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R Taub

Publications and source records attributed to R Taub.

At least 37 records · Page 2Linked to original sources
PubMed1998

The gene encoding human nuclear protein tyrosine phosphatase, PRL-1. Cloning, chromosomal localization, and identification of an intron enhancer.

Expression of the rat PRL-1 gene, which encodes a unique nuclear protein tyrosine phosphatase, is positively associated with cellular growth during liver development, regeneration, and oncogenesis but with differentiation in intestine and other tissues. Here, we analyzed the structure of the human PRL-1 gene and localized it to chromosome 6 within band q12. Human, rat, and mouse PRL-1 are 100% conserved at the amino acid level and 55% identical to a newly identified Caenorhabditis elegans PRL-1. The presence of two promoter activities, P1 and P2, in the human PRL-1 gene were identified by primer extension and RNase protection assays. A functional TATA box was identified in promoter P1 upstream of the non-coding first exon. A non-canonical internal promoter, P2, was found in the first intron that results in PRL-1 transcripts beginning 8 base pairs downstream of the 5'-end of exon 2 and causes no alteration in the encoded protein. The first 200-base pair region of either promoter P1 or P2 conferred high basal transcriptional activity. An enhancer that bound a developmentally regulated factor, PRL-1 intron enhancer complex (PIEC), was localized to the first intron of the human PRL-1 gene. The presence of PIEC correlated with the ability of the intron enhancer to confer transcriptional activation in HepG2 and F9 cells. The intron enhancer contributed significantly to PRL-1 promoter activity in HepG2 cells which contain PIEC but not to NIH 3T3 cells which do not.

3T3 Cells↗
PubMed1998

Carbon flux via the pentose phosphate pathway regulates the hepatic expression of the glucose-6-phosphatase and phosphoenolpyruvate carboxykinase genes in conscious rats.

Hepatic gene expression of P-enolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (Glc-6-Pase) is regulated in response to changes in the availability of substrates, in particular glucose (Glc; Massillon, D., Barzilai, N., Chen, W., Hu, M., and Rossetti, L. (1996) J. Biol. Chem. 271, 9871-9874). We investigated the mechanism(s) in conscious rats. Hyperglycemia per se caused a rapid and marked increase in Glc-6-Pase mRNA abundance and protein levels. By contrast, hyperglycemia decreased the abundance of PEPCK mRNA. Importantly, inhibition of glucokinase activity by glucosamine infusion blunted both the stimulation of Glc-6-Pase and the inhibition of PEPCK gene expression by Glc, suggesting that an intrahepatic signal (metabolite) generated by the metabolism of glucose at or beyond Glc-6-P was responsible for the regulatory effect of Glc. The effect of Glc on the L-type pyruvate kinase gene is mediated by xylulose-5-P (Doiron, B., Cuif, M., Chen, R., and Kahn, A. (1996) J. Biol. Chem. 271, 5321-5324). Thus, we next investigated whether an isolated increase in the hepatic concentration of this metabolite can also reproduce the effects of Glc on Glc-6-Pase and PEPCK gene expression in vivo. Xylitol, which is directly converted to xylulose-5-P in the liver, was infused to raise the hepatic concentration of xylulose-5-P by approximately 3-fold. Xylitol infusion did not alter the levels of Glc-6-P and of fructose-2,6-biphosphate. However, it replicated the effects of hyperglycemia on Glc-6-Pase and PEPCK gene expression and resulted in a 75% increase in the in vivo flux through Glc-6-Pase (total glucose output).

Animals↗
PubMed1997

Alternative splicing and structure of the human and mouse SFRS5/HRS/SRp40 genes.

HRS/SRp40/SFRS5 (HRS) is an SR (serine-arginine-rich) protein which regulates both alternative splicing and basal splicing. HRS mRNA contains several transcripts, including HRS-SF and HRS-LF which have different temporal patterns of expression in proliferating liver. As previously reported, HRS-SF mRNA encodes the SR splicing factor. However, the identity of HRS-LF remained unknown. Here, we cloned and characterized the mouse HRS gene, partial human HRS gene, and several cDNAs derived from HRS-LF mRNA. The mouse HRS gene spans 5050 bp and contains eight exons and seven introns. HRS-LF mRNA contains a 1.2 kb insert within the SF mRNA with stop codons in all three reading frames. A comparison of HRS-LF and the HRS gene revealed that HRS-LF mRNA is an intron-retaining product which contains intron 5. At most, HRS-LF encodes a truncated HRS protein with one RNA binding domain. Interestingly, intron 5 demonstrates 90% identity between the mouse and human HRS genes, implying that intron 5 might play an important role in regulating HRS gene splicing or expression.

