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Walter Luyten

Publications and source records attributed to Walter Luyten.

8 recordsLinked to original sources
PubMed2006

Obestatin does not activate orphan G protein-coupled receptor GPR39.

Recently, the ligand of the orphan G protein-coupled receptor GPR39 has been identified as obestatin, a 23-amino acid peptide derived from the ghrelin precursor protein. We used two methods to study the possible activation of GPR39 by obestatin: cAMP measurements based on a luminescent reporter gene and a fluorometric Ca(2+) flux method. The former was similar to that reported in the original publication of Zhang et al. [J.V. Zhang, P.G. Ren, O. Avsian-Kretchmer, C.W. Luo, R. Rauch, C. Klein, Obestatin, a peptide encoded by the ghrelin gene, opposes ghrelin's effects on food intake, Science 310 (2005) 996-999]. The latter method used promiscuous as well as chimaeric G-proteins commonly used to couple orphan G protein-coupled receptors to the phospholipase C pathway, that leads to intracellular Ca(2+) rise. We could, however, not demonstrate activation of the GPR39 receptor by obestatin via any of these signal transduction pathways. We could activate GPR39 by high concentrations of Zn(2+), demonstrating cell surface expression of a functional receptor that could elicit a Ca(2+) response. The Zn(2+) response was not affected by obestatin. The identity of the native ligand for GPR39 remains to be elucidated.

Cell Line↗
PubMed2005

p53-independent regulation of p21Waf1/Cip1 expression and senescence by Chk2.

The Chk2 kinase is a tumor suppressor and key component of the DNA damage checkpoint response that encompasses cell cycle arrest, apoptosis, and DNA repair. It has also been shown to have a role in replicative senescence resulting from dysfunctional telomeres. Some of these functions are at least partially exerted through activation of the p53 transcription factor. High-level expression of virally transduced Chk2 in A549 human lung carcinoma cells led to arrested proliferation, apoptosis, and senescence. These were accompanied by various molecular events, including p21(Waf1/Cip1) (p21) transcriptional induction, consistent with p53 activation. However, Chk2-dependent senescence and p21 transcriptional induction also occurred in p53-defective SK-BR-3 (breast carcinoma) and HaCaT (immortalized keratinocyte) cells. Small interfering RNA-mediated knockdown of p21 in p53-defective cells expressing Chk2 resulted in a decrease in senescent cells. These results revealed a p53-independent role for Chk2 in p21 induction and senescence that may contribute to tumor suppression and genotoxic treatment outcome.

Apoptosis↗
PubMed2004

Functional characterization of the putative orphan neuropeptide G-protein coupled receptor C26F1.6 in Caenorhabditis elegans.

In this study, we describe the cloning and the characterization of the third FMRFamide-related peptide (FaRP) receptor in Caenorhabditis elegans, the VRFa receptor 1. Numerous structurally different FaRPs were synthesized and used to screen the orphan C26F1.6 receptor for activation. Two peptides ending in M(orL)VRFamide elicited a calcium response in receptor expressing mammalian cells. The response is dose-dependent and appeared to be very specific, since very closely related FaRPs were less active, even the other peptides ending in M(orL)VRFamide. Pharmacological profiling of the most active peptide suggests that SMVRFa is the most active binding core. N-terminal extension decreases peptide activity.

Amino Acid Sequence↗
PubMed2002

Genetic and physiological data implicating the new human gene G72 and the gene for D-amino acid oxidase in schizophrenia.

A map of 191 single-nucleotide polymorphism (SNPs) was built across a 5-Mb segment from chromosome 13q34 that has been genetically linked to schizophrenia. DNA from 213 schizophrenic patients and 241 normal individuals from Canada were genotyped with this marker set. Two 1,400- and 65-kb regions contained markers associated with the disease. Two markers from the 65-kb region were also found to be associated to schizophrenia in a Russian sample. Two overlapping genes G72 and G30 transcribed in brain were experimentally annotated in this 65-kb region. Transfection experiments point to the existence of a 153-aa protein coded by the G72 gene. This protein is rapidly evolving in primates, is localized to endoplasmic reticulum/Golgi in transfected cells, is able to form multimers and specifically binds to carbohydrates. Yeast two-hybrid experiments with the G72 protein identified the enzyme d-amino acid oxidase (DAAO) as an interacting partner. DAAO is expressed in human brain where it oxidizes d-serine, a potent activator of N-methyl-D-aspartate type glutamate receptor. The interaction between G72 and DAAO was confirmed in vitro and resulted in activation of DAAO. Four SNP markers from DAAO were found to be associated with schizophrenia in the Canadian samples. Logistic regression revealed genetic interaction between associated SNPs in vicinity of two genes. The association of both DAAO and a new gene G72 from 13q34 with schizophrenia together with activation of DAAO activity by a G72 protein product points to the involvement of this N-methyl-d-aspartate receptor regulation pathway in schizophrenia.

