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D J Marsh

Publications and source records attributed to D J Marsh.

At least 55 records · Page 3Linked to original sources
PubMed1999

Response of melanocortin-4 receptor-deficient mice to anorectic and orexigenic peptides.

Mutations reducing the functional activity of leptin, the leptin receptor, alpha-melanocyte stimulating hormones (alpha-MSH) and the melanocortin-4 receptor (Mc4r) all lead to obesity in mammals. Moreover, mutant mice that ectopically express either agouti (Ay/a mice) or agouti-related protein (Agrp), antagonists of melanocortin signalling, become obese. These data suggest that alpha-MSH signalling transduced by Mc4r tonically inhibits feeding; however, it is not known to what extent this pathway mediates leptin signalling. We show here that Mc4r-deficient (Mc4r-/-) mice do not respond to the anorectic actions of MTII, an MSH-like agonist, suggesting that alpha-MSH inhibits feeding primarily by activating Mc4r. Obese Mc4r-/-mice do not respond significantly to the inhibitory effects of leptin on feeding, whereas non-obese Mc4r-/- mice do. These data demonstrate that melanocortin signalling transduced by Mc4r is not an exclusive target of leptin action and that factors resulting from obesity contribute to leptin resistance. Leptin resistance of obese Mc4r-/- mice does not prevent their response to the anorectic actions of ciliary neurotrophic factor (CNTF), corticotropin releasing factor (CRF), or urocortin; or the orexigenic actions of neuropeptide Y (NPY) or peptide YY (PYY), indicating that these neuromodulators act independently or downstream of Mc4r signalling.

Animals↗
PubMed1999

Mutation and deletion analysis of GFR alpha-1, encoding the co-receptor for the GDNF/RET complex, in human brain tumours.

Glial cell line-derived neurotrophic factor (GDNF) plays a key role in the control of vertebrate neuron survival and differentiation in both the central and peripheral nervous systems. GDNF preferentially binds to GFRalpha-1 which then interacts with the receptor tyrosine kinase RET. We investigated a panel of 36 independent cases of mainly advanced sporadic brain tumours for the presence of mutations in GDNF and GFRalpha-1. No mutations were found in the coding region of GDNF. We identified six previously described GFRalpha-1 polymorphisms, two of which lead to an amino acid change. In 15 of 36 brain tumours, all polymorphic variants appeared to be homozygous. Of these 15 tumours, one also had a rare, apparently homozygous, sequence variant at codon 361. Because of the rarity of the combination of homozygous sequence variants, analysis for hemizygous deletion was pursued in the 15 samples and loss of heterozygosity was found in 11 tumours. Our data suggest that intragenic point mutations of GDNF or GFRalpha-1 are not a common aetiologic event in brain tumours. However, either deletion of GFRalpha-1 and/or nearby genes may contribute to the pathogenesis of these tumours.

Brain Neoplasms↗
PubMed1999

PTEN is inversely correlated with the cell survival factor Akt/PKB and is inactivated via multiple mechanismsin haematological malignancies.

PTEN is a novel tumour suppressor gene that encodes a dual-specificity phosphatase with homology to adhesion molecules tensin and auxillin. It recently has been suggested that PTEN dephosphorylates phosphatidylinositol 3,4,5-trisphosphate [PtdIns(3, 4,5)P3], which mediates growth factor-induced activation of intracellular signalling, in particular through the serine-threonine kinase Akt, a known cell survival-promoting factor. PTEN has been mapped to 10q23.3, a region disrupted in several human tumours including haematological malignancies. We have analysed PTEN in a series of primary acute leukaemias and non-Hodgkin's lymphomas (NHLs) as well as in cell lines. We have also examined whether a correlation could be found between PTEN and Akt levels in these samples. We show here that the majority of cell lines studied carries PTEN abnormalities. At the structural level, we found mutations and hemizygous deletions in 40% of these cell lines, while a smaller number of primary haematological malignancies, in particular NHLs, carries PTEN mutations. Moreover, one-third of the cell lines had low PTEN transcript levels, and 60% of these samples had low or absent PTEN protein, which could not be attributed to gene silencing by hypermethylation. In addition, we found that PTEN and phosphorylated Akt levels are inversely correlated in the large majority of the examined samples. These findings suggest that PTEN plays a role in the pathogenesis of haematological malignancies and that it might be inactivated through a wider range of mechanisms than initially considered. The finding that PTEN levels inversely correlate with phosphorylated Akt supports the hypothesis that PTEN regulates PtdIns(3,4,5)P3and suggests a role for PTEN in apoptosis.

