PubMed Health⌕ Search

Biomedical subjects

I S Roberts

Publications and source records attributed to I S Roberts.

At least 19 recordsLinked to original sources
PubMed1999

Circulating vascular endothelial growth factor is not increased during relapses of steroid-sensitive nephrotic syndrome.

BACKGROUND: An uncharacterized circulating factor that increases vascular permeability has previously been described in childhood steroid-sensitive nephrotic syndrome (SSNS). The aim of this study was to determine whether this factor is vascular endothelial growth factor (VEGF), the recently described endothelial cell mitogen and enhancer of vascular permeability. METHODS: Plasma and urine VEGF levels were measured in children with SSNS in both relapse and remission and in normal age- and sex-matched controls. Semiquantitative reverse transcriptase-polymerase chain reaction studies investigating VEGF mRNA expression were performed on peripheral blood mononuclear cells isolated from children with SSNS in relapse and controls. In two experimental models (one-hour and three-day follow-up postinfusion), Sprague-Dawley rats were intravenously administered 50 microg rVEGF to determine whether this induced either proteinuria or glomerular histologic change. RESULTS: Plasma VEGF levels and urine VEGF/creatinine ratios were not elevated in SSNS relapse compared with remission and control samples. Peripheral blood mononuclear cell VEGF mRNA expression was no different in SSNS patients compared with controls. The administration of VEGF to rats induced an acute reversible fall in systemic blood pressure but did not result in the development of either proteinuria or glomerular histologic change. CONCLUSION: Increased circulating VEGF levels are not responsible for the proteinuria observed during relapses of SSNS. Further studies are warranted to investigate intrarenal VEGF expression.

Adrenal Cortex Hormones↗
PubMed1999

Genetic organization of the Escherichia coli K10 capsule gene cluster: identification and characterization of two conserved regions in group III capsule gene clusters encoding polysaccharide transport functions.

Analysis of the Escherichia coli K10 capsule gene cluster identified two regions, regions 1 and 3, conserved between different group III capsule gene clusters. Region 1 encodes homologues of KpsD, KpsM, KpsT, and KpsE proteins, and region 3 encodes homologues of the KpsC and KpsS proteins. An rfaH mutation abolished K10 capsule production, suggesting that expression of the K10 capsule was regulated by RfaH in a manner analogous to group II capsule gene clusters. An IS3 element and a phiR73-like prophage, both of which may have played a role in the acquisition of group III capsule gene clusters, were detected flanking the K10 capsule genes.

Amino Acid Sequence↗
PubMed1998

Characterization of the glycosyltransferase enzyme from the Escherichia coli K5 capsule gene cluster and identification and characterization of the glucuronyl active site.

Bacterial capsular polysaccharides play an important role in virulence and survival. The Escherichia coli K5 capsule consists of a repeat structure of -4)GlcA-beta(1,4)-GlcNAc alpha(1-, identical to N-acetylheparosan. A 60-kDa protein, KfiC, has been identified as a bifunctional glycosyltransferase, responsible for the alternating alpha and beta addition of each UDP-sugar to the nonreducing end of the polysaccharide chain. Using hydrophobic cluster analysis, a conserved secondary structure motif characteristic of beta-glycosyltransferases was identified along with two highly conserved aspartic acid residues at positions 301 and 352 within the KfiC protein. Site-directed mutagenesis was used to identify catalytically active amino acids within domain A of the KfiC protein. The conserved aspartic acid residues at 301 and 352 were shown to be critical for the beta addition of UDP-GlcA (uridine diphosphoglucuronic acid) to defined nonreducing end oligosaccharide acceptors, suggesting that these conserved aspartic acid residues are catalytically important for beta-glycosyltransferase activity. A deleted derivative of the kfiC gene was generated, which encoded for a truncated KfiC (kfiC') protein. This protein lacked 139 amino acids at the C terminus. This enzyme had no UDP-GlcA transferase activity but still retained UDP-GlcNAc transferase activity, indicating that two separate active sites are present within the KfiC protein.

Amino Acid Sequence↗
PubMed1998

Sclerosing epithelioid fibrosarcoma: a study of five cases emphasizing diagnostic criteria.

