Chen Zhangguo, Rola-Pleszczynski Marek, Stankova Jana
Department of Pediatrics, Faculty of Medicine, Université de Sherbrooke, Sherbrooke, Quebec, Canada J1H 5N4.
Cell Signal. 2003 Sep;15(9):843-50. doi: 10.1016/s0898-6568(03)00056-1.
Platelet-activating factor (PAF) is a potent pro-inflammatory phospholipid mediator involved in a broad range of physiological and pathophysiological processes. The receptor of PAF (PAFR) is a heptahelical G-protein-coupled receptor. We have shown previously that upon agonist stimulation, PAFR internalised through clathrin-coated vesicles in an arrestin-dependent, but G-protein-coupling-independent manner. In the current report, we demonstrate that PAF stimulates Erk1/2 phosphorylation and: (1). dominant negative mutants of arrestins and dynamin do not influence Erk1/2 activation, (2). hypertonic conditions do not decrease the extent of Erk1/2 phosphorylation, (3). internalisation-deficient and/or G-protein-coupling-deficient mutants of PAFR activate Erk1/2 as efficiently as the wild-type PAFR, and (4). inhibition of epidermal growth factor receptor (EGFR) does not block Erk1/2 activation. Taken together, our results suggest that PAFR-mediated activation of mitogen-activated protein kinases Erk1/2 does not require receptor endocytosis, receptor tyrosine kinase transactivation or G-protein activation. In addition, our studies reveal that PAFR-mediated signals of G-protein activation, receptor internalisation and MAPK activation are differentially regulated by receptor structure and/or conformation.
血小板活化因子（PAF）是一种强效的促炎磷脂介质，参与广泛的生理和病理生理过程。PAF的受体（PAFR）是一种七螺旋G蛋白偶联受体。我们之前已经表明，在激动剂刺激下，PAFR通过网格蛋白包被的囊泡以内吞素依赖性但G蛋白偶联非依赖性的方式内化。在本报告中，我们证明PAF刺激Erk1/2磷酸化，并且：（1）. 内吞素和发动蛋白的显性负突变体不影响Erk1/2的激活，（2）. 高渗条件不会降低Erk1/2磷酸化的程度，（3）. PAFR的内化缺陷和/或G蛋白偶联缺陷突变体与野生型PAFR一样有效地激活Erk1/2，以及（4）. 表皮生长因子受体（EGFR）的抑制不会阻断Erk1/2的激活。综上所述，我们的结果表明，PAFR介导的丝裂原活化蛋白激酶Erk1/2的激活不需要受体内化、受体酪氨酸激酶转活化或G蛋白激活。此外，我们的研究表明，PAFR介导的G蛋白激活、受体内化和MAPK激活信号受受体结构和/或构象的差异调节。
