Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P01178 (oxytocin)
 15,767 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We analyzed the properties of a G protein-coupled receptor localized in cholesterol-poor vs. cholesterol-rich microdomains of the plasma membrane. For this purpose, the human oxytocin receptor, which is very sensitive against alterations of the membrane cholesterol level, was stably expressed in HEK293 cells. To calculate the total number of receptors independent of ligand binding studies, the oxytocin receptor was tagged with an enhanced green fluorescent protein (EGFP) which did not change the functional properties of the receptor. Only 1% of the oxytocin receptors were present in cholesterol-rich detergent-insoluble domains. In contrast, employing a detergent-free fractionation scheme that preserves the functional activity of the receptor, we detected 10-15% of the receptors in cholesterol-rich low-density membranes and therein the high-affinity state receptors were twofold enriched. In cholesterol-poor vs. cholesterol-rich domains, high-affinity oxytocin receptors behaved similar with respect to their agonist binding kinetics and GTP sensitivity. However, high-affinity oxytocin receptors localized in cholesterol-rich low-density membranes showed a markedly enhanced (t (1/2) approximately threefold) stability at 37 degrees C as compared with the oxytocin receptors localized in the cholesterol-poor high-density membranes. Addition of cholesterol to the high-density membranes fully protected the oxytocin receptors against loss of function. The importance of cholesterol to stabilize the oxytocin receptor was supported in experiments with solubilized receptors. Cholesterol markedly delayed the inactivation of oxytocin receptors solubilized with Chapso. In conclusion, the data of this report suggest that functional properties of heptahelical receptor proteins could differ in dependence of their localization in different membrane microdomains.
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PMID:Human oxytocin receptors in cholesterol-rich vs. cholesterol-poor microdomains of the plasma membrane. 1078 67

Cholesterol affects the ligand binding function of the oxytocin receptor in a highly specific manner. While the structurally-related cholecystokinin receptor shows a strong correlation between the membrane fluidity and its binding function, the oxytocin receptor behaves differently. A stringent and unique requirement of the affinity state of the oxytocin receptor for structural features of the sterol molecule has been found. The molecular requirements differ both from those postulated for sterol-phospholipid interactions and from those known to be necessary for the activity of other proteins. Employing a new detergent-free subcellular fractionation protocol, a two-fold enrichment of the oxytocin receptors (10-15% of total receptors) has been detected in the cholesterol-rich, caveolin-containing membrane domains of the plasma membrane. While most of the properties of the oxytocin receptors were indistinguishable in cholesterol-poor versus cholesterol-rich membrane compartments, high-affinity oxytocin receptors localised in caveolin-enriched low-density membranes showed about a 3-fold higher stability against thermal denaturation at 37 degrees C compared with the oxytocin receptors localised in high-density membranes. Moreover, addition of cholesterol to the cholesterol-poor high-density membranes fully protected the oxytocin receptors against thermal denaturation and partially rescued high-affinity oxytocin binding. Although the membrane fluidity of the caveolin-enriched domains was lower than that in the high-density membranes, there was no correlation between the stability of oxytocin receptors and the fluidity level of the membrane domains. Finally, in a molecular modelling approach a putative cholesterol binding motif on the extracellular surface of the oxytocin receptor was found.
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PMID:Oxytocin receptors and cholesterol: interaction and regulation. 1079 5

Cholesterol, an integral component of membranes in Eucaryota, is a modifier of membrane properties. In vivo studies have demonstrated that cholesterol can also modulate activities of some G protein-coupled receptors (GPCRs), which are integral membrane proteins. This can result either from an effect of cholesterol on the membrane fluidity or from specific interactions of the membrane cholesterol with the receptor, as recently demonstrated for the cholecystokinin type beta (CCKRbeta) or the oxytocin receptor (OTR). Using molecular modelling, we studied conformational preferences of cholesterol and several of its analogues. Subsequently, we simulated the distributions of their preferred conformations around the surface of OTR, CCKRbeta and a chimeric oxytocin/cholecystokinin receptor. Consequently, we suggest residues on the surface of OTR which are potentially significant in the OTR/cholesterol interaction.
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PMID:Molecular modelling study of the role of cholesterol in the stimulation of the oxytocin receptor. 1144 Jan 86

Uterine quiescence is essential for successful pregnancy. Cholesterol and triglycerides are markedly increased in pregnancy. Cholesterol is enriched in microdomains of the plasma membrane known as rafts and caveolae. Both lipid rafts and caveolae have been implicated in cellular signaling cascades. The purpose of this work was to investigate whether manipulation of cholesterol content alters uterine contractility. Late pregnancy (19-21 days) rats were humanely euthanized and strips of longitudinal myometrium were then dissected. Force and Ca(2+) measurements were simultaneously recorded and cholesterol increased by the addition of 5 mg/ml cholesterol or 0.25 mg/ml low-density lipoproteins (LDLs) or reduced by 2% methyl-beta-cyclodextrin (MCD) or 2 U/ml cholesterol oxidase addition to the perfusate. Both LDLs and cholesterol profoundly inhibited spontaneous uterine force production and associated Ca(2+) transients; frequency, amplitude, and duration of contraction were all significantly reduced compared with preceding control contractions. Force and Ca(2+) were also reduced by cholesterol when 1 nM oxytocin was used to stimulate the myometrium. Uterine activity was significantly increased by cholesterol extraction with MCD or cholesterol oxidase treatment. Electron microscopy confirmed the lipid raft disrupting effect of MCD, as formerly electron microscopy-visible caveolae in the myometrial cell membrane all but disappeared after MCD treatment. These data show that uterine smooth muscle cell cholesterol content is critically important for functional activity. A novel finding of our study is that cholesterol is inhibitory for force generation. It may be one of the mechanisms operating to maintain uterine quiescence throughout gestation and may also contribute to difficulties in labor suffered by obese women.
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PMID:Increased cholesterol decreases uterine activity: functional effects of cholesterol alteration in pregnant rat myometrium. 1561 97

