Mason D R, Arora K K, Mertz L M, Catt K J
Endocrinology and Reproduction Research Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892.
Endocrinology. 1994 Sep;135(3):1165-70. doi: 10.1210/endo.135.3.8070359.
GnRH is known to down-regulate its pituitary receptors by mechanisms that include endocytosis of the agonist-receptor complex. To evaluate the extent to which changes in receptor synthesis contribute to this process, the effects of GnRH and its analogs on GnRH receptor number and messenger RNA (mRNA) levels were analyzed in the alpha T3-1 gonadotroph cell line. Treatment with GnRH or its potent agonist analog, des-Gly10-[D-Ala6]GnRH N-ethylamide, reduced GnRH receptor number in a time- and dose-dependent manner, with a half-maximal decrease in response to 10(-6) M GnRH or agonist analog by 75 min. The maximum decrease in receptor number (to 31% of the control value) was sustained for up to 72 h. In alpha T3-1 cells incubated with 10(-8) M GnRH or agonist analog, the GnRH receptors fell by 28% and 46% after 2 h, respectively; no change in receptors occurred after treatment with 10(-8) M GnRH antagonist ([D-pGlu1,D-Phe2,D-Trp3,6]GnRH). Time- and dose-dependent reductions in the level of receptor mRNA were also observed after treatment of alpha T3-1 cells with GnRH and the agonist analog. However, the maximal reduction in mRNA levels (to 60-70% of the control value) was consistently less than the decline in receptor number. These results indicate that the mechanism of GnRH receptor down-regulation in alpha T3-1 gonadotrophs includes reduction of receptor synthesis secondary to decreases in receptor mRNA levels. The finding that reductions in mRNA levels were relatively less than the decreases in receptor number is consistent with the involvement of additional mechanisms, including endocytosis and degradation, in down-regulation of the GnRH receptor.
已知促性腺激素释放激素（GnRH）通过包括激动剂 - 受体复合物内吞作用在内的机制下调其垂体受体。为了评估受体合成变化对这一过程的影响程度，在αT3 - 1促性腺激素细胞系中分析了GnRH及其类似物对GnRH受体数量和信使核糖核酸（mRNA）水平的影响。用GnRH或其强效激动剂类似物去甘氨酸10 - [D - 丙氨酸6]GnRH N - 乙酰胺处理，以时间和剂量依赖的方式降低了GnRH受体数量，在10(-6) M GnRH或激动剂类似物作用下，75分钟时半数最大降低率出现，受体数量最大降低（降至对照值的31%）可持续长达72小时。在与10(-8) M GnRH或激动剂类似物孵育的αT3 - 1细胞中，2小时后GnRH受体分别下降了28%和46%；用10(-8) M GnRH拮抗剂（[D - 焦谷氨酸1，D - 苯丙氨酸2，D - 色氨酸3，6]GnRH）处理后受体无变化。在用GnRH和激动剂类似物处理αT3 - 1细胞后，也观察到受体mRNA水平的时间和剂量依赖性降低。然而，mRNA水平的最大降低（降至对照值的60 - 70%）始终小于受体数量的下降。这些结果表明，αT3 - 1促性腺激素细胞中GnRH受体下调的机制包括受体mRNA水平降低继发的受体合成减少。mRNA水平降低相对小于受体数量下降这一发现与包括内吞作用和降解在内的其他机制参与GnRH受体下调一致。
