Berg J P, Torjesen P A, Haug E
Hormone Laboratory, Aker Hospital, University of Oslo, Norway.
Acta Endocrinol (Copenh). 1991 Nov;125(5):574-80. doi: 10.1530/acta.0.1250574.
The FRTL-5 cell line is widely used as a model for normal thyroid follicular cells. These cells have retained their ability to alter cAMP production, cell proliferation, iodine uptake, and thyroglobulin synthesis in response to thyrotropin. We have previously shown that calcitriol attenuated both basal and TSH stimulated cAMP production dose-dependently in FRTL-5 cells. Cytosol fractions (105,000 g, 60 min, 4 degrees C) prepared from FRTL-5 cell homogenates possessed calcitriol-binding components with a sedimentation coefficient of approximately 3.7 S in high salt (0.3 mol/l KCl) sucrose gradients (5-20%). At 4 degrees C, specific binding increased rapidly during the first 4 h and reached a plateau after 8 h. The specific binding (18 h, 4 degrees C) was maximal at a [3H]calcitriol concentration of approximately 0.5 nmol/l. Scatchard analysis of the binding data indicated one single class of high affinity binding sites with Kd = 105 +/- 2 pmol/l and Bmax = 38.5 +/- 4.7 pmol/g cytosol protein (mean +/- SD, N = 6). In conclusion, our results suggest that the FRTL-5 cells possess functional receptors for calcitriol with the same physicochemical properties as the receptors found in normal rat tissues.
FRTL-5细胞系被广泛用作正常甲状腺滤泡细胞的模型。这些细胞保留了响应促甲状腺激素而改变环磷酸腺苷（cAMP）生成、细胞增殖、碘摄取和甲状腺球蛋白合成的能力。我们之前已经表明，骨化三醇在FRTL-5细胞中剂量依赖性地减弱基础和促甲状腺激素刺激的cAMP生成。从FRTL-5细胞匀浆制备的胞质溶胶组分（105,000 g，60分钟，4℃）在高盐（0.3 mol/l氯化钾）蔗糖梯度（5 - 20%）中具有沉降系数约为3.7 S的骨化三醇结合成分。在4℃下，特异性结合在最初4小时内迅速增加，并在8小时后达到平台期。特异性结合（18小时，4℃）在[3H]骨化三醇浓度约为0.5 nmol/l时最大。结合数据的Scatchard分析表明存在一类单一的高亲和力结合位点，Kd = 105 ± 2 pmol/l，Bmax = 38.5 ± 4.7 pmol/g胞质溶胶蛋白（平均值 ± 标准差，N = 6）。总之，我们的结果表明FRTL-5细胞具有骨化三醇的功能性受体，其理化性质与在正常大鼠组织中发现的受体相同。
