scholarly journals Phosphodiesterase 4 in macrophages: relationship between cAMP accumulation, suppression of cAMP hydrolysis and inhibition of [3H]R-(—)-rolipram binding by selective inhibitors

1996 ◽  
Vol 318 (2) ◽  
pp. 425-436 ◽  
Author(s):  
John J KELLY ◽  
Peter J BARNES ◽  
Mark A GIEMBYCZ
Keyword(s):  
Binding Site ◽  
Rank Order ◽  
Smooth Muscle Relaxation ◽  
Camp Accumulation ◽  
Functional Responses ◽  
Camp Content ◽  
Phosphodiesterase 4 ◽  
Ic50 Values ◽  
Membrane Bound ◽  
Camp Hydrolysis

A perplexing phenomenon identified in several tissues is the lack of correlation between inhibition of phosphodiesterase 4 (PDE4) and certain functional responses such as smooth muscle relaxation, gastric acid secretion and cAMP accumulation. Interpretation of these data is complicated further by the finding that function correlates with the ability of PDE4 inhibitors to displace [3H]rolipram [4-(3-cyclopentenyloxy-4-methoxyphenyl)-2-pyrrolidone] from a high-affinity site in rat brain that is apparently distinct from the catalytic centre of the enzyme. We have investigated this discrepancy by using guinea pig macrophages as a source of PDE4 and have confirmed that the ability of a limited range of structurally dissimilar PDE inhibitors (Org 20241, nitraquazone and the enantiomers of rolipram and benafentrine) to increase cAMP content did not correlate with their potency as inhibitors of partly purified PDE4, whereas a significant linear and rank order correlation was found when cAMP accumulation was related to the displacement of [3H]R-(-)-rolipram from a specific site identified in macrophage lysates. An explanation for these data emerged from the finding that the IC50 values and rank order of potency of these compounds for inhibition of partly purified PDE4 and the native (membrane-bound) form of the same enzyme were distinct. Similarly, no correlation was found when membrane-bound PDE4 was compared with the same enzyme that had been solubilized with Triton X-100. These unexpected results were attributable to a selective decrease in the potency of those inhibitors [nitraquazone, R-(-)- and S-(+)-rolipram] that interacted preferentially with the rolipram binding site. Indeed, if membrane-bound PDE4 was used as the enzyme preparation, excellent linear and rank order correlations between inhibition of cAMP hydrolysis, displacement of [3H]R-(-)-rolipram and cAMP accumulation were found, which improved further in the presence of the vanadyl (Vo)/2.GSH complex. Moreover, using Vo/2.GSH-treated membranes, the IC50 values of nitraquazone and the enantiomers of rolipram for the inhibition of PDE4 approached their affinity for the rolipram binding site. Collectively, these data suggest that the rolipram binding site and the catalytic domain on CPPDE4 might represent part of the same entity. In addition, these results support the concept that PDE4 can exist in different conformational states [Barnett, Manning, Cieslinski, Burman, Christensen and Torphy (1995) J. Pharmcol. Exp. Ther. 273, 674–679] and provide evidence that the cAMP content in macrophages is regulated primarily by a conformer of PDE4 for which rolipram has nanomolar affinity.

Membrane‐bound calmodulin in Xenopus laevis oocytes as a novel binding site for melatonin

1998 ◽  
Vol 12 (13) ◽  
pp. 1401-1408 ◽  
Author(s):  
M. Paz Romero ◽  
Antonio García‐Pergañeda ◽  
Juan M. Guerrero ◽  
Carmen Osuna
Keyword(s):  
Xenopus Laevis ◽  
Binding Site ◽  
Xenopus Laevis Oocytes ◽  
Membrane Bound

scholarly journals Characterization of the stilbenedisulphonate binding site on band 3 Memphis variant II (Pro-854→Leu)

