Ford K A, LaBarbera A R
Department of Obstetrics and Gynecology, Northwestern University Medical School, Chicago, Illinois 60611.
Endocrinology. 1988 Nov;123(5):2374-81. doi: 10.1210/endo-123-5-2374.
The purpose of these studies was to determine whether changes in FSH receptors correlated with FSH-induced attenuation of FSH-responsive adenylyl cyclase in immature porcine granulosa cells. Cells were incubated with FSH (1-1000 ng/ml) for up to 24 h, treated with acidified medium (pH 3.5) to remove FSH bound to cells, and incubated with [125I]iodo-porcine FSH to quantify FSH-binding sites. FSH increased binding of FSH in a time-, temperature-, and FSH concentration-dependent manner. FSH (200 ng/ml) increased binding approximately 4-fold within 16 h. Analysis of equilibrium saturation binding data indicated that the increase in binding sites reflected a 2.3-fold increase in receptor number and a 5.4-fold increase in apparent affinity. The increase in binding did not appear to be due to 1) a decrease in receptor turnover, since the basal rate of turnover appeared to be very slow; 2) an increase in receptor synthesis, since agents that inhibit protein synthesis and glycosylation did not block the increase in binding; or 3) an increase in intracellular receptors, since agents that inhibit cytoskeletal components had no effect. Agents that increase intracellular cAMP did not affect FSH binding. The increase in binding appeared to result from unmasking of cryptic FSH-binding sites, since FSH increased binding in cell-free membrane preparations to the same extent as in cells. Unmasking of cryptic sites was hormone specific, and the sites bound FSH specifically. Unmasking of sites was reversible in a time- and temperature-dependent manner after removal of bound FSH. The similarity between the FSH dose-response relationships for unmasking of FSH-binding sites and attenuation of FSH-responsive cAMP production suggests that the two processes are functionally linked.
这些研究的目的是确定促卵泡激素（FSH）受体的变化是否与FSH诱导的未成熟猪颗粒细胞中FSH反应性腺苷酸环化酶的衰减相关。将细胞与FSH（1 - 1000 ng/ml）孵育长达24小时，用酸化培养基（pH 3.5）处理以去除与细胞结合的FSH，然后与[125I]碘猪FSH孵育以定量FSH结合位点。FSH以时间、温度和FSH浓度依赖性方式增加FSH的结合。FSH（200 ng/ml）在16小时内使结合增加约4倍。平衡饱和结合数据分析表明，结合位点的增加反映了受体数量增加2.3倍和表观亲和力增加5.4倍。结合的增加似乎不是由于：1）受体周转减少，因为基础周转速率似乎非常缓慢；2）受体合成增加，因为抑制蛋白质合成和糖基化的试剂并未阻止结合的增加；或3）细胞内受体增加，因为抑制细胞骨架成分的试剂没有作用。增加细胞内cAMP的试剂不影响FSH结合。结合的增加似乎是由于隐蔽的FSH结合位点的暴露，因为FSH在无细胞膜制剂中增加结合的程度与在细胞中相同。隐蔽位点的暴露是激素特异性的，并且这些位点特异性结合FSH。在去除结合的FSH后，位点的暴露以时间和温度依赖性方式可逆。FSH结合位点暴露的FSH剂量反应关系与FSH反应性cAMP产生衰减之间的相似性表明这两个过程在功能上是相关的。
