Site of dopamine D1 receptor binding to Gs protein mapped with synthetic peptides

The Role of the Mammalian Prion Protein in the Control of Sleep

Sleep disruption is a prevalent clinical feature in many neurodegenerative disorders, including human prion diseases where it can be the defining dysfunction, as in the case of the "eponymous" fatal familial insomnia, or an early-stage symptom as in certain types of Creutzfeldt-Jakob disease. It is important to establish the role of the cellular prion protein (PrP^C), the key molecule involved in prion pathogenesis, within the sleep-wake system in order to understand fully the mechanisms underlying its contribution to both healthy circadian rhythmicity and sleep dysfunction during disease. Although severe disruption to the circadian rhythm and melatonin release is evident during the pathogenic phases of some prion diseases, untangling whether PrP^C plays a role in circadian rhythmicity, as suggested in mice deficient for PrP^C expression, is challenging given the lack of basic experimental research. We provide a short review of the small amount of direct literature focused on the role of PrP^C in melatonin and circadian rhythm regulation, as well as suggesting mechanisms by which PrP^C might exert influence upon noradrenergic and dopaminergic signaling and melatonin synthesis. Future research in this area should focus upon isolating the points of dysfunction within the retino-pineal pathway and further investigate PrP^C mediation of pinealocyte GPCR activity.

[Prospects for use of peptides and their derivatives, structurally corresponding to the G protein-coupled receptors, in medicine]

The regulation of signaling pathways involved in the control of many physiological functions is carried out via the heterotrimeric G protein-coupled receptors (GPCR). The search of effective and selective regulators of GPCR and intracellular signaling cascades coupled with them is one of the important problems of modern fundamental and clinical medicine. Recently data suggest that synthetic peptides and their derivatives, structurally corresponding to the intracellular and transmembrane regions of GPCR, can interact with high efficiency and selectivity with homologous receptors and influence, thus, the functional activity of intracellular signaling cascades and fundamental cellular processes controlled by them. GPCR-peptides are active in both in vitro and in vivo. They regulate hematopoiesis, angiogenesis and cell proliferation, inhibit tumor growth and metastasis, and prevent the inflammatory diseases and septic shock. These data show greatest prospects in the development of the new generations of drugs based on GPCR-derived peptides, capable of regulating the important functions of the organism.

D1R/GluN1 complexes in the striatum integrate dopamine and glutamate signalling to control synaptic plasticity and cocaine-induced responses

Convergent dopamine and glutamate signalling onto the extracellular signal-regulated kinase (ERK) pathway in medium spiny neurons (MSNs) of the striatum controls psychostimulant-initiated adaptive processes underlying long-lasting behavioural changes. We hypothesised that the physical proximity of dopamine D1 (D1R) and glutamate NMDA (NMDAR) receptors, achieved through the formation of D1R/NMDAR complexes, may act as a molecular bridge that controls the synergistic action of dopamine and glutamate on striatal plasticity and behavioural responses to drugs of abuse. We found that concomitant stimulation of D1R and NMDAR drove complex formation between endogenous D1R and the GluN1 subunit of NMDAR. Conversely, preventing D1R/GluN1 association with a cell-permeable peptide (TAT-GluN1C1) left individual D1R and NMDAR-dependent signalling intact, but prevented D1R-mediated facilitation of NMDAR-calcium influx and subsequent ERK activation. Electrophysiological recordings in striatal slices from mice revealed that D1R/GluN1 complexes control the D1R-dependent enhancement of NMDAR currents and long-term potentiation in D1R-MSN. Finally, intra-striatal delivery of TAT-GluN1C1 did not affect acute responses to cocaine but reduced behavioural sensitization. Our findings uncover D1R/GluN1 complexes as a major substrate for the dopamine-glutamate interaction in MSN that is usurped by addictive drugs to elicit persistent behavioural alterations. They also identify D1R/GluN1 complexes as molecular targets with a therapeutic potential for the vast spectrum of psychiatric diseases associated with an imbalance between dopamine and glutamate transmission.

Inhibition of the ethanol-induced potentiation of α1 glycine receptor by a small peptide that interferes with Gβγ binding

BACKGROUND

Gβγ interaction with GlyR is an important determinant in ethanol potentiation of this channel.