Alternative Splicing↗
PubMed1997

Cloning, human chromosomal assignment, and adipose and hepatic expression of the CL-6/INSIG1 gene.

Rat CL-6 is the most highly insulin-induced gene in a liver cell line and is expressed in proliferating liver during regeneration and development. CL-6 is now denoted INSIG1 (insulin-induced gene 1). Human INSIG1 was isolated and found to be 80% identical to the rat gene within the translated region. It was located on human chromosome 7 within band q36. The human INSIG1 promoter conferred a high level of expression in both liver and fibroblast cell lines. INSIG1 expression was upregulated at the transcriptional level in rat regenerating liver and induced in a model of murine adipocyte differentiation, suggesting that INSIG1 may play a role in growth and differentiation of tissues involved in metabolic control.

Adipose Tissue↗
PubMed1997

Expression analysis and chromosomal assignment of the human SFRS5/SRp40 gene.

Alternative splicing plays a major role in the regulation of gene expression. SFRS5/SRp40 is a member of the serine/arginine (SR) protein family of regulators of alternative pre-mRNA splicing. We cloned the human SFRS5 cDNA and observed two major SFRS5 transcripts, an approximately 1.8-kb short form and an approximately 3.3-kb long form, in both human and rat tissues. Both transcripts were detected in all human tissues examined, but there were notable tissue-specific differences in their relative abundance, the short form being most abundant in retina. Affinity-purified SFRS5 antisera recognized a single 40-kDa polypeptide in human and mouse retinal lysates. The abundant retinal expression of SFRS5 was not restricted to any specific cell type, since immunofluorescent labeling of human retinal sections identified the SFRS5 protein in nuclei of all three nuclear layers of the retina. The human SFRS5 gene was localized to human chromosome 14q24 by fluorescence in situ hybridization and PCR analysis of a human/hamster somatic cell hybrid panel.

Alternative Splicing↗
PubMed1997

A multicomponent insulin response sequence mediates a strong repression of mouse glucose-6-phosphatase gene transcription by insulin.

Glucose-6-phosphatase (G6Pase) catalyzes the final step in the gluconeogenic and glycogenolytic pathways. The transcription of the gene encoding the catalytic subunit of G6Pase is stimulated by glucocorticoids, whereas insulin strongly inhibits both basal G6Pase gene transcription and the stimulatory effect of glucocorticoids. To identify the insulin response sequence (IRS) in the G6Pase promoter through which insulin mediates its action, we have analyzed the effect of insulin on the basal expression of mouse G6Pase-chloramphenicol acetyltransferase (CAT) fusion genes transiently expressed in hepatoma cells. Deletion of the G6Pase promoter sequence between -271 and -199 partially reduces the inhibitory effect of insulin, whereas deletion of additional sequence between -198 and -159 completely abolishes the insulin response. The presence of this multicomponent IRS may explain why insulin potently inhibits basal G6Pase-CAT expression. The G6Pase promoter region between -198 and -159 contains an IRS, since it can confer an inhibitory effect of insulin on the expression of a heterologous fusion gene. This region contains three copies of the T(G/A)TTTTG sequence, which is the core motif of the phosphoenolpyruvate carboxykinase (PEPCK) gene IRS. This suggests that a coordinate increase in both G6Pase and PEPCK gene transcription is likely to contribute to the increased hepatic glucose production characteristic of patients with non-insulin-dependent diabetes mellitus.

Animals↗
PubMed1997

HRS/SRp40-mediated inclusion of the fibronectin EIIIB exon, a possible cause of increased EIIIB expression in proliferating liver.

