Normal levels of the vitamin D receptor and its message in psoriatic skin

Treatment with vitamin D3 analogs improves psoriasis. The vitamin D receptor (VDR) mediates most, if not all, the effects of vitamin D3. The purpose of this study was to determine the levels of the VDR mRNA and VDR protein in normal and in involved and uninvolved psoriatic skin. Although VDR mRNA was not detected by Northern analysis of human skin samples, it was readily detectable by use of the more sensitive ribonuclease protection assay. The VDR mRNA levels were normal in acute guttate as well as in chronic plaque lesions. There was also no difference in VDR mRNA levels between normal and uninvolved psoriatic skin. The VDR protein was detected by Western analysis using the monoclonal 9A7 gamma anti-VDR antibody and a polyclonal rabbit anti-VDR antibody. For comparison, VDR levels were analyzed in cultures of normal human keratinocytes and the epithelial cell line MCF-7. Studies of the extraction procedures for VDR showed that at least 60% of Escherichia coli-expressed VDR added to the skin biopsy specimens was recovered. The VDR concentration in normal human adult skin was approximately 50 pg/microgram protein, and the concentrations of VDR in involved and uninvolved psoriatic skin were of the same order of magnitude. Using the 9A7 gamma anti-VDR antibody, the VDR (M(r) 53,000) was constantly present in lower amounts than a band of M(r) 80,000 in both skin specimens and keratinocyte cultures. This high-molecular-weight band is most likely a cross-reacting protein not related to VDR, because it was absent when using the polyclonal anti-VDR antibody.