¹Laboratory Molecular Genetics of Hematology, Graduate School of Health Sciences, Tokyo Medical and Dental University, Tokyo, Japan

Correspondence: Dr T Koyama, MD, PhD, Graduate School of Health Sciences, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8519, Japan. E-mail: koyama.lmg@tmd.ac.jp

Received 15 December 2006; Revised 30 January 2007; Accepted 2 February 2007; Published online 2 April 2007.

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 1,25-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-B (NF-B), 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-B, 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-B in the nucleus without affecting phosphorylation of the NF-B 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-B 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.