Birnbaumer M, Antaramian A, Themmen A P, Gilbert S
Department of Cell Biology, Baylor College of Medicine, Houston, Texas 77030.
J Biol Chem. 1992 Jun 15;267(17):11783-8.
Three main pathways have been implicated in desensitization of receptors that stimulate adenylylcyclase (AC): cAMP-mediated phosphorylation; cAMP-independent phosphorylation, and receptor internalization. Cell lines derived from the murine Ltk- cell were found useful in exploring the contribution of cAMP-dependent phosphorylation in V2 vasopressin receptor desensitization. The HTB-2 cell expresses the human V2 vasopressin receptor, introduced by transfection of human genomic DNA, and the prostaglandin E1 (PGE1) receptor, endogenous to the Ltk- cell. The A7 cell expresses the hamster beta 2-adrenoceptor, which undergoes the above-mentioned desensitization processes. Treatment of HTB-2 cells with arginine-vasopressin (AVP) had no effect on AC responsiveness to PGE1, but promoted desensitization of the AVP response. This was seen as a 5-6-fold right shift in the dose-response curves for AVP action (cAMP accumulation in intact cells and AC stimulation in homogenates and isolated membranes) and in a decrease in the maximum effect of AVP on these parameters. AVP treatment caused a decrease in cell surface receptors to approximately 75% of control without changes in KD, as determined by Scatchard analysis. When cAMP was increased by treatment with 10 microM PGE1 and isobutylmethylxanthine, desensitization of the PGE1 receptor was observed but not of the AVP receptor. In A7 cells the same treatment caused, as expected, a 3-fold right shift in the dose-response curve for AC stimulation by isoproterenol, indicating that L cells can mediate heterologous desensitization. These data demonstrate that the V2 vasopressin and the PGE1 receptors undergo homologous desensitization in the absence of cAMP-mediated phosphorylation and that this component is not required for vasopressin receptor internalization.
三种主要途径与刺激腺苷酸环化酶（AC）的受体脱敏有关：cAMP介导的磷酸化；不依赖cAMP的磷酸化以及受体内化。发现源自小鼠Ltk-细胞的细胞系有助于探究cAMP依赖性磷酸化在V2血管加压素受体脱敏中的作用。HTB-2细胞表达通过转染人基因组DNA引入的人V2血管加压素受体以及Ltk-细胞内源性的前列腺素E1（PGE1）受体。A7细胞表达仓鼠β2-肾上腺素能受体，该受体经历上述脱敏过程。用精氨酸血管加压素（AVP）处理HTB-2细胞对AC对PGE1的反应性没有影响，但促进了AVP反应的脱敏。这表现为AVP作用的剂量反应曲线（完整细胞中的cAMP积累以及匀浆和分离膜中的AC刺激）向右移动5-6倍，并且AVP对这些参数的最大作用降低。通过Scatchard分析确定，AVP处理使细胞表面受体减少至对照的约75%，而KD没有变化。当用10μM PGE1和异丁基甲基黄嘌呤处理使cAMP增加时，观察到PGE1受体脱敏，但AVP受体未脱敏。在A7细胞中，相同处理如预期那样使异丙肾上腺素刺激AC的剂量反应曲线向右移动3倍，表明L细胞可以介导异源脱敏。这些数据表明，V2血管加压素和PGE1受体在没有cAMP介导的磷酸化的情况下发生同源脱敏，并且该成分不是血管加压素受体内化所必需的。
