Biomedical subjects

G Thomas

Publications and source records attributed to G Thomas.

At least 73 records · Page 4Linked to original sources

PubMed2001

The activity and signaling range of mature BMP-4 is regulated by sequential cleavage at two sites within the prodomain of the precursor.

Proteolytic maturation of proBMP-4 is required to generate an active signaling molecule. We show that proBMP-4 is cleaved by furin in a sequential manner. Cleavage at a consensus furin site adjacent to the mature ligand domain allows for subsequent cleavage at an upstream nonconsensus furin site within the prodomain. BMP-4 synthesized from precursor in which the upstream site is noncleavable is less active, signals at a shorter range, and accumulates at lower levels than does BMP-4 cleaved from native precursor. Conversely, BMP-4 cleaved from precursor in which both sites are rapidly cleaved is more active and signals over a greater range. Differential use of the upstream cleavage site could provide for tissue-specific regulation of BMP-4 activity and signaling range.

Amino Acid Sequence↗

PubMed2001

Insulin signaling: lessons from the Drosophila tuberous sclerosis complex, a tumor suppressor.

The genes that encode the proteins composing the tuberous sclerosis complex (TSC) are tumor suppressors. Experiments in the model organism Drosophila melanogaster have provided insight into the identity of these genes and their functions in regulating cell size and proliferation. Montagne et al. describe the various genetic interactions that show TSC to be a regulator of the insulin signaling pathway and a regulator of progression through the cell cycle, which explains its effects on cell size and tissue and tumor growth.

Animals↗

PubMed2001

Furin inhibition results in absent or decreased invasiveness and tumorigenicity of human cancer cells.

Pro-protein convertases such as furin are expressed in many human tumor lines and primary tumors. Furin processes stromelysin-3, membrane type 1 matrix metalloproteinase (MMPs) involved in tumor cell invasiveness, as well as growth factors such as transforming growth factor beta1. Evaluation of furin expression in head and neck squamous cell carcinoma (HNSCC) cells exhibiting different invasive ability showed that furin overexpression correlated with their respective invasiveness. The use of a selective furin inhibitor, alpha 1-PDX (PDX) was studied in three furin-expressing invasive HNSCC cell lines. The effects of PDX transfection were evaluated in vivo and in vitro to determine changes in the malignant phenotype. Transfection of HNSCC cell lines with PDX resulted in significant decrease or absence of tumorigenicity after s.c. inoculation into severe combined immunodeficient mice. Likewise, in vitro invasiveness was reduced approximately 50%. The in vivo invasion assay using tracheal xenotransplants showed even more drastic reductions of the invasive ability of PDX-transfected cells (up to an 80% decrease). PDX-transfected cells did not invade or penetrated less into the tracheal wall tissues than their vector alone-transfected counterparts. In addition, the former cells showed a remarkable decrease in MMP-2 processing and activity. After PDX transfection the cells were less efficient in processing the tumor progression-associated furin substrates transforming growth factor beta1 and pro-membrane type 1-MMP. These findings indicate that furin inhibition is a feasible approach to attenuate and even abolish certain critical attributes of the advanced malignant phenotype. Thus, furin should be considered as a promising target for cancer therapy.

Animals↗

PubMed2001

Enhanced sensitivity of PTEN-deficient tumors to inhibition of FRAP/mTOR.

Recent evidence places the FRAP/mTOR kinase downstream of the phosphatidyl inositol 3-kinase/Akt-signaling pathway, which is up-regulated in multiple cancers because of loss of the PTEN tumor suppressor gene. We performed biological and biochemical studies to determine whether PTEN-deficient cancer cells are sensitive to pharmacologic inhibition of FRAP/mTOR by using the rapamycin derivative CCI-779. In vitro and in vivo studies of isogenic PTEN(+/+) and PTEN(-/-) mouse cells as well as human cancer cells with defined PTEN status showed that the growth of PTEN null cells was blocked preferentially by pharmacologic FRAP/mTOR inhibition. Enhanced tumor growth caused by constitutive activation of Akt in PTEN(+/+) cells also was reversed by CCI-779 treatment, indicating that FRAP/mTOR functions downstream of Akt in tumorigenesis. Loss of PTEN correlated with increased S6 kinase activity and phosphorylation of ribosomal S6 protein, providing evidence for activation of the FRAP/mTOR pathway in these cells. Differential sensitivity to CCI-779 was not explained by differences in biochemical blockade of the FRAP/mTOR pathway, because S6 phosphorylation was inhibited in sensitive and resistant cell lines. These results provide rationale for testing FRAP/mTOR inhibitors in PTEN null human cancers.

