title: Enhancement of radiation-induced apoptosis by 6-formylpterin.
abstract: Radiation-induced apoptosis and its possible enhancement in the presence of 6-formylpterin (6-FP), a metabolite of folic acid, were examined in human myelomonocytic lymphoma U937 cells. When cells were treated with 6-FP at a nontoxic concentration of 300 microM, and then exposed to X-rays at a dose of 10 Gy, significant enhancement of radiation-induced apoptosis as determined by nuclear morphological change, phosphatidylserine (PS) externalization and DNA fragmentation were observed. Flow cytometry for the detection of intracellular hydrogen peroxide (H2O2) revealed that 6-FP increased the formation of intracellular H2O2, which further increased when the cells were irradiated. Decrease of mitochondria trans-membrane potential (MMP), release of cytochrome c from mitochondria, and activation of caspase-3 were enhanced after the combined treatment. Remarkable activation of protein kinase C delta (PKC delta) and its translocation from cytosol to mitochondria were detected in combined treatment. Increase of intracellular Ca2+ concentrations ([Ca2+]i) was also observed, however, neither calpain I nor calpain II could inhibit the apoptosis. In addition, c-Jun NH2-terminal kinase (JNK) activation was not enhanced in the combined treatment. A protein involved in a caspase-independent apoptosis pathway, apoptosis inducing factor (AIF), remained unchanged even 3 h after treatment. These results indicate that intracellular H2O2 generated by 6-FP enhances radiation-induced apoptosis via the mitochondria-mediated caspase-dependent pathway, with the active involvement of PKC delta.
authors.affiliation: Department of Radiological Sciences, Faculty of Medicine, Toyama Medical and Pharmaceutical University, 2630 Sugitani, Toyama 930-0194, Japan.
authors.forename: Zheng-Guo
authors.initials: ZG
authors.lastname: Cui
authors.forename: Takashi
authors.initials: T
authors.lastname: Kondo
authors.forename: Ryohei
authors.initials: R
authors.lastname: Ogawa
authors.forename: Loreto B
authors.initials: LB
authors.lastname: Feril
authors.forename: Qing-Li
authors.initials: QL
authors.lastname: Zhao
authors.forename: Shigehito
authors.initials: S
authors.lastname: Wada
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Arai
authors.forename: Keisuke
authors.initials: K
authors.lastname: Makino
mesh_terms: D017209:Apoptosis; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D020169:Caspases / Q000378:metabolism; D045304:Cytochromes c / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D053938:DNA Fragmentation; D004307:Dose-Response Relationship, Radiation; D004789:Enzyme Activation; D005434:Flow Cytometry; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D048031:JNK Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D008564:Membrane Potentials; D008928:Mitochondria / Q000378:metabolism; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D008954:Models, Biological; D010100:Oxygen / Q000378:metabolism; D010718:Phosphatidylserines / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism; D021381:Protein Transport; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D011622:Pterins / Q000494:pharmacology*; D017382:Reactive Oxygen Species; D020298:U937 Cells; D019014:fas Receptor / Q000096:biosynthesis
chemical_list: D010718:Phosphatidylserines; D019253:Proto-Oncogene Proteins c-bcl-2; D011622:Pterins; D017382:Reactive Oxygen Species; D019014:fas Receptor; C005926:2-amino-4-hydroxy-6-formylpteridine; D045304:Cytochromes c; D006861:Hydrogen Peroxide; D011493:Protein Kinase C; D048031:JNK Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D020929:Mitogen-Activated Protein Kinase Kinases; D020169:Caspases; D010100:Oxygen; D002118:Calcium