Blotting, Northern↗
PubMed1999

PTEN mutation spectrum and genotype-phenotype correlations in Bannayan-Riley-Ruvalcaba syndrome suggest a single entity with Cowden syndrome.

Germline mutations in the tumour suppressor gene PTEN have been implicated in two hamartoma syndromes that exhibit some clinical overlap, Cowden syndrome (CS) and Bannayan-Riley-Ruvalcaba syndrome (BRR). PTEN maps to 10q23 and encodes a dual specificity phosphatase, a substrate of which is phosphatidylinositol 3,4,5-triphosphate, a phospholipid in the phosphatidylinositol 3-kinase pathway. CS is characterized by multiple hamartomas and an increased risk of benign and malignant disease of the breast, thyroid and central nervous system, whilst the presence of cancer has not been formally documented in BRR. The partial clinical overlap in these two syndromes is exemplified by the hallmark features of BRR: macrocephaly and multiple lipomas, the latter of which occur in a minority of individuals with CS. Additional features observed in BRR, which may also occur in a minority of CS patients, include Hashimoto's thyroiditis, vascular malformations and mental retardation. Pigmented macules of the glans penis, delayed motor development and neonatal or infant onset are noted only in BRR. In this study, constitutive DNA samples from 43 BRR individuals comprising 16 sporadic and 27 familial cases, 11 of which were families with both CS and BRR, were screened for PTEN mutations. Mutations were identified in 26 of 43 (60%) BRR cases. Genotype-phenotype analyses within the BRR group suggested a number of correlations, including the association of PTEN mutation and cancer or breast fibroadenoma in any given CS, BRR or BRR/CS overlap family ( P = 0.014), and, in particular, truncating mutations were associated with the presence of cancer and breast fibroadenoma in a given family ( P = 0.024). Additionally, the presence of lipomas was correlated with the presence of PTEN mutation in BRR patients ( P = 0.028). In contrast to a prior report, no significant difference in mutation status was found in familial versus sporadic cases of BRR ( P = 0.113). Comparisons between BRR and a previously studied group of 37 CS families suggested an increased likelihood of identifying a germline PTEN mutation in families with either CS alone or both CS and BRR when compared with BRR alone ( P = 0.002). Among CS, BRR and BRR/CS overlap families that are PTEN mutation positive, the mutation spectra appear similar. Thus, PTEN mutation-positive CS and BRR may be different presentations of a single syndrome and, hence, both should receive equal attention with respect to cancer surveillance.

Abnormalities, Multiple↗
PubMed1999

Norepinephrine is required for leptin effects on gene expression in brown and white adipose tissue.