RESULTS

A small peptide, RQH(C7), can inhibit ethanol potentiation of GlyR currents.

CONCLUSION

Results with RQH(C7) indicate that ethanol mediated potentiation of GlyR is in part by Gβγ activation.

SIGNIFICANCE

Molecular interaction between Gβγ and GlyR could be used as a target for pharmacological modification of ethanol effects. Previous studies indicate that ethanol can modulate glycine receptors (GlyR), in part, through Gβγ interaction with basic residues in the intracellular loop. In this study, we show that a seven-amino acid peptide (RQH(C7)), which has the primary structure of a motif in the large intracellular loop of GlyR (GlyR-IL), was able to inhibit the ethanol-elicited potentiation of this channel from 47 ± 2 to 16 ± 4%, without interfering with the effect of Gβγ on GIRK (G protein activated inwardly rectifying potassium channel) activation. RQH(C7) displayed a concentration-dependent effect on ethanol action in evoked and synaptic currents. A fragment of GlyR-IL without the basic amino acids did not interact with Gβγ or inhibit ethanol potentiation of GlyR. In silico analysis using docking and molecular dynamics allowed to identify a region of ~350Å(2) involving aspartic acids 186, 228, and 246 in Gβγ where we propose that RQH(C7) binds and exerts its blocking action on the effect of ethanol in GlyR.

Stimulation of the D5 dopamine receptor acidifies the lysosomal pH of retinal pigmented epithelial cells and decreases accumulation of autofluorescent photoreceptor debris

Optimal neuronal activity requires that supporting cells provide both efficient nutrient delivery and waste disposal. The incomplete processing of engulfed waste by their lysosomes can lead to accumulation of residual material and compromise their support of neurons. As most degradative lysosomal enzymes function best at an acidic pH, lysosomal alkalinization can impede enzyme activity and increase lipofuscin accumulation. We hypothesize that treatment to reacidify compromised lysosomes can enhance degradation. Here, we demonstrate that degradation of ingested photoreceptor outer segments by retinal pigmented epithelial cells is increased by stimulation of D5 dopamine receptors. D1/D5 receptor agonists reacidified lysosomes in cells alkalinized by chloroquine or tamoxifen, with acidification dependent on protein kinase A. Knockdown with siRNA confirmed acidification was mediated by the D5 receptor. Exposure of cells to outer segments increased lipofuscin-like autofluorescence, but SKF 81297 reduced autofluorescence. Likewise, SKF 81297 increased the activity of lysosomal protease cathepsin D in situ. D5DR stimulation also acidified lysosomes of retinal pigmented epithelial cells from elderly ABCA4(-/-) mice, a model of recessive Stargardt's retinal degeneration. In conclusion, D5 receptor stimulation lowers compromised lysosomal pH, enhancing degradation. The reduced accumulation of lipofuscin-like autofluorescence implies the D5 receptor stimulation may enable cells to better support adjacent neurons.

Signal protein-derived peptides as functional probes and regulators of intracellular signaling

The functionally important regions of signal proteins participating in their specific interaction and responsible for transduction of hormonal signal into cell are rather short in length, having, as a rule, 8 to 20 amino acid residues. Synthetic peptides corresponding to these regions are able to mimic the activated form of full-size signal protein and to trigger signaling cascades in the absence of hormonal stimulus. They modulate protein-protein interaction and influence the activity of signal proteins followed by changes in their regulatory and catalytic sites. The present review is devoted to the achievements and perspectives of the study of signal protein-derived peptides and to their application as selective and effective regulators of hormonal signaling systems in vitro and in vivo. Attention is focused on the structure, biological activity, and molecular mechanisms of action of peptides, derivatives of the receptors, G protein α subunits, and the enzymes generating second messengers.

