RESUMEN
ALX40-4C is a small peptide inhibitor of the chemokine receptor CXCR4 that can inhibit X4 strains of HIV-1. Prior to the discovery of chemokine receptors as the HIV coreceptors, ALX40-4C was used in phase I/II clinical trials to evaluate its therapeutic potential against HIV-1, making ALX40-4C the first anticoreceptor inhibitor to be tested in humans against HIV-1. Patients in the highest dose groups achieved ALX40-4C levels above the effective concentration of the drug for nearly the entire 1-month treatment period. ALX40-4C was well tolerated by 39 of 40 asymptomatic HIV-infected patients, despite the critical role of CXCR4 in normal development and hematopoiesis. No significant or consistent reductions in viral load were observed, but only 12 of the enrolled patients harbored virus types that used CXCR4. We also found that ALX40-4C interacts with the second extracellular loop of CXCR4 and inhibits infection exclusively by blocking direct virus-CXCR4 interactions.
Asunto(s)
Fármacos Anti-VIH/uso terapéutico , Infecciones por VIH/tratamiento farmacológico , VIH-1/efectos de los fármacos , Oligopéptidos/uso terapéutico , Receptores CXCR4/antagonistas & inhibidores , Adulto , Fármacos Anti-VIH/administración & dosificación , Fármacos Anti-VIH/metabolismo , Fármacos Anti-VIH/farmacocinética , Linfocitos T CD4-Positivos/efectos de los fármacos , Linfocitos T CD8-positivos/efectos de los fármacos , Línea Celular , Seguridad de Productos para el Consumidor , Femenino , Infecciones por VIH/sangre , Humanos , Masculino , Persona de Mediana Edad , Oligopéptidos/administración & dosificación , Oligopéptidos/metabolismo , Oligopéptidos/farmacocinética , Receptores CXCR4/genética , Receptores CXCR4/metabolismo , Receptores CXCR4/fisiologíaRESUMEN
Despite recent studies depicting the capacity of G protein-coupled receptors (GPCRs) to activate mitogenic signaling pathways more commonly associated with receptor tyrosine kinases (RTKs), little is known regarding the interactive effects of GPCR and RTK activation on cell growth and signal transduction. Such interactions likely mediate the physiologic growth in most cells in vivo as well as the aberrant, non-neoplastic growth that occurs in diseases such as asthma, where disruptions of the local hormonal or inflammatory state can contribute to significant GPCR activation. In this study, we show that numerous inflammatory or contractile agents, including thrombin, histamine, and carbachol, potentiate epidermal growth factor (EGF)-stimulated proliferation of human airway smooth muscle (ASM), thus demonstrating a clear synergy between RTK and GPCR activation. Alterations in promitogenic nuclear signaling were evidenced by additive or synergistic increases in Elk-1 and activator protein-1 activation, and by increases in cyclin D1 expression. Interestingly, GPCR activation did not cause EGF receptor tyrosine phosphorylation nor did it increase EGF-stimulated autophosphorylation. In the presence of EGF, histamine or carbachol did not alter the time-dependent phosphorylation of p42/p44, whereas thrombin was capable of increasing phospho-p42/p44 levels at selected time points in some, but not all, cultures. In contrast to their relative inability to alter EGF receptor-linked p42/p44 activation, thrombin, histamine, and carbachol consistently increased the late phase (> 1 h) activity of p70 S6 kinase. Collectively, these findings suggest that inflammatory and contractile agents that activate GPCRs can significantly modulate RTK-mediated ASM growth through a p70 S6 kinase-dependent, p42/p44-independent mechanism.
Asunto(s)
Proteínas de Unión al GTP/metabolismo , Músculo Liso/metabolismo , Proteínas Tirosina Quinasas Receptoras/metabolismo , Tráquea/efectos de los fármacos , Carbacol/farmacología , Células Cultivadas , Ciclina D1/metabolismo , Replicación del ADN/efectos de los fármacos , Activación Enzimática , Factor de Crecimiento Epidérmico/farmacología , Histamina/farmacología , Humanos , Músculo Liso/enzimología , Fosforilación , Trombina/farmacología , Tráquea/enzimología , Tráquea/metabolismoRESUMEN
The G protein-coupled chemokine receptor CXCR4 serves as the primary coreceptor for entry of T-cell tropic human immunodeficiency virus. CXCR4 undergoes tonic internalization as well as internalization in response to stimulation with phorbol esters and ligand (SDF-1alpha). We investigated the trafficking of this receptor, and we attempted to define the residues of CXCR4 that were critical for receptor internalization. In both COS-1 and HEK-293 cells transiently overexpressing CXCR4, SDF-1alpha and phorbol esters (PMA) promoted rapid internalization of cell surface receptors as assessed by both enzyme-linked immunosorbent assay and immunofluorescence analysis. Expression of GRK2 and/or arrestins promoted modest additional CXCR4 internalization in response to both PMA and SDF. Both PMA- and SDF-mediated CXCR4 internalization was inhibited by coexpression of dominant negative mutants of dynamin-1 and arrestin-3. Arrestin was also recruited to the plasma membrane and appeared to colocalize with internalized receptors in response to SDF but not PMA. We then evaluated the ability of CXCR4 receptors containing mutations of serines and threonines, as well as a dileucine motif, within the C-terminal tail to be internalized and phosphorylated in response to either PMA or SDF-1alpha. This analysis showed that multiple residues within the CXCR4 C-terminal tail appear to mediate both PMA- and SDF-1alpha-mediated receptor internalization. The ability of coexpressed GRK2 and arrestins to promote internalization of the CXCR4 mutants revealed distinct differences between respective mutants and suggested that the integrity of the dileucine motif (Ile-328 and Leu-329) and serines 324, 325, 338, and 339 are critical for receptor internalization.
