Nucleic Acids Research, Vol 25, Issue 21 4307-4313, Copyright © 1997 by Oxford University Press
JP Kahlen and C Carlberg
Genomic actions of the hormone 1alpha,25-dihydroxy-vitamin D3(VD) are
mediated by the transcription factor VDR, which is a member of the nuclear
receptor superfamily. VDR acts in most cases as a heterodimeric complex
with the retinoid X receptor (RXR) from specific DNA sequences in the
promoter of VD target genes called VD response elements (VDREs). This study
describes a mutation (K45A) of the VDR DNA binding domain that enhances the
affinity and ligand responsiveness of VDR-RXR heterodimers on some VDREs.
In analogy to a homologous mutation in the glucocorticoid receptor (K461A),
this lysine residue appears to function as an allosteric 'lock'.
Interestingly, overexpression of RXR was found to reduce the responsiveness
and sensitivity of wild type VDR to VD, but enhance the response of
VDRK45A. Moreover, the transactivation domains of both VDR and RXR were
shown to be essential for obtaining responsiveness of the heterodimers to
VD and 9- cis retinoic acid (the RXR ligand). This indicates that RXR is an
active rather than silent partner of the VDR on the VDREs tested. Taken
together, transactivation by VDR-RXR heterodimers can be triggered
individually by all components of the protein-DNA complex, but full potency
appears to be reached through allosteric interaction.
ARTICLES
Allosteric interaction of the 1alpha,25-dihydroxyvitamin D3 receptor and the retinoid X receptor on DNA
Clinique de Dermatologie, Hopital Cantonal Universitaire, CH-1211 Geneve 14, Switzerland and Institut fur Physiologische Chemie I, Heinrich-Heine-Universitat Dusseldorf, D-40001 Dusseldorf, Germany.
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