PROTEIN-KINASE-C ACTIVATION IS INVOLVED IN ULTRAVIOLET-B IRRADIATION-INDUCED ENDOTHELIAL-CELL ICAM-1 UP-REGULATION AND LYMPHOCYTE-ENDOTHELIUM INTERACTION IN-VITRO

Lymphocyte-endothelium interactions are pivotal steps in mediating inf lammatory responses. The authors have analysed the influence of ultrav iolet B (UVB) irradiation on intercellular adhesion molecule (ICAM)-1 expression on cells of the human microvascular endothelial cell line ( HMEC)-1 and the intracellular signalling pathways involved. Flow cytom etry revealed dose-dependent ICAM-1 up-regulation with maximum induced expression 24 h after sublethal UVB irradiation of IO mJ/cm(2). While anti-tumour necrosis Factor (TNF)-alpha antibodies or recombinant hum an interleukin (IL)-10 did not influence ellis response, anti-interfer on (IFN)-gamma antibodies blocked the UVB-induced ICAM-1 up-regulation . Significant induction of intracellular/membrane-bound IFN-gamma was measured as early as 6 h post-UVB. Since previous work has shown a dif ferential role of protein kinase C (PKC) in cytokine induced ICAM-1 ex pression, the effect of a selective bisindolylmaleimide-derived PKC-in hibitor (GF109203X) was studied. Ultraviolet B-induced ICAM-1 up-regul ation was effectively blocked by the PKC-inhibitor, whereas a PKA-inhi bitor was ineffective. Moreover, immunofluorescence analysis showed a radiation-induced membrane translocation of PKC-alpha, indicative of e nzyme activation, in HMEC-1 tells already 30 min post-UVB. The functio nal relevance of the UVB-induced ICAM-1 expression and involvement of PKC in this process was demonstrated in an adhesion assay with periphe ral blood mononuclear cells, In conclusion, UVB-induced ICAM-1 express ion on human endothelial cells involves PKC-dependent pathways and can be prevented by a PKC-inhibitor. The use of PKC-inhibitors as additiv e modulators in immune reactions may bear clinical potential. The mech anisms of IFN-gamma induction in endothelial cells by UVB deserve furt her investigation.