Asunto(s)
Arrestinas/metabolismo , GTP Fosfohidrolasas/metabolismo , VIH/fisiología , Receptores CXCR4/química , Receptores CXCR4/metabolismo , Secuencia de Aminoácidos , Sustitución de Aminoácidos , Animales , Arrestinas/genética , Células COS , Línea Celular , Membrana Celular/efectos de los fármacos , Membrana Celular/fisiología , Quimiocina CCL5/farmacología , Quimiocina CXCL12 , Quimiocinas CXC/farmacología , Dinamina I , Dinaminas , Endocitosis/efectos de los fármacos , GTP Fosfohidrolasas/genética , Humanos , Cinética , Datos de Secuencia Molecular , Mutagénesis Sitio-Dirigida , Receptores CCR5/metabolismo , Receptores CXCR4/genética , Proteínas Recombinantes/química , Proteínas Recombinantes/metabolismo , Alineación de Secuencia , Serina , Células del Estroma/fisiología , Acetato de Tetradecanoilforbol/farmacología , TransfecciónRESUMEN
Asthma is frequently associated with abnormal airway smooth muscle (ASM) growth that may contribute to airway narrowing and hyperresponsiveness to contractile agents. Although numerous hormones and cytokines have been shown to induce human ASM (HASM) proliferation, the cellular and molecular mechanisms underlying HASM hyperplasia are largely unknown. Here we characterize the roles of the mitogen-activated protein kinase (MAPK) superfamily [p42/p44 MAPK, c-Jun amino-terminal kinase/stress-activated protein kinase (JNK/SAPK), and p38] in mediating hormone- and cytokine-induced HASM proliferation. Significant enhancement of [(3)H]thymidine incorporation in HASM cultures was observed only by treatment with agents (epidermal growth factor, platelet-derived growth factor, thrombin, and phorbol 12-myristate 13-acetate) that promoted a strong and sustained activation of p42/p44 MAPK. Significant activation of the JNK/SAPK and p38 pathways was only observed on stimulation with interleukin (IL)-1beta and tumor necrosis factor-alpha, agents that did not appreciably stimulate HASM proliferation. Two different inhibitors of MAPK/extracellular signal-regulated kinase kinase (MEK), PD-98059 and U-0126, inhibited mitogen-induced [3H]thymidine incorporation in a manner consistent with their ability to inhibit p42/p44 activation. Elk-1 and activator protein-1 reporter activation by mitogens was similarly inhibited by inhibition of MEK, suggesting a linkage between p42/p44 activation, transcription factor activation, and HASM proliferation. These findings establish a fundamental role for p42/p44 activation in regulating HASM proliferation and provide insight into species-specific differences observed among studies in ASM mitogenesis.
Asunto(s)
Proteínas de Unión al ADN , Regulación de la Expresión Génica , Proteínas Quinasas Activadas por Mitógenos/genética , Familia de Multigenes/genética , Músculo Liso/fisiología , Proteínas Serina-Treonina Quinasas , Tráquea/fisiología , Factores de Transcripción , División Celular/efectos de los fármacos , División Celular/fisiología , Células Cultivadas , Activación Enzimática/efectos de los fármacos , Activación Enzimática/fisiología , Humanos , MAP Quinasa Quinasa 1 , MAP Quinasa Quinasa 2 , Proteína Quinasa 1 Activada por Mitógenos/fisiología , Proteína Quinasa 3 Activada por Mitógenos , Quinasas de Proteína Quinasa Activadas por Mitógenos/antagonistas & inhibidores , Proteínas Quinasas Activadas por Mitógenos/metabolismo , Proteínas Quinasas Activadas por Mitógenos/fisiología , Mitosis/fisiología , Músculo Liso/citología , Proteínas Tirosina Quinasas/antagonistas & inhibidores , Proteínas Proto-Oncogénicas/genética , Tráquea/citología , Factor de Transcripción AP-1/genética , Transcripción Genética , Proteína Elk-1 con Dominio etsRESUMEN
To better understand the means by which cells such as human platelets regulate the binding of the integrin alphaIIbbeta3 to fibrinogen, we have examined agonist-initiated inside-out and outside-in signalling in CHRF-288 cells, a megakaryoblastic cell line that expresses alphaIIbbeta3 and the human thrombin receptor, PAR1. The results show several notable similarities and differences. (1) Activation of PAR1 caused CHRF-288 cells to adhere and spread on immobilized fibrinogen in an alphaIIbbeta3-dependent manner, but did not support the binding of soluble fibrinogen or PAC-1, an antibody specific for activated alphaIIbbeta3. (2) Direct