生长抑素受体介导的放射性核素治疗

生长抑素受体介导的放射性核素治疗(peptide receptor radionuclide therapy,PRRT)是用于不能手术治疗或有远处转移的胃、肠和胰腺等神经内分泌肿瘤病人的一种新型治疗方法,本文旨在综述近年来不同核素标记生长抑素类似物的临床评价及相关研究。     

Specificity of Muscarinic Acetylcholine Receptor Regulation by Receptor Activity

Abstract— Regulation of muscarinic acetylcholine receptor concentration by receptor activity in neuron-like NG108-15 hybrid cells is a highly specific process. Receptor levels, monitored by binding of [³H]quinuclidinyl benzilate ([³H]QNB), decreased 50-75% following 24-h incubation of cells with muscarinic agonists, but none of the following cellular processes was altered by this chronic receptor stimulation: (1) glycolytic energy metabolism, measured by [³H]deoxy- d -glucose ([³H]DG) uptake and retention; (2) rate of cell division; (3) transport, measured by [³H]valine and [³H]uridine uptake; (4) RNA biosynthesis, measured by [³H]uridine incorporation; (5) protein biosynthesis, measured by [³H]valine and [³⁵S]methionine incorporation into total protein and into protein fractions obtained by polyacrylamide gel electrophoresis. In contrast, chronic stimulation did cause a threefold decrease in the capacity of carbachol to stimulate phosphatidylinositol (PI) turnover, a receptor-mediated response. In addition to cholinomimetics, the neuroeffector adenosine (1 m m for 24 h) also caused a decrease in [³H]QNB binding levels, but chronic stimulation of α -adrenergic, opiate, prostaglandin E₁, and prostaglandin F_2α receptors found on NG108-15 cells caused no changes. The data indicate that loss of muscarinic receptors caused by receptor stimulation is not a consequence of fundamental changes evoked in overall cellular physiology but reflects a specific regulation of cholinoceptive cell responsiveness.     

触觉受体NOMPC及听觉受体TMC的发现

人类感觉包括:视觉、听觉、嗅觉、味觉、触觉,还有温觉、痛觉等.生物体是如何感知物理世界的问题一直吸引着人类,虽然在不同感知觉受体的发现及研究过程中不断取得新的突破性进展,但是对这些感知觉基础生物学层面的理解仍然有限.2021年度诺贝尔生理学或医学奖授予感知觉研究领域,以表彰David Julius和Ardem Pata...     

Kinin-Stimulated B1 Receptor Signaling Depends on Receptor Endocytosis Whereas B2 Receptor Signaling Does Not

Kinins are potent pro-inflammatory peptides that act through two G protein-coupled receptor subtypes, B1 (B1R) and B2 (B2R). Kinin-stimulated B2R signaling is often transient, whereas B1R signaling is sustained. This was confirmed by monitoring agonist-stimulated intracellular Ca²⁺ mobilization in A10 smooth muscle cells expressing human wild-type B2R and B1R. We further studied the role of receptor membrane trafficking in receptor-mediated phosphoinositide (PI) hydrolysis in model HEK293 cell lines stably expressing the receptors. Treatment of cells with brefeldin A, to inhibit maturation of de novo synthesized receptors, or hypertonic sucrose, to inhibit receptor endocytosis, showed that the basal cell surface receptor turnover was considerably faster for B1R than for B2R. Inhibition of endocytosis, which stabilized B1R on the cell surface, inhibited B1R signaling, whereas B2R signaling was not perturbed. Signaling by a B1R construct in which the entire C-terminal domain was deleted remained sensitive to inhibition of receptor endocytosis, whereas signaling by a B1R construct in which this domain was substituted with the corresponding domain in B2R was not sensitive. B2R and B1R co-expression, which also appeared to stabilize B1R on the cell surface, presumably by receptor hetero-dimerization, also inhibited B1R signaling, whereas B2R signaling was slightly enhanced. Furthermore, the B2R-specific agonist bradykinin (BK) directed both receptors through a common endocytic pathway, whereas the B1R-specific agonist Lys-desArg⁹-BK was unable to do so. These results suggest that B1R-mediated PI hydrolysis depends on a step in receptor endocytosis, whereas B2R-mediated PI hydrolysis does not. We propose that B1R uses at least part of the endocytic machinery to sustain agonist-promoted signaling.     