Exogenous leptin enhances energy utilization in ob/ob mice by binding its hypothalamic receptor and selectively increasing peripheral fat oxidation. Leptin also increases uncoupling protein 1 (UCP1) expression in brown adipose tissue (BAT), but the neurotransmitter that mediates this effect has not been established. The present experiments sought to determine whether leptin regulates UCP1 expression in BAT and its own expression in white adipose tissue (WAT) through the long or short forms of leptin receptor and modulation of norepinephrine release. Mice lacking dopamine beta-hydroxylase (Dbh-/-), the enzyme responsible for synthesizing norepinephrine and epinephrine from dopamine, were treated with leptin (20 microg/g body weight/day) for 3 days before they were euthanized. UCP1 messenger RNA (mRNA) and protein expression were 5-fold higher in BAT from control (Dbh+/-) compared with Dbh-/- mice. Leptin produced a 4-fold increase in UCP1 mRNA levels in Dbh+/- mice but had no effect on UCP1 expression in Dbh-/-. The beta3-adrenergic agonist, CL-316,243 increased UCP1 expression and established that BAT from both groups of mice was capable of responding to beta-adrenergic stimulation. Similarly, exogenous leptin reduced leptin mRNA in WAT from Dbh+/- but not Dbh-/- mice. In separate experiments, leptin produced comparable reductions in food intake in both Dbh+/- and Dbh-/- mice, illustrating that norepinephrine is not required for leptin's effect on food intake. Lastly, db/db mice lacking the long form of the leptin receptor failed to increase UCP1 mRNA in response to exogenous leptin but increased UCP1 mRNA in response to CL-316,243. These studies establish that norepinephrine is required for leptin to regulate its own expression in WAT and UCP1 expression in BAT and indicate that these effects are likely mediated through the centrally expressed long form of the leptin receptor.

Adipose Tissue↗
PubMed1999

Glucocorticoids differentially inhibit expression of the RET proto-oncogene.

The RET proto-oncogene encodes a receptor tyrosine kinase activated by the binding of factors from the glial cell line-derived neurotrophic factor (GDNF) family to receptor-alpha components such as GDNF family receptor alpha-1 (GFR alpha-1). Mutations within the sequence of the RET proto-oncogene are associated with multiple endocrine neoplasia type 2 (MEN 2), an inherited tumor syndrome characterized by the development of medullary thyroid carcinoma (MTC) and other neuroendocrine tumors. Despite Northern analysis showing that RET is expressed in the majority of MTCs, the factors regulating this expression are poorly understood. To address this issue we examined RET expression in response to glucocorticoids in the TT cell line, derived from a metastatic MTC. The synthetic glucocorticoid dexamethasone was found to reduce RET expression at both mRNA and protein levels. This effect was dose responsive and maximal at 24 h. The reduction in RET mRNA was shown to be specific to glucocorticoids and was also seen in a primary MTC culture. Nuclear run-on studies revealed the reduction in steady-state RNA to be due to a decrease in RET mRNA transcription and the effect was shown to be independent of new protein synthesis or RNA stability. Dexamethasone was also found to exert an inhibitory effect upon cell growth, suggesting a potential use for glucocorticoids in the treatment of medullary carcinoma and MEN 2.

Carcinoma, Medullary↗
PubMed1998

Germline PTEN mutation in a family with Cowden syndrome and Bannayan-Riley-Ruvalcaba syndrome.

Clinical overlap between Cowden disease and Bannayan-Riley-Ruvalcaba syndrome has rarely been described and identical germline mutations in the PTEN gene have been demonstrated in a few families with Cowden disease and some cases of Bannayan-Riley-Ruvalcaba syndrome. We report on a mother with Cowden disease and a son with Bannayan-Riley-Ruvalcaba syndrome. Mutation analysis of the PTEN gene demonstrated a heterozygous nonsense mutation R130X in both individuals. This might suggest that Cowden disease and Bannayan-Riley-Ruvalcaba syndrome are one causal entity.

Adolescent↗
PubMed1998

Ethanol consumption and resistance are inversely related to neuropeptide Y levels.

Genetic linkage analysis of rats that were selectively bred for alcohol preference identified a chromosomal region that includes the neuropeptide Y (NPY) gene. Alcohol-preferring rats have lower levels of NPY in several brain regions compared with alcohol-non-preferring rats. We therefore studied alcohol consumption by mice that completely lack NPY as a result of targeted gene disruption. Here we report that NPY-deficient mice show increased consumption, compared with wild-type mice, of solutions containing 6%, 10% and 20% (v/v) ethanol. NPY-deficient mice are also less sensitive to the sedative/hypnotic effects of ethanol, as shown by more rapid recovery from ethanol-induced sleep, even though plasma ethanol concentrations do not differ significantly from those of controls. In contrast, transgenic mice that overexpress a marked NPY gene in neurons that usually express it have a lower preference for ethanol and are more sensitive to the sedative/hypnotic effects of this drug than controls. These data are direct evidence that alcohol consumption and resistance are inversely related to NPY levels in the brain.