activation of protein kinase C with PMA or disruption of the actin cytoskeleton with low concentrations of cytochalasin D also caused CHRF-288 cells to adhere to fibrinogen. (3) Despite the failure to bind soluble fibrinogen, activation of PAR1 in CHRF-288 cells caused phosphoinositide hydrolysis, arachidonate mobilization and the phosphorylation of p42MAPK, phospholipase A2 and the Rac exchange protein, Vav, all of which occur in platelets. PAR1 activation also caused an increase in cytosolic Ca2+, which, when prevented, blocked adhesion to fibrinogen. (4) Finally, as in platelets, adhesion of CHRF-288 cells to fibrinogen was followed by a burst of integrin-dependent ('outside-in') signalling, marked by FAK phosphorylation and a more prolonged phosphorylation of p42MAPK. However, in contrast to platelets, adhesion to fibrinogen had no effect on Vav phosphorylation. Collectively, these observations show that signalling initiated through PAR1 in CHRF-288 cells can support alphaIIbbeta3 binding to immobilized ligand, but not the full integrin activation needed to bind soluble ligand. This would suggest that there has been an increase in integrin avidity without an accompanying increase in affinity. Such increases in avidity are thought to be due to integrin clustering, which would also explain the results obtained with cytochalasin D. The failure of alphaIIbbeta3 to achieve the high affinity state in CHRF-288 cells was not due to the failure of PAR1 activation to initiate a number of signalling events that normally accompany platelet activation nor did it prevent at least some forms of outside-in signalling. However, at least one marker of outside-in signalling, the augmentation of Vav phosphorylation seen during platelet aggregation, did not occur in CHRF-288 cells.
Asunto(s)
Proteínas de Ciclo Celular , Complejo GPIIb-IIIa de Glicoproteína Plaquetaria/metabolismo , Receptores de Trombina/metabolismo , Plaquetas/metabolismo , Calcio/metabolismo , Adhesión Celular , Línea Celular , Fibrinógeno/metabolismo , Humanos , Indoles/farmacología , Maleimidas/farmacología , Fragmentos de Péptidos/farmacología , Fosfatidilinositol 3-Quinasas/metabolismo , Fosforilación , Unión Proteica , Proteínas Proto-Oncogénicas/metabolismo , Proteínas Proto-Oncogénicas c-vav , Receptor PAR-1 , Transducción de Señal , Acetato de Tetradecanoilforbol/farmacología , Trombina/farmacologíaRESUMEN
Hypertrophy and hyperplasia of airway smooth muscle (ASM) are important pathological features that contribute to airflow obstruction in chronic severe asthma. Despite considerable research effort, the cellular mechanisms that modulate ASM growth remain unknown. Recent evidence suggests that mitogen-induced activation of phosphoinositide (PI)-specific phospholipase C (PLC) and PI-dependent calcium mobilization are neither sufficient nor necessary to stimulate human ASM proliferation. In this study, we identify phosphatidylinositol (PtdIns) 3-kinase as a key regulator of human ASM proliferation. Pretreatment of human ASM with the PtdIns 3-kinase inhibitors wortmannin and LY-294002 significantly reduced thrombin- and epidermal growth factor (EGF)-induced DNA synthesis (IC(50) approximately 10 nM and approximately 3 microM, respectively). In separate experiments, wortmannin and LY-294002 markedly inhibited PtdIns 3-kinase and 70-kDa S6 protein kinase (pp70(S6k)) activation induced by stimulation of human ASM cells with EGF and thrombin but had no effect on EGF- and thrombin-induced p42/p44 mitogen-activated protein kinase (MAPK) activation. The specificity of wortmannin and LY-294002 was further suggested by the demonstrated inability of these compounds to alter thrombin-induced calcium transients, total PI hydrolysis, or basal cAMP levels. Transient expression of constitutively active PtdIns 3-kinase (p110*) activated pp70(S6k), whereas a dominant-negative PtdIns 3-kinase (Deltap85) blocked EGF- and thrombin-stimulated pp70(S6k) activity. Collectively, these data suggest that activation of PtdIns 3-kinase is required for the mitogenic effect of EGF and thrombin in human ASM cells. Further investigation of the role of PtdIns 3-kinase may offer new therapeutic approaches in the treatment of diseases characterized by smooth muscle cell hyperplasia such as asthma and chronic bronchitis.