Toll-Like Receptor Signaling

Toll-like receptors sense pathogen-associated molecular patterns (e.g., lipopolysaccharides) and trigger gene-expression changes that ultimately eradicate the invading microbes.Toll-like receptors (TLRs) are protective immune sentries that sense pathogen-associated molecular patterns (PAMPs) such as unmethylated double-stranded DNA (CpG), single-stranded RNA (ssRNA), lipoproteins, lipopolysaccharide (LPS), and flagellin. In innate immune myeloid cells, TLRs induce the secretion of inflammatory cytokines (Newton and Dixit 2012), thereby engaging lymphocytes to mount an adaptive, antigen-specific immune response (see Fig. 1) that ultimately eradicates the invading microbes (Kawai and Akira 2010).Open in a separate windowFigure 1.TLR signaling (simplified view).Identification of TLR innate immune function began with the discovery that Drosophila mutants in the Toll gene are highly susceptible to fungal infection (Lemaitre et al. 1996). This was soon followed by identification of a human Toll homolog, now known as TLR4 (Medzhitov et al. 1997). To date, 10 TLR family members have been identified in humans, and at least 13 are present in mice. All TLRs consist of an amino-terminal domain, characterized by multiple leucine-rich repeats, and a carboxy-terminal TIR domain that interacts with TIR-containing adaptors. Nucleic acid–sensing TLRs (TLR3, TLR7, TLR8, and TLR9) are localized within endosomal compartments, whereas the other TLRs reside at the plasma membrane (Blasius and Beutler 2010; McGettrick and O’Neill 2010). Trafficking of most TLRs from the endoplasmic reticulum (ER) to either the plasma membrane or endolysosomes is orchestrated by ER-resident proteins such as UNC93B (for TLR3, TLR7, TLR8, and TLR9) and PRAT4A (for TLR1, TLR2, TLR4, TLR7, and TLR9) (Blasius and Beutler 2010). Once in the endolysosomes, TLR3, TLR7, and TLR9 are subject to stepwise proteolytic cleavage, which is required for ligand binding and signaling (Barton and Kagan 2009). For some TLRs, ligand binding is facilitated by coreceptors, including CD14 and MD2.Following ligand engagement, the cytoplasmic TIR domains of the TLRs recruit the signaling adaptors MyD88, TIRAP, TRAM, and/or TRIF (see Fig. 2). Depending on the nature of the adaptor that is used, various kinases (IRAK4, IRAK1, IRAK2, TBK1, and IKKε) and ubiquitin ligases (TRAF6 and pellino 1) are recruited and activated, culminating in the engagement of the NF-κB, type I interferon, p38 MAP kinase (MAPK), and JNK MAPK pathways (Kawai and Akira 2010; Morrison 2012). TRAF6 is modified by K63-linked autoubiquitylation, which enables the recruitment of IκB kinase (IKK) through a ubiquitin-binding domain of the IKKγ (also known as NEMO) subunit. In addition, a ubiquitin-binding domain of TAB2 recognizes ubiquitylated TRAF6, causing activation of the associated TAK1 kinase, which then phosphorylates the IKKβ subunit. Pellino 1 can modify IRAK1 with K63-linked ubiquitin, allowing IRAK1 to recruit IKK directly. TLR4 signaling via the TRIF adaptor protein leads to K63-linked polyubiquitylation of TRAF3, thereby promoting the type I interferon response via interferon regulatory factor (IRFs) (Hacker et al. 2011). Alternatively, TLR4 signaling via MyD88 leads to the activation of TRAF6, which modifies cIAP1 or cIAP2 with K63-linked polyubiquitin (Hacker et al. 2011). The cIAPs are thereby activated to modify TRAF3 with K48-linked polyubiquitin, causing its proteasomal degradation. This allows a TRAF6–TAK1 complex to activate the p38 MAPK pathway and promote inflammatory cytokine production (Hacker et al. 2011). TLR signaling is turned off by various negative regulators: IRAK-M and MyD88 short (MyD88s), which antagonize IRAK1 activation; FADD, which antagonizes MyD88 or IRAKs; SHP1 and SHP2, which dephosphorylate IRAK1 and TBK1, respectively; and A20, which deubiquitylates TRAF6 and IKK (Flannery and Bowie 2010; Kawai and Akira 2010).Open in a separate windowFigure 2.TLR signaling. (Adapted with kind permission of Cell Signaling Technology [http://www.cellsignal.com].)Deregulation of the TLR signaling cascade causes several human diseases. Patients with inherited deficiencies of MyD88, IRAK4, UNC93B1, or TLR3 are susceptible to recurrent bacterial or viral infections (Casanova et al. 2011). Chronic TLR7 and/or TLR9 activation in autoreactive B cells, in contrast, underlies systemic autoimmune diseases (Green and Marshak-Rothstein 2011). Furthermore, oncogenic activating mutations of MyD88 occur frequently in the activated B-cell-like subtype of diffuse large B-cell lymphoma and in other B-cell malignancies (Ngo et al. 2011). Inhibitors of various TLRs or their associated kinases are currently being developed for autoimmune or inflammatory diseases and also hold promise for the treatment of B-cell malignancies with oncogenic MyD88 mutations. Many TLR7 and TLR9 agonists are currently in clinical trials as adjuvants to boost host antitumor responses in cancer patients (Hennessy et al. 2010).     

