Requirements for Skp1 processing by cytosolic prolyl 4(trans)-hydroxylase and α-N-acetylglucosaminyltransferase enzymes involved in O₂ signaling in dictyostelium

The social amoeba Dictyostelium expresses a hypoxia inducible factor-α (HIFα) type prolyl 4-hydroxylase (P4H1) and an α-N-acetylglucosaminyltransferase (Gnt1) that sequentially modify proline-143 of Skp1, a subunit of the SCF (Skp1/Cullin/F-box protein) class of E3 ubiquitin ligases. Prior genetic studies have implicated Skp1 and its modification by these enzymes in O(2) regulation of development, suggesting the existence of an ancient O(2)-sensing mechanism related to modification of the transcription factor HIFα by animal prolyl 4-hydroxylases (PHDs). To better understand the role of Skp1 in P4H1-dependent O(2) signaling, biochemical and biophysical studies were conducted to characterize the reaction product and the basis of Skp1 substrate selection by P4H1 and Gnt1. (1)H NMR demonstrated formation of 4(trans)-hydroxyproline as previously found for HIFα, and highly purified P4H1 was inhibited by Krebs cycle intermediates and other compounds that affect animal P4Hs. However, in contrast to hydroxylation of HIFα by PHDs, P4H1 depended on features of full-length Skp1, based on truncation, mutagenesis, and competitive inhibition studies. These features are conserved during animal evolution, as even mammalian Skp1, which lacks the target proline, became a good substrate upon its restoration. P4H1 recognition may depend on features conserved for SCF complex formation as heterodimerization with an F-box protein blocked Skp1 hydroxylation. The hydroxyproline-capping enzyme Gnt1 exhibited similar requirements for Skp1 as a substrate. These and other findings support a model in which the protist P4H1 conditionally hydroxylates Skp1 of E3(SCF)ubiquitin ligases to control half-lives of multiple targets, rather than the mechanism of animal PHDs where individual proteins are hydroxylated leading to ubiquitination by the evolutionarily related E3(VBC)ubiquitin ligases.

Inhibition of colonic motility and defecation by RS-127445 suggests an involvement of the 5-HT2B receptor in rodent large bowel physiology

BACKGROUND

5-HT(2B) receptors are localized within the myenteric nervous system, but their functions on motor/sensory neurons are unclear. To explore the role of these receptors, we further characterized the 5-HT(2B) receptor antagonist RS-127445 and studied its effects on peristalsis and defecation.

EXPERIMENTAL APPROACH

Although reported as a selective 5-HT(2B) receptor antagonist, any interactions of RS-127445 with 5-HT(4) receptors are unknown; this was examined using the recombinant receptor and Biomolecular Interaction Detection technology. Mouse isolated colon was mounted in tissue baths for isometric recording of neuronal contractions evoked by electrical field stimulation (EFS), or under an intraluminal pressure gradient to induce peristalsis; the effects of RS-127445 on EFS-induced and on peristaltic contractions were measured. Faecal output of rats in grid-bottom cages was measured over 3 h following i.p. RS-127445 and separately, validation of the effective doses was achieved by determining the free, unbound fraction of RS-127445 in blood and brain.

KEY RESULTS

RS-127445 (up to 1 micromol x L(-1)) did not interact with the 5-HT(4) receptor. RS-127445 (0.001-1 micromol x L(-1)) did not affect EFS-induced contractions of the colon, although at 10 micromol x L(-1) the contractions were reduced (to 36 +/- 8% of control, n= 4). RS-127445 (0.1-10 micromol x L(-1)) concentration-dependently reduced peristaltic frequency (n= 4). RS-127445 (1-30 mg x kg(-1)), dose-dependently reduced faecal output, reaching significance at 10 and 30 mg x kg(-1) (n= 6-11). In blood and brain, >98% of RS-127445 was protein-bound.

CONCLUSIONS AND IMPLICATIONS

High-protein binding of RS-127445 indicates that relatively high doses are required for efficacy. The results suggest that 5-HT(2B) receptors tonically regulate colonic motility.

