Hormones – Cytokines – Signaling
Kidney International (2000) 58, 559–568; doi:10.1046/j.1523-1755.2000.00202.x
Identification of 25-hydroxyvitamin D3 1
-hydroxylase gene expression in macrophages
Toshiaki Monkawa, Tadashi Yoshida, Matsuhiko Hayashi and Takao Saruta
Department of Internal Medicine, School of Medicine, Keio University, Tokyo, Japan
Correspondence: Matsuhiko Hayashi M. D., Department of Internal Medicine, School of Medicine, Keio University, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan. E-mail: matuhiko@mc.med.keio.ac.jp
Received 14 April 1999; Revised 4 February 2000; Accepted 13 March 2000.
Abstract
Identification of 25-hydroxyvitamin D3 1
-hydroxylase gene expression in macrophages.
Background
The 25-hydroxyvitamin D3 1
-hydroxylase (1-hydroxylase) is almost exclusively expressed in the kidney. However, 1-hydroxylase activities have been observed in some extrarenal tissues, including inflammatory cells of the monocyte/macrophage lineage. In sarcoidosis, macrophage 1-hydroxylase causes overproduction of 1,25-(OH)2D3, resulting in hypercalcemia. In this study, we investigated the regulation of macrophage 1-hydroxylase at a molecular level.
Methods
We used the human monocytic cell line THP-1, which can be differentiated into macrophage-like cells by treatment with phorbol ester. The expression of 1-hydroxylase in THP-1 cells was examined by Northern blotting and immunoblotting using an antibody raised against a synthetic peptide corresponding to the 14 C-terminal amino acids of 1-hydroxylase. We investigated the regulation of 1-hydroxylase mRNA expression by RNase protection assay.
Results
Northern blot and immunoblot analyses confirmed the expression of 1-hydroxylase in THP-1 cells at the mRNA and protein levels. Although parathyroid hormone and calcitonin, known stimulators of renal 1-hydroxylase, did not affect the expression of 1-hydroxylase mRNA, 8-Br-cAMP (5 
10-4 mol/L) increased the expression of 1-hydroxylase mRNA in THP-1 cells (198 
9%). 1,25-(OH)2D3, known as a suppressor of renal 1-hydroxylase, did not affect the expression of 1-hydroxylase mRNA. By contrast, 1,25-(OH)2D3 markedly increased the expression of 25-hydroxyvitamin D3 24-hydroxylase mRNA. Interferon-
(2000 IU/mL) increased the expression of 1-hydroxylase mRNA in differentiated THP-1 cells (922 25%).
Conclusions
The present results suggest that 1-hydroxylase activity in macrophages is mediated by the same enzyme as in kidney. Interferon- treatment increases macrophage 1-hydroxylase levels via directly increasing gene expression of this enzyme.
Keywords:
vitamin D3, interferon-, THP-1 cells, RNase protection assay