白介素17受体

白介素17受体是1995年发现的,与任何已知的受体家族不具同源性,可能属于一类新型的尚未鉴定的受体家族.已有的研究表明可溶性小鼠白介素17受体（smIL-17R）不仅能抑制T细胞的活化,而且在已建立的移植模型中,有抑制异种抗原应答的作用.     

Deorphanization of Dresden G Protein-Coupled Receptor for an Odorant Receptor

Dresden G protein-coupled receptor (D-GPCR) is one of orphan G protein-coupled receptors (GPCR). Here we report the identification of the ligands and the characterization of D-GPCR. We investigated over 5000 compounds to evoke the response mediated by D-GPCR and identified 3-methyl-valeric acid and 4-methyl-valeric acid as agonists using a cAMP assay. It is of interest that they dramatically enhanced the intracellular cAMP accumulation and the CRE-luciferase activity in CHO-K1 cells and HEK293 cells expressing the chimeric protein of D-GPCR with a rhodopsin-tag at its N-terminus. Our results established new characteristics of D-GPCR as an olfactory receptor. First, agonists of D-GPCR belong to odorants. Second, D-GPCR mRNA is expressed in the olfactory bulb. In addition, D-GPCR was reported to have similar sequences and its genome locus nearby other olfactory receptors. These results suggest D-GPCR is an olfactory receptor.     

甘氨酸受体的研究进展

甘氨酸受体(GlyR)是中枢神经系统中一种重要的抑制性受体.GlyR是氯离子(Cl^－)选择性通道蛋白,属于配体门控离子通道超家族的一员.天然GlyR是由α和β亚基组装而成的五聚体.介绍了近年来有关GlyR的结构、功能、药理特性研究的重要进展,并结合本实验室工作,论述GlyR的调制及其可能机制.     