Alcohol Drinking↗
PubMed1998

Response of neuropeptide Y-deficient mice to feeding effectors.

Neuropeptide Y (NPY) is thought to be an important central regulator of feeding behavior and body weight. However, mice lacking NPY due to targeted genetic deletion do not display abnormalities in food intake or body weight with ad libitum access to food or in response to fasting. In this study, we investigate the response of NPY-deficient (NPY-/-) mice to anorexic and orexigenic treatments. The dose-dependent stimulation of food intake by central NPY administration was unaltered in NPY-/- mice. Peripheral administration of various doses of leptin for 2 days elicited a two-fold greater inhibition of food intake in NPY-/- mice than in wildtype (NPY+/+) mice. In addition, lateral ventricular administration of leptin (1 microg) suppressed refeeding in NPY-/- mice after a 24 h fast, but had little effect in NPY+/+ mice. However, the response to other feeding inhibitors such as corticotrophin releasing factor (CRF), dexfenfluramine, and a melanocortin 4 receptor (MC4R) agonist, MTII, was unaltered in NPY-/- mice. These results indicate that the appetite-suppressant action of exogenous leptin is uniquely amplified in NPY-/- mice, and suggest that NPY may tonically antagonize leptin action.

Animals↗
PubMed1998

Germline mutations in PTEN are an infrequent cause of genetic predisposition to breast cancer.

Heterozygous germline mutations in PTEN are responsible for most cases of Cowden Syndrome, a rare familial trait characterized by hamartomas and by predisposition to cancer of the breast and thyroid. The variable and often subtle clinical findings that characterize Cowden Syndrome are frequently unrecognized, raising the possibility that germline PTEN mutations may confer susceptibility to breast cancer in women who have not been diagnosed with this syndrome. To determine whether such mutations contribute to genetic predisposition to breast cancer within the general population, we analysed a cohort of women with early-onset breast cancer (< age 40), a subset of the population at increased risk for genetic susceptibility. Lymphoblast cell lines were analysed using either direct nucleotide sequencing (28 cases), denaturing gradient gel electrophoresis (DGGE) (34 cases) or a yeast-based truncation assay (110 cases). No definitive, truncating mutations were observed in 172 patients. Missense changes were noted in the germline of 2/60 patients analysed by direct nucleotide sequencing or DGGE, including a non-conservative amino acid substitution within the phosphatase domain, but neither showed loss of the wild-type allele in the corresponding breast tumor specimen. We conclude that germline mutations in PTEN are an uncommon cause of genetic predisposition to breast cancer within the general population.

Adult↗
PubMed1998

A highly conserved processed PTEN pseudogene is located on chromosome band 9p21.

PTEN/MMAC1/TEP1, encoding a dual-specificity phosphatase, is a tumor suppressor gene which has recently been cloned and mapped to chromosome 10q23.3. We have shown that germline mutations of PTEN are present in individuals with two hamartoma syndromes: Cowden Syndrome, associated with a predisposition to breast and thyroid cancers, and Bannayan-Zonana syndrome. Somatic mutations of PTEN have been reported in a variety of human cancer cell lines, suggesting a potential role for this gene in the pathogenesis of human malignancies. We report the identification of a highly conserved PTEN processed pseudogene, psiPTEN, which shares over 98% homology with the coding region of functional PTEN, and its localisation to chromosome 9p21. The high sequence homology of psiPTEN with the PTEN transcript may potentially lead to misinterpretation when performing mutation analyses based on cDNA templates. Caution should be exerted when using such screening approaches.

Amino Acid Sequence↗
PubMed1998

Allelic imbalance, including deletion of PTEN/MMACI, at the Cowden disease locus on 10q22-23, in hamartomas from patients with Cowden syndrome and germline PTEN mutation.

