Vouret-Craviari V, Auberger P, Pouysségur J, Van Obberghen-Schilling E
Centre de Biochimie, CNRS-UMR134, Parc Valrose, Nice, France.
J Biol Chem. 1995 Mar 3;270(9):4813-21. doi: 10.1074/jbc.270.9.4813.
We have compared the desensitization of two receptors, the thrombin receptor which displays dual coupling to both pertussis toxin-sensitive (Gi) and -insensitive (Gq) proteins and the serotonin type 2 (5-HT2) receptor which selectively couples to Gq. In the case of the thrombin receptor, cleavage induces activation and irreversible receptor modification followed by rapid (T1/2 = 3 min) and extensive desensitization of the receptor's ability to modulate phospholipase C (Gq). 5-HT-induced desensitization of its receptor is markedly slower (T1/2 = 10 min) and by 60 min only 50% of the phospholipase C response is lost. This effect occurs with a parallel disappearance of 5-HT receptors from the cell surface. Whole cell phosphorylation studies showed that the thrombin receptor is rapidly phosphorylated upon activation. In contrast, the 5-HT2 receptor displays a low basal level of phosphorylation which is not increased upon agonist treatment. The cytoplasmic tail of the 5-HT2 receptor which contains several protein kinase consensus sequences was found not to be involved in receptor activation or desensitization. However, a chimeric receptor having the core of the 5-HT2 receptor and the cytoplasmic tail of the thrombin receptor was able to undergo 5-HT-induced desensitization and phosphorylation. These results indicate that (i) both 5-HT2 and thrombin receptors have unique shut-off mechanisms, and (ii) that sequences in the carboxyl terminus of the thrombin receptor are sufficient to trigger rapid uncoupling of the receptor from its G protein(s) and downstream effector(s).
我们比较了两种受体的脱敏作用，一种是凝血酶受体，它与百日咳毒素敏感蛋白（Gi）和不敏感蛋白（Gq）均呈双重偶联；另一种是5-羟色胺2型（5-HT2）受体，它选择性地与Gq偶联。对于凝血酶受体而言，蛋白水解作用诱导其激活及不可逆的受体修饰，随后受体调节磷脂酶C（Gq）的能力迅速（半衰期 = 3分钟）且广泛地脱敏。5-羟色胺诱导其受体的脱敏作用明显较慢（半衰期 = 10分钟），到60分钟时，只有50%的磷脂酶C反应丧失。这种效应伴随着5-HT受体从细胞表面的平行消失。全细胞磷酸化研究表明，凝血酶受体激活后会迅速磷酸化。相比之下，5-HT2受体的基础磷酸化水平较低，激动剂处理后也不会升高。发现5-HT2受体的胞质尾含有几个蛋白激酶共有序列，但它不参与受体的激活或脱敏。然而，一种具有5-HT2受体核心和凝血酶受体胞质尾的嵌合受体能够发生5-羟色胺诱导的脱敏和磷酸化。这些结果表明：（i）5-HT2和凝血酶受体都有独特的关闭机制；（ii）凝血酶受体羧基末端的序列足以触发受体与其G蛋白及下游效应器的快速解偶联。
