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Biomedical subjects

P Briata

Publications and source records attributed to P Briata.

29 records · Page 2Linked to original sources
PubMed1992

Differential DNA binding properties of three human homeodomain proteins.

The products of three human homeobox containing (HOX) genes, 2C, 3C and 4B, were produced in insect cells using the Baculovirus expression system and purified to near homogeneity. In this system we observed that the DNA binding forms of the three proteins are not glycosylated. HOX 3C and 4B are phosphorylated in insect cells, while HOX 2C is not. The three HOX proteins bind to a DNA sequence known to be a target site for Antennapedia protein with a very similar affinity (Kd = 1-2 x 10(-9) M). We then measured their binding properties to four human sequences present in the HOX 3D, 4C, 1C and 4B promoters. Two of these sequences have been reported to be binding sites for HOX proteins. HOX 2C, 3C and 4B behaved quite differently, showing low affinity for promoters of genes located upstream from their own gene in the HOX clusters and a higher affinity for regulatory sequences of their own gene and downstream HOX genes.

Animals↗
PubMed1992

Protein kinase C mRNA levels and activity in reconstituted normal human epidermis: relationships to cell differentiation.

Although keratinocytes are a major target of phorbol ester actions, the activity and the expression of the eight cloned protein kinase C (PKC) isoenzymes have not been studied in detail in human epidermis. Starting from normal human keratinocytes, we reconstituted in culture a multilayered epithelial tissue which presents many hystological, biochemical, and molecular features of the authentic epidermis and we used it as a model to investigate the PKC activity and mRNA levels. We found that i) PKC activity is higher in differentiated than in non-differentiated cells; ii) the mRNA levels of PKC delta and -eta/L, while are differently affected by spontaneous keratinocyte differentiation, are down-regulated during phorbol esters-induced cell differentiation. Our findings could represent a basis to investigate the involvement of PKC isoforms in the keratinocyte differentiation process.

Base Sequence↗
PubMed1992

Androgens increase insulin receptor mRNA levels, insulin binding, and insulin responsiveness in HEp-2 larynx carcinoma cells.

Androgen receptors have been found in human larynx and androgens have been supposed to play an important role in promoting the growth of laryngeal carcinomas. The molecular mechanism underlaying this phenomenon is not at all understood. Aim of this work was to investigate the effects of two androgens (testosterone and dihydrotestosterone) on insulin receptor mRNA levels and insulin binding activity as well as on either metabolic or growth-promoting actions of insulin in a human larynx carcinoma cell line (HEp-2). We found that HEp-2 cells express a high affinity insulin receptor. Both androgens significantly increase insulin receptor mRNA levels and insulin receptor number in HEp-2 cells. Insulin action, evaluated either as total glucose utilization or as [3H]thymidine incorporation into DNA, significantly increased in HEp-2 treated with androgens in comparison to control cultures. Altogether, our data allow us to speculate that the increased insulin effectiveness we observed in the larynx carcinoma cell line HEp-2 after androgen treatment might be involved in the regulation of larynx cancer cells growth.

Carcinoma, Squamous Cell↗
PubMed1991

Insulin receptor gene expression is reduced in cells from a progeric patient.

We have studied a 15-year-old girl (P1) suffering from the Hutchinson-Gilford syndrome (progeria) associated with a severe insulin resistance. Insulin binding activity to P1 erythrocytes was 85% reduced when compared to that measured in ten normal controls matched for sex and age. This finding was confirmed in Epstein-Barr virus (EBV)-transformed lymphoblasts and depends on a reduction in insulin receptor number. Also the amount of total insulin receptors, [35S]methionine labeled and immunoprecipitated, was 90% reduced in P1 lymphoblasts when compared to controls. Next, we measured insulin receptor mRNA levels and we found undetectable levels of insulin receptor transcript in P1 EBV-transformed lymphoblasts, in the absence of any rearrangement of insulin receptor gene as evaluated by Southern blot analysis. The marked reduction in insulin receptor gene expression probably accounts for the severe insulin resistance presented by the patient. Despite extensive studies, the molecular basis of progeria is still unknown. The near complete absence of a molecule crucial in the transduction of cell growth and differentiation signals could be involved in the accelerated aging of the patient.

Adolescent↗
PubMed1990

Multifactorial control of insulin receptor gene expression in human cell lines.

Taking advantage of a computer program to align DNA sequences we scanned the 5'-flanking region of the insulin receptor gene to localize putative regulatory elements. Using this approach as a start point, we investigated the effect of several agents on insulin receptor gene expression in human cells. We found that (i) forskolin reduces insulin receptor mRNA levels; (ii) the effects of either forskolin or dexamethasone on insulin receptor mRNA levels are near completely abolished in glucose-starved cells; (iii) 2-mercaptoethanol and heat shock, besides previously described stress conditions (glycosylatyon inhibitors), reduce insulin receptor mRNA levels.

Base Sequence↗
PubMed1990

Glucose starvation and glycosylation inhibitors reduce insulin receptor gene expression: characterization and potential mechanism in human cells.

