Niimi S, Hayakawa T, Tanaka A
Division of Biological Chemistry and Biologicals, National Institute of Hygienic Sciences, Tokyo, Japan.
Endocrinology. 1990 Aug;127(2):688-94. doi: 10.1210/endo-127-2-688.
The hormonal regulation of GH receptors was studied by measuring specific binding of [125I]human GH to primary cultured rat hepatocytes. The binding of labeled GH to primary cultured hepatocytes decreased during culture, but addition of dexamethasone (100 nM) compensated for this decrease and even increased GH binding. After addition of dexamethasone, the binding increased to a maximum after 10 h, and after 24 h was about 6 times that of control cells. Glucagon (100 nM) did not have any significant effect on GH binding by itself, but enhanced the increased binding caused by dexamethasone about 1.5-fold. For this effect, glucagon could be replaced by (Bu)2cAMP. Insulin (10 nM) and epidermal growth factor (20 ng/ml) reduced the increase by dexamethasone plus glucagon by about half. Scatchard plot analysis showed that the changes of GH binding induced by various hormones were due to changes in the number of binding sites without significant changes in their affinity. The GH bound to dexamethasone or dexamethasone plus glucagon-treated cells was not replaced by unlabeled ovine PRL. This strongly suggests that the number of somatogenic (GH) receptors may be subject to hormonal regulation: dexamethasone alone or with glucagon may induce GH receptors, whereas insulin and EGF may suppress the induction of GH receptors. These patterns of hormonal regulations were almost the same as those of proteins whose expressions were known to be differentiated functions of liver. On the other hand, the increase of GH binding by dexamethasone was inhibited by cycloheximide and actinomycin D, though the GH binding was inhibited by cycloheximide, but not by actinomycin D in the cells cultured without dexamethasone. This result suggests that the increased binding induced by dexamethasone is dependent on the synthesis of new protein and is probably regulated at a pretranslational level.
通过测量[125I]人生长激素（GH）与原代培养大鼠肝细胞的特异性结合，研究了GH受体的激素调节。在培养过程中，标记的GH与原代培养肝细胞的结合减少，但添加地塞米松（100 nM）可补偿这种减少，甚至增加GH结合。添加地塞米松后，结合在10小时后增加到最大值，24小时后约为对照细胞的6倍。胰高血糖素（100 nM）本身对GH结合没有任何显著影响，但可使地塞米松引起的结合增加约1.5倍。对于这种作用，胰高血糖素可用（Bu）2cAMP替代。胰岛素（10 nM）和表皮生长因子（20 ng/ml）使地塞米松加胰高血糖素引起的增加减少约一半。Scatchard作图分析表明，各种激素诱导的GH结合变化是由于结合位点数量的变化，而其亲和力没有显著变化。与地塞米松或地塞米松加胰高血糖素处理细胞结合的GH不能被未标记的羊催乳素（PRL）取代。这强烈表明，促生长（GH）受体的数量可能受激素调节：单独的地塞米松或与胰高血糖素一起可能诱导GH受体，而胰岛素和表皮生长因子可能抑制GH受体的诱导。这些激素调节模式与已知为肝脏分化功能的蛋白质的调节模式几乎相同。另一方面，地塞米松引起的GH结合增加受到环己酰亚胺和放线菌素D的抑制，尽管在无地塞米松培养的细胞中，GH结合受到环己酰亚胺抑制，但不受放线菌素D抑制。该结果表明，地塞米松诱导的结合增加依赖于新蛋白质的合成，并且可能在翻译前水平受到调节。
