from radiation-induced apoptosis, and to define the mechanism of such protection.


METHODS
Thymocytes from BALB/c mice or T-lymphocyte clones were incubated at 43 degrees C for 1 hour to induce HSP 70, then irradiated. Control cells were irradiated but not heated. Fragmentation of DNA was quantitated, and p53, bax, and bcl-2 expression was analyzed at various times by the Western blot method.


RESULTS
Only heated cells expressed HSP 70. The induction of HSP 70 increased basal apoptosis but significantly decreased radiation-induced apoptosis. Furthermore, introduction of an HSP 70 antisense oligomer prior to heating reversed the protective effect of HSP 70. Induction of HSP 70 in T-cell clones with sodium arsenite had a similar protective effect against radiation-induced apoptosis. Irradiation induced p53 and markedly up-regulated bax. The expression of p53 peaked at 4 hours and preceded maximal bax induction. Induction of HSP 70 prior to irradiation suppressed p53 and significantly decreased bax levels. Levels of bcl-2 were unaffected.


CONCLUSIONS
Our data show that HSP 70 induction protects thymocytes from radiation-induced apoptosis by down-regulating p53 and bax expression. The induction of HSP 70 may represent a novel mechanism by which the immunosuppressive effects and the associated infectious complications of radiation therapy can be minimized.
Gordon
S A
SA
Department of Surgery, University of Pittsburgh Medical Center, Pa, USA.
Hoffman
R A
RA
Simmons
R L
RL
Ford
H R
HR
D000818:Animals; D016375:Antisense Elements (Genetics); D017209:Apoptosis / Q000502:physiology*; D002453:Cell Cycle / Q000528:radiation effects*; D002478:Cells, Cultured / Q000528:radiation effects; D002999:Clone Cells; D015536:Down-Regulation; D005260:Female; D005720:Gamma Rays; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2; D013601:T-Lymphocytes / Q000502:physiology* / Q000528:radiation effects; D013997:Time Factors; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D051028:bcl-2-Associated X Protein
D016375:Antisense Elements (Genetics); C494827:Bax protein, mouse; D018840:HSP70 Heat-Shock Proteins; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D016159:Tumor Suppressor Protein p53; D051028:bcl-2-Associated X Protein