In this study, we have investigated the dependence of Na+ transport regulation on membrane cholesterol content in A6 renal epithelia. We continuously monitored short-circuit current (Isc), transepithelial conductance (GT), and transepithelial capacitance (CT) to evaluate the effects of cholesterol extraction from the apical and basolateral membranes in steady-state conditions and during activation with hyposmotic shock, oxytocin, and adenosine. Cholesterol extraction was achieved by perfusing the epithelia with methyl-beta-cyclodextrin (mbetaCD) for 1 h. In steady-state conditions, apical membrane cholesterol extraction did not significantly affect the electrophysiological parameters; in contrast, marked reductions were observed during basolateral mbetaCD treatment. However, apical mbetaCD application hampered the responses of Isc and GT to hypotonicity, oxytocin, and adenosine. Analysis of the blocker-induced fluctuation in Isc demonstrated that apical mbetaCD treatment decreased the epithelial Na+ channel (ENaC) open probability (Po) in the steady state as well as after activation of Na+ transport by adenosine, whereas the density of conducting channels was not significantly changed as confirmed by CT measurements. Na+ transport activation by hypotonicity was abolished during basolateral mbetaCD treatment as a result of reduced Na+/K+ pump activity. On the basis of the findings in this study, we conclude that basolateral membrane cholesterol extraction reduces Na+/K+ pump activity, whereas the reduced cholesterol content of the apical membranes affects the activation of Na+ transport by reducing ENaC Po.
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PMID:Membrane cholesterol extraction decreases Na+ transport in A6 renal epithelia. 1610 7

The authors elucidate cholesterol's effect on human uterine contractility and calcium signaling to test the hypotheses that elevation of cholesterol decreases uterine activity and that oxytocin cannot augment contraction when cholesterol is elevated. The effects of cholesterol extraction with methyl beta-cyclodextrin and enrichment with low-density lipoproteins and cholesterol on contractile activity and intracellular calcium signaling in spontaneous or oxytocin-stimulated myometrium are determined. Force occurring spontaneously and with oxytocin is significantly increased by cholesterol extraction. Cholesterol enrichment profoundly inhibits force production in a dose-dependent manner and could reverse the effects of cholesterol extraction. Qualitatively similar results are found for nonpregnant and pregnant laboring and non-laboring myometrium. These contractile changes are related to changes in intracellular Ca2+ . Thus, elevated cholesterol is deleterious to contractility and Ca2+ signaling in human myometrium. Cholesterol may contribute to uterine quiescence but could cause difficulties in labor in obese/dyslipidemic women, consistent with their increased cesarean delivery rates.
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PMID:Contractility and calcium signaling of human myometrium are profoundly affected by cholesterol manipulation: implications for labor? 1791 65

The G protein coupled oxytocin receptor (OTR) reveals some specific molecular and physiological characteristics. Ligand-receptor interaction has been analysed by photoaffinity labelling, site-directed mutagenesis, the construction of receptor chimeras and molecular modelling. Major results of these studies will be summarized. The N-terminus of the OTR is mainly involved in agonist binding. Notably, antagonists that are derived from the ground structure of oxytocin, bind the receptor at distinct sites partly non-overlapping with the agonist binding site. OTRs are able to couple to different G proteins, with a subsequent stimulation of phospholipase C-beta isoforms. In dependence on G protein coupling, OTRs can transduce growth-inhibitory or proliferatory signals. Some evidence is provided that OTRs are also present in form of dimeric or oligomeric complexes at the cell surface. The affinity of the receptor for ligands is strongly dependent on the presence of divalent cations (Mg(2+)) and cholesterol that both act like positive allosteric modulators. While the high-affinity state of the receptor for agonists requires divalent cations and cholesterol, the high-affinity state for antagonists is only dependent on a sufficient amount of cholesterol. Cholesterol affects ligand-binding affinity, receptor signalling and stability. Since the purification of the OTR has never been achieved, alternative methods to study the receptor in its native environment are necessary. Promising strategies for the site-specific labelling of the OTR will be presented. The employment of diverse reporter molecules introduced at different positions within the OTR might allow us in the near future to measure conformational changes of the receptor in its native lipid environment.
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PMID:Oxytocin receptors: ligand binding, signalling and cholesterol dependence. 1865 83