Cowden disease (CD) is a rare, autosomal dominant inherited cancer syndrome characterized by multiple benign and malignant lesions in a wide spectrum of tissues. While individuals with CD have an increased risk of breast and thyroid neoplasms, the primary features of CD are hamartomas. The gene for CD has been mapped by linkage analysis to a 6 cM region on the long arm of chromosome 10 at 10q22-23. Loss of heterozygosity (LOH) studies of sporadic follicular thyroid adenomas and carcinomas, both component tumors of CD, have suggested that the putative susceptibility gene for CD is a tumor suppressor gene. Somatic missense and nonsense mutations have recently been identified in breast, prostate, and brain tumor cell lines in a gene encoding a dual specificity phosphatase, PTEN/MMACI, mapped at 10q23.3. Furthermore, germline PTEN/MMACI mutations are associated with CD. In the present study, 20 hamartomas from 11 individuals belonging to ten unrelated families with CD have been examined for LOH of markers flanking and within PTEN/MMACI. Eight of these ten families have germline PTEN/MMACI mutations. LOH involving microsatellite markers within the CD interval, and including PTEN/MMACI, was identified in two fibroadenomas of the breast, a thyroid adenoma, and a pulmonary hamartoma belonging to 3 to 11 (27%) of these patients. The wild-type allele was lost in these hamartomas. Semi-quantitative PCR performed on RNA from hamartomas from three different tissues from a CD patient suggested substantial reduction of PTEN/MMACI RNA levels in all of these tissues. The LOH identified in samples from individuals with CD and the suggestion of allelic loss and reduced transcription in hamartomas from a CD patient provide evidence that PTEN/MMACI functions as a tumor suppressor in CD.

Chromosomes, Human, Pair 10↗
PubMed1998

Absence of MEN2A- or 2B-type RET mutations in primary neuroblastoma tumour tissue.

Specific germline mutations in the RET proto-oncogene predispose to the familial cancer syndromes: multiple endocrine neoplasia (MEN) types 2A and 2B, and familial medullary thyroid carcinoma. Expression of the RET receptor tyrosine kinase is tightly restricted to tumours of neural crest origin, such as neuroblastoma, and neuroblastoma has been observed in RET transgenic mice. Neuroblastoma tumour cell lines transfected with the MEN2A RET gene exhibit spontaneous neuritic differentiation, whereas MEN2B-type RET transfectants demonstrate altered cell adhesion and enhanced metastatic potential. In this study, the authors examined genomic DNA from 26 primary neuroblastoma tumours for MEN2A and MEN2B RET mutations, using restriction enzyme digestion of polymerase chain reaction products as an alternative to direct sequencing. Examination of RET exons 10 (codons 611, 618, 620), 11 (codons 632, 633, 634) and 16 (codon 918) in all 26 tumours revealed no RET mutations. Taken together these data suggest that abnormalities of the RET signalling pathway, rather than oncogenic, MEN2-type RET activation by mutation, may play a role in neuroblastoma tumorigenesis.

DNA, Neoplasm↗
PubMed1998

Role of the Y5 neuropeptide Y receptor in feeding and obesity.

Neuropeptide Y (NPY), a 36-amino-acid neuromodulator abundantly expressed in the brain, has been implicated in the regulation of food intake and body weight. Pharmacological data suggest that NPY's stimulatory effect on appetite is transduced by the G-protein-coupled NPY Y5 receptor (Y5R). We have inactivated the Y5R gene in mice and report that younger Y5R-null mice feed and grow normally; however, they develop mild late-onset obesity characterized by increased body weight, food intake and adiposity. Fasting-induced refeeding is unchanged in younger Y5R-null mice and they exhibit normal sensitivity to leptin. Their response to intracerebroventricular (i.c.v.) administration of NPY and related peptides is either reduced or absent. NPY deficiency attenuates the obesity syndrome of mice deficient for leptin (ob/ob), but these effects are not mediated by NPY signaling through the Y5R because Y5R-null ob/ob mice are equally obese. These results demonstrate that the Y5R contributes to feeding induced by centrally administered NPY and its analogs, but is not a critical physiological feeding receptor in mice.

