Gacad M A, Adams J S
Burns and Allen Research Institute and Division of Endocrinology and Metabolism, Cedars-Sinai Medical Center, University of California School of Medicine, Los Angeles 90048, USA.
J Clin Endocrinol Metab. 1998 Apr;83(4):1264-7. doi: 10.1210/jcem.83.4.4725.
Most New World primates evolved to express a form of compensated resistance to steroid hormones from the gonads and adrenal glands as well as to the hydroxylated vitamin D3 prohormone, 25-hydroxyvitamin D3 (25OHD3), and the vitamin D hormone 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] originating from the liver and kidney, respectively. We recently demonstrated that this form of resistance is associated with the overexpression of a novel member of the 70-kDa heat shock protein (hsp-70) molecular chaperone family, which we have termed the intracellular vitamin D binding protein (IDBP). In the current report we more closely examine the ligand-binding capability of purified IDBP and two other mammalian hsp-70 family members, heat-inducible (hsp-70) and constitutively expressed (hsc-70) hsp-70 proteins. Purified IDBP, hsp-70, and hsc-70 all bound 25OHD3 with relatively high affinity; the mean Kd for 25OHD3 ranged from 0.5-2.2 nmol/L (rank order: IDBP > or = hsp-70 > or = hsc-70). By Scatchard analysis, high affinity, specific binding of 1,25-(OH)2D3 was not reproducibly observed for any of the three members of the hsp-70 family. Unlike purified IDBP, hsc-70 and hsp-70 were also competent binders of the gonadal steroid 17beta-estradiol (mean Kd for 25OHD3, 2.5 and 6.6 nmol/L by hsc-70 and hsp-70, respectively), but not of two other gonadal hormones, progesterone and testosterone. These data suggest that IDBP is relatively specific for 25OHD3 and that additional hsp-70-like binding proteins are present in unpurified New World primate cell extracts that are specific for 1-hydroxylated vitamin D metabolites as well as other gonadal steroid hormones.
大多数新大陆灵长类动物进化出了一种对性腺和肾上腺分泌的类固醇激素以及对肝脏和肾脏分别产生的羟基化维生素D3前体激素25-羟基维生素D3（25OHD3）和维生素D激素1,25-二羟基维生素D3 [1,25-(OH)2D3]的代偿性抵抗形式。我们最近证明，这种抵抗形式与70-kDa热休克蛋白（hsp-70）分子伴侣家族的一个新成员的过表达有关，我们将其称为细胞内维生素D结合蛋白（IDBP）。在本报告中，我们更深入地研究了纯化的IDBP以及另外两个哺乳动物hsp-70家族成员热诱导型（hsp-70）和组成型表达型（hsc-70）hsp-70蛋白的配体结合能力。纯化的IDBP、hsp-70和hsc-70都以相对较高的亲和力结合25OHD3；25OHD3的平均解离常数（Kd）范围为0.5 - 2.2 nmol/L（排序：IDBP ≥ hsp-70 ≥ hsc-70）。通过Scatchard分析，未在hsp-70家族的这三个成员中的任何一个中可重复观察到1,25-(OH)2D3的高亲和力、特异性结合。与纯化的IDBP不同，hsc-70和hsp-70也是性腺类固醇17β-雌二醇的有效结合蛋白（hsc-70和hsp-70对25OHD3的平均Kd分别为2.5和6.6 nmol/L），但对另外两种性腺激素孕酮和睾酮则无结合能力。这些数据表明，IDBP对25OHD3相对特异，并且在未纯化的新大陆灵长类动物细胞提取物中存在额外的hsp-70样结合蛋白，它们对1-羟基化维生素D代谢物以及其他性腺类固醇激素具有特异性。