1996 ◽  
Vol 317 (2) ◽  
pp. 509-514 ◽  
Author(s):  
James M. SALHANY ◽  
Renee L. SLOAN ◽  
Lawrence M. SCHOPFER
Keyword(s):  
Binding Site ◽  
Conformational Changes ◽  
Covalent Binding ◽  
Band 3 ◽  
Blood Group Antigen ◽  
Cross Linking ◽  
Anion Exchange Protein ◽  
Membrane Bound ◽  
And Control

Band 3 Memphis variant II is a mutant anion-exchange protein associated with the Diego a+ blood group antigen. There are two mutations in this transporter: Lys-56 → Glu within the cytoplasmic domain, and Pro-854 → Leu within the membrane-bound domain. The Pro-854 mutation, which is thought to give rise to the antigenicity, is located within the C-terminal subdomain of the membrane-bound domain. Yet, there is an apparent enhancement in the rate of covalent binding of H2DIDS (4,4´-di-isothiocyanatodihydro-2,2´-stilbenedisulphonate) to ‘lysine A’ (Lys-539) in the N-terminal subdomain, suggesting widespread conformational changes. In this report, we have used various kinetic assays which differentiate between conformational changes in the two subdomains, to characterize the stilbenedisulphonate site on band 3 Memphis variant II. We have found a significantly higher H2DIDS (a C-terminal-sensitive inhibitor) affinity for band 3 Memphis variant II, due to a lower H2DIDS ‘off’ rate constant, but no difference was found between mutant and control when DBDS (4,4´-dibenzamido-2,2´-stilbenedisulphonate) (a C-terminal-insensitive inhibitor) ‘off’ rates were measured. Furthermore, there were no differences in the rates of covalent binding to lysine A, for either DIDS (4,4´-di-isothiocyanato-2,2´-stilbenedisulphonate) or H2DIDS. However, the rate of covalent intrasubunit cross-linking of Lys-539 and Lys-851 by H2DIDS was abnormally low for band 3 Memphis variant II. These results suggest that the Pro-854 → Leu mutation causes a localized conformational change in the C-terminal subdomain of band 3.

Tissue- and species-specific differences in ligand binding to thromboxane A2 receptors

1991 ◽  
Vol 261 (1) ◽  
pp. R145-R153 ◽  
Author(s):  
G. W. Dorn
Keyword(s):  
Smooth Muscle ◽  
Vascular Smooth Muscle ◽  
Ligand Binding ◽  
Binding Site ◽  
Dissociation Constants ◽  
Rank Order ◽  
Thromboxane A2 ◽  
Saphenous Veins ◽  
Rabbit Platelets ◽  
Highly Correlated

The ligand binding site of vascular smooth muscle (VSM) and platelet thromboxane A2 (TxA2) receptors was characterized in humans and rabbits using the TxA2 mimetic [125I]BOP. Vessel contraction and platelet aggregation studies demonstrated that unlabeled I-BOP and the prostaglandin H2 (PGH2) mimetic U-46619 were potent agonists in rabbit aortas, human saphenous veins, and washed human and rabbit platelets. [125I]BOP bound saturably to a single site on cultured vascular smooth muscle (VSM) cells from rabbit aortas and human saphenous veins with dissociation constants (Kd) of 392 +/- 8 (n = 5) and 390 +/- 120 pM (n = 6) and binding capacities (Bmax) of 5,322 +/- 200 and 2,017 +/- 322 sites/cell, respectively. [125I]BOP also bound saturably to one site on rabbit platelets (Kd = 415 +/- 15 pM, Bmax = 594 +/- 43 sites/platelet, n = 4) but, in agreement with previous studies, to two sites on human platelets (high-affinity Kd = 118 +/- 24 pM, Bmax = 121 +/- 33 sites/platelet; low-affinity Kd = 1.1 +/- 0.47 nM, Bmax 232 +/- 23 sites/platelet, n = 4). [125I]BOP was displaced from its binding site on rabbit and human VSM and platelets by stable TxA2/PGH2 analogues possessing either agonist or antagonist activity but not by other prostaglandins. The rank orders of the binding inhibition constants (IC50) for the TxA2/PGH2 analogues were compared among the four tissues and were highly correlated (r = 0.963) in VSM and platelets from rabbits but not humans (r = 0.699), suggesting that human VSM TxA2 receptors may be distinct from platelet TxA2 receptors. The IC50 rank order was also highly correlated (r = 0.935) between human and rabbit platelets.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Discovery and Design of Novel Small Molecule GSK-3 Inhibitors Targeting the Substrate Binding Site

