Granulocyte-macrophage colony-stimulating factor rescues TF-1 leukemia cells from ionizing radiation-induced apoptosis through a pathway mediated by protein kinase Cα

Protein kinase C (PKC) activity has a recognized role in mediating apoptosis, However, the role of individual PKC isoforms in apoptosis is pearly 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. PKC alpha 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 Go 6976, an inhibitor of classical PKC isoforms, abrogated the rescue effect of GM-CSF. The calcium-independent novel PKC isoform, PKC delta 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 PKC alpha subcellular distribution, these data implicate a role for ceramide in mediating the rapid postirradiation translocation and inhibition of PKC alpha 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 PKC alpha and increased expression of Bcl 2 after gamma irradiation determine survival in TF-1 cells rescued from apoptosis with GM-CSF and that PKC delta plays a role in mediating signals involved in sensing cellular damage and/or regulation of cell damage repair. (C) 1998 by The American Society of Hematology.