G蛋白偶联受体激酶的调控

G蛋白偶联受体激酶(G protein-coupled receptor kinase,GRK)特异地使活化的G蛋白偶联受体(G protein-coupled receptor,GPCR)发生磷酸化及脱敏化,从而终止后者介导的信号转导通路。研究表明,GRK的功能被高度调控,并具有下行调节GPCR的能力。调控GRK功能的机制包括两个层次：(1)多种途径调控激酶的亚细胞定位及活性,包括GPCR介导、G蛋白偶联、磷脂作用、Ca^2 结合蛋白调控、蛋白激酶C活化、MAPK反馈抑制、小窝蛋白抑制等;(2)调控GRK表达水平,主要体现在其与某些疾病的联系。     

G蛋白偶联受体激酶5在有丝分裂中的作用

G蛋白偶联受体激酶（GRK）是G蛋白偶联受体（GPCR）信号通路的负性调节因子。近来的研究发现,GRK除了磷酸化G蛋白偶联受体使其脱敏外,还能与其他非受体底物结合,功能呈现多样性。GRK5是GRK家族成员之一,该研究探索了GRK5在细胞周期和有丝分裂中的作用,结果显示：在细胞内干扰GRK5的表达导致分裂中期的细胞数目增多和细胞凋亡。进一步的研究发现,干扰GRK5的表达导致有丝分裂中期的染色体不能正常排列到赤道板,而对分裂后期染色质分离以及胞质分裂没有影响。在细胞内干扰GRK蛋白家族的另一个成员GRK2对有丝分裂则没有明显影响。该研究提示GRK5是细胞有丝分裂的重要调控蛋白。     

G蛋白偶联受体激酶5在稳定表达α-Synuclein的SHSY5Y细胞中的基因表达调控功能

目的观测G蛋白偶联受体激酶5（G protein-coupled receptor kinase,GRK5）在稳定表达hα-synuclein（人突触核蛋白）的SHSY5Y细胞的胞核、胞浆中的表达情况并对其在帕金森病中的可能作用进行研究。方法应用Western blotting、组蛋白去乙酰化酶（histone deacetylase,HDAC）活性检测技术以及shRNA干扰技术等对稳定表达hα-synuclein的SHSY5Y细胞中GRK5的表达及其亚细胞分布、胞核内GRK5蛋白的功能进行研究。结果发现GRK5蛋白在过表达hα-synuclein的细胞核以及细胞浆内均表达增加,胞核中的GRK5蛋白通过影响组蛋白去乙酰化酶的活性对bcl-2基因的转录和表达进行调控。结论帕金森模型中GRK5通过对bcl-2基因的表达进行调控发挥作用。     

成瘾性药物对大鼠脑内G蛋白耦联受体激酶5 mRNA和蛋白水平的调控

G蛋白耦联受体激酶5(GRK5)在G蛋白耦联受体信号转导中起重要调节作用。本文研究了单次给予成瘾性药物吗啡、海洛因和可卡因对大鼠脑内GRK5mRNA水平的调控作用,并选取吗啡为代表,观察单次或多次给予吗啡后大鼠脑内GRK5蛋白含量的变化。结果发现：(1)单次给予吗啡(10mg／kg)、海洛因(1mg／kg)或可卡因(15mg／kg)均可引起大鼠大脑顶叶皮层、颞叶皮层和海马的GRK5 mRNA水平显著上升;(2)单次或多次给予吗啡注射可以显著上调大鼠大脑皮层GRK5蛋白含量,而多次给予吗啡显著下调丘脑GRK5含量。我们的结果首次证明成瘾性药物对大脑皮层、海马等脑区的GRK5在mRNA水平和蛋白水平都有调控作用,提示GRK5可能在精神活性物质的成瘾中起作用。     

G蛋白偶联受体在血管发育中的作用

血管发育包括血管发生和血管生成两个阶段。近年研究表明, G蛋白偶联受体广泛参与调控成血管细胞的分化、迁移和接合, 尖端细胞和柄细胞命运决定, 内皮细胞的增殖、迁移和管腔形成等多个过程。文章以血管发育中的这些关键事件为主线, 总结了G蛋白偶联受体家族成员特别是视紫红质类和卷曲类受体在调节血管发育方面的最新研究进展。文章着重介绍了斑马鱼作为模式生物在血管发育生物学研究中的独特优势, 并展望了利用斑马鱼深入开展G蛋白偶联受体相关研究的广阔前景。     

PI3K/AKT通路在动物葡萄糖代谢中的研究进展

葡萄糖代谢稳态对维持动物健康水平至关重要.磷脂酰肌醇3-激酶(phosphoinositide 3-kinase,PI3K)是受体酪氨酸激酶(receptor tyrosine kinase,RTK)和G蛋白偶联受体(G protein-coupled receptor,GPCR)共同调控的下游效应因子.它能够磷酸化磷...     