AIMS: To study the clinical and histopathological features of sclerosing epithelioid fibrosarcoma, and to define diagnostic criteria for this uncommon soft-tissue tumour. METHODS AND RESULTS: Standard histological, immunohistochemical and ultrastructural techniques were applied to five tumours from head and neck, chest wall and groin. Tumours consisted of groups of monomorphic rounded/epithelioid cells surrounded by a prominent collagenous stroma. Tumour cells showed positive vimentin staining but were negative for other markers. They contained prominent rough endoplasmic reticulum and a large Golgi apparatus which in one case was producing collagen secretion granules, an ultrastructural marker for collagen production. Three patients had medium to long-term survival (3-7 years). Of these, one was disease-free for 3 years, and two experienced multiple recurrences: one of the latter died of metastatic disease. CONCLUSION: Criteria for diagnosing this uncommon tumour include: small to medium cell size, clear or pale cytoplasm, cellular arrangement in cords and strands, dense collagenous stroma; vimentin staining; rough endoplasmic reticulum and a Golgi apparatus producing, in well preserved examples, collagen secretion granules. The paper emphasizes the value of electron microscopy, supporting an appropriate histological picture and immunophenotype, in identifying these relatively low-grade sarcomas.

Adult↗
PubMed1997

Expression of a dominant-negative mutant TGF-beta type II receptor in transgenic mice reveals essential roles for TGF-beta in regulation of growth and differentiation in the exocrine pancreas.

Using a dominant-negative mutant receptor (DNR) approach in transgenic mice, we have functionally inactivated transforming growth factor-beta (TGF-beta) signaling in select epithelial cells. The dominant-negative mutant type II TGF-beta receptor blocked signaling by all three TGF-beta isoforms in primary hepatocyte and pancreatic acinar cell cultures generated from transgenic mice, as demonstrated by the loss of growth inhibitory and gene induction responses. However, it had no effect on signaling by activin, the closest TGF-beta family member. DNR transgenic mice showed increased proliferation of pancreatic acinar cells and severely perturbed acinar differentiation. These results indicate that TGF-beta negatively controls growth of acinar cells and is essential for the maintenance of a differentiated acinar phenotype in the exocrine pancreas in vivo. In contrast, such abnormalities were not observed in the liver. Additional abnormalities in the pancreas included fibrosis, neoangiogenesis and mild macrophage infiltration, and these were associated with a marked up-regulation of TGF-beta expression in transgenic acinar cells. This transgenic model of targeted functional inactivation of TGF-beta signaling provides insights into mechanisms whereby loss of TGF-beta responsiveness might promote the carcinogenic process, both through direct effects on cell proliferation, and indirectly through up-regulation of TGF-betas with associated paracrine effects on stromal compartments.

Animals↗
PubMed1997

Physiological and biochemical studies on psychrotolerance in Listeria monocytogenes.

Studies were undertaken to explain the ability of Listeria monocytogenes to grow at low temperatures in a chemostat. It was found that when grown in continuous culture at a dilution rate of 0.02 h-1 L. monocytogenes had a lower proportion of anteiso-17:0, and a higher proportion of anteiso-15:0, and smaller chain fatty acids when grown at 10 degrees C compared to 30 degrees C. A previously unreported glycolipid was only seen after growth at low temperature. Growth temperature had no effect on the rate of glucose uptake.

Antimetabolites↗
PubMed1997

Regulation of the Escherichia coli K5 capsule gene cluster by transcription antitermination.

The expression of the Escherichia coli K5 (group II) capsular polysaccharide requires the rfaH gene. By reverse transcriptase-polymerase chain reaction (RT-PCR) it was possible to demonstrate that RfaH increases the transcription of region 2 genes by readthrough transcription from the region 3 promoter. A mutation in the rfaH gene reduced this readthrough transcription from the region 3 promoter by 10-fold as measured by quantitative RT-PCR. The region 3 promoter was mapped to 741 bp 5' of the initiation codon of the kpsM gene. Deletion and insertion mutagenesis of the JUMPstart sequence, which is 28 bp 5' of kpsM and is conserved upstream of RfaH-regulated operons and other polysaccharide biosynthesis genes, confirmed that this sequence was required for expression of the K5 antigen and for the antitermination activity of RfaH. The JUMPstart sequence could cause RfaH-dependent antitermination at other Rho-dependent terminators, suggesting that the JUMPstart sequence may function in a manner analogous to a lambda nut site. On the basis of these results we propose a model by which RfaH regulates expression of E. coli group II capsule gene clusters by allowing readthrough transcription to proceed from region 3 into region 2 and that sequences within the JUMPstart sequence are essential for this process.

Antigens, Bacterial↗
PubMed1997

Interstitial myofibroblasts: predictors of progression in membranous nephropathy.

