Protein kinase inhibitors modulate time-dependent effects of UV and ionizing irradiation on ICAM-1 expression on human hepatoma cells

Purpose: To investigate modulation of the expression of the adhesion protein ICAM-1 by UV and ionizing irradiation. Materials and methods: HepG2 hepatoma cells were irradiated in vitro with UVB (20 mJ cm^-2) or X-rays (5 Gy), respectively. Gene expression of ICAM-1 after irradiation was quantified by RT-PCR. Cell surface density of ICAM-1 was determined by flow cytometry. Protein or lipid kinase inhibitors were used to clarify radiation-induced transducdon pathways that control ICAM-1 expression. Immuno-electron microscopy and dot-blot analysis were used to examine localization of ICAM-1. Results: The study showed time-dependent effects of ionizing and UV irradiation on ICAM-1 expression of HepG2 cells. After an immediate transient decrease of ICAM-1 cell surface expression within minutes to hours, ICAM-1 expression increased up to 1.35-fold over normal level at 48 h post-irradiation. Irradiation caused ICAM-1 to become internalized into lysosomes. Additionally, ICAM-1 together with parts of the cell were pinched off. Finally, ICAM-1 levels were down- and up-regulated by decreased or increased gene expression. The early decrease of ICAM-1 expression could be blocked by a potent PKC inhibitor (BisX), whereas the increase of ICAM-1 after 24 h was prevented by addition of the p38 MAP kinase inhibitor SB 203580. Conclusion: The data suggest that ICAM-1 expression is modulated by UV, as well as ionizing radiation, in a time-dependent way involving PKC and p38 MAP kinase pathways.