Animals↗
PubMed1998

Analysis of the PTEN gene in human meningiomas.

Previous observations demonstrated that the neurofibromatosis type 2 gene (NF2) plays an important role in the pathogenesis of the transitional, fibroblastic and malignant variants of human meningiomas. No specific genes have been associated with the pathogenesis of meningothelial meningiomas and with the progression to anaplastic meningiomas. However, allelic losses on chromosomal arms 1p, 10q and 14q have been implicated in the process of malignant progression. Recently, PTEN (phosphatase and tensin homolog deleted on chromosome ten) also termed MMAC1 (mutated in multiple advanced cancers 1) or TEP1 (TGF--regulated and epithelial cell-enriched phosphatase), emerged as a candidate gene on chromosome 10q23.3. Initial studies revealed mutations of PTEN in limited series of glioblastomas, breast, kidney and prostate carcinomas mainly as cell lines. In order to evaluate the involvement of PTEN in the development of meningiomas, we have analysed the entire coding sequence of the gene in a series of 55 meningiomas (WHO grade I). 10 atypical meningiomas (WHO grade II) and 10 anaplastic meningiomas (WHO grade III). No PTEN mutations were seen in the WHO grade I meningiomas. However, one of the anaplastic meningiomas carried a somatic mutation. In addition, all tumours were examined for the presence of homozygous deletions of PTEN but these were not detected in any of the meningiomas. Our data suggest that mutations in PTEN are not involved in the formation of low grade meningiomas, but may contribute to malignant progression in a fraction of anaplastic meningiomas.

Chromosomes, Human, Pair 10↗
PubMed1998

Mutation spectrum and genotype-phenotype analyses in Cowden disease and Bannayan-Zonana syndrome, two hamartoma syndromes with germline PTEN mutation.

The tumour suppressor gene PTEN , which maps to 10q23.3 and encodes a 403 amino acid dual specificity phosphatase (protein tyrosine phosphatase; PTPase), was shown recently to play a broad role in human malignancy. Somatic PTEN deletions and mutations were observed in sporadic breast, brain, prostate and kidney cancer cell lines and in several primary tumours such as endometrial carcinomas, malignant melanoma and thyroid tumours. In addition, PTEN was identified as the susceptibility gene for two hamartoma syndromes: Cowden disease (CD; MIM 158350) and Bannayan-Zonana (BZS) or Ruvalcaba-Riley-Smith syndrome (MIM 153480). Constitutive DNA from 37 CD families and seven BZS families was screened for germline PTEN mutations. PTEN mutations were identified in 30 of 37 (81%) CD families, including missense and nonsense point mutations, deletions, insertions, a deletion/insertion and splice site mutations. These mutations were scattered over the entire length of PTEN , with the exception of the first, fourth and last exons. A 'hot spot' for PTEN mutation in CD was identified in exon 5 that contains the PTPase core motif, with 13 of 30 (43%) CD mutations identified in this exon. Seven of 30 (23%) were within the core motif, the majority (five of seven) of which were missense mutations, possibly pointing to the functional significance of this region. Germline PTEN mutations were identified in four of seven (57%) BZS families studied. Interestingly, none of these mutations was observed in the PTPase core motif. It is also worthy of note that a single nonsense point mutation, R233X, was observed in the germline DNA from two unrelated CD families and one BZS family. Genotype-phenotype studies were not performed on this small group of BZS families. However, genotype-phenotype analysis inthe group of CD families revealed two possible associations worthy of follow-up in independent analyses. The first was an association noted in the group of CD families with breast disease. A correlation was observed between the presence/absence of a PTEN mutation and the type of breast involvement (unaffected versus benign versus malignant). Specifically and more directly, an association was also observed between the presence of a PTEN mutation and malignant breast disease. Secondly, there appeared to be an interdependent association between mutations upstream and within the PTPase core motif, the core motif containing the majority of missense mutations, and the involvement of all major organ systems (central nervous system, thyroid, breast, skin and gastrointestinal tract). However, these observations would need to be confirmed by studying a larger number of CD families.

Chromosome Mapping↗