Adaptor Proteins, Signal Transducing↗

PubMed2001

Differences in telomere length between homologous chromosomes in humans.

Telomeres are important structures for DNA replication and chromosome stability during cell growth. Telomere length has been correlated with the division potential of human cells and has been found to decrease with age in healthy individuals. Nevertheless, telomere lengths within the same cell are heterogeneous and certain chromosome arms typically have either short or long telomeres. Both the origin and the physiological consequences of this heterogeneity in telomere length remain unknown. In this study we used quantitative telomeric FISH combined with a method to identify the parental origin of chromosomes to show that significant differences in relative telomere intensities are frequently observed between chromosomal homologs in short-term stimulated cultures of peripheral blood lymphocytes. These differences appear to be stable for at least 4 months in vivo, but disappear after prolonged proliferation in vitro. The telomere length differences are also stable during in vitro growth of telomerase-negative fibroblast cells but can be abolished by exogenous telomerase expression in these cells. These findings suggest the existence of a mechanism maintaining differences in telomere length between chromosome homologs that is independent of telomere length itself.

Cell Division↗

PubMed2001

Estimating Lyapunov exponents in biomedical time series.

Among nonlinear dynamical invariants, determination of the largest Lyapunov exponent is well suited to positive identification of chaos in observed time series. When analyzing the dynamics of biomedical series, such as an electro-encephalogram (EEG), model-based methods should be used. Moreover, in the absence of any well founded theoretical model, and because of unexplained variability in the data, candidate models must provide for a stochastic component. Here we use nonlinear autoregressive stochastic modeling to estimate the dominant Lyapunov exponent in an EEG series and compute confidence intervals from surrogate data. The results are found to differ from those of approaches which aim at deleting noise prior to analysis.

Algorithms↗

PubMed2001

Mutations within a furin consensus sequence block proteolytic release of ectodysplasin-A and cause X-linked hypohidrotic ectodermal dysplasia.

X-linked hypohidrotic ectodermal dysplasia (XLHED) is a heritable disorder of the ED-1 gene disrupting the morphogenesis of ectodermal structures. The ED-1 gene product, ectodysplasin-A (EDA), is a tumor necrosis factor (TNF) family member and is synthesized as a membrane-anchored precursor protein with the TNF core motif located in the C-terminal domain. The stalk region of EDA contains the sequence -Arg-Val-Arg-Arg156-Asn-Lys-Arg159-, representing overlapping consensus cleavage sites (Arg-X-Lys/Arg-Arg( downward arrow)) for the proprotein convertase furin. Missense mutations in four of the five basic residues within this sequence account for approximately 20% of all known XLHED cases, with mutations occurring most frequently at Arg156, which is shared by the two consensus furin sites. These analyses suggest that cleavage at the furin site(s) in the stalk region is required for the EDA-mediated cell-to-cell signaling that regulates the morphogenesis of ectodermal appendages. Here we show that the 50-kDa EDA parent molecule is cleaved at -Arg156Asn-Lys-Arg(159 downward arrow)- to release the soluble C-terminal fragment containing the TNF core domain. This cleavage appears to be catalyzed by furin, as release of the TNF domain was blocked either by expression of the furin inhibitor alpha1-PDX or by expression of EDA in furin-deficient LoVo cells. These results demonstrate that mutation of a functional furin cleavage site in a developmental signaling molecule is a basis for human disease (XLHED) and raise the possibility that furin cleavage may regulate the ability of EDA to act as a juxtacrine or paracrine factor.

Amino Acid Sequence↗

PubMed2001

Association of NOD2 leucine-rich repeat variants with susceptibility to Crohn's disease.

