The role of intracellular calcium in the cellular response to ionizing radiation.
Calcium is required as a cofactor by primer recognition proteins involved in DNA synthesis and by protein kinase C (PKC), which is activated by ionizing radiation. Because these processes may be involved in radiation-mediated regulation of the progression of cells through the phases of the cell cycle, we studied the effects of the intracellular Ca2+ chelator, acetoxymethyl-1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (AM-BAPTA), on PKC activation, expression of c-jun and Gadd45 and distribution of cells in the phases of the cell cycle after irradiation. AM-BAPTA prevented ionizing-radiation-induced activation of PKC and expression of c-jun in cells of human tumor cell lines. Conversely, calcium chelation had no effect on X-ray-induced expression of the Gadd45 gene. To determine whether changes in the intracellular Ca2+ concentration ([Ca2+]i) occurred during irradiation, we measured [Ca2+]i in single cells using fura-2-based microfluorimetry. There was no increase in [Ca2+]i during or after irradiation of cells of the human tumor cell lines RIT-3, SQ-20B or HL-60 or normal human fibroblast strain IMR-90. The percentage of human tumor cells crossing the G1/S-phase border was reduced by pretreatment with AM-BAPTA. These data indicate that calcium is required for ionizing radiation-induced cell cycle regulation and PKC activation, but that increases in [Ca2+]i do not occur in cells of the cell lines irradiated in this study.
Hallahan
D E
DE
Department of Radiation and Cellular Oncology, University of Chicago, IL 60637.
Bleakman
D
D
Virudachalam
S
S
Lee
D
D
Grdina
D
D
Kufe
D W
DW
Weichselbaum
R R
RR
D000595:Amino Acid Sequence; D002118:Calcium / Q000502:physiology*; D002453:Cell Cycle / Q000187:drug effects / Q000528:radiation effects*; D002470:Cell Survival / Q000528:radiation effects; D002614:Chelating Agents; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004789:Enzyme Activation / Q000528:radiation effects; D005720:Gamma Rays; D006801:Humans; D066298:In Vitro Techniques; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D011493:Protein Kinase C / Q000502:physiology; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism; D011839:Radiation, Ionizing; D014407:Tumor Cells, Cultured; D014965:X-Rays
D002614:Chelating Agents; D010455:Peptides; D016755:Proto-Oncogene Proteins c-jun; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D004533:Egtazic Acid; D011493:Protein Kinase C; D002118:Calcium