Filipeanu Catalin M, Zhou Fuguo, Fugetta Erin K, Wu Guangyu
Department of Pharmacology and Experimental Therapeutics, Louisiana State University Health Sciences Center, 1901 Perdido St., New Orleans, LA 70112, USA.
Mol Pharmacol. 2006 May;69(5):1571-8. doi: 10.1124/mol.105.019984. Epub 2006 Feb 3.
The molecular mechanism underlying the export from the endoplasmic reticulum (ER) to the cell surface and its role in the regulation of signaling of adrenergic receptors (ARs) remain largely unknown. In this report, we determined the role of Rab1, a Ras-like GTPase that coordinates protein transport specifically from the ER to the Golgi, in the cell surface targeting and function of endogenous beta- and alpha1-ARs in neonatal rat ventricular myocytes. Adenovirus-driven expression of Rab1 into myocytes selectively increased the cell-surface number of alpha1-AR, but not beta-AR, whereas the dominant-negative mutant Rab1N124I significantly reduced the cell-surface expression of beta-AR and alpha1-AR. Brefeldin A inhibited beta-AR and alpha1-AR export and antagonized the Rab1 effect on alpha1-AR expression. Manipulation of Rab1 function similarly influenced the transport of alpha1A- and alpha1B-ARs as well as beta1- and beta2-ARs. Fluorescent microscopy analysis demonstrated that expression of Rab1N124I and Rab1 small interfering RNA induced a marked accumulation of GFP-tagged beta2-AR and alpha1B-AR in the ER. Consistent with the effects on receptor cell-surface targeting, Rab1 selectively enhanced ERK1/2 activation and hypertrophic growth in response to the alpha1-AR agonist phenylephrine but not to the beta-AR agonist isoproterenol. Rab1N124I inhibited both agonist-mediated ERK1/2 activation and hypertrophic growth in neonatal myocytes. These results demonstrate that the cell-surface targeting and signaling of beta- and alpha1-ARs require Rab1 and are differentially modulated by augmentation of Rab1 function. Our data provide strong evidence implicating the ER-to-Golgi traffic as a site for selective manipulation of distinct AR function in cardiac myocytes.
内质网（ER）向细胞表面输出的分子机制及其在肾上腺素能受体（ARs）信号调节中的作用在很大程度上仍不清楚。在本报告中，我们确定了Rab1（一种Ras样GTP酶，专门协调从内质网到高尔基体的蛋白质转运）在新生大鼠心室肌细胞中内源性β-和α1-ARs的细胞表面靶向和功能中的作用。腺病毒驱动的Rab1在心肌细胞中的表达选择性地增加了α1-AR的细胞表面数量，但未增加β-AR的数量，而显性负性突变体Rab1N124I显著降低了β-AR和α1-AR的细胞表面表达。布雷菲德菌素A抑制β-AR和α1-AR的输出，并拮抗Rab1对α1-AR表达的影响。操纵Rab1功能同样影响α1A-和α1B-ARs以及β1-和β2-ARs的转运。荧光显微镜分析表明，Rab1N124I和Rab1小干扰RNA的表达诱导了内质网中绿色荧光蛋白标记的β2-AR和α1B-AR的明显积累。与对受体细胞表面靶向的影响一致，Rab1选择性地增强了对α1-AR激动剂去氧肾上腺素的ERK1/2激活和肥大生长，但对β-AR激动剂异丙肾上腺素无此作用。Rab1N124I抑制新生心肌细胞中激动剂介导的ERK1/2激活和肥大生长。这些结果表明，β-和α1-ARs的细胞表面靶向和信号传导需要Rab1，并且通过增强Rab1功能受到不同的调节。我们的数据提供了有力证据，表明内质网到高尔基体的运输是心肌细胞中选择性操纵不同AR功能的一个位点。