2020 ◽  
Vol 21 (22) ◽  
pp. 8709
Author(s):  
Ido Rippin ◽  
Netaly Khazanov ◽  
Shirley Ben Joseph ◽  
Tania Kudinov ◽  
Eva Berent ◽  
...  
Keyword(s):  
Binding Site ◽  
Small Molecule ◽  
Substrate Binding ◽  
Pharmacophore Model ◽  
Drug Induced ◽  
Substrate Binding Site ◽  
Zinc Database ◽  
Competitive Inhibitors ◽  
Ic50 Values ◽  
Critical Binding

The serine/threonine kinase, GSK-3, is a promising drug discovery target for treating multiple pathological disorders. Most GSK-3 inhibitors that were developed function as ATP competitive inhibitors, with typical limitations in specificity, safety and drug-induced resistance. In contrast, substrate competitive inhibitors (SCIs), are considered highly selective, and more suitable for clinical practice. The development of SCIs has been largely neglected in the past because the ambiguous, undefined nature of the substrate-binding site makes them difficult to design. In this study, we used our previously described structural models of GSK-3 bound to SCI peptides, to design a pharmacophore model and to virtually screen the “drug-like” Zinc database (~6.3 million compounds). We identified leading hits that interact with critical binding elements in the GSK-3 substrate binding site and are chemically distinct from known GSK-3 inhibitors. Accordingly, novel GSK-3 SCI compounds were designed and synthesized with IC50 values of~1–4 μM. Biological activity of the SCI compound was confirmed in cells and in primary neurons that showed increased β-catenin levels and reduced tau phosphorylation in response to compound treatment. We have generated a new type of small molecule GSK-3 inhibitors and propose to use this strategy to further develop SCIs for other protein kinases.

LUMI-AGGREGOMETER STUDIES OF THE INITIAL ATP-SECRETION FROM COLLAGEN-ADHERENT PLATELETS

1987 ◽  
Author(s):  
R Malmgren
Keyword(s):  
Platelet Adhesion ◽  
Rank Order ◽  
Shape Change ◽  
Dense Granule ◽  
Dependent Manner ◽  
Equal Degree ◽  
Atp Secretion ◽  
Ic50 Values ◽  
Dose Dependent ◽  
Platelet Shape

We have earlier, with the use of a lumi-aggregometer and sub-aggregating doses of collagen (0.2-0.8 ug/ml PRP), been able to detect the initial, aspirin-insensitive secretion of ATP from the collagen-adherent platelets, and to correlate this secretion to the doses of collagen, and onset and degree of subsequent shape change of non-adherent platelets (Malmgren, Thromb Res 4:445, 1986). The present study shows, that 200 ATU of hirudin,which reduced near-maximal aggregation and ATP-secretion induced by high collagen doses (2.5 ug/ml PRP) from 3.35 ± 0.2 uM to 2.85 ± 0.1 uM, did neither reduce the secreted amount of ATP that were 82.5 ± 15 nM in control samples and 90 ± 27.5 nM in hirudin-treated samples, nor reduce platelet shape change when platelets were challenged with 0.31 ug collagen /ml PRP. (200 ATU hirudin completely abolished an equal degree of platelet shape change induced by 0.01 U thrombin). Assuming that 3 % of the platelets in PRP were actually adhering to the collagen fibrils, the secreted amount corresponds to 14.6 ±0.04 pmoles ATP/106adheringplatelets, amounts which closely represented 100 % of their dense granule content. The finding confirms that hirudin does not inhibit platelet adhesion and also indicates, that thrombin-mediated activation of secretory pathways appears not to be involved during the initial phase of platelet-collagen interactions.Dipyridamole (DPA) and dibutyryl cAMP (DBcAMP) inhibited ATP-secretion and platelet aggregation in a dose-dependent manner at high collagen concentrations, but only DBcAMP caused a dose-dependent reduction of ATP secretion (IC50 =10-4 M) induced by sub-aggregating doses of collagen. DPA was devoid of effect in this respect and thus did not inhibit platelet adhesion.Yohimbine, dihydroergotamine and phentolamine reduced ATP-secretion induced by sub-aggregating collagen doses in the mentioned rank order of potency, and with IC50 values in the micromolar range. Ketanserin, ritanserin and propranolol were devoid of effect. The findings suggest that the initial collagen-plate-let interaction involve alfareceptor-mediated mechanisms that may encompass adhesion, while DBcAMP probably interacts with secretory mechanisms connected to phosphatidylinositol turnover.