G蛋白偶联受体结构生物学进展

G蛋白偶联受体(GPCR)是具有7次跨膜螺旋的细胞整合膜蛋白,它们广泛地参与感光、气味、神经传递以及细胞增殖、分化、迁移等各类生理活动的调控.是现代药物研发的重要靶点.然而,GPCR结构生物学研究却受到高质量蛋白制备、稳定性以及结晶方法等方面的限制.近年来,随着新型膜蛋白表达体系、新型去污剂、膜蛋白纯化及结晶技术的发展.使得G蛋白偶联受体结构解析工作取得了可喜的进展,也为进一步解析更多GPCR精细结构及相关药物研发奠定重要基础.     

与癌症相关的G 蛋白偶联受体及通路的研究进展

G蛋白偶联受体(G protein-coupled receptors,GPCRs)是一类重要的细胞膜表面跨膜蛋白受体超家族,具有7个跨膜螺旋结构。GPCRs的细胞内信号由G蛋白介导,可将激素、神经递质、药物、趋化因子等多种物理和化学的细胞外刺激穿过细胞膜转导到细胞内不同的效应分子,激活相应的信号级联系统进而影响恶性肿瘤的生长迁移过程。虽然目前药物市场上有很多治疗癌症的小分子药物属于G蛋白受体相关药物,但所作用的靶点集中于少数特定G蛋白偶联受体。因此,新的具有成药性的G蛋白偶联受体的开发具有很大的研究价值和市场潜力。本文主要以在癌症发生、发展中起重要作用的溶血磷脂酸(LPA),G蛋白偶联受体30(GPR30)、内皮素A受体(ETAR)等不同G蛋白偶联受体为分类依据,综述其与相关的信号通路在癌症进程中的作用,并对相应的小分子药物的临床应用和研究进展进行展望。     

去棕榈酰化修饰下G蛋白偶联受体激酶6核定位信号鉴定

G蛋白偶联受体激酶6(G protein-coupled receptor kinase 6,GRK6)依赖去棕榈酰化修饰及特定核定位序列(nuclear localization sequence,NLS)实现胞核定位,但NLS的关键基团及其对激酶活性的影响尚不清楚。该研究首先通过构建一系列缺失突变子,初筛去棕榈酰化条件下GRK6的NLS结构域;然后采用点突变技术进一步确定NLS结构域中Lys(K)~(389)、Lys(K)~(390)、Lys(K)~(3913)个关键基团;最后通过检测内源性毒蕈碱M3受体介导的细胞内钙流,证实NLS突变子对M3受体介导的细胞内钙流信号的抑制作用无明显影响。该研究为进一步揭示GRK6胞核转运机制及其功能提供了有价值的信息。     

GPCR在类风湿关节炎中的作用机制研究进展

类风湿关节炎(rheumatoid arthritis, RA)是一种以滑膜炎为特征的自身免疫性疾病,伴有异常免疫反应。G蛋白偶联受体(G protein coupled receptor, GPCR)是人体最大的跨膜受体家族,介导RA的发生发展过程,其相关信号通路在RA炎症和免疫应答过程中发挥重要作用。研究发现,GPCR/AC/cAMP相关通路,如β2-ARs/AC/cAMP、EP2/4/AC/cAMP和CXCR/AC/cAMP等信号通路,以及相关调节蛋白,如GRK和β-arrestins等,可能参与RA的淋巴细胞功能异常、血管生成及关节破坏等病理过程。由此,β2-ARs等受体以及GRK等调节蛋白可能作为RA的潜在治疗靶标。现通过简要阐述GPCR相关通路及其调节蛋白的特点,以期加深对GPCR参与RA调控的认识,为类风湿关节炎药物的开发提供新的思路。     

G protein-coupled receptor kinase 2 positively regulates epithelial cell migration

Cell migration requires integration of signals arising from both the extracellular matrix and messengers acting through G protein-coupled receptors (GPCRs). We find that increased levels of G protein-coupled receptor kinase 2 (GRK2), a key player in GPCR regulation, potentiate migration of epithelial cells towards fibronectin, whereas such process is decreased in embryonic fibroblasts from hemizygous GRK2 mice or upon knockdown of GRK2 expression. Interestingly, the GRK2 effect on fibronectin-mediated cell migration involves the paracrine/autocrine activation of a sphingosine-1-phosphate (S1P) Gi-coupled GPCR. GRK2 positively modulates the activity of the Rac/PAK/MEK/ERK pathway in response to adhesion and S1P by a mechanism involving the phosphorylation-dependent, dynamic interaction of GRK2 with GIT1, a key scaffolding protein in cell migration processes. Furthermore, decreased GRK2 levels in hemizygous mice result in delayed wound healing rate in vivo, consistent with a physiological role of GRK2 as a regulator of coordinated integrin and GPCR-directed epithelial cell migration.     

