Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0043167 (pertussis)
 19,595 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Recently, we developed a technique that allows the in vivo visualization in man of somatostatin receptor-positive neuroendocrine tumors after i.v. injection of [125I-Tyr3]octreotide or [111In-DTPA-D-Phe1]octreotide. Radiotherapy of such tumors using somatostatin analogs coupled to alpha- or beta-emitting radionuclides has been proposed as an application for radiolabeled somatostatin analogs. To develop this concept further, it is of importance to know whether the above-mentioned radiolabeled somatostatin analogs are internalized by the tumor cells, and whether it might be possible to manipulate the degree of internalization. In the present study we investigated the internalization of a stable somatostatin analog, [125I-Tyr3]octreotide, by mouse AtT20/D16V pituitary tumor cells and primary cultures of human GH-secreting pituitary tumor cells. Treatment of the cells with low pH was used to distinguish between membrane-bound (acid-releasable) and internalize (acid-resistant) radioligand. [125I-Tyr3]octreotide showed a time-dependent increasing accumulation in AtT20 cells; after 4 h of incubation, values up to 6-8% of the dose of radioligand added were obtained. Binding and internalization of [125I-Tyr3]octreotide were temperature dependent and inhibited by pertussis toxin. Inhibitors of lysosomal degradation did not increase the amount of internalized radioligand. After 4 h of incubation, 88% of the radioactivity present in the cells was still peptide bound, suggesting a low intracellular breakdown of this radioligand. Six of seven human GH-secreting adenoma cell cultures also internalized [125I-Tyr3]octreotide (variation between 0.24-4.98% of the dose radioligand added). Displacement of binding and internalization of [125I-Tyr3]octreotide by unlabeled octreotide showed a bell-shaped curve in AtT20 cells. At low concentrations (0.1 and 1 nM), binding and internalization were increased, whereas at higher concentrations, saturation occurred. In contrast to this, binding of [125I-Tyr3]octreotide to a broken cell preparation of AtT20 cells was displaced in a dose-dependent manner by unlabeled octreotide, with an IC50 of 0.1 nM. Similar observations were made in the human GH-secreting adenoma cell cultures. In conclusion, a high amount of [125I-Tyr3]octreotide is internalized in a specific-, time-, temperature-, and pertussis toxin-sensitive GTP-binding protein-dependent manner by mouse AtT20 and human GH-secreting pituitary tumor cells. In the presence of a low concentration of unlabeled octreotide, a rapid increase in the amount of [125I-Tyr3]octreotide internalized by AtT20 cells and by the majority of the human GH-secreting adenoma cell cultures was found.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Internalization of the radioiodinated somatostatin analog [125I-Tyr3]octreotide by mouse and human pituitary tumor cells: increase by unlabeled octreotide. 764 74

Previously, we have demonstrated that somatostatin mediates all of its inhibitory effects on glucose-induced insulin secretion from the HIT-T15 cell through pertussis toxin-sensitive G-proteins and that the membrane fraction of this clonal line of pancreatic beta-cells contains six such proteins: G(i) alpha 1, G(i) alpha 2, G(i) alpha 3, and three forms of G(o) alpha. To determine the specificity of somatostatin receptor-G-protein coupling in HIT-T15 cells, we examined the ability of antisera specific for the COOH-terminus of G alpha subtypes to inhibit somatostatin-induced augmentation of membrane GTPase activity. GTPase activity increased in membranes as a function of GTP. At all concentrations of GTP studied, 1 mumol/l somatostatin stimulated GTPase activity. Pertussis-toxin pretreatment prevented the effects of somatostatin. Antisera selective for G(o) alpha subtypes reduced the effects of somatostatin on GTPase activity (GTPase activity in absence of antisera, 125 +/- 3% of control; in the presence of antisera 976, 110 +/- 2% of control; n = 13, P < 0.001), whereas antisera directed against G(i) alpha 1, G(i) alpha 2, G(i) alpha 3, and Gs alpha were without effect. Somatostatin also significantly prevented cyclic AMP accumulation during perifusion with 11.1 mmol/l glucose through a pertussis toxin-sensitive mechanism. These data indicate that the somatostatin receptor couples to G(o) alpha in the HIT-T15 cell and suggest that G(o) alpha may link somatostatin to cyclic AMP metabolism in pancreatic beta-cells.
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PMID:Somatostatin selectively couples to G(o) alpha in HIT-T15 cells. 781 19