Asunto(s)
Mitógenos/farmacología , Músculo Liso/citología , Fosfatidilinositol 3-Quinasas/fisiología , Tráquea/citología , Androstadienos/farmacología , Calcio/metabolismo , Proteínas Quinasas Dependientes de Calcio-Calmodulina/metabolismo , División Celular/efectos de los fármacos , División Celular/fisiología , Células Cultivadas , Cromonas/farmacología , AMP Cíclico/metabolismo , Activación Enzimática/efectos de los fármacos , Activación Enzimática/fisiología , Inhibidores Enzimáticos/farmacología , Factor de Crecimiento Epidérmico/farmacología , Humanos , Morfolinas/farmacología , Fosfatidilinositol 3-Quinasas/metabolismo , Fosfatidilinositoles/metabolismo , Inhibidores de las Quinasa Fosfoinosítidos-3 , Proteínas Quinasas S6 Ribosómicas/metabolismo , Trombina/farmacología , WortmaninaRESUMEN
We investigated the role of arrestins in the trafficking of human alpha2-adrenergic receptors (alpha2-ARs) and the effect of receptor trafficking on p42/p44 MAP kinase activation. alpha2-ARs expressed in COS-1 cells demonstrated a modest level of agonist-mediated internalization, with alpha2c > alpha2b > alpha2a. However, upon coexpression of arrestin-2 (beta-arrestin-1) or arrestin-3 (beta-arrestin-2), internalization of the alpha2b AR was dramatically enhanced and redistribution of receptors to clathrin coated vesicles and endosomes was observed. Internalization of the alpha2c AR was selectively promoted by coexpression of arrestin-3, while alpha2a AR internalization was only slightly stimulated by coexpression of either arrestin. Coexpression of GRK2 had no effect on the internalization of any alpha2-AR subtype, either in the presence or absence of arrestins. Internalization of the alpha2b and alpha2c ARs was inhibited by coexpression of dominant negative dynamin-K44A. However, alpha2-AR-mediated activation of either endogenous or cotransfected p42/p44 mitogen-activated protein (MAP) kinase was not affected by either dynamin-K44A or arrestin-3. Moreover, activation of p42/p44 MAP kinase by endogenous epidermal growth factor, lysophosphatidic acid, and beta2-adrenergic receptors was also unaltered by dynamin-K44A. In summary, our data suggest that internalization of the alpha2b, alpha2c, and to a lesser extent alpha2a ARs, is both arrestin- and dynamin-dependent. However, endocytosis does not appear to be required for alpha2-adrenergic, epidermal growth factor, lysophosphatidic acid, or beta2-adrenergic receptor-mediated p42/p44 MAP kinase activation in COS-1 cells.
Asunto(s)
Arrestinas/fisiología , Endocitosis/fisiología , Receptores Adrenérgicos alfa 2/fisiología , Transducción de Señal/fisiología , Secuencia de Aminoácidos , Animales , Células COS , Proteínas Quinasas Dependientes de Calcio-Calmodulina/metabolismo , Activación Enzimática , Factor de Crecimiento Epidérmico/fisiología , Proteínas de Unión al GTP/metabolismo , Humanos , Lisofosfolípidos/fisiología , Microscopía Fluorescente , Datos de Secuencia Molecular , Proteínas Tirosina Quinasas Receptoras/metabolismo , Receptores Adrenérgicos beta 2/fisiologíaRESUMEN
Thromboxane A2 (TXA2) potently stimulates platelet aggregation and smooth muscle constriction and is thought to play a role in myocardial infarction, atherosclerosis, and bronchial asthma. The TXA2 receptor (TXA2R) is a member of the G protein-coupled receptor family and is found as two alternatively spliced isoforms, alpha (343 residues) and beta (407 residues), which share the first 328 residues. In the present report, we demonstrate by enzyme-linked immunosorbent assay and immunofluorescence microscopy that the TXA2Rbeta, but not the TXA2Ralpha, undergoes agonist-induced internalization when expressed in HEK293 cells as well as several other cell types. Various dominant negative mutants were used to demonstrate that the internalization of the TXA2Rbeta is dynamin-, GRK-, and arrestin-dependent in HEK293 cells, suggesting the involvement of receptor phosphorylation and clathrin-coated pits in this process. Interestingly, the agonist-stimulated internalization of both the alpha and beta isoforms, but not of a mutant truncated after residue 328, can be promoted by overexpression of arrestin-3, identifying the C-tails of both receptors as necessary in arrestin-3 interaction. Simultaneous mutation of two dileucine motifs in the C-tail of TXA2Rbeta did not affect agonist-promoted internalization. Analysis of various C-tail deletion mutants revealed that a region between residues 355 and 366 of the TXA2Rbeta is essential for agonist-promoted internalization. These data demonstrate that alternative splicing of the TXA2R plays a critical role in regulating arrestin binding and subsequent receptor internalization.
