Grabowska D, Jayaraman M, Kaltenbronn K M, Sandiford S L, Wang Q, Jenkins S, Slepak V Z, Smith Y, Blumer K J
Department of Cell Biology and Physiology, Washington University School of Medicine, 660 South Euclid Avenue, St. Louis, MO 63110, USA.
Neuroscience. 2008 Feb 19;151(4):969-82. doi: 10.1016/j.neuroscience.2007.11.045. Epub 2007 Dec 8.
Members of the regulator of G protein signaling 7 (RGS7) (R7) family and Gbeta5 form obligate heterodimers that are expressed predominantly in the nervous system. R7-Gbeta5 heterodimers are GTPase-activating proteins (GAPs) specific for Gi/o-class Galpha subunits, which mediate phototransduction in retina and the action of many modulatory G protein-coupled receptors (GPCRs) in brain. Here we have focused on the R7-family binding protein (R7BP), a recently identified palmitoylated protein that can bind R7-Gbeta5 complexes and is hypothesized to control the intracellular localization and function of the resultant heterotrimeric complexes. We show that: 1) R7-Gbeta5 complexes are obligate binding partners for R7BP in brain because they co-immunoprecipitate and exhibit similar expression patterns. Furthermore, R7BP and R7 protein accumulation in vivo requires Gbeta5. 2) Expression of R7BP in Neuro2A cells at levels approximating those in brain recruits endogenous RGS7-Gbeta5 complexes to the plasma membrane. 3) R7BP immunoreactivity in brain concentrates in neuronal soma, dendrites, spines or unmyelinated axons, and is absent or low in glia, myelinated axons, or axon terminals. 4) RGS7-Gbeta5-R7BP complexes in brain extracts associate inefficiently with detergent-resistant lipid raft fractions with or without G protein activation. 5) R7BP and Gbeta5 protein levels are upregulated strikingly during the first 2-3 weeks of postnatal brain development. Accordingly, we suggest that R7-Gbeta5-R7BP complexes in the mouse or rat could regulate signaling by modulatory Gi/o-coupled GPCRs in the developing and adult nervous systems.
G蛋白信号调节因子7（RGS7）家族成员与Gβ5形成专性异二聚体，主要在神经系统中表达。R7 - Gβ5异二聚体是特异性作用于Gi/o类Gα亚基的GTP酶激活蛋白（GAP），其介导视网膜中的光转导以及大脑中许多调节性G蛋白偶联受体（GPCR）的作用。在此，我们聚焦于R7家族结合蛋白（R7BP），它是最近发现的一种棕榈酰化蛋白，能够结合R7 - Gβ5复合物，并被推测可控制所形成的异三聚体复合物的细胞内定位和功能。我们发现：1）R7 - Gβ5复合物是大脑中R7BP的专性结合伙伴，因为它们能共同免疫沉淀并呈现相似的表达模式。此外，R7BP和R7蛋白在体内的积累需要Gβ5。2）在Neuro2A细胞中表达的R7BP水平接近大脑中的水平时，可将内源性RGS7 - Gβ5复合物募集到质膜。3）大脑中的R7BP免疫反应性集中在神经元胞体、树突、棘突或无髓轴突中，而在神经胶质细胞、有髓轴突或轴突终末中不存在或含量很低。4）无论有无G蛋白激活，大脑提取物中的RGS7 - Gβ5 - R7BP复合物与抗去污剂脂质筏组分的结合效率都很低。5）在出生后大脑发育的前2 - 3周，R7BP和Gβ5蛋白水平显著上调。因此，我们认为小鼠或大鼠中的R7 - Gβ5 - R7BP复合物可能在发育中和成年神经系统中通过调节性Gi/o偶联GPCR来调节信号传导。