Platelet-activating factor and somatostatin receptors, two G protein-coupled receptors expressed in the rat hippocampus, were analyzed for the downstream signaling pathways in Chinese hamster ovary cells stably expressing each receptor. Ligand stimulation to each CHO cell line induced (1) inhibition of forskolin-induced accumulation of cAMP, (2) arachidonate release, and (3) activation of mitogen-activated protein kinase and MAP kinase kinase. In contrast, inositol phosphate breakdown was seen only in the PAF-stimulated CHO cells. The induction of these signals accompanied no detectable Ras activation. Suppression of the signals by pertussis toxin was almost complete for the somatostatin receptor but partial for the PAF receptor, suggesting that the somatostatin receptor couples only with PTX-sensitive G protein, while the PAF receptor couples with both PTX-sensitive and -insensitive G proteins. A model of G protein-mediated signaling pathways was proposed in which the signals from Gi and those from Gq converge at MAP kinase kinase and lead to arachidonate release. The present system using CHO cells is useful for analyzing signaling pathways from G proteins to MAP kinase kinase and will thereby provide clues for understanding the mechanisms underlying the physiological and pathological events mediated by PAF, somatostatin, and other G protein-coupled receptors in the central nervous system and other tissues.
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PMID:Activation of mitogen-activated protein kinase and arachidonate release via two G protein-coupled receptors expressed in the rat hippocampus. 782 32

Somatostatin receptors are abundantly expressed on a variety of human endocrine and epithelial tumors. The ability of these receptors to couple to effector pathways that inhibit the growth of these tumor cells has prompted the use of somatostatin agonists in the treatment of human neoplasms. It has been demonstrated that somatostatin stimulates a phosphotyrosine phosphatase in human tumor cells through a receptor-mediated process. This stimulation may counteract the growth-promoting properties of growth factors and the receptor tyrosine kinases that they activate. The recent cloning and characterization of distinct somatostatin receptor subtypes raise the possibility that different receptor subtypes mediate distinct effector pathways. To determine whether cloned somatostatin receptors could mediate coupling to phosphotyrosine phosphotyrosine phosphatase activity, we examined phosphatase activity after somatotostatin activation of the rat somatostatin receptors SSTR1 and SSTR2 after their stable expression in heterologous Chinese Hamster Ovary (CHO-K1) cells. We found that stimulation of SSTR1 cells was capable of increasing phosphotyrosine phosphatase activity, despite the coupling of both receptors to the inhibition of adenylyl cyclase in these cells. This activation was characterized by an EC50 of 70 nM and was sensitive to pertussis toxin. In addition, we demonstrate that activation of phosphotyrosine phosphatase activity in pituitary cell lines correlates with the endogenous expression of the SSTR1 gene within these cells.
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PMID:The somatostatin receptor SSTR1 is coupled to phosphotyrosine phosphatase activity in CHO-K1 cells. 785 46

Somatostatin has been shown to exert diverse biological effects in various tissues. Recently, the human genes encoding five subtypes of somatostatin receptor (SSTR1-SSTR5) were cloned. Among these subtypes SSTR2 is present in many endocrine tumors as well as normal tissues and may mediate the effects of somatostatin analog, SMS201-995. In this study, we have investigated the intracellular effect of SSTR2 stably expressed in Chinese hamster ovary cells. Somatostatin-14 does not affect the forskolin stimulated cAMP formation when human SSTR2 is expressed in CHO cells, which lack internal Gi alpha 1 protein. However, somatostatin-14 inhibits the adenylyl cyclase in a dose dependent and pertussis toxin-sensitive manner when human SSTR2 is co-expressed with Gi alpha 1 in CHO cells. These results indicate that human SSTR2 is functionally coupled to Gi alpha 1 protein but not to Gi alpha 2 or Gi alpha 3 when expressed in CHO cells.
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PMID:Human somatostatin receptor, SSTR2, is coupled to adenylyl cyclase in the presence of Gi alpha 1 protein. 791 78

