Genomic actions of 1,25-dihydroxyvitamin D3.
Recent studies have identified a heterodimer of the vitamin D receptor (VDR) and the retinoid X receptor (RXR) as the active complex for mediating positive transcriptional effects of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], the active hormonal form of vitamin D. The VDR-RXR heterodimer has been shown to bind to direct repeat vitamin D-responsive elements (VDREs) upstream of positively controlled genes in the target tissues for vitamin D, including bone (osteocalcin, osteopontin, and beta 3 integrin), kidney (24-hydroxylase) and intestine (calbindin). Residues that participate in heterodimer formation have been identified in the C-terminal hormone-binding domain by analysis of VDR mutants. The role of the 1,25(OH)2D3 ligand in transcriptional activation by the VDR-RXR heterodimer is not entirely clear, but studies of two natural VDR mutants suggest that the binding of both hormone and RXR are required to induce a receptor conformation that is competent to activate transcription. A final level of complexity is added by recent observations that VDR is modified by phosphorylation. Thus, the VDR-mediated action of 1,25(OH)2D3 is now known to involve multiple factors that may provide a conceptual basis for future understanding of the tissue-specific genomic effects of 1,25(OH)2D3.
Whitfield
G K
GK
Department of Biochemistry, University of Arizona College of Medicine, Tucson 85724, USA.
Hsieh
J C
JC
Jurutka
P W
PW
Selznick
S H
SH
Haussler
C A
CA
MacDonald
P N
PN
Haussler
M R
MR
D000818:Animals; D001483:Base Sequence; D002117:Calcitriol / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D018167:Receptors, Calcitriol / Q000378:metabolism*; D018168:Receptors, Retinoic Acid / Q000378:metabolism*; D047488:Retinoid X Receptors; D014157:Transcription Factors / Q000378:metabolism*; D015533:Transcriptional Activation / Q000187:drug effects; D014801:Vitamin A / Q000378:metabolism
D018167:Receptors, Calcitriol; D018168:Receptors, Retinoic Acid; D047488:Retinoid X Receptors; D014157:Transcription Factors; D014801:Vitamin A; D002117:Calcitriol