G Protein-coupled Receptor Kinase-2 Constitutively Regulates D2 Dopamine Receptor Expression and Signaling Independently of Receptor Phosphorylation

We investigated the regulatory effects of GRK2 on D₂ dopamine receptor signaling and found that this kinase inhibits both receptor expression and functional signaling in a phosphorylation-independent manner, apparently through different mechanisms. Overexpression of GRK2 was found to suppress receptor expression at the cell surface and enhance agonist-induced internalization, whereas short interfering RNA knockdown of endogenous GRK2 led to an increase in cell surface receptor expression and decreased agonist-mediated endocytosis. These effects were not due to GRK2-mediated phosphorylation of the D₂ receptor as a phosphorylation-null receptor mutant was regulated similarly, and overexpression of a catalytically inactive mutant of GRK2 produced the same effects. The suppression of receptor expression is correlated with constitutive association of GRK2 with the receptor complex as we found that GRK2 and several of its mutants were able to co-immunoprecipitate with the D₂ receptor. Agonist pretreatment did not enhance the ability of GRK2 to co-immunoprecipitate with the receptor. We also found that overexpression of GRK2 attenuated the functional coupling of the D₂ receptor and that this activity required the kinase activity of GRK2 but did not involve receptor phosphorylation, thus suggesting the involvement of an additional GRK2 substrate. Interestingly, we found that the suppression of functional signaling also required the Gβγ binding activity of GRK2 but did not involve the GRK2 N-terminal RH domain. Our results suggest a novel mechanism by which GRK2 negatively regulates G protein-coupled receptor signaling in a manner that is independent of receptor phosphorylation.     

LDL受体对清道夫受体活性的影响

应用经ＰＭＡ诱导衍生的ＴＨＰ－１巨噬细胞为模型,以单克隆抗体Ｃ７Ｂ封闭ｏｘＬＤＬ上的ＬＤＬ受体结合位点,结果发现,正常细胞在摄取ｏｘＬＤＬ时ＬＤＬ受体与清道夫受体起协同作用;但Ｃ７Ｂ作用于蓄积了脂质的ＴＨＰ－１巨噬细胞时,对细胞脂质蓄积程度无明显影响,清道夫受体活性不但不降低反而有所升高,说明由于脂质蓄积ＬＤＬ受体的作用减弱．     

Nuclear Receptor Liver X Receptor Is O-GlcNAc-modified in Response to Glucose

Post-translational modification of nucleocytoplasmic proteins by O-linked β-N-acetylglucosamine (O-GlcNAc) has for the last 25 years emerged as an essential glucose-sensing mechanism. The liver X receptors (LXRs) function as nutritional sensors for cholesterol-regulating lipid metabolism, glucose homeostasis, and inflammation. LXRs are shown to be post-translationally modified by phosphorylation, acetylation, and sumoylation, affecting their target gene specificity, stability, and transactivating and transrepressional activity, respectively. In the present study, we show for the first time that LXRα and LXRβ are targets for glucose-hexosamine-derived O-GlcNAc modification in human Huh7 cells. Furthermore, we observed increased hepatic LXRα O-GlcNAcylation in vivo in refed mice and in streptozotocin-induced refed diabetic mice. Importantly, induction of LXRα O-GlcNAcylation in both mouse models was concomitant with increased expression of the lipogenic gene SREBP-1c (sterol regulatory element-binding protein 1c). Furthermore, glucose increased LXR/retinoic acid receptor-dependent activation of luciferase reporter activity driven by the mouse SREBP-1c promoter via the hexosamine biosynthetic pathway in Huh7 cells. Altogether, our results suggest that O-GlcNAcylation of LXR is a novel mechanism by which LXR acts as a glucose sensor affecting LXR-dependent gene expression, substantiating the crucial role of LXR as a nutritional sensor in lipid and glucose metabolism.     