Hemolytic uremic syndrome associated with invasive pneumococcal disease: the United kingdom experience

OBJECTIVE

To describe the presentation, management, and outcome of 43 cases of pneumococcal-associated hemolytic uremic syndrome (P-HUS). An increased incidence of P-HUS has been noted in the United Kingdom between January 1998 and May 2005.

STUDY DESIGN

Cases with microangiopathic hemolytic anemia (Hb <10 g/dL with fragmented RBCs), thrombocytopenia (platelet count < 130 x 10(9)/L), acute renal impairment with oliguria and elevated plasma creatinine for age, confirmed or suspected pneumococcal infection and/or T-activation were included.

RESULTS

The median age at presentation was 13 months (range, 5-39 months). Pneumococcus was identified in 34 of 43 cases; T-activation was identified in 36 of 37 cases. Twelve strains were serotyped: serotypes 3 (n = 2), 6A (n = 2), 12F (n = 1), 14 (n = 1), 19A (n = 6). Empyema was present in 23 of 35 pneumonia cases; 13 cases had confirmed (9) or suspected (4) pneumococcal meningitis; 36 cases required dialysis (median, 10 days; range, 2-240 days). The mortality rate was 11%, comprising 3 cases of meningitis, 1 case of sepsis and 1 case of pulmonary embolism at 8 months follow up while on dialysis. Follow-up data were available for 35 of 38 patients who survived (median follow-up period, 9 months; range, 1-63 months); of these, 10 patients had renal dysfunction, 1 patient was dialysis-dependent, 5 patients had hypertension and 8 patients had at least 1+ proteinuria on urinalysis.

CONCLUSION

P-HUS has increased compared with historic surveys (0/288 in 1985-1988; 8/413 in 1997-2001, 43/315 in 1998-May 2005). Early mortality remains high (8-fold that of VTEC-induced HUS). Ten of 12 strains identified would not be covered by the PCV7 vaccine.

Daytime variability of baroreflex function in patients with obstructive sleep apnoea: implications for hypertension

Obstructive events during sleep in patients with obstructive sleep apnoea (OSA) cause large alterations in blood pressure, and this may lead to changes in baroreflex function with implications for long-term blood pressure control. This study examined the daytime variations in the responses to carotid baroreceptor stimulation in OSA patients. We determined the cardiac and vascular responses every 3 h between 09.00 and 21.00 h in 20 patients with OSA, using graded suctions and pressures applied to a neck collar. These responses were plotted against estimated carotid sinus pressures and, from these plots, baroreflex sensitivities and operating points were taken as the maximal slopes and the corresponding carotid sinus pressures, respectively. We found that at 09.00 h, sensitivity for the control of vascular resistance was at its lowest (--1.2 +/- 0.2% mmHg(-1), compared with --1.9 +/- 0.3% mmHg(-1) at 12.00 h, P < 0.02) and operating point for control of mean arterial pressure was at its highest (101.1 +/- 5.8 mmHg, compared with 94.1 +/- 5.8 mmHg at 12.00 h, P < 0.05). This is in contrast to previous data from normal subjects, in whom sensitivity was highest and operating point lowest at 09.00 h. We suggest that the higher baroreflex sensitivity and lower operating point seen in the mornings in normal subjects may provide a protective mechanism against hypertension and that this protection is absent in patients with OSA. It is possible that the reduced reflex sensitivity and increased operating point in the mornings may actually promote hypertension.