AIMS: To determine the role of interstitial myofibroblasts in the progression of membranous nephropathy; and to assess the predictive value of quantifying myofibroblasts in determining long term renal outcome. METHODS: All cases of membranous nephropathy, diagnosed by renal biopsy at University Hospital of South Manchester between 1984 and 1987, were studied retrospectively. The biopsy specimens (n = 26) were reviewed and analysed morphometrically to measure interstitial volume as a proportion of the total volume of renal cortex, and numbers of interstitial myofibroblasts (cells positive for alpha-smooth muscle actin within the interstitium). Clinical data, with a follow up of seven to eight years, was available for 24 patients, and renal outcome was correlated with pathological changes in the initial diagnostic biopsy specimen. RESULTS: The number of myofibroblasts and interstitial volume were inversely correlated with creatinine clearance at the initial biopsy, and at the end of follow up. Percentage sclerosed glomeruli or stage of glomerular disease, assessed by electron microscopy, did not correlate with renal function at initial biopsy or during follow up. The number of myofibroblasts, but not interstitial volume, correlated with severity of proteinuria at initial biopsy. Of 15 biopsy specimens showing no or mild interstitial fibrosis, four showed a notable increase in the number of interstitial myofibroblasts. All of these patients developed chronic renal failure, compared with three of 11 patients whose specimens showed no or a mild increase in myofibroblast numbers. CONCLUSIONS: Interstitial myofibroblasts play a role in the development of interstitial fibrosis and progressive renal failure in membranous nephropathy. Increased numbers of myofibroblasts in biopsy specimens showing only mild fibrosis may predict subsequent chronic renal failure.

Actins↗
PubMed1996

Prevention of chronic rejection by donor-specific blood transfusion in a new model of chronic cardiac allograft rejection.

Chronic graft rejection is now a major barrier to the long-term survival of cardiac transplants. A major hallmark of chronic rejection is intimal thickening of arteries in the graft leading to vascular occlusion. Current animal models of chronic rejection generally utilize immunosuppression to prevent acute rejection of grafts disparate at major histocompatibility antigens or graft disparities involving minor histocompatibility antigens alone. In the present communication we describe a new model of chronic rejection involving grafting of PVG-R23 hearts into PVG-RT1(u) recipients. The R23 hearts, which differ from the RT1(u) recipients at class II MHC, are rejected with a chronic time course and demonstrate extensive severe vascular myointimal proliferation within the coronary arteries. Furthermore we demonstrate for the first time that donor-specific blood transfusion can prevent chronic rejection and the intimal thickening of the coronary arteries.

Animals↗
PubMed1996

Response of Mycobacterium smegmatis to acid stress.

Evidence was sought for the existence of an inducible acid tolerance response in Mycobacterium smegmatis. Exposure of M. smegmatis to a sub-lethal, adaptive acidic pH was found to confer a significant level of protection against subsequent exposure to a lethal pH, compared to unadapted cells. Adaptation was dependent on de novo protein synthesis.

Acids↗
PubMed1996

Transcriptional organization and regulation of expression of region 1 of the Escherichia coli K5 capsule gene cluster.

The transcriptional organization and regulation of region 1 expression of the Escherichia coli K5 capsule gene cluster were studied. Region 1 was transcribed as an 8.0-kb polycistronic mRNA which was processed to form a separate 1.3-kb transcript encoding the 3'-most gene kpsS. Transcription of region 1 of the E. coli K5 capsule gene cluster was directed from a single promoter 225 bp upstream of a previously unidentified gene, kpsF. The promoter had -35 and -10 consensus sequences typical of an E. coli sigma 70 promoter, with no similarities to binding sites for other sigma factors. Two integration host factor (IHF) binding site consensus sequences were identified 110 bp upstream and 130 bp downstream of the transcription start site. In addition, two AT-rich regions separated by 16 bp identified upstream of the region 1 promoter were conserved upstream of the region 3 promoter. The kpsF gene was 98.8% identical with the kpsF gene identified in the E. coli K1 antigen gene cluster and confirms that the kpsF gene is conserved among group II capsule gene clusters. An intragenic Rho-dependent transcriptional terminator was discovered within the kpsF gene. No essential role for KpsF in the expression of the K5 antigen could be established. The temperature regulation of region 1 expression was at the level of transcription, with no transcription detectable in cells grown at 18 degrees C. Mutations in regulatory genes known to control temperature-dependent expression of a number of virulence genes had no effect on the temperature regulation of region 1 expression. Likewise, RfaH, which is known to regulate expression of E. coli group II capsules had no effect on the expression of region 1. Mutations in the himA and himD genes which encode the subunits of the IHF led to a fivefold reduction in the expression of KpsE at 37 degrees C, confirming a regulatory role for IHF in the expression of region 1 genes.

Bacterial Capsules↗