Differential Regulation of TauT by Calcitriol and Retinoic Acid via VDR/RXR in LLC-PK1 and MCF-7 Cells - Advances in Experimental Medicine and Biology - page 277

Fig. 27.1 ( continued )

to LLC-PK1 cells, and the effect was synergized by addition of 1,25(OH) 2 D 3 after
treatment with atRA for 3 days. This synergetic effect was not observed in the cells
treated with 9- cis RA and 1,25(OH) 2 D 3 (Fig. 27.1c ). These observations were
confirmed by enhanced taurine uptake and Western blot analysis in the LLC-PK1
cells treated with 1,25(OH) 2 D 3 with or without RA (Fig. 27.1d, e, f ).

27.3.2 Activation of Retinoic Acid and Vitamin D Receptors

by RA and/or Vitamin D in LLC-PK1 Kidney Cells

To study if RA and/or 1,25(OH) 2 D 3 activate RXR and/or VDR, which in turn regu-
late TauT expression in LLC-PK1 renal cells, we treated the cells with RA and/or
1,25(OH) 2 D 3 as described above. As shown in Fig. 27.2a , LLC-PK1 cells express
both RXR and VDR, which are upregulated by RA and/or 1,25(OH) 2 D 3 . Expression
of TauT was enhanced after activation of RXR or VDR, respectively. Expression of
TauT , RXR, and VDR was further elevated in the cells treated with RA and
1,25(OH) 2 D3 (Fig. 27.2a, b ).
Western blot analysis showed that expression of RXR was increased by RA, and
addition of 1,25(OH) 2 D 3 after 3 days of pretreatment with RA induced expression
of a 35 kDa RXR subunit in LLC-PK1 cells. Addition of 1,25(OH) 2 D 3 alone or
pretreatment of cells with 1,25(OH) 2 D 3 had a slight effect on RXR expression.