A cyclic peptide mimicking the third intracellular loop of the V2 vasopressin receptor inhibits signaling through its interaction with receptor dimer and G protein

In this study, we investigated the mechanism by which a peptide mimicking the third cytoplasmic loop of the vasopressin V2 receptor inhibits signaling. This loop was synthesized as a cyclic peptide (i3 cyc) that adopted defined secondary structure in solution. We found that i3 cyc inhibited the adenylyl cyclase activity induced by vasopressin or a nonhydrolyzable analog of GTP, guanosine 5'-O-(3-thio)triphosphate. This peptide also affected the specific binding of [3H]AVP by converting vasopressin binding sites from a high to a low affinity state without any effect on the global maximal binding capacity. The inhibitory actions of i3 cyc could also be observed in the presence of maximally uncoupling concentration of guanosine 5'-O-(3-thio)triphosphate, indicating a direct effect on the receptor itself and not exclusively on the interaction between the Gs protein and the V2 receptor (V2-R). Bioluminescence resonance energy-transfer experiments confirmed this assumption, because i3 cyc induced a significant inhibition of the bioluminescence resonance energy-transfer signal between the Renilla reniformis luciferase and the enhanced yellow fluorescent protein fused V2-R. This suggests that the proper arrangement of the dimer could be an important prerequisite for triggering Gs protein activation. In addition to its effect on the receptor itself, the peptide exerted some of its actions at the G protein level, because it could also inhibit guanosine 5'-O-(3-thio)triphosphate-stimulated AC activity. Taken together, the data demonstrate that a peptide mimicking V2-R third intracellular loop affects both the dimeric structural organization of the receptor and has direct inhibitory action on Gs.

A novel transduction mechanism mediating dopamine-induced vascular relaxation: opening of BKCa channels by cyclic AMP-induced stimulation of the cyclic GMP-dependent protein kinase

Dopamine dilates the coronary, renal and other vascular beds; however, the signaling pathway underlying this effect is unclear. In this study the signal-transduction process mediating dopamine-induced relaxation of porcine coronary arteries was investigated in isolated vessels and single arterial myocytes. Dopamine-induced relaxation of arteries was mediated through the DA- receptor and involved K+ efflux, and subsequent patch-clamp studies demonstrated that either dopamine or fenoldopam, a selective DA-1 agonist, increased the opening probability of the large-conductance, calcium- and voltage-activated K+ (BKCa) channel in coronary myocytes. Moreover, blockade of this channel by iberiotoxin prevented dopamine-induced coronary relaxation. Dopamine stimulation of BKCa channels was completely prevented by a DA-1-receptor antagonist, but was unaffected by propranolol. Furthermore, inhibiting adenylyl cyclase activity prevented stimulation of BKCa channel activity, whereas chlorophenylthio (CPT)-cyclic adenosine monophosphate (AMP), a membrane-permeable analog of cyclic AMP, mimicked the effects of dopamine. Interestingly, inhibiting the cyclic AMP-dependent protein kinase (PKA) did not affect the response to dopamine, whereas dopamine-induced channel activity was completely blocked by inhibiting the activity of the cyclic guanosine monophosphate (GMP)-dependent protein kinase (PKG). These findings demonstrate that activation of DA-1 receptors causes stimulation of BKCa channel activity by a mechanism involving cyclic AMP-dependent stimulation of PKG, but not PKA, and further suggest that this cross-reactivity mediates dopamine-induced coronary vasodilation.

Mediation of cyclic AMP signaling by the first intracellular loop of the gonadotropin-releasing hormone receptor

The gonadotropin-releasing hormone (GnRH) receptor, which is a unique G protein-coupled receptor without a C-terminal cytoplasmic domain, activates both inositol phosphate (InsP) and cAMP signaling responses. The function of the highly basic first intracellular (1i) loop of the GnRH receptor in signal transduction was evaluated by mutating selected residues located in its N and C termini. Replacements of Leu58, Lys59, Gln61, and Lys62 at the N terminus, and Leu73, Ser74, and Leu80 at the C terminus, caused no change in binding affinity. The agonist-induced InsP and cAMP responses of the Q61E and K59Q,K62Q receptors were also unaffected, but the L58A receptor showed a normal InsP response and an 80% decrease in cAMP production. At the C terminus, the InsP response of the L73R receptor was normal, but cAMP production was reduced by 80%. The EC50 for GnRH-induced InsP responses of the S74E and L80A receptors was increased by about one order of magnitude, and the cAMP responses were essentially abolished. These findings indicate that cAMP signaling from the GnRH receptor is dependent on specific residues in the 1i loop that are not essential for activation of the phosphoinositide signaling pathway.

