In summary, the present research suggests that ambient temperature appeared to affect BP

25(OH)2D3 inhibits ubiquitination and thereby proteasomal degradation of the VDR in the keratinocyte cell line HaCaT [22] and in Cos-1 cells [34]. 1,25(OH)2D3 might inhibit the proteasomal degradation of the VDR by inducing conformational changes of the VDR either directly or by promoting the association between VDR and RXR. Alternatively, 1,25(OH)2D3 might influence the expression of molecules involved in VDR degradation such as SUG1 [71] and CDK11B [72] and thereby affect VDR degradation. Future studies are required to precisely elucidate the mechanisms by which 1,25(OH)2D3 inhibits the proteasomal degradation of the VDR. Finally, we found that in parallel with up-regulation of VDR protein expression, proteasome inhibition leads to enhanced 1,25(OH)2D3-induced gene regulation. This is in good agreement with previous studies that found VDR up-regulation and enhanced sensitivity to 1,25(OH)2D3 following proteasome inhibition in keratinocytes and osteoblasts [22,35]. Whereas most ligands desensitize their receptors, 1,25(OH)2D3 up-regulates its receptor and thereby increases the sensitivity of T cells for 1,25(OH)2D3. Combined with our observation that the � VDR is expressed by all naive T cells independently of the cytokine environment during the early stages of activation this substantiates that 1,25(OH)2D3 can play important roles in the early stages of T cell differentiation if found in sufficiently high local concentrations [38�46,62]. � In conclusion, our study establishes that naive human CD4+ T cells do not express the VDR but that they start to express the VDR following stimulation via the TCR and CD28 independently of the presence of Th1, Th2 and Th17 polarizing PCI-32765 19651432″ title=View Abstract(s)”>PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19651432 cytokines. We further show that activated CD4+ T ce