Amino Acid Sequence↗
PubMed2002

Characterization of an orphan G protein-coupled receptor localized in the dorsal root ganglia reveals adenine as a signaling molecule.

The cloning of novel G protein-coupled receptors and the search for their natural ligands, a process called reverse pharmacology, is an excellent opportunity to discover novel hormones and neurotransmitters. Based on a degenerate primer approach we have cloned a G protein-coupled receptor whose mRNA expression profile indicates highest expression in the dorsal root ganglia, specifically in the subset of small neurons, suggesting a role in nociception. In addition, moderate expression was found in lung, hypothalamus, peripheral blood leukocytes, and ovaries. Guided by a receptor-activation bioassay, we identified adenine as the endogenous ligand, which activated the receptor potently and with high structural stringency. Therefore, we propose to name this receptor as the adenine receptor. Hormonal functions have already been demonstrated for adenine derivatives like 6-benzylaminopurine in plants and 1-methyladenine in lower animals. Here, we demonstrate that adenine functions as a signaling molecule in mammals. This finding adds a third family besides P1 and P2 receptors to the class of purinergic receptors.

Adenine↗
PubMed1999

Contribution of mutations in the cytochrome P450 14alpha-demethylase (Erg11p, Cyp51p) to azole resistance in Candida albicans.

The cytochrome P450 14alpha-demethylase, encoded by the ERG11 (CYP51) gene, is the primary target for the azole class of antifungals. Changes in the azole affinity of this enzyme caused by amino acid substitutions have been reported as a resistance mechanism. Nine Candida albicans strains were used in this study. The ERG11 base sequence of seven isolates, of which only two were azole-sensitive, were determined. The ERG11 base sequences of the other two strains have been published previously. In these seven isolates, 12 different amino acid substitutions were identified, of which six have not been described previously (A149V, D153E, E165Y, S279F, V452A and G4655). In addition, 16 silent mutations were found. Two different biochemical assays, subcellular sterol biosynthesis and CO binding to reduced microsomal fractions, were used to evaluate the sensitivity of the cytochromes for fluconazole and itraconazole. Enzyme preparations from four isolates showed reduced itraconazole susceptibility, whereas more pronounced resistance to fluconazole was observed in five isolates. A three-dimensional model of C. albicans Cyp51p was used to position all 29 reported substitutions, 98 in total identified in 53 sequences. These 29 substitutions were not randomly distributed over the sequence but clustered in three regions from amino acids 105 to 165, from 266 to 287 and from 405 to 488, suggesting the existence of hotspot regions. Of the mutations found in the two N-terminal regions only Y132H was demonstrated to be of importance for azole resistance. In the C-terminal region three mutations are associated with resistance, suggesting that the non-characterized substitutions found in this region should be prioritized for further analysis.

Amino Acid Sequence↗
PubMedDate not supplied

Discovering H-bonding rules in crystals with inductive logic programming.

In the domain of crystal engineering, various schemes have been proposed for the classification of hydrogen bonding (H-bonding) patterns observed in 3D crystal structures. In this study, the aim is to complement these schemes with rules that predict H-bonding in crystals from 2D structural information only. Modern computational power and the advances in inductive logic programming (ILP) can now provide computational chemistry with the opportunity for extracting structure-specific rules from large databases that can be incorporated into expert systems. ILP technology is here applied to H-bonding in crystals to develop a self-extracting expert system utilizing data in the Cambridge Structural Database of small molecule crystal structures. A clear increase in performance was observed when the ILP system DMax was allowed to refer to the local structural environment of the possible H-bond donor/acceptor pairs. This ability distinguishes ILP from more traditional approaches that build rules on the basis of global molecular properties.

Artificial Intelligence↗