DIFFERENCES IN RADIOSENSITIVITY OF THE RESPIRATORY BURST GENERATED INHL-60 CELLS VIA DIFFERENT SIGNAL-TRANSDUCTION PATHWAYS

Induced differentiation of the promyelocytic leukaemia cell line, HL-6 0, is associated with the acquisition of functional properties, like t he expression of specific receptors and the competence to exert the re spiratory burst (RB). In this system we evaluated the effects of ioniz ing radiation on the signal transduction processes involved in the act ivation of the respiratory burst/NADPH oxidase. HL-60 cells were X-irr adiated with up to 1 Gy and induced towards granulocytic differentiati on by treatment with 1.25% DMSO on day 0. The expression of the formyl peptide receptor (FPR), the development of responsiveness of the cell s to its ligand (f-MLP) and to 4 beta-phorbol 12-myristate 13-acetate (PMA) were measured up to day 7 postinduction/irradiation. Using flow cytometry, fluorescinated formyl-hexapeptide or unlabelled f-MLP as li gands and dihydrorhodamine 123 (DHR 123) as an indicator of RB activit y, respectively, the acquisition of functional responsiveness to both stimuli was determined. Immature FPR were identified at day 2 after in duction which responded to the agonist from day 3 on. F-MLP receptor-m ediated RB oxidase activation was completely radioresistant to 1 Gy, w hile protein kinase C (PKC)-stimulated triggering of the enzyme via PM A was inhibited by about 50% by 0.5 and 1.0 Gy. We conclude that diffe rent signal transduction pathways as triggered by f-MLP and PMA respec tively exhibit differences in radiosensitivity, with PRC subspecies an d downstream responses being possible sites of radiation damage.