REGULATION OF HORMONE-RESPONSIVE ADENYLATE CYCLASE

我们一直在研究的机制，脱敏的 哺乳动物细胞中的腺苷酸环化酶。 暴露 小鼠Leydig瘤细胞对人绒毛膜促性腺激素的克隆性 (hCG)导致hCG刺激的腺苷酸环化酶迅速减弱 活动 这种脱敏是时间和剂量依赖性的， 发生时细胞表面hCG受体没有任何损失， 对hCG的亲和力。 当细胞被激活时， 但当蛋白质合成被阻断时， 放线菌酮。 hCG刺激的腺苷酸环化酶的脱敏作用也 在暴露于佛波醇酯的细胞中发生，佛波醇酯激活蛋白激酶 C. 32 p掺入细胞hCG受体的量增加 通过hCG或佛波酯脱敏。 因此，受体 磷酸化可能是脱敏的基础。 激动剂和 佛波酯引起的肾上腺素能刺激的 腺苷酸环化酶在大鼠胶质瘤C6细胞中的表达，但机制不同。 任何一种治疗都会引起血浆中β受体的重新分布 膜到较轻密度的膜部分，其缺乏 腺苷酸环化酶活性。 用Concanaval预先处理细胞 阻止了受体的这种转变。 凝集素预处理还 阻止佛波醇酯，但不是激动剂介导的 脱敏。 最后，β-受体功能活性降低， 细胞通过它与腺苷酸环化酶的物理分离而脱敏。 在 相比之下，佛波酯介导的脱敏只涉及物理 从腺苷酸环化酶中分离受体。 受体 磷酸化可能参与这两种类型的脱敏，但在 受体上的不同位点。

We have been investigating the mechanism of densensitization of hormone-stimulated adenylate cyclase in mammalian cells. Exposure of a clonal line of murine Leydig tumor cells to human chorionic gonadotropin (hCG) resulted in a rapid attenuation of hCG-stimulated adenylate cyclase activity. This desensitiation was both time and dose dependent and occurred without any loss of cell surface hCG-receptors or any change in their affinity for hCG. Desensitization did not occur when the cells were exposed to hCG at OoC but did occur when protein synthesis was blocked by cycloheximide. Desensitization of hCG-stimulated adenylate cyclase also occured in cells exposed to phorbol esters which activate protein kinase C. There was increased incorporation of 32p into the hCG-receptor of cells desensitized by either hCG or phorbol esters. Thus, receptor phosphorylation may be the basis for desensitization. Both agonists and phorbol esters caused desensitization of the adrenergic-stimulated adenylate cyclase in rat glioma C6 cells but by distinct mechanisms. Either treatment caused a redistribution of beta-receptors from the plasma membrane to a lighter density membrane fraction which was devoid of adenylate cyclase activity. Prior treatment of the cells with concanaval in A prevented this shift in receptors. The lectin pretreatment also prevented the phorbol ester-, but not the agonist-mediated desensitization. Finally, beta-receptor functional activity was reduced in cells desensitized by it physical separation from adenylate cyclase. In contrast, phorbol ester-mediated desensitization involves only the physical separation of the receptor from adenylate cyclase. Receptor phosphorylation may be involved in both types of desensitization but at different sites on the receptor.