Glucose affects the expression of several genes in many cell types. In this work (i) we stably cultured three human cell lines in media containing different glucose concentrations (from 0 to 25 mM), (ii) we characterized glucose effects on insulin receptor gene expression, (iii) we investigated the mechanism by which glucose produces these effects. We found that: (i) glucose starvation reduces insulin receptor gene expression likely affecting insulin receptor gene transcription rates; (ii) a hexose that undergoes to interconversion with glucose metabolites (D-fructose), added to low-glucose media, increases either insulin receptor mRNA levels or insulin binding activity, while hexoses unable to enter the cell (L-glucose) or not metabolizable (3-O-methylglucose), do not produce any effect; (iii) glycosylation inhibitors (2-deoxyglucose and tunicamycin) reduce, in a time-dependent manner, insulin receptor mRNA levels. Our data indicate that glucose affects insulin receptor gene expression in human cells and that protein glycosylation plays a role in this regulatory mechanism.

Blotting, Northern↗
PubMed1989

c-myc gene expression in human cells is controlled by glucose.

The c-myc oncogene is implicated in normal growth and differentiation processes. Human cell lines IM9 and HepG2 stably cultured at "low" glucose concentrations (5.5 mM) show c-myc mRNA levels 3-4 times higher than cells cultured at "high" glucose concentrations (25 nM). D-fructose (a metabolizable exose) substitutes for D-glucose in reducing c-myc expression while 3-ortho-methylglucose (a non metabolizable exose) is uneffective. c-myc expression is up-regulated (by PMA) or down-regulated (by dexamethasone and long-term exposure to FCS) in human cells cultured at "low" glucose but not in cells cultured at "high" glucose. We previously demonstrated that insulin receptor gene expression in human cell lines in enhanced by glucose. Therefore, glucose controls in an opposite way the expression of two genes important in the regulation of eukaryotic cell growth and differentiation.

3-O-Methylglucose↗
PubMed1989

Effect of two different glucose concentrations on insulin receptor mRNA levels in human hepatoma HepG2 cells.

Glucose is known to affect mRNA levels of several genes. In order to investigate possible effects of glucose on insulin receptor mRNA levels, we cultured human hepatoma cells (HepG2) in two different culture media: DMEM containing 100 mg/dl glucose and DMEM containing 450 mg/dl glucose. Insulin receptor mRNA levels and insulin binding activity were reduced in HepG2 cultured at lower glucose concentrations. These data suggest that glucose affects insulin receptor gene expression.

Carcinoma, Hepatocellular↗
PubMed1989

Alternative splicing of HLA-DQB transcripts and secretion of HLA-DQ beta-chain proteins: allelic polymorphism in splicing and polyadenylylation sites.

HLA class II antigens are highly polymorphic cell-surface proteins involved in initiation and regulation of the immune response. Allelic sequence variation primarily affects the structure of the first external domains of alpha and beta component chains. Here we provide evidence for other types of allelic polymorphism for the genes encoding these chains. Sequences of two cDNA clones corresponding to HLA-DQB mRNAs from an HLA-homozygous cell line exhibit both alternative splicing and read-through of polyadenylylation. Furthermore, alternative splicing that deletes the transmembrane exon is associated with only a subset of HLA-DQB alleles, while the polyadenylylation-site read-through is found in a larger subset. This suggest that polymorphic cis-acting elements within the HLA-DQB gene control both processing steps. Proteins, presumably encoded by alternatively spliced mRNAs lacking transmembrane exons, are immunoprecipitated with a monomorphic monoclonal antibody directed against HLA-DQ. These proteins are found in supernatants of cultured cell lines for which secretion is predicted, but not in those of cell lines that do not contain alternatively spliced mRNAs.

Alleles↗
PubMed1986

[Left ventricular diastolic function in type I diabetes. A longitudinal echocardiographic study].

The present study was performed to assess the extent of left ventricular diastolic abnormalities and their possible progression with time in patients with type I (insulin dependent) diabetes. Two echocardiographic examinations were performed at an interval of 5 years in 18 study patients. Left ventricular diastolic function was assessed by computer digitized analysis of the M-mode echocardiographic tracings. During the study period all patients remained in satisfactory metabolic control and without retinopathy. Twelve normal subjects, matched for age and sex, were used as control group. Peak rate of left ventricular posterior wall excursion and the peak rate of increase in left ventricular internal dimensions were significantly reduced in patients with diabetes (14.12 +/- 2.5; 16.48 +/- 3.9 cm/sec) compared with controls (17.25 +/- 2.8; 20.41 +/- 3.6 cm/sec) (p less than .005; p less than .01). In addition time to peak rate of increase in left ventricular internal dimensions, isovolumic relaxation index and isovolumic relaxation time were significantly prolonged in patients with diabetes (63.66 +/- 16.5; 23.9 +/- 9; 72.7 +/- 14 msec) compared to controls (46.83 +/- 9.8; 13.4 +/- 4; 61.1 +/- 12 msec) (p less than .005; p less than .001; p less than .05). In the study patients, no relation was found between the extent of diastolic abnormalities and age, duration of the disease and insulin dosage. The extent of left ventricular diastolic dysfunction did not show significant changes during follow-up. Our results indicate that diastolic abnormalities are common in patients with type I diabetes and are not related to the duration of the disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Diabetes Mellitus, Type 1↗