INTERFERON ENHANCES TUMOR NECROSIS FACTOR-INDUCED VASCULAR CELL-ADHESION MOLECULE-1 (CD106) EXPRESSION IN HUMAN ENDOTHELIAL-CELLS BY AN INTERFERON-RELATED FACTOR 1-DEPENDENT PATHWAY

Tumor necrosis factor (TNF) and interleukin 1 are known to initiate en dothelial vascular cell adhesion molecule (VCAM)-1 transcription prima rily by activating nuclear factor (NF)-kappa B, which translocates to the nucleus. In addition to two NF-kappa B elements found within the m inimal cytokine-inducible VCAM-1 promoter, an interferon-related facto r (IRF) element (IRF-1) has been identified close to the transcription initiation site, suggesting that cytokines that induce IRF-1 might af fect VCAM-1 expression levels. We therefore investigated the effects o f interferons (IFNs), which strongly induce IRF-1, on VCAM-1 transcrip tion and expression. We show that IFN-alpha and -gamma enhance TNF-ind uced VCAM-1 mRNA transcription and protein expression in human endothe lial cells. IFN enhancement of TNF-induced expression is also seen usi ng chloramphenicol acetyl transferase reporter genes linked to the min imal cytokine inducible VCAM-1 promoter. Nuclear IRF-1 is the molecula r basis of IFN enhancement, because (a) IFN plus TNF-treated cells dis played increased nuclear IRF-1 levels and increased IRF-1 binding to t he VCAM-1 promoter, compared with cells treated with TNF alone; (b) ki netics of nuclear IRF-1 levels correlated with VCAM-1 mRNA levels; (c) transfection with an IRF-1 construct substituted for IFN treatment; a nd (d) transfection with an expression construct encoding IRF-2, a com petitive inhibitor of IRF-1, reduced TNF-induced VCAM-1 expression. Ou r experiments show that IFN amplifies TNF-induced VCAM-1 expression at the transcriptional level by an IRF-1-dependent pathway.