The relationship between the effects of short-chain fatty acids on intestinal motility in vitro and GPR43 receptor activation

The G protein-coupled receptors, GPR41 and GPR43, are activated by short-chain fatty acids (SCFAs), with distinct rank order potencies. This study investigated the possibility that SCFAs modulate intestinal motility via these receptors. Luminal SCFA concentrations within the rat intestine were greatest in the caecum (c. 115 mmol L(-1)) and proximal colon. Using similar concentrations (0.1-100 mmol L(-1)), SCFAs were found to inhibit electrically evoked, neuronally mediated contractions of rat distal colon, possibly via a prejunctional site of action; this activity was independent of the presence or absence of the mucosa. By contrast, SCFAs reduced the amplitude but also reduced the threshold and increased the frequency of peristaltic contractions in guinea-pig terminal ileum. In each model, the rank-order of activity was acetate (C2) approximately propionate (C3) approximately butyrate (C4) > pentanoate (C5) approximately formate (C1), consistent with activity at the GPR43 receptor. GPR43 mRNA was expressed throughout the rat gut, with highest levels in the colon. However, the ability of SCFAs to inhibit neuronally mediated contractions of the colon was similar in tissues from wild-type and GPR43 gene knockout mice, with identical rank-orders of potency. In conclusion, SCFAs can modulate intestinal motility, but these effects can be independent of the GPR43 receptor.

Dental health of 5-year-old children and parents' perceptions for oral health in the prefectures of Athens and Piraeus in the Attica County of Greece

OBJECTIVES

This study was undertaken in 2001 in order to investigate the dental health status of 5-year-olds in an urban community within Attica County in Greece and the views of the carers of this age group.

METHODS

Three hundred and forty-five nursery children were examined, using the WHO methods and criteria. Parents' views were recorded in a questionnaire.

RESULTS

Overall, 48.4% had some experience of dental decay. The mean dmft of the whole study population was 2.6, whereas the mean dmft of the subjects with active decay was 5.4; in these cases untreated decay was the highest component (mean dt = 5.0). A questionnaire using phone calls to the children's homes achieved a 100% response rate. Ninety-five per cent of parents thought that a child should visit the dentist at this early age and 79.5% of responders answered that they had already visited the dentist with their child for different reasons. Three-quarters (75.4%) of parents had received information about fluoride, whereas 72.5% answered that did not use any type of fluoride for their child at home. It was reported that 63.5% of children ate snacks, sweets, cakes, biscuits, and gums between the main meals of the day and 31% of the subjects more than once per day.

CONCLUSIONS

Caries indicies were higher from the National 2003-4 survey and were attributed to the increasing number of immigrants in some areas. The population under investigation had the appropriate information for the prevention of dental decay but they appear to maintain unhealthy behaviours in their everyday living.

β-Glycosides of Hydroxyproline via an Umpolung Approach

Reaction of 1,2-O-dibutylstannylene-3,4-6-tri-O-benzyl-beta-D-mannopyranose with Nalpha-fluorenylmethoxycarbonyl-cis-4-trifluoromethanesulfonyloxyproline allyl ester led to formation of a beta-mannoside of trans-4-hydroxyproline. Subsequent manipulation of the C2 hydroxy group gave rise to beta-D-Glc and beta-D-GlcNAc derivatives.

A classification of hemolytic uremic syndrome and thrombotic thrombocytopenic purpura and related disorders

The diagnostic terms hemolytic uremic syndrome (HUS) and thrombotic thrombocytopenic purpura (TTP) are based on historical and overlapping clinical descriptions. Advances in understanding some of the causes of the syndrome now permit many patients to be classified according to etiology. The increased precision of a diagnosis based on causation is important for considering logical approaches to treatment and prognosis. It is also essential for research. We propose a classification that accommodates both a current understanding of causation (level 1) and clinical association in cases for whom cause of disease is unclear (level 2). We tested the classification in a pediatric disease registry of HUS. The revised classification is a stimulus to comprehensive investigation of all cases of HUS and TTP and is expected to increase the proportion of cases in whom a level 1 etiological diagnosis is confirmed.