Expression and purification of the Saccharomyces cerevisiae alpha-factor receptor (Ste2p), a 7-transmembrane-segment G protein-coupled receptor

A plasmid vector was developed that permitted high-level expression of a functional form of the Saccharomyces cerevisiae alpha-factor receptor (the STE2 gene product) tagged at its C-terminal end with an epitope (FLAG) and a His6 tract. When expressed in yeast from this plasmid, Ste2p was produced at a level at least 3-fold higher than that reported previously for any other 7-transmembrane-segment receptor expressed in the same cells. For purification, isolated cell membranes containing the overexpressed receptor were solubilized with detergent under specific conditions and subjected to immobilized metal affinity chromatography. Yields as high as 1 mg of nearly homogeneous (95%) receptor were routinely obtained even from relatively small scale preparations (60 g of frozen cell paste). The purified receptor was reconstituted into artificial phospholipid vesicles. Radioligand binding studies demonstrated that the purified receptor, in the reconstituted vesicles, bound its tridecapeptide ligand (alpha-factor) with a KD (155 nM) consistent with the affinity expected for this receptor in the absence of its associated G protein. Efficient restoration of ligand binding activity upon reconstitution required the addition of solubilized membranes prepared from a yeast strain lacking the receptor. Sufficient amounts of active material can be obtained by this procedure to allow physical studies of this receptor and other 7-transmembrane-segment receptors expressed in this system.

A new linear V1A vasopressin antagonist and its use in characterizing receptor/G protein interactions

We characterized a new iodinated, high affinity, linear V1a vasopressin antagonist, phenylacetylD-Tyr(Et)Phe-Gln-Asn-Lys-Pro-Arg-Tyr-NH2. The antagonist bound specifically to the V1a vasopressin receptor in crude rat liver membranes with an apparent Kd value of 0.168 nM. This affinity is approximately 1 order of magnitude greater than that of the natural agonist, vasopressin. The inhibitory activity of the antagonist can be demonstrated by its inability to elicit activation and uncoupling of G proteins from the receptor. Thus, after occupancy of receptor sites in rat liver membranes with labeled antagonist and detergent solubilization, the labeled receptor (approximately 60 kDa) was eluted as a stable 400-kDa complex on size-exclusion chromatography. In contrast, when the receptor sites were occupied by the agonist [3H]vasopressin, the receptor eluted as a 60-kDa peak. Coincubation of membranes with iodinated antagonist and an excess of unlabeled vasopressin caused both reduced antagonist binding and a complete shift from the 400-kDa to the 60-kDa peak. The addition of vasopressin to unliganded 400-kDa fractions resulted in a 75% increase in [35S]guanosine-5'-O-(3-thio)triphosphate binding activity, indicating that the 400-kDa fraction contains complexes between the V1a receptor and G proteins. The vasopressin-elicited increase was inhibited by antagonist. Using specific antibodies and immunoadsorption to protein A/Sepharose columns, we found that G protein isotypes G(alpha q/11), G(alpha i3), and G(alpha s), and effector enzymes PLC-beta1, PLC-gamma2 and PLA-2 were associated with the antagonist-labeled receptor in the 400-kDa fraction. Because the 400-kDa complex was found in the absence of ligand, the V1a receptor and the appropriate G proteins and effector enzymes are likely preassociated with each other and do not aggregate after antagonist addition. The association of V1a receptor with the different specific G proteins and effector enzymes is consistent with the multiple actions of vasopressin on liver cells. Antibodies directed against a portion of the carboxyl-terminal domain of the V1a receptor interacted with 60-kDa antagonist-occupied receptor but not with receptor in the 400-kDa complex. These results suggest that the carboxyl-terminal region of the receptor is sterically hindered when coupled to G proteins. The iodinated linear vasopressin antagonist therefore allows stable receptor/G protein complexes and can be an important tool (along with the antisera) for use in the study of factors that control V1a receptor/G protein coupling.