We examined the mechanism of arachidonate release induced by somatostatin-14 (SS14) in CHO-K1 cells overexpressing rat hippocampal somatostatin receptor SSTR4. SSTR4 couples to pertussis toxin (PTX)-sensitive G-protein in CHO cells and does not lead to phosphoinositides breakdown or intracellular calcium ([Ca2+]i) mobilization (Bito et al.: J. Biol. Chem. 269, 12722-12730, 1994). SSTR4 activated mitogen-activated protein (MAP) kinase and induced the phosphorylation of 85kDa cytosolic phospholipase A2 (cPLA2), in a PTX-sensitive manner. Furthermore, activations of both MAP kinase and cPLA2 were inhibited by treatment with wortmannin, at almost identical IC50 values. Thus, SSTR4 appears to stimulate MAP kinase and cPLA2 in a Gi-dependent, and through a wortmannin-sensitive pathway. We also showed that stimulation with SS14, in combination with calcium-ionophore, strongly enhanced arachidonate release from these cells.
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PMID:On the mechanism of cytosolic phospholipase A2 activation in CHO cells carrying somatostatin receptor: wortmannin-sensitive pathway to activate mitogen-activated protein kinase. 799 20

We transfected the COS-7 cells with cDNAs encoding different human somatostatin receptor (hSSTR) subtypes, and found that hSSTR subtypes mediate not only the inhibition of forskolin-induced cAMP accumulation but also the stimulation of phospholipase C (PLC) and Ca2+ mobilization. Activation of PLC by 1 microM somatostatin (SRIF) was in the order of: hSSTR5 > hSSTR2 > hSSTR3 > hSSTR4 >> hSSTR1. Pertussis toxin (PTX) treatment completely or partially reversed the PLC activation. 1 nM SRIF was equally effective for adenylate cyclase (AC) inhibition in a PTX-sensitive manner, in all the cells expressing different hSSTRs, except for hSSTR1. Nevertheless, SRIF stimulated AC even in the presence of forskolin at higher doses of SRIF in PTX-treated hSSTR5-expressing cells. We conclude that the cloned hSSTRs differentially couple to PTX-sensitive and -insensitive G-proteins to modulate PLC, Ca2+ mobilization and AC.
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PMID:Phospholipase C activation and Ca2+ mobilization by cloned human somatostatin receptor subtypes 1-5, in transfected COS-7 cells. 803 40

The prolactin secreting rat pituitary tumor cell line, GH3, expresses high affinity receptors for both vasoactive intestinal peptide (VIP) and somatostatin (SS14). VIP induces prolactin secretion by GH3 cells, an action which is antagonized by SS14. This in vitro model was used to examine the mechanism of action of two synthetic somatostatin analogs, D-Phe-Cys-Phe-D-Trp-Lys-Thr-Cys-Thr-OH (octreotide; SMS 201-995) and cyclo(aminoheptanoyl-Phe-D-Trp-Lys-Thr (benzyl)) (cyclic pentapeptide; CPP). Octreotide and CPP bind to the pituitary somatostatin receptor with lower affinity than does SS14 (KD = 1.3 +/- 1.1; 80 +/- 29; 211 +/- 107 nM for SS14, octreotide and CPP, respectively). SS14 and octreotide were equally effective as inhibitors of VIP-mediated accumulation of cAMP (40% and 45% inhibition, respectively, P < 0.01). SS14 and octreotide also inhibited forskolin-mediated accumulation of cAMP (42% and 40% inhibition of cAMP production, respectively; P < 0.01). The inhibitory action of somatostatin and octreotide on both VIP- and forskolin-mediated cAMP accumulation was blocked by pre-treatment of GH3 cells with pertussis toxin (P < 0.001). Neither SS14 nor octreotide affects the apparent affinity of VIP for its specific receptors on GH3 cells; thus, the inhibitory action of SS14 and octreotide appears to be mediated at the locus of the G-protein-adenylate cyclase complex. In contrast, CPP inhibited VIP-mediated cAMP accumulation slightly, but had no effect on forskolin-mediated cAMP production. Pertussis toxin did not attenuate CPP affects on VIP-mediated cAMP accumulation. However, pre-incubation of GH3 cells with CPP decreased the apparent affinity of receptors for VIP, suggesting that effects of CPP are attributable to interference with VIP binding rather than inhibition at the G-protein-adenylate cyclase complex.
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PMID:Mechanisms of action of long-acting analogs of somatostatin. 809 91