Good prognosis cytogenetics in B-cell chronic lymphocytic leukemia is associated in vitro with low susceptibility to apoptosis and enhanced immunogenicity

Chromosomal abnormalities in B-cell chronic lymphocytic leukemia (B-CLL) have been shown to correlate with prognosis. Little is known about the relationship between chromosomal abnormalities and biological behavior of B-CLL cells in vitro. The present study was designed to explore the impact of chromosomal abnormalities determined by interphase fluorescence in situ hybridization (FISH) on the in vitro survival and immunogenicity of B-CLL. Considerable heterogeneity was noted in the in vitro survival and expression of costimulatory, adhesion, and antigen-presenting molecules by B-CLL cells. Spontaneous apoptosis of B-CLL cells in vitro was significantly lower in samples with good prognosis cytogenetics when compared to samples with poor prognosis cytogenetics. In contrast, B-CLL cells from samples with good prognosis cytogenetics exhibited higher basal expression of molecules involved in costimulation, cellular adhesion, and antigen presentation, and induced significantly more T-cell proliferation in mixed lymphocyte cultures. We conclude that chromosomal aberrations of B-CLL cells correlate with the in vitro biological behavior of B-CLL. Our data indicate that good prognosis cytogenetics correlates with less spontaneous apoptosis but greater in vitro immunogenicity. These findings could have significant implications on the design of future therapeutic approaches in patients with CLL, and the likelihood of response based on cytogenetics.

The impact of pyrrolidine hydroxylation on the conformation of proline-containing peptides

[structure: see text] A series of eight dipeptides of the general formula Ac-Phe-Pro-NHMe was synthesized and the thermodynamics of the cis --> trans isomerization about the central amide bond were studied by NMR. Pro* represents the following prolines: l-proline (Pro), l-trans-4-hydroxyproline (Hyp), l-cis-4-hydroxyproline (hyp), l-cis-4-methoxyproline (hyp[OMe]), l-trans-3-hydroxyproline (3-Hyp), l-cis-3-hydroxyproline (3-hyp), l-2,3-trans-3,4-cis-3,4-dihydroxyproline (DHP), and l-2,3-cis-3,4-trans-3,4-dihydroxyproline (dhp). The conformation of the pyrrolidine ring in each case is discussed in light of previous structural studies, analysis of potential stereoelectronic effects, and NMR data. Hydroxy substituents at C-4 have a greater impact on cis --> trans isomerization than analogous substituents at C-3 as a result of the intervening bond distances and bridging groups. The position of the equilibrium and its dependence on temperature are a reflection of both enthalpic and entropic factors, the latter being complicated in this study by an Ar-Pro interaction in the cis conformation. The substituents on the pyrrolidine ring determine the conformation of the five-membered ring, which in turn influences the strength of the Ar-Pro interaction, backbone dihedral angles, and the relative energy of the cis and trans species. The ultimate position of the equilibrium depends on a complex blend of steric, electronic, and conformational factors.

Factors affecting conformation in proline-containing peptides

[reaction: see text] NMR was used to study the thermodynamics of the cis --> trans isomerization for prolyl amide bonds in the compounds shown. The magnitude of K(t/c) for C-terminal esters is greater than for the corresponding amides, signifying stronger backbone stereoelectronic effects in esters. Increasing the steric bulk of the N-terminal residue from Ac- to Ac-Gly- favors the trans conformation. Incorporation of a Phe residue N-terminal to Pro, however, shifts the equilibrium in favor of the cis conformation, via a stabilizing aromatic-proline interaction.

Clinico-pathological findings in diarrhoea-negative haemolytic uraemic syndrome

This is a retrospective, national clinico-pathological study of past and current patients with haemolytic uraemic syndrome not associated with diarrhoea (D- HUS). Thirty-four patients were analysed and notified by members of the British Association for Paediatric Nephrology in 1998-1999. There was a 2:1 excess of males. Ten presented in infancy. The aetiology included 5 patients with complement abnormalities, 2 patients with complications of pneumococcal infection, and 2 with malignancies. Parental consanguinity was noted in 6 patients. Five children died, 9 developed chronic renal failure, and 10 end-stage renal failure. Only 7 made full recoveries. With a single exception, the pathological findings were unlike the previously reported glomerular thrombosis that is characteristic of diarrhoea-associated HUS, or HUS complicating verocytotoxin-producing Escherichia coli infection. Early and late glomerulopathy could be distinguished. Arteriolar and arterial disease was observed in 8 and 7 patients, respectively. Arterial disease correlated with a poor outcome. The pathology of D- HUS is of prognostic value, but this study was not powered to identify specific aetiological/pathological correlations.

