title: Granulocyte-macrophage colony-stimulating factor rescues TF-1 leukemia cells from ionizing radiation-induced apoptosis through a pathway mediated by protein kinase Calpha.
abstract: Protein kinase C (PKC) activity has a recognized role in mediating apoptosis. However, the role of individual PKC isoforms in apoptosis is poorly defined. Therefore, we investigated the translocation of individual PKC isoforms during radiation-induced apoptosis with and without rescue from apoptosis by granulocyte-macrophage colony-stimulating factor (GM-CSF) in the human erythroleukemia cell line TF-1. PKCalpha was translocated from the particulate to cytosolic fraction of TF-1 cells within 5 minutes of treatment with apoptosis-inducing levels of ionizing radiation. However, this postirradiation translocation did not occur when cells were rescued from apoptosis by GM-CSF. Furthermore, treatment of cells with Gö 6976, an inhibitor of classical PKC isoforms, abrogated the rescue effect of GM-CSF. The calcium-independent novel PKC isoform, PKCalpha appeared to be degraded in both the particulate and cytosolic fractions of TF-1 cells after treatment with apoptosis-inducing levels of ionizing radiation in either the presence or absence of GM-CSF rescue. Levels of ceramide, a lipid mediator of apoptosis, were measured at 2, 4, 8, 10, and 60 minutes after treatment with ionizing radiation and were substantially reduced in TF-1 cells rescued from apoptosis by GM-CSF compared with apoptotic TF-1 cells. The largest decrease in ceramide production seen was at 4 minutes postirradiation, with a 46% reduction in ceramide levels in TF-1 cells rescued from apoptosis by GM-CSF compared with those in apoptotic TF-1 cells. Because ceramide has been shown to affect PKCalpha subcellular distribution, these data implicate a role for ceramide in mediating the rapid postirradiation translocation and inhibition of PKCalpha in TF-1 cells not rescued from apoptosis by GM-CSF. Expression of the antiapoptotic protein Bcl-2 doubled in TF-1 cells rescued from apoptosis by GM-CSF, but did not increase in unrescued cells. Our findings suggest that activated PKCalpha and increased expression of Bcl-2 after gamma irradiation determine survival in TF-1 cells rescued from apoptosis with GM-CSF and that PKCalpha plays a role in mediating signals involved in sensing cellular damage and/or regulation of cell damage repair.
authors.affiliation: Interdisciplinary Program in Molecular and Cellular Biology, Tulane University, New Orleans, LA 70112, USA.
authors.forename: M L
authors.initials: ML
authors.lastname: Kelly
authors.forename: Y
authors.initials: Y
authors.lastname: Tang
authors.forename: N
authors.initials: N
authors.lastname: Rosensweig
authors.forename: S
authors.initials: S
authors.lastname: Clejan
authors.forename: B S
authors.initials: BS
authors.lastname: Beckman
mesh_terms: D017209:Apoptosis / Q000187:drug effects* / Q000528:radiation effects*; D002227:Carbazoles / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016179:Granulocyte Colony-Stimulating Factor / Q000494:pharmacology*; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D007938:Leukemia / Q000473:pathology* / Q000503:physiopathology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects*; D014407:Tumor Cells, Cultured
chemical_list: D002227:Carbazoles; D004791:Enzyme Inhibitors; D007211:Indoles; C081021:Go 6976; D016179:Granulocyte Colony-Stimulating Factor; D011493:Protein Kinase C