The effect of differentiation on 1,25 dihydroxyvitamin D-mediated gene expression in the enterocyte-like cell line, Caco-2

✍ Scribed by Min Cui; Anna Klopot; Yan Jiang; James C. Fleet

• Publisher: John Wiley and Sons
• Year: 2009
• Tongue: English
• Weight: 247 KB
• Volume: 218
• Category: Article
• ISSN: 0021-9541
• DOI: 10.1002/jcp.21574

✦ Synopsis

Abstract

We examined 1,25 dihydroxyvitamin D (1,25(OH)~2~D~3~)‐induced expression of 25‐hydroxyvitamin D~3~ 24‐hydroxylase (CYP24) and apical calcium channel (TRPV6) mRNA levels in 2‐, 9‐, and 15‐day cultures Caco‐2 cells that model proliferating, post‐proliferative, and differentiated enterocytes. 1,25(OH)~2~D~3~‐induced (10 nM, 8 h) CYP24 and TRPV6 mRNA levels were significantly greater in differentiated and post‐proliferative than proliferating Caco‐2 cells (>16X and >3X, respectively). Neither CYP24 mRNA half‐life nor induction of a −298 bp rat CYP24 promoter‐luciferase reporter construct (10 nM 1,25(OH)~2~D~3~, 24 h) were different between proliferating and post‐proliferating Caco‐2 cells. We next tested whether the blunted response of natural genes to 1,25(OH)~2~D~3~ in proliferating Caco‐2 cells is due to altered chromatin remodeling. VDR and coactivator protein levels do not increase with differentiation but the level of the co‐repressor Alien falls by 50% with differentiation. Over‐expression of Alien reduced 1,25(OH)~2~D~3~‐induced activity of a minimal VDRE containing promoter‐luciferase construct by more than 60% in differentiated Caco‐2 cells while siRNA knockdown of Alien in proliferating Caco‐2 cells increased 1,25(OH)~2~D~3~‐induced CYP24 mRNA level by 40%. These observations suggest that Alien is a regulator of VDR‐mediated gene transcription in Caco‐2 cells. In addition, we found that 1,25(OH)~2~D~3~‐induced association of VDR with chromatin and with the CYP24 promoter was lower in proliferating cells. This suggests that decreased recruitment of VDR to vitamin D response elements also contributes to the blunted transcriptional responsiveness to 1,25(OH)~2~D~3~ in proliferating Caco‐2 cells. J. Cell. Physiol. 218: 113–121, 2009. © 2008 Wiley‐Liss, Inc.