1,25(OH)2D3 blocks TNF-induced monocytic tissue factor expression by inhibition of transcription factors AP-1 and NF-κB

Abstract

An essential coagulation factor, tissue factor (TF), is rapidly expressed by human monocytes when exposed to a variety of agonists, such as lipopolysaccharide or tumor necrosis factor (TNF). We previously found that 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3) and its potent synthetic analogs downregulate TF and upregulate thrombomodulin expression on monocytic cells, counteracting the effects of TNF at the level of transcription. The human TF gene has characteristic binding sequences for activator protein-1 (AP-1) (c-Jun/c-Fos), nuclear factor-κB (NF-κB), Sp-1, and early growth response factor-1 (Egr-1). In this study, we investigated the regulatory mechanisms by which 1,25(OH)2D3 inhibits TNF-induced TF expression in human monocytic cells. 1,25(OH)2D3 reduced basal and TNF-induced TF activities. Gel-shift assay and luciferase assay with the respective reporter vectors showed that 1,25(OH)2D3 reduced basal and TNF-induced activities of the nuclear proteins AP-1 and NF-κB, but not Egr-1. 1,25(OH)2D3 inhibited TNF-induced phosphorylation of c-Jun without affecting phosphorylation of the other pathways. On the other hand, 1,25(OH)2D3 directly inhibited nuclear binding and activities of NF-κB in the nucleus without affecting phosphorylation of the NF-κB activation pathway. These results indicate that 1,25(OH)2D3 suppresses basal and TNF-induced TF expression in monocytic cells by inhibition of AP-1 and NF-κB activation pathways, but not of Egr-1. Our results may help to elucidate the regulatory mechanisms of 1,25(OH)2D3 in TF induction, and may have physiological significance in the clinical challenge to use potential 1,25(OH)2D3 analogs in antithrombotic therapy as well as immunomodulation and antineoplastic therapy of leukemia.