Asunto(s)
Proteínas de Drosophila , Receptores de Tromboxanos/metabolismo , Factor de Crecimiento Transformador alfa , Ácido 15-Hidroxi-11 alfa,9 alfa-(epoximetano)prosta-5,13-dienoico/farmacología , Empalme Alternativo/genética , Secuencia de Aminoácidos , Arrestinas/genética , Línea Celular , Dinaminas , Endocitosis/efectos de los fármacos , Ensayo de Inmunoadsorción Enzimática , Técnica del Anticuerpo Fluorescente , GTP Fosfohidrolasas/genética , Humanos , Proteínas de Insectos/genética , Cinética , Datos de Secuencia Molecular , Mutación/genética , Fosforilación , Isoformas de Proteínas/agonistas , Isoformas de Proteínas/metabolismo , Receptores de Superficie Celular/metabolismo , Receptores de Tromboxanos/agonistas , Receptores de Tromboxanos/genética , Transfección , Factores de Crecimiento Transformadores/genéticaRESUMEN
The interaction of the chemokine stromal cell-derived factor 1 (SDF-1) with its receptor CXCR4 is vital for cell trafficking during development, is capable of inhibiting human immunodeficiency virus type 1 (HIV-1) utilization of CXCR4 as a coreceptor, and has been implicated in delaying disease progression to AIDS in vivo. Because of the importance of this chemokine-chemokine receptor pair to both development and disease, we investigated the molecular basis of the interaction between CXCR4 and its ligands SDF-1 and HIV-1 envelope. Using CXCR4 chimeras and mutants, we determined that SDF-1 requires the CXCR4 amino terminus for binding and activates downstream signaling pathways by interacting with the second extracellular loop of CXCR4. SDF-1-mediated activation of CXCR4 required the Asp-Arg-Tyr motif in the second intracellular loop of CXCR4, was pertussis toxin sensitive, and did not require the distal C-terminal tail of CXCR4. Several CXCR4 mutants that were not capable of binding SDF-1 or signaling still supported HIV-1 infection, indicating that the ability of CXCR4 to function as a coreceptor is independent of its ability to signal. Direct binding studies using the X4 gp120s HXB, BH8, and MN demonstrated the ability of HIV-1 gp120 to bind directly and specifically to the chemokine receptor CXCR4 in a CD4-dependent manner, using a conformationally complex structure on CXCR4. Several CXCR4 variants that did not support binding of soluble gp120 could still function as viral coreceptors, indicating that detectable binding of monomeric gp120 is not always predictive of coreceptor function.
Asunto(s)
Quimiocinas CXC/metabolismo , Proteína gp120 de Envoltorio del VIH/metabolismo , Receptores CXCR4/metabolismo , Secuencia de Aminoácidos , Línea Celular , Quimiocina CXCL12 , Humanos , Datos de Secuencia Molecular , Receptores CXCR4/genética , Transducción de SeñalRESUMEN
We have constructed and optimized a high yielding Escherichia coli expression system to produce glycosylation-free human procathepsin K and have developed conditions for refolding this enzyme. Recombinant human procathepsin K (EC 3.4.22.38) was expressed in E. coli, refolded from inclusion bodies, and further purified by Superdex 75 size-exclusion chromatography. Purified procathepsin K had a [MH]+ of 35,063 Da which is in agreement with the predicted mass of the construct. Amino-terminal sequence analysis matched the predicted sequence with no secondary sequence detected. Purified procathepsin K activated under autocatalytic conditions to a final specific activity of 23 micromol 7-amido-4-methylcoumarin liberated/min/mg of enzyme using the fluorescent peptide substrate benzyloxycarbonyl-phenylalanine-arginine-7-amido-4-methylcoumarin. This expression and refolding procedure yielded 50 mg of purified, glycosylation-free human procathepsin K from 1 liter of E. coli cell culture and enabled the determination of the structure of human procathepsin K at 2.6 A resolution.
Asunto(s)
Catepsinas/biosíntesis , Osteoclastos/enzimología , Precursores de Proteínas/biosíntesis , Secuencia de Aminoácidos , Catepsina K , Catepsinas/química , Catepsinas/genética , Catepsinas/aislamiento & purificación , Cumarinas/metabolismo , Dipéptidos/metabolismo , Activación Enzimática , Escherichia coli , Colorantes Fluorescentes/metabolismo , Humanos , Cuerpos de Inclusión/enzimología , Datos de Secuencia Molecular , Precursores de Proteínas/química , Precursores de Proteínas/genética , Precursores de Proteínas/aislamiento & purificación , Proteínas Recombinantes de Fusión/química , Proteínas Recombinantes de Fusión/aislamiento & purificaciónRESUMEN
Cathepsin K is a cysteine protease present in human osteoclasts that plays an important role in bone resorption. Cathepsin K is synthesized as an inactive proenzyme and activated under conditions of low pH. Autoproteolytic processing of the N-terminal 99 amino acid propeptide produces the active, mature form of cathepsin K. It is presumed that the activation of procathepsin K in vivo occurs in the bone resorption pit, which has a low-pH environment. We have determined the structure of human procathepsin K at 2.8 A resolution. The structure of the mature enzyme domain within procathepsin K is virtually identical to that of mature cathepsin K. The fold of the propeptide of procathepsin K is similar to that observed in procathepsins B and L despite differences in length and sequence. A portion of the propeptide occupies the active site cleft of cathepsin K. Hydrophobic interactions, salt bridges, and hydrogen-bonding interactions are observed in the structure of the propeptide and between the propeptide and the mature enzyme of procathepsin K. These interactions suggest an explanation for the stability of the proenzyme. The structure of procathepsin K contributes to an understanding of the molecular basis of inhibition by the propeptide portion of the molecule and activation of this important member of the cysteine protease family.