DARPins as Bispecific Receptor Antagonists Analyzed for Immunoglobulin E Receptor Blockage

The concept of multispecific antibodies is of high therapeutic interest but has failed to produce pharmaceutical products due to the poor biophysical properties of such molecules. Here, we propose an alternative and simple way to generate bispecific binding molecules using designed ankyrin repeat proteins (DARPins). For this purpose, monovalent DARPins with different epitope specificities were selected against the α chain of the high-affinity receptor for human immunoglobulin E (IgE) (Fc?RIα). Two of the isolated binders interfering with IgE binding to the receptor were joined to each other or to themselves via a flexible protein linker. The resulting bivalent and bispecific DARPins were tested for their ability to prevent allergen-induced cell degranulation using rat basophilic leukemia cells stably transfected with human Fc?RIα. The bispecific DARPin construct was the most potent one, efficiently blocking the IgE-Fc?RI interaction and preventing the release of proinflammatory mediators. Noteworthy, the multivalent and multispecific DARPin construct did not show any alteration of the beneficial biophysical properties of the monovalent parental DARPins. Hence, bispecific DARPins may be used to generate receptor antagonists simultaneously targeting different epitopes on the same molecule. Moreover, they easily overcome the limiting immunoglobulin binding paradigm (one binding molecule = one epitope) and thereby represent an alternative to monoclonal antibodies in cases where the immunoglobulin scaffold is unsuitable.     

Activation of Calcitonin Receptor and Calcitonin Receptor-like Receptor by Membrane-anchored Ligands

G protein-coupled receptors (GPCRs) are the most important pharmaceutical targets, and more than 40% of drugs in use today modulate GPCR signaling. A major hurdle in the development of therapies targeting GPCRs is the drug candidate''s nonselective actions in multiple tissues. The ability to spatially control GPCR signaling would provide a venue for developing therapies that require targeted GPCR signaling. Here, we show that the fusion of a RAMP1 co-receptor with the calcitonin gene-related peptide (CGRP), or calcitonin, transforms the RAMP1 from a co-receptor to bona fide membrane-anchored ligands (CGRP-RAMP1 and CAL-RAMP1). The CAL-RAMP1 selectively activates the calcitonin receptor (CR), whereas, the CGRP-RAMP1 activates both the calcitonin receptor-like receptor (CLR) and CR. Unlike a free peptide, which moves freely in the extracellular space and differentiates targets based on molecular affinity, the anchored CGRP-RAMP1 and CAL-RAMP1 ligands confine their activities to individual cells. In addition, our study showed that a CGRP8–37-RAMP1 chimera, but not RAMP1, functions as an antagonist for CGRP-RAMP1-mediated signaling, suggesting that the activation of CLR by CGRP-RAMP1 shares similar molecular mechanisms with the CGRP-mediated activation of CLR/RAMP1 receptor complexes. Taken together, our finding thus provides a novel class of ligands that activate CR and CLR exclusively in an autocrine manner and a proof-of-concept demonstration for future development of targeted therapies aimed at these receptors in specific cell populations.     

Allosteric Activation of a G Protein-coupled Receptor with Cell-penetrating Receptor Mimetics

G protein-coupled receptors (GPCRs) are remarkably versatile signaling systems that are activated by a large number of different agonists on the outside of the cell. However, the inside surface of the receptors that couple to G proteins has not yet been effectively modulated for activity or treatment of diseases. Pepducins are cell-penetrating lipopeptides that have enabled chemical and physical access to the intracellular face of GPCRs. The structure of a third intracellular (i3) loop agonist, pepducin, based on protease-activated receptor-1 (PAR1) was solved by NMR and found to closely resemble the i3 loop structure predicted for the intact receptor in the on-state. Mechanistic studies revealed that the pepducin directly interacts with the intracellular H8 helix region of PAR1 and allosterically activates the receptor through the adjacent (D/N)PXXYYY motif through a dimer-like mechanism. The i3 pepducin enhances PAR1/Gα subunit interactions and induces a conformational change in fluorescently labeled PAR1 in a very similar manner to that induced by thrombin. As pepducins can potentially be made to target any GPCR, these data provide insight into the identification of allosteric modulators to this major drug target class.