Myelin associated glycoprotein cross-linking triggers its partitioning into lipid rafts, specific signaling events and cytoskeletal rearrangements in oligodendrocytes

Myelin-associated glycoprotein (MAG) has been implicated in inhibition of nerve regeneration in the CNS. This results from interactions between MAG and the Nogo receptor and gangliosides on the apposing axon, which generates intracellular inhibitory signals in the neuron. However, because myelin-axon signaling is bidirectional, we undertook an analysis of potential MAG-activated signaling in oligodendrocytes (OLs). In this study, we show that antibody cross-linking of MAG on the surface of OLs (to mimic axonal binding) leads to the redistribution of MAG into detergent (TX-100)-insoluble complexes, hyperphosphorylation of Fyn, dephosphorylation of serine and threonine residues in specific proteins, including lactate dehydrogenase and the beta subunit of the trimeric G-protein-complex, and cleavage of alpha-fodrin followed by a transient depolymerization of actin. We propose that these changes are part of a signaling cascade in OLs associated with MAG function as a mediator of axon-glial communication which might have implications for the mutual regulation of the formation and stability of axons and myelin.

Renal function following liver transplantation for unresectable hepatoblastoma

Combination of cyclosporine (CsA) and tacrolimus immunosuppression post-liver transplantation (LT) and the chemotherapeutic drugs used to treat hepatoblastoma (HB), are nephrotoxic. We aimed to determine the severity and duration of nephrotoxicity in children following LT for unresectable HB. We reviewed all children undergoing LT for unresectable HB at the Liver Unit, Birmingham Children's Hospital, UK, from 1991 to July 2000. Thirty-six children undergoing LT for biliary atresia, matched for age and sex, were selected as controls to compare pre- and post-LT renal function. Renal function was determined by estimation of glomerular filtration rate (eGFR) derived from plasma creatinine using Schwartz's formula. Twelve children with HB (mean age of diagnosis 33 months) who underwent LT (mean age 47 months) and 36 controls (mean age of LT 34 months) were studied. CsA was the main immunosuppressive drug used in each group. The median eGFR before, and at 3, 6, 12, 24 and 36 months after LT in HB group was significantly lower than controls (93 vs. 152, 66 vs. 79, 62 vs. 86, 66 vs. 87, 64 vs. 94, 53 vs. 90 mL/min/1.73 m2, respectively; 0.01 < p < 0.03). The reductions in the median eGFR of both the HB group and controls before and at 36 months after LT were 49 and 41%, respectively. At 36 months after LT, there was a trend for partial recovery of the eGFR in the controls but not in the HB group. Children who underwent LT for unresectable HB had renal dysfunction before transplantation that persisted for 36 months after LT.

Introduction, audit and review of guidelines for delegated authorization of nuclear medicine investigations in compliance with the Ionising Radiation (Medical Exposure) Regulations 2000

The introduction of the Ionising Radiation (Medical Exposure) Regulations 2000 in Great Britain required every nuclear medicine investigation to be justified by a practitioner holding an appropriate Administration of Radioactive Substances Committee (ARSAC) certificate. The task of authorizing the radiation exposure may be performed by the practitioner (direct authorization) or delegated to an appropriately trained operator working to written guidelines approved by the practitioner (delegated authorization). In this study, we look at the process of implementation, audit and review of a set of Delegated Authorization Guidelines (DAG). The process of drafting the DAG is outlined. Following the introduction of the DAG, an audit of nuclear medicine referrals was performed at two sites for a period of 3 months. Each referral was compared with the DAG to determine whether it matched the criteria set out. If it did not match, it was further categorized as being due to: (1) insufficient referral information; or (2) clinical indication not included in the DAG. All non-matching requests were reviewed by the practitioner. Four hundred and thirty-seven of 632 (69%) referrals fitted the DAG, 12% (n=75) required clarification from the referrer before fitting with the criteria and 19% (n=120) were directly authorized by the practitioner. From those referrals that were directly authorized, some additional indications were identified and the DAG were subsequently revised. In conclusion, a delegated authorization procedure for nuclear medicine investigations can be implemented successfully. Regular audit is essential. This study identified the need to improve the format of the request card and to obtain additional referral information from the referrer.