Asunto(s)
Catepsinas/química , Precursores Enzimáticos/química , Sitios de Unión , Catepsina B/química , Catepsina K , Catepsina L , Catepsinas/antagonistas & inhibidores , Cristalización , Cristalografía por Rayos X , Inhibidores Enzimáticos/química , Humanos , Hidrólisis , Sustancias Macromoleculares , Fragmentos de Péptidos/química , Procesamiento Proteico-Postraduccional , Señales de Clasificación de Proteína/química , Estructura Terciaria de Proteína , Homología de Secuencia de Aminoácido , Electricidad EstáticaRESUMEN
Arrestins have been shown to act as adaptor proteins that mediate the interaction of G protein-coupled receptors with the endocytic machinery. In this study, the role of arrestin-3 in receptor internalization was investigated by constructing different arrestin-3 minigenes that could potentially act as dominant negative inhibitors of arrestin function. Expression of arrestin-3 proteins containing amino acids 1-320 or 201-409 resulted in the inhibition of beta2-adrenergic receptor internalization in HEK-293 cells by approximately 40%. Both of these arrestins were diffusely localized within the cytoplasm of transfected cells, were unable to mediate redistribution of receptors to clathrin-coated pits, and did not localize to coated pits in either the presence or absence of receptor and agonist. Arrestin-3(1-320), but not arrestin-3(201-409), bound to light-activated phosphorylated rhodopsin with an affinity comparable with that of wild-type arrestin-3. In contrast, expression of arrestin-3 proteins composed of only the clathrin binding domain, arrestin-3(284-409), and arrestin-3(290-409) resulted in the constitutive localization of these arrestins to coated pits. Arrestin-3(284-409) and arrestin-3(290-409) acted as dominant negative inhibitors of wild-type arrestin function, inhibiting receptor internalization by 70 and 30%, respectively. Carboxyl-terminal deletions of arrestin-3 retained the ability to promote internalization until residues amino-terminal to amino acid 350 were deleted, suggesting that residues in this region also compose part of the clathrin binding domain in addition to the major binding site between residues 371-379. These studies characterize at least two distinct mechanisms, competition for either receptor or clathrin binding, by which dominant negative arrestins inhibit receptor internalization and further define residues within arrestin-3 that constitute the clathrin binding domain.
Asunto(s)
Arrestinas/genética , Arrestinas/metabolismo , Receptores Adrenérgicos beta 2/metabolismo , Antagonistas de Receptores Adrenérgicos beta 2 , Animales , Arrestinas/química , Sitios de Unión , Células COS , Línea Celular , Endocitosis , Humanos , Riñón , Cinética , Biosíntesis de Proteínas , Proteínas Recombinantes/química , Proteínas Recombinantes/metabolismo , Rodopsina/metabolismo , TransfecciónRESUMEN
The CXCR4 chemokine receptor has been shown to respond to the C-X-C chemokine stromal-derived factor (SDF-1) and has recently been shown to be an important coreceptor for HIV-1 infection. In the present paper we have tested a number of human lymphocyte cell lines, including Jurkat, HUT78, CEM, and Sup-T1 for the presence of CXCR4 receptors. We found that these T cell lines bind SDF-1alpha and SDF-1beta with high affinity. The CXCR4 Ab 12G5 inhibited both SDF-1 binding and HIV-1LAI-mediated fusion of CEM. Scatchard analysis revealed the presence of approximately 150,000 SDF-1alpha-binding sites per cell with a Kd between 5 and 10 nM. Cross-competition experiments using unlabeled SDF-1alpha and SDF-1beta revealed that both chemokines are equally capable of displacing their radiolabeled counterparts. Internalization studies with [125]I-SDF-1alpha revealed that Jurkat cells internalized greater than 90% of the ligand by 2 h at 37 degrees C. SDF-1alpha was also chemotactic for Jurkat cells and caused an increase in the rate of extracellular acidification that was half-maximal at 18 nM SDF-1alpha and could be inhibited by pretreatment with the SDF-1 proteins, pertussis toxin, or the Ab 12G5. Finally, SDF-1alpha also caused an increase in the cytosolic Ca2+ concentration in Sup-T1 cells that was abolished by preincubating the cells with pertussis toxin or PMA and inhibited by the Ab 12G5. This molecular characterization of CXCR4 receptors should prove useful in clarifying receptor interaction with SDF-1 proteins and with HIV-1 glycoprotein, with the ultimate aim of targeting the viral interaction for therapeutic intervention.
