Role of inducible heat shock protein 70 in radiation-induced cell death.
We previously demonstrated the protective effect of inducible heat shock protein 70 (Hsp70) against gamma radiation. Herein, we extend our studies on the possible role of Hsp70 to ionizing radiation-induced cell cycle regulation. The growth rate of inducible hsp70-transfected cells was 2-3 hours slower than that of control cells. Flow cytometric analysis of cells at G1 phase synchronized by serum starvation also showed the growth delay in the Hsp70-overexpressing cells. In addition, reduced cyclin D1 and Cdc2 levels and increased dephosphorylated phosphoretinoblastoma (pRb) were observed in inducible hsp70-transfected cells, which were probably responsible for the reduction of cell growth. To find out if inducible Hsp70-mediated growth delay affected radiation-induced cell cycle regulation, flow cytometric and molecular analyses of cell cycle regulatory proteins and their kinase were performed. The radiation-induced G2/M arrest was found to be inhibited by Hsp70 overexpression and reduced p21Waf induction and its kinase activity by radiation in the Hsp70-transfected cells. In addition, radiation-induced cyclin A or B1 expressions together with their kinase activities were also inhibited by inducible Hsp70, which represented reduced mitotic cell death. Indeed, hsp70 transfectants showed less induction of radiation-induced apoptosis. When treated with nocodazole, radiation-induced mitotic arrest was inhibited by inducible Hsp70. These results strongly suggested that inducible Hsp70 modified growth delay (increased G1 phase) and reduced G2/M phase arrest, subsequently resulting in inhibition of radiation-induced cell death.
Lee
S J
SJ
Laboratory of Radiation Effect, Korea Cancer Center Hospital, Seoul.
Choi
S A
SA
Lee
K H
KH
Chung
H Y
HY
Kim
T H
TH
Cho
C K
CK
Lee
Y S
YS
D016475:3T3 Cells; D000818:Animals; D017209:Apoptosis / Q000502:physiology / Q000528:radiation effects*; D016203:CDC2 Protein Kinase / Q000378:metabolism; D002453:Cell Cycle / Q000502:physiology / Q000528:radiation effects*; D019925:Cyclin A / Q000378:metabolism; D019926:Cyclin B / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000235:genetics / Q000378:metabolism; D005434:Flow Cytometry; D005720:Gamma Rays; D005786:Gene Expression Regulation / Q000502:physiology; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism*; D015151:Immunoblotting; D051379:Mice; D011233:Precipitin Tests; D015398:Signal Transduction / Q000502:physiology; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism
C493957:Cdkn1a protein, mouse; D019925:Cyclin A; D019926:Cyclin B; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D018840:HSP70 Heat-Shock Proteins; D016159:Tumor Suppressor Protein p53; D016203:CDC2 Protein Kinase