Crohn's disease and ulcerative colitis, the two main types of chronic inflammatory bowel disease, are multifactorial conditions of unknown aetiology. A susceptibility locus for Crohn's disease has been mapped to chromosome 16. Here we have used a positional-cloning strategy, based on linkage analysis followed by linkage disequilibrium mapping, to identify three independent associations for Crohn's disease: a frameshift variant and two missense variants of NOD2, encoding a member of the Apaf-1/Ced-4 superfamily of apoptosis regulators that is expressed in monocytes. These NOD2 variants alter the structure of either the leucine-rich repeat domain of the protein or the adjacent region. NOD2 activates nuclear factor NF-kB; this activating function is regulated by the carboxy-terminal leucine-rich repeat domain, which has an inhibitory role and also acts as an intracellular receptor for components of microbial pathogens. These observations suggest that the NOD2 gene product confers susceptibility to Crohn's disease by altering the recognition of these components and/or by over-activating NF-kB in monocytes, thus documenting a molecular model for the pathogenic mechanism of Crohn's disease that can now be further investigated.

Alleles↗

PubMed2001

PACS-1 binding to adaptors is required for acidic cluster motif-mediated protein traffic.

PACS-1 is a cytosolic protein involved in controlling the correct subcellular localization of integral membrane proteins that contain acidic cluster sorting motifs, such as furin and human immunodeficiency virus type 1 (HIV-1) NEF: We have now investigated the interaction of PACS-1 with heterotetrameric adaptor complexes. PACS-1 associates with both AP-1 and AP-3, but not AP-2, and forms a ternary complex between furin and AP-1. A short sequence within PACS-1 that is essential for binding to AP-1 has been identified. Mutation of this motif yielded a dominant-negative PACS-1 molecule that can still bind to acidic cluster motifs on cargo proteins but not to adaptor complexes. Expression of dominant-negative PACS-1 causes a mislocalization of both furin and mannose 6-phosphate receptor from the trans-Golgi network, but has no effect on the localization of proteins that do not contain acidic cluster sorting motifs. Furthermore, expression of dominant-negative PACS-1 inhibits the ability of HIV-1 Nef to downregulate MHC-I. These studies demonstrate the requirement for PACS-1 interactions with adaptor proteins in multiple processes, including secretory granule biogenesis and HIV-1 pathogenesis.

Adaptor Protein Complex 3↗

PubMed2001

Microsatellite instability and hMLH1/hMSH2 expression in Barrett esophagus-associated adenocarcinoma.

BACKGROUND: Microsatellite instability (MSI) has been documented in malignancies associated with hereditary nonpolyposis colon carcinoma and in sporadic malignancies of the colon, stomach, and endometrium. In these malignancies, MSI is associated with defects in the DNA mismatch repair enzymes hMSH2 and hMLH1. Defects in these enzymes result in a phenotype characterized by instability of multiple microsatellite repeat sequences throughout the genome. This study sought to determine the prevalence of MSI in 80 primary Barrett esophagus-associated adenocarcinomas (BEAd) and to examine the relation of MSI with the clinical and pathologic features of the tumors. METHODS: Eighty BEAd were evaluated for the presence of MSI by using the microsatellite markers BAT25, BAT26, D10S219, D10S541, and D10S551. These tumors also were evaluated for immunohistochemical expression of hMSH2 and hMLH1. RESULTS: High levels of MSI were not found in any of the tumors examined. Furthermore, immunohistochemical expression of hMSH2 and hMLH1 was retained in all cases evaluated. Evidence of low level MSI was found in 16% of tumors. In none of these tumors, however, was MSI present in more than two of five loci. The presence of MSI did not correlate with patient age, tumor stage, degree of differentiation, or with patient survival. CONCLUSIONS: High level MSI and loss of hMLH1/hMSH2 expression is uncommon in BEAd. A subset of BEAd demonstrate low level MSI. The presence of low level MSI was not associated with the clinicopathologic features of the tumors examined.

Adaptor Proteins, Signal Transducing↗

PubMed2001

Allelic loss of 10q23, the PTEN tumour suppressor gene locus, in Barrett's oesophagus-associated adenocarcinoma.