G Protein-coupled receptor kinase 5 is localized to centrosomes and regulates cell cycle progression

G protein-coupled receptor kinases (GRKs) are important regulators of G protein-coupled receptor function and mediate receptor desensitization, internalization, and signaling. While GRKs also interact with and/or phosphorylate many other proteins and modify their function, relatively little is known about the cellular localization of endogenous GRKs. Here we report that GRK5 co-localizes with γ-tubulin, centrin, and pericentrin in centrosomes. The centrosomal localization of GRK5 is observed predominantly at interphase and although its localization is not dependent on microtubules, it can mediate microtubule nucleation of centrosomes. Knockdown of GRK5 expression leads to G2/M arrest, characterized by a prolonged G2 phase, which can be rescued by expression of wild type but not catalytically inactive GRK5. This G2/M arrest appears to be due to increased expression of p53, reduced activity of aurora A kinase and a subsequent delay in the activation of polo-like kinase 1. Overall, these studies demonstrate that GRK5 is localized in the centrosome and regulates microtubule nucleation and normal cell cycle progression.     

G protein-coupled receptor kinase 2 (GRK2) in migration and inflammation

G protein-coupled receptor kinase 2 (GRK2) is a key modulator of G protein-coupled receptors and other plasma membrane receptors stimulated by chemotactic messengers. On top of that, GRK2 has been reported to interact with a variety of signal transduction proteins related to cell migration such as MEK, Akt, PI3Kgamma or GIT. Interestingly, the levels of expression and activity of this kinase are altered in a number of inflammatory disorders (as rheumatoid arthritis or multiple sclerosis), thus suggesting that it may play an important role in the onset or development of these pathologies. This review summarizes the mechanisms involved in the control of GRK2 expression and function and highlights novel functional interactions of this protein that might help to explain how altered GRK2 levels affects cell migration in different cell types and pathological settings.     

G protein-coupled receptor kinase 5 phosphorylates nucleophosmin and regulates cell sensitivity to polo-like kinase 1 inhibition

G protein-coupled receptor kinases (GRKs) phosphorylate activated G protein-coupled receptors, leading to their desensitization and endocytosis. GRKs have also been implicated in phosphorylating other classes of proteins and can localize in a variety of cellular compartments, including the nucleus. Here, we attempted to identify potential nuclear substrates for GRK5. Our studies reveal that GRK5 is able to interact with and phosphorylate nucleophosmin (NPM1) both in vitro and in intact cells. NPM1 is a nuclear protein that regulates a variety of cell functions including centrosomal duplication, cell cycle control, and apoptosis. GRK5 interaction with NPM1 is mediated by the N-terminal domain of each protein, and GRK5 primarily phosphorylates NPM1 at Ser-4, a site shared with polo-like kinase 1 (PLK1). NPM1 phosphorylation by GRK5 and PLK1 correlates with the sensitivity of cells to undergo apoptosis with cells having higher GRK5 levels being less sensitive and cells with lower GRK5 being more sensitive to PLK1 inhibitor-induced apoptosis. Taken together, our results demonstrate that GRK5 phosphorylates Ser-4 in nucleophosmin and regulates the sensitivity of cells to PLK1 inhibition.     

Regulation of G protein-coupled receptor kinase subtypes by calcium sensor proteins

G protein-coupled receptor homologous desensitization is intrinsically related to the function of a class of S/T kinases named G protein-coupled receptor kinases (GRK). The GRK family is composed of six cloned members, named GRK1 to 6. Studies from different laboratories have demonstrated that different calcium sensor proteins (CSP) can selectively regulate the activity of GRK subtypes. In the presence of calcium, rhodopsin kinase (GRK1) is inhibited by the photoreceptor-specific CSP recoverin through direct binding. Several other recoverin homologues (including NCS 1, VILIP 1 and hippocalcin) are also able to inhibit GRK1. The ubiquitous calcium-binding protein calmodulin (CaM) can inhibit GRK5 with a high affinity (IC(50)=40-50 nM). A direct interaction between GRK5 and Ca(2+)/CaM was documented and this binding does not influence the catalytic activity of the kinase, but rather reduced GRK5 binding to the membrane. These studies suggest that CSP act as functional analogues in mediating the regulation of different GRK subtypes by Ca(2+). This mechanism is, however, highly selective with respect to the GRK subtypes: while GRK1, but not GRK2 and GRK5, is regulated by recoverin and other NCS, GRK4, 5 and 6, that belong to the GRK4 subfamily, are potently inhibited by CaM, which had little or no effect on members of other GRK subfamilies.     

