The Effects of Adenosine on Enhanced ICAM-1 Expression by IFN-gamma in Cultured Human Keratinocyte Cell Line HaCaT Cells

Lim, Yeon Soon; Choi, Jee Ho; Sung, Kyung Jeh; Myung, Ki Bum

Abstract

BACKGROUND: Intercellular adhesion molecule(ICAM)-1 mediates cell to cell adhesion by acting as a receptor for leukocyte surface antigen. Increased ICAM-1 expression was observed in chronic inflammatory skin diseases, such as psoriasis, atopic dermatitis and allergic contact dermatitis. Adenosine is an endogenous antiinflammatory agent released by cells under metabolically unfavorable conditions, recently the studies about antiinflammatory effects of adenosine in various tissues were increased, but there are few studies about the effect of adenosine on epidermal keratinocytes.
OBJECTIVE
We investigated the effects of adenosine on ICAM-1 expression in cultured human keratinocyte cell line HaCaT cells.
METHODS
Our study analyses the ICAM-1 expression in HaCaT cells by various stimulants and the effects of adenosine, adenosine receptor agonist&antagonist and an inhibitor of cellular adenosine uptake on ICAM-1 expression of cells stimulated by IFN-gamma through the cell-ELISA (enzyme-linked immunosorbent assay)&FACS (fluorescence-activated cell sorter) analysis.
RESULTS
The results are summerized as follows: 1. ICAM-1 expression was significantly increased by IFN-gamma(500U/ml), IFN-gamma&TNF-alpha(10-8M) and IFN-gamma&LPS(10-8M)(p<0.05), but not by TNF-alpha, LPS and TNF-alpha & LPS. 2. Incubation of HaCaT cells with IFN-gamma(1-2000U/ml) for 48 hours induced dose-dependent expression of ICAM-1 at above 500U/ml of IFN-gamma. 3. Adenosine had no effect on ICAM-1 expression of unstimulated cells. 4. Adenosine(esp. 10-4M) significantly inhibited ICAM-1 expression of cells stimulated by IFN-gamma(p<0.01). 5. Adenosine(10-4M) significantly inhibited ICAM-1 expression of cells stimulated by IFN-gamma(p<0.01), IFN-gamma & TNF-alpha(p<0.05) and IFN-gamma&LPS. 6. The inhibition of ICAM-1 expression was not observed when cells were preincubated with an adenosine A1 receptor agonist(R-PIA) or an adenosine A2 receptor agonist (NECA). 7. The inhibition of ICAM-1 expression of adenosine was not affected by pretreatment state with an adenosine A1 & A2 receptor antagonist(theophylline)(p<0.01). 8. The inhibition of ICAM-1 expression of adenosine was not observed by pretreatment state with an inhibitor of adenosine cellular uptake (dipyridamole). CONCLUSION: High concentration of adenosine inhibits enhanced ICAM-1 expression on HaCaT cells by stimulated with IFN-gamma and these inhibitory effects of adenosine are mediated through other adenosine receptors excect adenosine A1 and A2 receptors. And we suggest that there may be an unknown intracellular mechanism about inhibition of ICAM-1 expression via intracellular-uptaken adenosine.