PTEN is a putative tumour suppressor gene located on chromosome band 10q23. Mutations in PTEN have been identified in numerous human malignancies, including cancers of the brain, endometrium, ovary, and prostate. In this study, we screened 80 Barrett's oesophagus-associated adenocarcinomas (BOAd) for loss of heterozygosity (LOH) at 10q23, using the microsatellite markers D10S541, D10S219, and D10S551. Tumours demonstrating LOH were then screened for the presence or absence of PTEN mutations. LOH at one or more loci was identified in 17/80 (21%) cases. In none of these cases did we detect mutations in PTEN. The presence of LOH did not correlate with patient age, tumour stage, degree of differentiation, presence of perineural or vascular invasion, or overall survival. We conclude that LOH at chromosome 10q23 is uncommon in BOAd, is not associated with mutations in the PTEN tumour suppressor gene, and does not correlate with the clinical or pathologic features of these tumours. It is possible that PTEN is inactivated through other mechanisms in BOAd.

Adenocarcinoma↗

PubMed2001

An acidic motif retains vesicular monoamine transporter 2 on large dense core vesicles.

The release of biogenic amines from large dense core vesicles (LDCVs) depends on localization of the vesicular monoamine transporter VMAT2 to LDCVs. We now find that a cluster of acidic residues including two serines phosphorylated by casein kinase 2 is required for the localization of VMAT2 to LDCVs. Deletion of the acidic cluster promotes the removal of VMAT2 from LDCVs during their maturation. The motif thus acts as a signal for retention on LDCVs. In addition, replacement of the serines by glutamate to mimic phosphorylation promotes the removal of VMAT2 from LDCVs, whereas replacement by alanine to prevent phosphorylation decreases removal. Phosphorylation of the acidic cluster thus appears to reduce the localization of VMAT2 to LDCVs by inactivating a retention mechanism.

Amino Acid Motifs↗

PubMed2001

Evolution of instability at coding and non-coding repeat sequences in human MSI-H colorectal cancers.

A number of human genes containing coding mononucleotide repeat sequences are particularly prone to mutations in tumors with defects in mismatch repair (MMR) genes (MSI-H cancers). In a large series of MSI-H colorectal tumors, we looked for mutations in 25 coding repeats contained in eight genes already known to be mutated in these cancers or in 17 other genes with an expected role in carcinogenesis. Mutations were found in 19 of the 25 candidate genes. Using a maximum likelihood statistical method, they were separated into two different groups that differed significantly in their mutation frequencies, and were likely to represent mutations that do or do not provide selective pressures during MSI-H tumoral progression, respectively. Three new target genes were found (GRB-14, RHAMM, RAD50). Our results provide evidence that MSI-H tumoral progression involves the cumulative mutations of a large number of genes. For each MSI-H tumor we calculated indexes representing the number of mutations found in genes of these groups. We also evaluated a shortening index at both the Bat-25 and Bat-26 non-coding mononucleotide tracts that are known to be almost always unstable in MSI-H cancers. A significant correlation was observed between instability at both coding and non-coding repeats, suggesting that Bat-25 and Bat-26 could be used as simple phenotypical markers of the tumoral evolution. A preferential order of mutations was deduced. During this process, hMSH3 alterations, a target gene encoding for a MMR protein, was found to play an important role by increasing the instability phenomenon characterizing these cancers.

Base Pair Mismatch↗

PubMed2001

Testing a preoperative pain management intervention for elders.

The investigators examined whether elders who have been taught pain management communication skills and pain management information obtain greater postoperative pain relief than elders not taught this information. Thirty-one elders were randomly assigned preoperatively to a control or communication group in this posttest-only experiment with repeated measures. Communication group participants were taught pain management, pain communication skills, and the use of two pain-intensity scales. Control group participants were taught to use the two pain-intensity scales. Pain was measured with the McGill Pain Questionnaire Short Form. The communication group elders reported less postoperative pain over the course of their hospital stay. Pain management knowledge alone may have enabled the elders to obtain greater pain relief. Nurses may want to incorporate similar pain management information and pain communication skills when teaching elders how to obtain greater postoperative pain relief.