scholarly journals Identification of Membrane-bound Variant of Metalloendopeptidase Neurolysin (EC 3.4.24.16) as the Non-angiotensin Type 1 (Non-AT1), Non-AT2Angiotensin Binding Site

2011 ◽  
Vol 287 (1) ◽  
pp. 114-122 ◽  
Author(s):  
Naomi J. Wangler ◽  
Kira L. Santos ◽  
Ines Schadock ◽  
Fred K. Hagen ◽  
Emanuel Escher ◽  
...  
Keyword(s):  
Binding Site ◽  
Membrane Bound ◽  
Angiotensin Type

Stimulation of cAMP accumulation and lipolysis in hamster adipocytes with forskolin

1984 ◽  
Vol 246 (1) ◽  
pp. C63-C68 ◽  
Author(s):  
R. J. Schimmel
Keyword(s):  
Adipose Tissue ◽  
Adenosine Deaminase ◽  
Camp Accumulation ◽  
Camp Content ◽  
Lipolytic Action ◽  
White Adipocytes ◽  
Free Media ◽  
Phenylisopropyl Adenosine ◽  
Camp Levels ◽  
Stimulation Of

This study compares the effects of forskolin and isoproterenol on lipolysis and adenosine 3',5'-cyclic monophosphate (cAMP) accumulation in hamster white adipocytes. Rates of lipolysis in forskolin-stimulated cells were equivalent to those in cells incubated with isoproterenol, but cAMP levels were more than 10-fold greater in the presence of forskolin. The stimulatory effects of forskolin were partially inhibited by N6-phenylisopropyl adenosine but not by 2',5'-dideoxyadenosine. In other experiments, cells were exposed to forskolin in combination with either isoproterenol or adenosine deaminase. A concentration of forskolin that caused only a small increase in lipolysis was used. When isoproterenol or adenosine deaminase were added with forskolin, lipolysis increased dramatically, but cAMP content either did not change, as occurred with isoproterenol, or increased only slightly with adenosine deaminase. Isoproterenol potentiation of forskolin's lipolytic action persisted in the absence of extracellular K+, even though the lipolytic response to isoproterenol alone was absent in K+-free media. These data demonstrate that the lipolytic responses of adipose tissue are more complex than are responses simply in proportion to cellular concentration of cAMP. Such complexity could arise if lipolytic regulatory factors other than cAMP existed or if cAMP and protein kinase were functionally segregated within adipocytes.

scholarly journals Plasma membrane association of Acanthamoeba myosin I.

