Biology Reference
In-Depth Information
Chapter 27
Differential Regulation of
TauT
by Calcitriol
and Retinoic Acid via VDR/RXR in LLC-PK1
and MCF-7 Cells
Russell W. Chesney and Xiaobin Han
Abstract
The interaction between taurine and the absorption of fat-soluble vitamins,
such as vitamin A and D, has been an interesting topic in the field of nutrition sci-
ence, because taurine-conjugated bile acid optimizes fat and fat-soluble vitamin
absorption. However, whether the hormone calcitriol (1,25-dihydroxyvitamin D
3
) and
retinoic acid regulate the expression of the
TauT
gene is unknown. In this study, we
test the hypothesis that the
TauT
gene is regulated by vitamin D
3
(VD
3
) and retinoic
acid (RA) via activation of the vitamin D receptor (VDR) and retinoic acid recep-
tor (RXR). Taurine uptake, Western blotting, gene reporter assay, and immunohis-
tochemical analysis of TauT, VDR, and RXR were used in VD
3
- and/or RA-treated
LLC-PK1 and MCF-7 cells. We demonstrated that VD
3
alone had little effect on
TauT
expression in both LLC-PK1 and MCF-7 cells. Expression of
TauT
was
significantly increased by RA, which was synergized by the addition of VD
3
after
RXR activation in LLC-PK1 cells. In contrast, expression of
TauT
was signi fi cantly
decreased by the combination of VD
3
and RA in MCF-7 cells. Regulation of
TauT
by VD
3
/RA appears to occur at the transcriptional level, as determined by a reporter
gene assay of the
TauT
promoter. Immunohistochemical study showed that VDR
and RXR were activated by VD
3
and RA, respectively, in both LLC-PK1 and
MCF-7 cells. The activated VDR and RXR also colocated in nuclei of both cells,
suggesting that a VDR/RXR complex is involved in the transcriptional regulation
of
TauT
. Our results show that expression of TauT is differentially regulated by
VD
3
and RA via formation of VDR and RXR complexes in the nuclei in a cell
type-dependent manner.
R. W. Chesney , M.D. (
*
) X. Han , M.D., Ph.D.
Division of Nephrology, Department of Pediatrics ,
University of Tennessee Health Science Center,
Le Bonheur Children's Hospital, Children's Foundation Research Tower,
Rm 476R, 50 North Dunlap,
38103 Memphis , TN , USA
e-mail: rchesney@uthsc.edu ; xhan@uthsc.edu
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