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Molecular and Cellular Biology, November 2007, p. 7947-7954, Vol. 27, No. 22
0270-7306/07/$08.00+0 doi:10.1128/MCB.00813-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

The Institute of Molecular and Cellular Biosciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan,1 ERATO, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan2
Received 9 May 2007/ Returned for modification 11 June 2007/ Accepted 31 August 2007
Vitamin K is a fat-soluble vitamin that serves as a coenzyme for vitamin K-dependent carboxylase. Besides its canonical action, vitamin K binds to the steroid and xenobiotic receptor (SXR)/pregnane X receptor (PXR) and modulates gene transcription. To determine if the osteoprotective action of vitamin K is the result of the PXR/SXR pathway, we screened by two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis the PXR/SXR target genes in an osteoblastic cell line (MC3T3-E1) treated with a vitamin K2 (menaquinone 4 [MK4]). Osteoblastic differentiation of MC3T3-E1 cells was induced by MK4. Msx2, an osteoblastogenic transcription factor, was identified as an MK4-induced gene. Functional analysis of the Msx2 gene promoter mapped a vitamin K-responsive element (PXR-responsive element [PXRE]) that was directly bound by a PXR/retinoid X receptor
heterodimer. In a chromatin immunoprecipitation analysis, PXR was recruited together with a coactivator, p300, to the PXRE in the Msx2 promoter. MK4-bound PXR cooperated with estrogen-bound estrogen receptor
to control transcription at the Msx2 promoter. Knockdown of either PXR or Msx2 attenuated the effect of MK4 on osteoblastic differentiation. Thus, the present study suggests that Msx2 is a target gene for PXR activated by vitamin K and suggests that the osteoprotective action of MK4 in the human mediates, at least in part, a genomic pathway of vitamin K signaling.
Published ahead of print on 17 September 2007.
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