1989 ◽  
Vol 109 (4) ◽  
pp. 1519-1528 ◽  
Author(s):  
H Miyata ◽  
B Bowers ◽  
E D Korn
Keyword(s):  
Plasma Membrane ◽  
Binding Site ◽  
Heavy Chain ◽  
Membrane Fraction ◽  
Plasma Membranes ◽  
Actin Binding ◽  
Plasma Membrane Fraction ◽  
Myosin I ◽  
Membrane Bound ◽  
Actin Binding Site

Myosin I accounted for approximately 2% of the protein of highly purified plasma membranes, which represents about a tenfold enrichment over its concentration in the total cell homogenate. This localization is consistent with immunofluorescence analysis of cells that shows myosin I at or near the plasma membrane as well as diffusely distributed in the cytoplasm with no apparent association with cytoplasmic organelles or vesicles identifiable at the level of light microscopy. Myosin II was not detected in the purified plasma membrane fraction. Although actin was present in about a tenfold molar excess relative to myosin I, several lines of evidence suggest that the principal linkage of myosin I with the plasma membrane is not through F-actin: (a) KI extracted much more actin than myosin I from the plasma membrane fraction; (b) higher ionic strength was required to solubilize the membrane-bound myosin I than to dissociate a complex of purified myosin I and F-actin; and (c) added purified myosin I bound to KI-extracted plasma membranes in a saturable manner with maximum binding four- to fivefold greater than the actin content and with much greater affinity than for pure F-actin (apparent KD of 30-50 nM vs. 10-40 microM in 0.1 M KCl plus 2 mM MgATP). Thus, neither the MgATP-sensitive actin-binding site in the NH2-terminal end of the myosin I heavy chain nor the MgATP-insensitive actin-binding site in the COOH-terminal end of the heavy chain appeared to be the principal mechanism of binding of myosin I to plasma membranes through F-actin. Furthermore, the MgATP-sensitive actin-binding site of membrane-bound myosin I was still available to bind added F-actin. However, the MgATP-insensitive actin-binding site appeared to be unable to bind added F-actin, suggesting that the membrane-binding site is near enough to this site to block sterically its interaction with actin.

cAMP-secretion coupling is impaired in diabetic GK/Par rat β-cells: a defect counteracted by GLP-1

2011 ◽  
Vol 301 (5) ◽  
pp. E797-E806 ◽  
Author(s):  
Manuel Dolz ◽  
Jamileh Movassat ◽  
Danielle Bailbé ◽  
Hervé Le Stunff ◽  
Marie-Hélène Giroix ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Insulin Release ◽  
Camp Accumulation ◽  
Camp Content ◽  
Camp Generation ◽  
Stimulus Secretion Coupling ◽  
Glucagon Like Peptide 1 ◽  
The Relationship

cAMP-raising agents with glucagon-like peptide-1 (GLP-1) as the first in class, exhibit multiple actions that are beneficial for the treatment of type 2 diabetic (T2D) patients, including improvement of glucose-induced insulin secretion (GIIS). To gain additional insight into the role of cAMP in the disturbed stimulus-secretion coupling within the diabetic β-cell, we examined more thoroughly the relationship between changes in islet cAMP concentration and insulin release in the GK/Par rat model of T2D. Basal cAMP content in GK/Par islets was significantly higher, whereas their basal insulin release was not significantly different from that of Wistar (W) islets. Even in the presence of IBMX or GLP-1, their insulin release did not significantly change despite further enhanced cAMP accumulation in both cases. The high basal cAMP level most likely reflects an increased cAMP generation in GK/Par compared with W islets since 1) forskolin dose-dependently induced an exaggerated cAMP accumulation; 2) adenylyl cyclase (AC)2, AC3, and Gsα proteins were overexpressed; 3) IBMX-activated cAMP accumulation was less efficient and PDE-3B and PDE-1C mRNA were decreased. Moreover, the GK/Par insulin release apparatus appears less sensitive to cAMP, since GK/Par islets released less insulin at submaximal cAMP levels and required five times more cAMP to reach a maximal secretion rate no longer different from W. GLP-1 was able to reactivate GK/Par insulin secretion so that GIIS became indistinguishable from that of W. The exaggerated cAMP production is instrumental, since GLP-1-induced GIIS reactivation was lost in the presence the AC blocker 2′,5′-dideoxyadenosine. This GLP-1 effect takes place in the absence of any improvement of the [Ca2+]i response and correlates with activation of the cAMP-dependent PKA-dependent pathway.

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