Antibody cross-linking of myelin oligodendrocyte glycoprotein leads to its rapid repartitioning into detergent-insoluble fractions, and altered protein phosphorylation and cell morphology

Myelin oligodendrocyte glycoprotein (MOG) is, quantitatively, a relatively minor component of the myelin membrane. Nevertheless, peritoneal administration of MOG evokes potent cellular and humoral immunoreactivity, resulting in an experimental allergic encephalitis with immunopathology similar to multiple sclerosis. Moreover, antibodies against MOG cause myelin destruction in situ. Therefore, it appears that MOG-related demyelination is dependent on anti-MOG antibody, but the mechanism(s) by which it occurs is unclear. Of potential significance are observations that some proteins are selectively partitioned into specialized plasma membrane microdomains rich in glycosphingolipids and cholesterol ("lipid rafts"). In particular, during ligand or antibody cross-linking, various plasma membrane receptors undergo enhanced partitioning into rafts as an obligatory first step toward participation in early signal transduction events. In contrast to mature myelin, in oligodendrocytes (OLs) in culture MOG is not raft associated [Triton X-100 (TX-100) soluble, 4 degrees C]. However, in this study we show that antibody cross-linking (anti-MOG plus secondary antibody) of MOG on the surface of OLs results in the repartitioning of approximately 95% of MOG into the TX-100-insoluble fraction. This repartitioning of MOG is rapid (<or=1 min), antibody dose dependent, requires an intact cytoskeleton, leads to phosphorylation or dephosphorylation of tyrosine, serine, and threonine residues in specific proteins (e.g., beta-tubulin, Gbeta1-2), and invokes a rapid retraction of OL processes. After removal of the cross-linking antibodies, these events are reversed. We hypothesize that antibody-mediated repartitioning of MOG into TX-100-insoluble glycosphingolipid-cholesterol-rich microdomains initiates specific cellular signaling that could be related to initial steps of MOG-mediated demyelination.

Design, preparation, and characterization of mixed dimers of inducible nitric oxide synthase oxygenase domains

A limitation of site-directed mutagenesis of homodimeric proteins is that both subunits will carry the same mutation. We have devised a way to prepare mixed dimers, in which only one chain bears a desired mutation, or each chain can bear a different mutation. Using the inducible nitric oxide oxygenase domain as a model, our strategy focused on the co-expression of two differentially tagged versions of the oxygenase domain, with isolation of the desired mixed dimer in two chromatography steps. We evaluated expression vectors encoding polyhistidine (His(6)), cellulose binding domain, glutathione-S-transferase, and polyglutamate (Glu(7))-tagged versions of the oxygenase domain for satisfactory levels of soluble protein expression and for their ability to form mixed dimers. The combination of His(6)- and Glu(7)-tagged subunits was successful in both respects, and the mixed dimers could be separated from either form of homodimer by sequential immobilized metal affinity chromatography and anion exchange chromatography. The UV-Vis spectrum, substrate binding properties, and enzymatic activity were not altered in the mixed dimer wild-type (His(6)/Glu(7)) compared to the two homodimers (His(6)/His(6) and Glu(7)/Glu(7)). We then characterized a mixed dimer variant in which one chain contained an E371A substitution (which prevents binding of the substrate L-arginine) while the other subunit was left unaltered. This species binds L-arginine and has about one-half the activity of the wild-type homodimer. Mutants known to destabilize the iNOS dimer (E411A, D454A, and W188F) were also investigated; in these cases co-expression with the wild-type subunit did not lead to the formation of stable mixed dimers.