Hein L, Ishii K, Coughlin S R, Kobilka B K
Division of Cardiovascular Medicine, Stanford University Medical School, California 94305.
J Biol Chem. 1994 Nov 4;269(44):27719-26.
The receptor for the protease thrombin is a member of the G protein-coupled receptor family, but is activated by a unique proteolytic mechanism. The irreversibility of this proteolytic mechanism and the fact that the ligand is tethered to its receptor raise special questions about inactivation of cleaved receptors and recovery of thrombin responsiveness. We compared the intracellular trafficking of the thrombin receptor to that of the beta 2-adrenergic receptor in transfected Rat1 fibroblasts. In unstimulated cells almost all beta 2 receptors were located on the plasma membrane; by contrast, part of a cell's thrombin receptors were found in an intracellular membrane compartment which co-localized with Golgi markers. Stimulation by agonist caused internalization and subsequent recycling of the beta 2-adrenergic receptor, but most activated thrombin receptors were internalized and targeted to lysosomes. The intracellular pool of thrombin receptors found in unstimulated cells was protected from activation by thrombin, but was translocated to the plasma membrane upon activation of cell surface thrombin receptors. Replenishment of plasma membrane thrombin receptors correlated with recovery of thrombin responsiveness. These observations reveal a novel trafficking mechanism for resensitizing the thrombin receptor as opposed to the internalization/recycling pathway of other G protein-coupled receptors.
蛋白酶凝血酶的受体是G蛋白偶联受体家族的成员，但通过独特的蛋白水解机制被激活。这种蛋白水解机制的不可逆性以及配体与受体相连的事实，引发了关于裂解受体失活和凝血酶反应性恢复的特殊问题。我们在转染的大鼠1成纤维细胞中比较了凝血酶受体与β2 -肾上腺素能受体的细胞内运输情况。在未受刺激的细胞中，几乎所有的β2受体都位于质膜上；相比之下，细胞的部分凝血酶受体存在于与高尔基体标记物共定位的细胞内膜区室中。激动剂刺激导致β2 -肾上腺素能受体内化并随后再循环，但大多数活化的凝血酶受体被内化并靶向溶酶体。在未受刺激的细胞中发现的凝血酶受体细胞内池不受凝血酶激活的影响，但在细胞表面凝血酶受体激活后会转移到质膜上。质膜凝血酶受体的补充与凝血酶反应性的恢复相关。这些观察结果揭示了一种使凝血酶受体重新敏感化的新型运输机制，这与其他G蛋白偶联受体的内化/再循环途径不同。
