South China Research Center for Acupuncture and Moxibustion, Guangzhou University of Chinese Medicine, Guangzhou, 510006, China.
Department of Pharmacology and Toxicology, Medical College of Georgia, Augusta University, Augusta, GA, 30912, USA.
Sci Rep. 2019 Jul 17;9(1):10378. doi: 10.1038/s41598-019-46547-4.
The regulatory mechanisms of cell surface targeting of nascent G protein-coupled receptors (GPCRs) en route from the endoplasmic reticulum through the Golgi remain poorly understood. We have recently demonstrated that three Golgi-localized, γ-adaptin ear domain homology, ADP ribosylation factor-binding proteins (GGAs) mediate the post-Golgi export of α-adrenergic receptor (α-AR), a prototypic GPCR, and directly interact with the receptor. In particular, GGA1 interaction with α-AR is mediated via its hinge domain. Here we determined the role of a naturally occurring truncated form of GGA1 (GGA1t) which lacks the N-terminal portion of the hinge domain in α-AR trafficking and elucidated the underlying mechanisms. We demonstrated that both GGA1 and GGA1t were colocalized and mainly expressed at the Golgi. In marked contrast to GGA1, the expression of GGA1t significantly attenuated the cell surface export of newly synthesized α-AR from the Golgi and in parallel receptor-mediated signaling. Furthermore, we found that GGA1t formed homodimers and heterodimers with GGA1. More interestingly, GGA1t was unable to bind the cargo α-AR and to recruit clathrin onto the trans-Golgi network. These data provide evidence implicating that the truncated form of GGA1 behaviors as a dominant-negative regulator for the cell surface export of α-AR and this function of GGA1t is attributed to its abilities to dimerize with its wide type counterpart and to inhibit cargo interaction and clathrin recruitment to form specialized transport vesicles.
新生 G 蛋白偶联受体 (GPCR) 从内质网经高尔基体靶向细胞表面的调控机制仍知之甚少。我们最近证明，三种定位于高尔基体的 γ-衔接蛋白耳域同源物、ADP 核糖基化因子结合蛋白 (GGAs) 介导α-肾上腺素能受体 (α-AR) 的高尔基体后出口，α-AR 是一种典型的 GPCR，并与受体直接相互作用。特别是，GGA1 与 α-AR 的相互作用是通过其铰链结构域介导的。在这里，我们确定了缺乏铰链结构域 N 端部分的天然存在的 GGA1 截断形式 (GGA1t) 在 α-AR 运输中的作用，并阐明了潜在的机制。我们证明 GGA1 和 GGA1t 均共定位并主要在高尔基体表达。与 GGA1 形成鲜明对比的是，GGA1t 的表达显著减弱了新合成的 α-AR 从高尔基体到细胞表面的输出，以及受体介导的信号转导。此外，我们发现 GGA1t 与 GGA1 形成同源二聚体和异源二聚体。更有趣的是，GGA1t 无法与货物 α-AR 结合，并将网格蛋白募集到反式高尔基体网络。这些数据提供的证据表明，GGA1 的截断形式充当了 α-AR 细胞表面输出的显性负调控因子，而 GGA1t 的这种功能归因于其与野生型相互作用的能力以及抑制货物相互作用和网格蛋白募集以形成特殊运输囊泡的能力。
