van Leeuwen J P, Pols H A, Schilte J P, Visser T J, Birkenhäger J C
Department of Internal Medicine III, Erasmus University Medical School, Rotterdam, The Netherlands.
Calcif Tissue Int. 1991 Jul;49(1):35-42. doi: 10.1007/BF02555900.
The effects of epidermal growth factor (EGF) on basal 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) receptor level and on parathyroid hormone (PTH)-induced 1,25-(OH)2D3 receptor up-regulation were studied in the phenotypically osteoblastic cell line UMR 106. EGF in concentrations exceeding 0.1 ng/ml reduced the number of 1,25(OH)2D3 binding sites without changing the binding affinity. Maximal reduction was 30% at about 1 ng/ml. This reduction was independent of a change in cAMP content. EGF dose-dependently attenuated both PTH-induced 1,25(OH)2D3 receptor up-regulation and PTH-stimulated cAMP production, without an effect on the ED50 of the PTH effects. For both PTH responses the IC50 and the maximal effective dose were similar, 0.1 ng/ml and 1 ng/ml EGF, respectively. Reduction was first seen at 0.01 ng/ml EGF. At this concentration, EGF reduced PTH-stimulated 1,25-(OH)2D3 receptor binding without an inhibition of the cAMP response. Time-course studies with 1 ng/ml EGF revealed that at 2 h preincubation EGF reduced the heterologous up-regulation by PTH, and maximal inhibition was seen after 4 h. In contrast, PTH-stimulated cAMP production was just significantly inhibited only after 6 h, with 60% inhibition after 24 h preincubation. The effects of prostaglandin E2 and forskolin on both 1,25(OH)2D3 binding and cAMP production were inhibited in a similar fashion. On the other hand, dibutyryl cAMP- and 3-isobutyl-1-methylxanthine-stimulated 1,25(OH)2D3 binding were not affected by EGF. Taken together, our results demonstrate that EGF reduces both the basal number of 1,25(OH)2D3 binding sites and the heterologous up-regulation of the 1,25(OH)2D3 receptor. The current data suggest that EGF reduces heterologous up-regulation of the 1,25(OH)2D3 receptor independent of as well as dependent on the cAMP messenger system. The EGF effect is nor primarily located at the PTH receptor, at cAMP phosphodiesterase, or at protein kinase A level.
在表型成骨细胞系UMR 106中，研究了表皮生长因子（EGF）对基础1,25 - 二羟基维生素D3（1,25-(OH)2D3）受体水平以及甲状旁腺激素（PTH）诱导的1,25-(OH)2D3受体上调的影响。浓度超过0.1 ng/ml的EGF可减少1,25(OH)2D3结合位点的数量，但不改变结合亲和力。在约1 ng/ml时最大减少量为30%。这种减少与cAMP含量的变化无关。EGF剂量依赖性地减弱PTH诱导的1,25(OH)2D3受体上调和PTH刺激的cAMP产生，而对PTH效应的半数有效剂量（ED50）没有影响。对于PTH的两种反应，半数抑制浓度（IC50）和最大有效剂量相似，分别为0.1 ng/ml和1 ng/ml EGF。在0.01 ng/ml EGF时首次观察到减少。在此浓度下，EGF降低PTH刺激的1,25-(OH)2D3受体结合，但不抑制cAMP反应。用1 ng/ml EGF进行的时间进程研究表明，预孵育2小时时，EGF降低了PTH的异源上调，4小时后观察到最大抑制。相比之下，PTH刺激的cAMP产生仅在6小时后才被显著抑制，预孵育24小时后抑制率为60%。前列腺素E2和福斯可林对1,25(OH)2D3结合和cAMP产生的影响以类似方式被抑制。另一方面，二丁酰cAMP和3 - 异丁基 - 1 - 甲基黄嘌呤刺激的1,25(OH)2D3结合不受EGF影响。综上所述，我们的结果表明，EGF降低了1,25(OH)2D3结合位点的基础数量以及1,25(OH)2D3受体的异源上调。目前的数据表明，EGF降低1,25(OH)2D3受体的异源上调既不依赖于也依赖于cAMP信使系统。EGF的作用主要不在PTH受体、cAMP磷酸二酯酶或蛋白激酶A水平。
