Differences in radiosensitivity of the respiratory burst generated in HL-60 cells via different signal transduction pathways.

Induced differentiation of the promyelocytic leukaemia cell line, HL-60, is associated with the acquisition of functional properties, like the expression of specific receptors and the competence to exert the respiratory burst (RB). In this system we evaluated the effects of ionizing radiation on the signal transduction processes involved in the activation of the respiratory burst/NADPH oxidase. HL-60 cells were X-irradiated with up to 1 Gy and induced towards granulocytic differentiation by treatment with 1.25% DMSO on day 0. The expression of the formyl peptide receptor (FPR), the development of responsiveness of the cells 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 ligands and dihydrorhodamine 123 (DHR 123) as an indicator of RB activity, respectively, the acquisition of functional responsiveness to both stimuli was determined. Immature FPR were identified at day 2 after induction which responded to the agonist from day 3 on. F-MLP receptor-mediated RB oxidase activation was completely radioresistant to 1 Gy, while protein kinase C (PKC)-stimulated triggering of the enzyme via PMA was inhibited by about 50% by 0.5 and 1.0 Gy. We conclude that different signal transduction pathways as triggered by f-MLP and PMA respectively exhibit differences in radiosensitivity, with PKC subspecies and downstream responses being possible sites of radiation damage.