Demonstration of a 1,25-dihydroxyvitamin D3-responsive protein in human lymphocytes: immunologic crossreactivity and inverse regulation with the vitamin D receptor.

Using Western blot analysis with a monoclonal antibody recognizing a 17-amino acid epitope of the 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]receptor, we have detected two crossreacting proteins in activated normal human lymphocytes. The smaller of the two proteins (50 kDa) was indistinguishable from the classical 1,25(OH)2D3 receptor and, similar to the classical 1,25(OH)2D3 receptor, was upregulated in a dose-dependent fashion by 1,25(OH)2D3. The larger crossreacting protein exhibited an electrophoretic mobility of 80 kDa, was localized in the cell cytosol, and appeared to be specific for activated lymphocytes since it was not detected in several other human cells including monocytes. More strikingly, the 80-kDa protein was downregulated in a dose-dependent fashion by 1,25(OH)2D3; this effect was independent of the mode of lymphocyte activation and specific for the 1,25(OH)2D3 metabolite of vitamin D3. However, two potent immunosuppressive agents, glucocorticoids and cyclosporin A, also inhibited the 80-kDa protein. IMAGES:

本研究采用识别1,25-二羟维生素D3[1,25(OH)2D3]受体17个氨基酸表位的单克隆抗体开展蛋白质印迹（Western blot）分析，在活化的正常人淋巴细胞中检测到两种交叉反应蛋白。其中分子量较小的蛋白（50 kDa）与经典1,25(OH)2D3受体无显著差异；且与经典受体类似，其可被1,25(OH)2D3以剂量依赖性方式上调。分子量更大的交叉反应蛋白表观分子量为80 kDa，定位于细胞胞质中，且似乎仅特异性表达于活化淋巴细胞——因在包括单核细胞在内的多种其他人类细胞中均未检测到该蛋白。尤为引人关注的是，该80 kDa蛋白可被1,25(OH)2D3以剂量依赖性方式下调；该效应不受淋巴细胞活化方式的影响，且仅对维生素D3的1,25(OH)2D3代谢产物具有特异性。不过，两种强效免疫抑制剂——糖皮质激素与环孢素A（cyclosporin A）同样可抑制该80 kDa蛋白。图像：