Aged↗

PubMed2001

Genetic variation and population structure in Oryza malampuzhaensis Krish. et Chand. endemic to Western Ghats, South India.

Oryza malampuzhaensis Krish. et Chand. (2n = 4x = 48; Poaceae, Oryza) is endemic to Western Ghats, South India, and shows a highly localized distribution over a small geographical area in this region. This is the most poorly understood taxon in genus Oryza and is often misidentified as O. officinalis owing to their close morphology. We assessed the nature and distribution of genetic variation among 11 populations of O. malampuzhaensis using random amplified polymorphic DNA markers. The analysis revealed low genetic variation in O. malampuzhaensis. Cluster analysis of pairwise genetic distances of populations revealed three distinct clusters and the grouping of populations largely corresponded to their geographical proximity. Restricted gene flow and a geography-dependent differentiation were evident among populations. The altitude-influenced differences in ecological factors among the natural habitats of the populations seem to be the cause of the geography-dependent differentiation. Genetically isolated smaller populations and a narrow genetic base in O. malampuzhaensis point to its vulnerability to genetic drift and genetic depauperation. Thus O. malampuzhaensis appears to be under the threat of extinction and needs to be conserved by use of suitable methods. The present study also identified molecular markers diagnostic for O. malampuzhaensis.

Altitude↗

PubMed2001

Trans-Golgi network sorting.

The trans-Golgi network (TGN) is a major secretory pathway sorting station that directs newly synthesized proteins to different subcellular destinations. The TGN also receives extracellular materials and recycled molecules from endocytic compartments. In this review, we summarize recent progress on understanding TGN structure and the dynamics of trafficking to and from this compartment. Protein sorting into different transport vesicles requires specific interactions between sorting motifs on the cargo molecules and vesicle coat components that recognize these motifs. Current understanding of the various targeting signals and vesicle coat components that are involved in TGN sorting are discussed, as well as the molecules that participate in retrieval to this compartment in both yeast and mammalian cells. Besides proteins, lipids and lipid-modifying enzymes also participate actively in the formation of secretory vesicles. The possible mechanisms of action of these lipid hydrolases and lipid kinases are discussed. Finally, we summarize the fundamentally different apical and basolateral cell surface delivery mechanisms and the current facts and hypotheses on protein sorting from the TGN into the regulated secretory pathway in neuroendocrine cells.

Animals↗

PubMed2001

Pneumonostomy in the surgical management of bilateral hydatid cysts of the lung.

During the period 1994-1998, three patients with bilateral hydatid cysts of the lung (HCL) underwent operative removal of the cysts. In three of the six lungs operated upon the conventional technique was used: after removal of the cyst and suture closure of bronchial leaks, the chest was closed with an intercostal drainage tube. Two of these patients developed bronchopleural fistulae requiring rethoracotomy and prolonged hospital stays. The other three lungs were operated upon using the pneumonostomy technique: after excision of the cyst a separate catheter is fixed within the residual lung cavity and brought out through the adjacent chest wall, effectively marsupialising the residual cavity to the atmosphere. All these patients had an uneventful postoperative recovery. We conclude that the pneumonostomy technique is a very useful method of treating HCL surgically, especially when the cysts are bilateral and complicated.

Child↗

PubMed2001

Bilateral high loop ureterostomy in the primary management of posterior urethral valves in a developing country.

Of 200 consecutive cases of posterior urethral valves (PUV) managed in a single institution, 26 underwent bilateral high loop ureterostomy (BU) as their first operative intervention. Indications for BU were persistently raised serum creatinine levels after bladder drainage, severe urosepsis, and urinary ascites, especially in a neonate or infant. After a median period of 1 year of diversion, the serum creatinine fell from a median value of 2.5 to 0.6 mg%. Twelve cases have been fully undiverted without deleterious effects (median serum creatinine level 0.5 mg%). Three patients died. Of the 14 renal units with documented persistent vesicoureteric reflux at the time of undiversion, only 1 has been reimplanted. One child has undergone bladder augmentation.

Child, Preschool↗