Cloning and sequence analysis of a hypothalamic cDNA encoding a D1c dopamine receptor in tilapia

Physiological and pharmacological studies have indicated that during acid stress a D1-like dopamine receptor becomes functional on intermediate pituitary melanocyte-stimulating hormone cells of tilapia (Oreochromis mossambicus). As a first step towards physiological expression studies we isolated a D1-like dopamine receptor from a tilapia hypothalamus cDNA library. Construction of a phylogenetic tree of most of the D1-like receptors known in human, rat, Xenopus, goldfish and Drosophila revealed that the here presented clone is most likely the tilapia equivalent of the Xenopus D1c dopamine receptor.

Synthetic peptides corresponding to residues 551 to 555 and 650 to 653 of the rat testicular follicle-stimulating hormone (FSH) receptor are sufficient for post-receptor modulation of Sertoli cell responsiveness to FSH stimulation

We have recently demonstrated that synthetic peptides corresponding to the third cytoplasmic (3i) loop (residues 533 to 555) and a region in the carboxy-terminal cytoplasmic tail (residues 645 to 653) of the rat testicular follicle-stimulating hormone receptor (FSHR) affected signal transduction in rat testis membranes and cultured rat Sertoli cells. In order to define more precisely the peptide domains involved, we synthesized truncated peptide amides corresponding to FSHR residues 551-555 (KIAKR) and 650-653 (RKSH), respectively. These two regions were chosen since they contained a minimal structural motif present in G protein activator regions of several other G protein-coupled receptors (i.e., B-X-X-B-B or B-B-X-B, B representing a basic amino acid). Neither peptide inhibited binding of FSH to testis membrane receptors. Each peptide significantly reduced FSH-stimulated estradiol biosynthesis by intact cultured rat Sertoli cells. The same results were obtained with streptolysin O-permeabilized Sertoli cells. No effect was noted on forskolin-induced steroidogenesis, indicating that the peptide effects were not due to interaction with adenylyl cyclase. Each peptide amide, however, induced concentration-dependent increases in guanine nucleotide exchange in rat testis membranes. Our results indicate that interaction of FSH receptor with its associated G protein may involve relatively restricted peptide sequences, and include residues 551-555 (KIAKR) in the third cytoplasmic loop, and residues 650-653 (RKSH) in the carboxy-terminal cytoplasmic tail of the FSH receptor.

A synthetic peptide corresponding to residues 645-653 in the carboxyl terminal cytoplasmic domain of the rat testicular follicle stimulating hormone receptor modulates G protein coupled-receptor signaling in rat testis membranes and in intact cultured rat Sertoli cells

We examined the involvement of the carboxyl terminal cytoplasmic domain (residues 645-653) of the rat testicular FSH receptor in FSH signal transduction utilizing light membranes prepared from immature rat testes, intact cultured rat Sertoli cells, and a synthetic peptide approach. This region of the FSH receptor was selected because of its structural similarity to receptor-G protein contact sites identified in other G protein-coupled receptors. FSHR- (645-653) peptide amide promoted guanine nucleotide exchange in rat testis membranes, presumably via its interaction with membrane-associated G protein, but did not inhibit FSH binding to testis membrane receptors. When incubated with intact cultured Sertoli cells from immature rat testes, FSHR- (645-653) peptide amide consistently and significantly stimulated basal cAMP and estradiol biosynthesis. The peptide had no effect on forskolin stimulation of cAMP and estradiol, but inhibited FSH stimulation of each. FSH binding to receptor was unaffected by the peptide, these results suggest peptide interaction with receptor-associated G protein. The effects of FSHR- (645-653) peptide amide on FSH-stimulated estradiol biosynthesis were prevented by pretreating Sertoli cells with phenylarsine oxide, an inhibitor of FSH receptor internalization. These results suggest that peptide effects in intact Sertoli cells were related to peptide entry into the cell, presumably during receptor-mediated endocytosis of FSH, or by diffusion. Synthetic peptide amides not satisfying structural criteria for G protein coupling had no effect on either guanine nucleotide exchange or estradiol biosynthesis, even at concentrations significantly higher than used for FSHR- (645-653) peptide amide.(ABSTRACT TRUNCATED AT 250 WORDS)