ABSTRACT
Recent studies have implicated the lipid mediator platelet-activating factor (PAF) in UVB-mediated systemic immunosuppression known to be a major cause for skin cancers. Previously, our group has demonstrated that UVB irradiation triggers the production of PAF and oxidized glycerophosphocholines that act as PAF-receptor (PAF-R) agonists. The present studies explored the mechanisms by which UVB generates PAF-R agonists. UVB irradiation of human epidermal KB cells resulted in both increased levels of reactive oxygen species (ROS) and PAF-R agonistic activity. Pretreatment of KB cells with antioxidants vitamin C and N-acetylcysteine or the pharmacological inhibitor PD168393 specific for the epidermal growth factor receptor all inhibited UVB-induced ROS as well as PAF-R agonists, yet had no effect on fMLP-mediated PAF-R agonist production. In addition, in vivo production of PAF-R agonists from UVB-irradiated mouse skin was blocked by both systemic vitamin C administration and topical PD168393 application. Moreover, both vitamin C and PD168393 abolished UVB-mediated but not the PAF-R agonist 1-hexadecyl-2-N-methylcarbamoyl glycerophosphocholine-mediated immunosuppression as measured by the inhibition of delayed type contact hypersensitivity to the chemical dinitrofluorobenzene. These studies suggest that UVB-induced systemic immunosuppression is due to epidermal growth factor receptor-mediated ROS which results in PAF-R agonist formation.
Subject(s)
ErbB Receptors/physiology , Platelet Activating Factor/metabolism , Platelet Membrane Glycoproteins/agonists , Platelet Membrane Glycoproteins/radiation effects , Reactive Oxygen Species/metabolism , Reactive Oxygen Species/radiation effects , Receptors, G-Protein-Coupled/agonists , Receptors, G-Protein-Coupled/radiation effects , Ultraviolet Rays , Animals , Dermatitis, Contact/etiology , Dermatitis, Contact/immunology , Dermatitis, Contact/metabolism , Epithelial Cells/immunology , Epithelial Cells/metabolism , Epithelial Cells/radiation effects , ErbB Receptors/radiation effects , Humans , Immunosuppression Therapy , KB Cells , Mice , Mice, Hairless , Mice, Inbred C57BL , Platelet Activating Factor/radiation effects , Platelet Membrane Glycoproteins/biosynthesis , Reactive Oxygen Species/pharmacology , Receptors, G-Protein-Coupled/biosynthesis , Skin/immunology , Skin/metabolism , Skin/radiation effectsABSTRACT
UV-C irradiation has been shown to be effective for pathogen reduction in platelet concentrates, but preliminary work indicated that UV-C irradiation of platelets can induce platelet aggregation. In this study, the mechanism underlying this phenomenon was investigated. Irradiation of platelets with UV-C light (1500 J/m(2)) caused platelet aggregation, which was dependent on integrin alphaIIbbeta3 activation (GPIIb/IIIa). This activation occurred despite treatment with several signal transduction inhibitors known to block platelet activation. UV-C also induced activation of recombinant alphaIIbbeta3 in Chinese hamster ovary (CHO) cells, an environment in which physiologic agonists fail to activate. Activation of alphaIIbbeta3 requires talin binding to the beta3 tail, yet alphaIIbbeta3-Delta724 (lacking the talin binding site) was activated by UV-C irradiation, excluding a requirement for talin binding. The UV-C effect appears to be general in that beta(1) and beta(2) integrins are also activated by UV-C. To explain these findings, we investigated the possibility of UV-C-induced photolysis of disulfide bonds, in analogy with the activating effect of reducing agents on integrins. Indeed, UV-C induced a marked increase in free thiol groups in platelet surface proteins including alphaIIbbeta3. Thus, UV-C appears to activate alphaIIbbeta3 not by affecting intracellular signal transduction, but by reduction of disulfide bonds regulating integrin conformation.