Asunto(s)
Infecciones por VIH/inmunología , VIH-1/fisiología , Receptores CXCR4/metabolismo , Linfocitos T/metabolismo , Sitios de Unión , Fusión Celular/inmunología , Línea Celular , Quimiocina CXCL12 , Quimiocinas CXC/metabolismo , Citocinas/metabolismo , Proteínas de Unión al GTP/fisiología , Infecciones por VIH/metabolismo , Infecciones por VIH/patología , Humanos , Células Jurkat , Cinética , Ligandos , Receptores CXCR4/biosíntesis , Receptores CXCR4/química , Receptores CXCR4/fisiología , Receptores Virales/metabolismo , Linfocitos T/virología , Células Tumorales CultivadasRESUMEN
We introduced various mutations into the activation and RNA binding domains of human immunodeficiency virus type 1 (HIV-1) Tat in order to develop a novel and potent transdominant Tat protein and to characterize its mechanism of action. The different mutant Tat proteins were characterized for their abilities to activate the HIV LTR and inhibit the function of wild-type Tat in trans. A Tat protein containing a deletion of the basic domain (Tat(delta)49-57) localized exclusively to the cytoplasm of transfected human cells was nonfunctional and inhibited both HIV-1 and HIV-2 Tat function in a transdominant manner. Tat proteins containing mutations in the cysteine-rich and core domains were nonfunctional but failed to inhibit Tat function in trans. When Tat nuclear or nucleolar localization signals were fused to the carboxy terminus of Tat(delta)49-57, the chimeric proteins localized to the nucleus or nucleolus, respectively, and remained capable of acting in a transdominant manner. Introduction of secondary mutations in the cysteine-rich and core domains of the various transdominant Tat proteins completely eliminated their abilities to act in a transdominant fashion. Our data best support a mechanism in which these transdominant Tat proteins squelch a cellular factor or factors that interact with the Tat activation domain and are required for Tat to function.
Asunto(s)
Productos del Gen tat/metabolismo , VIH-1/metabolismo , VIH-2/metabolismo , Secuencia de Aminoácidos , Línea Celular , Núcleo Celular , Clonación Molecular , Citoplasma , Productos del Gen tat/genética , VIH-1/genética , VIH-2/genética , Células HeLa , Humanos , Datos de Secuencia Molecular , Mutagénesis , Productos del Gen tat del Virus de la Inmunodeficiencia HumanaRESUMEN
The human immunodeficiency virus, type 1 (HIV-1) promoter is known to be activated by proinflammatory cytokines and UV light. These stimuli also activate various members of the mitogen-activated protein kinase family, including JNK/SAPK and CSBP/p38. In HeLa cells containing an integrated HIV-1 long terminal repeat (LTR) -driven reporter, we now show that the specific p38 inhibitor, SB203580, inhibits activation of the HIV-1 LTR by interleukin-1, tumor necrosis factor, UV light, and osmotic stress. Inhibition was 70-90% in all but the case of tumor necrosis factor stimulation, where inhibition was 50%. Each of these stimuli activated p38, which was inhibited by SB203580 in vitro and in vivo with an IC50 (between 0.1 and 1 microM) similar to that required to inhibit transcription. In contrast, SB203580 had no effect on JNK, which was also activated by these stimuli. The NFkappaB sites in the HIV-1 LTR were required for a response to cytokines but not to UV, and SB203580 remained capable of inhibiting UV activation in the absence of the NFkappaB sites. Studies in which SB203580 was added at different times relative to UV stimulation suggested that the critical p38-mediated phosphorylation event occurred between 2 and 4 h after UV treatment. These data indicate that p38 is required for HIV-1 LTR activation but that the action of p38 is delayed, presumably due to substrate unavailability or inaccessibility.
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Proteínas Quinasas Dependientes de Calcio-Calmodulina/metabolismo , Citocinas/fisiología , Inhibidores Enzimáticos/farmacología , Regulación Viral de la Expresión Génica , Duplicado del Terminal Largo de VIH/genética , VIH-1/genética , Imidazoles/farmacología , Proteínas Quinasas Activadas por Mitógenos , Piridinas/farmacología , Estrés Fisiológico/metabolismo , Proteínas Quinasas Dependientes de Calcio-Calmodulina/antagonistas & inhibidores , Cicloheximida/farmacología , Regulación Viral de la Expresión Génica/efectos de la radiación , Células HeLa , Humanos , Cinética , FN-kappa B/metabolismo , Inhibidores de la Síntesis de la Proteína/farmacología , ARN Mensajero/genética , ARN Viral/genética , Transducción de Señal , Transcripción Genética , Rayos Ultravioleta , Equilibrio Hidroelectrolítico , Proteínas Quinasas p38 Activadas por MitógenosRESUMEN
We describe a single method to purify milligram amounts of authentic wild-type and mutant HIV-1 and HIV-2 Tat proteins overexpressed in Escherichia coli. This method takes advantage of the highly basic, positively charged RNA binding domain present in both HIV-1 and HIV-2 Tat, which also facilitated purification of HIV-1 and HIV-2 mutant Tat proteins. In contrast to previously described methods, our method does not require use of denaturing or reducing agents, since Tat is present in the soluble fraction after bacterial lysis. The activity of purified wild-type and mutant HIV-1 and HIV-2 Tat proteins was determined using cell-based uptake, in vitro transcription, and TAR binding assays. As expected, both HIV-1 and HIV-2 Tat efficiently transactivated the HIV-2 LTR, whereas HIV-2 Tat transactivated the HIV-1 LTR less efficiently than HIV-1 Tat. Purified HIV-2 Tat proteins in which the glutamic acid residue at position 77 was changed to either glycine or glutamine transactivated the HIV-1 LTR more efficiently than wild-type Tat-2, providing additional evidence that the net charge of this region may be responsible for nonreciprocal transactivation between Tat-1 and Tat-2. Our results demonstrate that this method can be used to rapidly purify authentic wild-type and mutant Tat proteins which are suitable for cell-based and in vitro functional studies.