Increased acute inflammation, leukotriene B4-induced chemotaxis, and signaling in mice deficient for G protein-coupled receptor kinase 6

Directed migration of polymorphonuclear neutrophils (PMN) is required for adequate host defense against invading organisms and leukotriene B(4) (LTB(4)) is one of the most potent PMN chemoattractants. LTB(4) exerts its action via binding to BLT1, a G protein-coupled receptor. G protein-coupled receptors are phosphorylated by G protein-coupled receptor kinases (GRK) in an agonist-dependent manner, resulting in receptor desensitization. Recently, it has been shown that the human BLT1 is a substrate for GRK6. To investigate the physiological importance of GRK6 for inflammation and LTB(4) signaling in PMN, we used GRK6-deficient mice. The acute inflammatory response (ear swelling and influx of PMN into the ear) after topical application of arachidonic acid was significantly increased in GRK6(-/-) mice. In vitro, GRK6(-/-) PMN showed increased chemokinetic and chemotactic responses to LTB(4). GRK6(-/-) PMN respond to LTB(4) with a prolonged increase in intracellular calcium and prolonged actin polymerization, suggesting impaired LTB(4) receptor desensitization in the absence of GRK6. However, pre-exposure to LTB(4) renders both GRK6(-/-) as well as wild-type PMN refractory to restimulation with LTB(4), indicating that the presence of GRK6 is not required for this process to occur. In conclusion, GRK6 deficiency leads to prolonged BLT1 signaling and increased neutrophil migration.     

The membrane-proximal portion of CD3 epsilon associates with the serine/threonine kinase GRK2

The activation of protein kinases is one of the primary mechanisms whereby T cell receptors (TCR) propagate intracellular signals. To date, the majority of kinases known to be involved in the early stages of TCR signaling are protein-tyrosine kinases such as Lck, Fyn, and ZAP-70. Here we report a constitutive association between the TCR and a serine/threonine kinase, which was mediated through the membrane-proximal portion of CD3 epsilon. Mass spectrometry analysis of CD3 epsilon-associated proteins identified G protein-coupled receptor kinase 2 (GRK2) as a candidate Ser/Thr kinase. Transient transfection assays and Western blot analysis verified the ability of GRK2 to interact with the cytoplasmic domain of CD3 epsilon within a cell. These findings are consistent with recent reports demonstrating the ability of certain G protein-coupled receptors (GPCR) and G proteins to physically associate with the alpha/beta TCR. Because GRK2 is primarily involved in arresting GPCR signals, its interaction with CD3 epsilon may provide a novel means whereby the TCR can negatively regulate signals generated through GPCRs.     

Distinct Cellular and Subcellular Distributions of G Protein-Coupled Receptor Kinase and Arrestin Isoforms in the Striatum

G protein-coupled receptor kinases (GRKs) and arrestins mediate desensitization of G protein-coupled receptors (GPCR). Arrestins also mediate G protein-independent signaling via GPCRs. Since GRK and arrestins demonstrate no strict receptor specificity, their functions in the brain may depend on their cellular complement, expression level, and subcellular targeting. However, cellular expression and subcellular distribution of GRKs and arrestins in the brain is largely unknown. We show that GRK isoforms GRK2 and GRK5 are similarly expressed in direct and indirect pathway neurons in the rat striatum. Arrestin-2 and arrestin-3 are also expressed in neurons of both pathways. Cholinergic interneurons are enriched in GRK2, arrestin-3, and GRK5. Parvalbumin-positive interneurons express more of GRK2 and less of arrestin-2 than medium spiny neurons. The GRK5 subcellular distribution in the human striatal neurons is altered by its phosphorylation: unphosphorylated enzyme preferentially localizes to synaptic membranes, whereas phosphorylated GRK5 is found in plasma membrane and cytosolic fractions. Both GRK isoforms are abundant in the nucleus of human striatal neurons, whereas the proportion of both arrestins in the nucleus was equally low. However, overall higher expression of arrestin-2 yields high enough concentration in the nucleus to mediate nuclear functions. These data suggest cell type- and subcellular compartment-dependent differences in GRK/arrestin-mediated desensitization and signaling.