Based on pharmacological, biochemical, and molecular criteria, multiple somatostatin receptor (SSTR) subtypes selective for somatostatin (SST)-14 and -28 have been postulated to exist in both the brain and periphery. We report here on the cloning and characterization of a human gene encoding a new member of the guanine nucleotide-binding protein-linked SSTR family, termed human (h)SSTR4. The 388-amino acid protein, with a predicted molecular mass of approximately 42 kDa, displays sequence similarity, particularly within putative transmembrane domains, with the recently cloned hSSTR1 (69%), hSSTR2 (56%), and hSSTR3 (58%). Membranes prepared from COS-7 cells transiently expressing the hSSTR4 gene bound 125I-[Leu8,D-Trp22,Tyr25]SST-28 in a saturable manner with high affinity (approximately 60 pM) and with a pharmacological profile and rank order of potency ([D-Trp8]SST-14 > SST-14 > SMS 201-995 > SST-28 > MK-678) indicative of a SST-14-selective receptor. Ki values for the inhibition of 125I-[Leu8,D-Trp22,Tyr25]SST-28 binding to the expressed receptor by these somatostatinergic peptides were 0.3, 1.1, 1.4, 2.2, and 6.5 nM, respectively. High affinity agonist binding to hSSTR4 was significantly reduced by GTP and pertussis toxin, indicating association of the expressed receptor with pertussis toxin-sensitive guanine nucleotide-binding proteins. Northern blot analysis revealed the presence of an SSTR4 mRNA species of approximately 4 kilobases in select regions of the monkey brain, including the hippocampus, hypothalamus, cortex, and striatum, with little or no receptor mRNA detected in either the olfactory tubercle, medulla, cerebellum, or amygdala. The SSTR4 gene maps to human chromosome 20. These findings document the existence of a novel human SSTR gene. Although the hSSTR4 displays an overall deduced amino acid homology of 86% with the recently reported rat homolog [Proc. Natl. Acad. Sci. USA 89:11151-11155 (1992)], the two gene products possess distinctive pharmacological profiles and affinities for the SST agonists SMS 201-995 and MK-678.
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PMID:Cloning and expression of a human somatostatin-14-selective receptor variant (somatostatin receptor 4) located on chromosome 20. 810 Mar 52

5'-(N-ethylcarboxamido)-adenosine (NECA) and N-[(R)-(phenylisopropyl)]-adenosine (PIA) were incubated in an adenylate cyclase assay of a particulate fraction of caudate-putamen tissue of the rat in order to examine the effect of somatostatin on adenosine receptors coupled adenylate cyclase subunits in vitro. Somatostatin was able to inhibit the enhancement of cyclic AMP formation induced by NECA in the presence of the hydrolysable guanine nucleotide guanosine-triphosphate. The adenosine receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine as well as the somatostatin receptor antagonist cyclo (7-aminoheptanoyl-Phe-D-Trp-Lys-O-benzyl-Thr) did not influence somatostatin induced inhibition of NECA-activated adenylate cyclase. Somatostatin did not modulate the effect mediated by the A-1 adenosine receptor agonist PIA. Both pertussis toxin and cholera toxin activated striatal adenylate cyclase acting on the guanine nucleotide regulatory subunit of the enzyme. The stimulation induced by pertussis toxin was antagonized by somatostatin, while in presence of cholera toxin somatostatin enhanced cyclic AMP formation. These results suggest that somatostatin acts through a stimulatory as well as an inhibitory guanine nucleotide regulatory protein subtype to affect probably postsynaptic A-2 adenosine receptor coupled adenylate cyclase activity.
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PMID:Somatostatin modulation of adenosine receptor coupled G-protein subunits in the caudate nucleus of the rat. 810 Sep 88


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