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Productos del Gen tat/genética , VIH-1/genética , VIH-2/genética , Secuencia de Aminoácidos , Western Blotting , Cloranfenicol O-Acetiltransferasa/metabolismo , Cromatografía en Agarosa , Electroforesis en Gel de Poliacrilamida , Escherichia coli/genética , Expresión Génica/genética , Productos del Gen tat/aislamiento & purificación , Productos del Gen tat/metabolismo , Genes Reporteros , Células HeLa/metabolismo , Humanos , Datos de Secuencia Molecular , Mutagénesis/genética , Mutación/genética , Plásmidos , Proteínas de Unión al ARN/genética , Proteínas de Unión al ARN/metabolismo , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/aislamiento & purificación , Secuencias Repetitivas de Ácidos Nucleicos/genética , Transcripción Genética/genética , Activación Transcripcional/efectos de los fármacos , Activación Transcripcional/genética , Productos del Gen tat del Virus de la Inmunodeficiencia HumanaRESUMEN
Recombinant human immunodeficiency virus (HIV-1) Tat protein added to the culture medium of rat cerebellar neurons promoted aggregation and formation of spoke-like neurites in a dose-dependent manner. Tat proteins containing mutations in the Arg-Gly-Asp (RGD) cell adhesion motif or a deletion of the cysteine-rich domain had no effect on neuronal morphology. In contrast, a Tat protein that contained a deletion of the proline-rich domain promoted neuronal aggregation. Aggregation of neurons was inhibited by the addition of monoclonal antibodies directed against the RGD and basic domains of Tat, but not against the proline-rich domain. The same domains of Tat required to induce aggregation also mediated adhesion of neurons to Tat-coated substrates. The HIV-2 Tat protein, which lacks an RGD sequence but contains cysteine-rich and basic domains similar to HIV-1 Tat, induced aggregation and acted as a substrate for adhesion when added at higher concentrations than HIV-1 Tat. Vitronectin, fibronectin, and RGD-containing peptides did not induce morphological changes in neurons or act as substrates for adhesion. The ability of Tat to induce morphological changes and promote adhesion was independent of the ability of Tat to transactivate HIV gene expression. Our results suggest that extracellular Tat protein most likely alters neuronal morphology and mediates adhesion by acting in a manner similar to an extracellular matrix protein.
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Adhesión Celular/efectos de los fármacos , Cerebelo/metabolismo , Productos del Gen tat/metabolismo , VIH-1/metabolismo , Secuencia de Aminoácidos , Animales , Células Cultivadas , Relación Dosis-Respuesta a Droga , Datos de Secuencia Molecular , Ratas , Productos del Gen tat del Virus de la Inmunodeficiencia HumanaRESUMEN
We have developed a simple and rapid procedure for the purification of large amounts of Rev protein overexpressed in E. coli. The purification method, which does not require denaturation of the protein, takes advantage of the positively charged nature of Rev and the ability of Rev to interact with nucleic acids. The purified protein was used to develop three novel murine monoclonal antibodies against Rev. Using fusion proteins between glutathione S-transferase (GST) and various fragments of the Rev protein, we mapped the specificity of these antibodies to different regions of the Rev protein. One antibody, 3H6, is directed against the nucleolar localization/RRE-binding domain of Rev between amino acids 38 and 44. Another antibody, 3G4, recognizes an epitope between amino acids 90 and 116 of Rev. A third antibody, 2G2, does not recognize any of the fusion proteins, and may be directed against a conformational epitope. All three antibodies are able to detect Rev on Western blots and to immunoprecipitate Rev under native conditions. However, only 3H6 and 3G4 immunoprecipitate Rev under denaturing conditions and are able to detect Rev expressed in transfected cells by indirect immunofluorescence. These antibodies should prove useful in further studies of Rev function.
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Anticuerpos Monoclonales/inmunología , Productos del Gen rev/inmunología , Productos del Gen rev/aislamiento & purificación , Anticuerpos Monoclonales/aislamiento & purificación , Secuencia de Bases , Escherichia coli/genética , Productos del Gen rev/genética , Humanos , Datos de Secuencia Molecular , Proteínas Recombinantes de Fusión/genética , Proteínas Recombinantes de Fusión/inmunología , Proteínas Recombinantes de Fusión/aislamiento & purificaciónRESUMEN
An Adverse Drug Reaction Surveillance Program (ADRSP) was implemented by the pharmacy department of the University of Maryland Medical System to address the institution's underreporting of adverse drug reactions. The program aims were to increase the number and quality of significant adverse drug reaction (ADR) reports by facilitating and standardizing the reporting process, to more actively involve the pharmacy staff, and to create a comprehensive database, thus enabling the intervention of future untoward events. During the program's first 2 years, the number of ADR reports more than doubled, primarily due to increased pharmacists' participation. The ADRSP has facilitated the reporting process, enhanced the submission of ADR reports to the FDA, and helped prevent ADRs.