Serine-arginine (SR)-rich proteins are believed to be important in mediating alternative pre-mRNA splicing. HRS/SRp40 expression is elevated in liver cell proliferation during development, regeneration, and oncogenesis. We tested whether HRS expression correlates with the appearance of alternatively spliced fibronectin transcripts during liver growth. HRS was highly expressed during the proliferative phase of liver development, correlating with expression of the fibronectin EIIIB alternative exon. In regenerating liver, HRS protein was induced in a time course consistent with the observed increase in fibronectin transcripts containing the EIIIB exon, particularly in nonparenchymal liver cells. Furthermore, in an in vivo assay, HRS, and not other SR proteins, directly mediated EIIIB exon inclusion in the fibronectin transcript. This alternative splicing was dependent on a purine-rich region within the EIIIB exon to which HRS specifically bound. We have established that HRS has the potential to contribute to the regulation of fibronectin pre-mRNA splicing during liver growth. Changes in fibronectin forms may be important in modifying liver architecture during the proliferative response, thus providing a potential mechanism by which SR proteins may participate in cellular growth control.

Alternative Splicing↗
PubMed1997

Sepsis-induced depression of rat glucose-6-phosphatase gene expression and activity.

Sepsis in rats decreases the hepatic expression of the gluconeogenic enzyme glucose-6-phosphatase (G6Pase). The aim of this study was to investigate the relationship among G6Pase transcription, mRNA, enzymatic activity, and serum glucose levels at different intervals during mild or fulminant sepsis. Both fulminant and mild sepsis immediately decreased hepatic G6Pase mRNA levels. In mild sepsis, levels began to recover late in the time course. Serum glucose levels were maintained in mild sepsis but decreased markedly in fulminant sepsis. G6Pase transcription after fulminant sepsis decreased and never recovered. A similar transcriptional decrease was noted in mild sepsis, but some recovery occurred in this state. Histochemistry after mild sepsis revealed a decrease in G6Pase protein and enzymatic activity that paralleled transcription. These studies suggest that changes in G6Pase transcription and activity are early markers for sepsis-induced alterations in hepatic function. Mechanisms other than gene expression and enzymatic activity serve to maintain glucose levels in mild sepsis, but in the fulminant disorder, compensatory mechanisms fail and hypoglycemia develops.

Animals↗
PubMed1996

Liver failure and defective hepatocyte regeneration in interleukin-6-deficient mice.

Liver regeneration stimulated by a loss of liver mass leads to hepatocyte and nonparenchymal cell proliferation and rapid restoration of liver parenchyma. Mice with targeted disruption of the interleukin-6 (IL-6) gene had impaired liver regeneration characterized by liver necrosis and failure. There was a blunted DNA synthetic response in hepatocytes of these mice but not in nonparenchymal liver cells. Furthermore, there were discrete G1 phase (prereplicative stage in the cell cycle) abnormalities including absence of STAT3 (signal transducer and activator of transcription protein 3) activation and depressed AP-1, Myc, and cyclin D1 expression. Treatment of IL-6-deficient mice with a single preoperative dose of IL-6 returned STAT3 binding, gene expression, and hepatocyte proliferation to near normal and prevented liver damage, establishing that IL-6 is a critical component of the regenerative response.

Animals↗
PubMed1996

Molecular analysis of the fructose transporter gene (GLUT5) in isolated fructose malabsorption.

Fructose, a naturally occurring monosaccharide, is increasingly used as an added sweetener in processed foods in the form of high fructose corn syrup. Increased fructose intake combined with the identification of children with clinical evidence of isolated fructose malabsorption (IFM) has stimulated interest in possible disorders of fructose absorption. The intestinal absorption of fructose is carried out by the facilitative hexose transporter, which has been designated as GLUT5. Functional properties and tissue distribution of GLUT5 suggest that IFM might be due to mutations in the GLUT5 gene. To test this hypothesis, we screened the GLUT5 gene for mutations in a group of eight patients with IFM and in one subject with global malabsorption, as compared with 15 healthy parents of subjects and up to 6 unrelated controls. No mutations were found in the protein coding region of this gene in any of the subjects. A single G to A substitution in the 5' untranslated region of exon 1 was identified in the subject with global malabsorption. This subject and her healthy mother were heterozygous for the variant sequence, suggesting that it was unlikely to be clinically significant. In addition, sequence analysis of each of the 12 GLUT5 exons was performed in the index case and confirmed the negative single-strand conformation polymorphism findings. These studies demonstrate that IFM does not result from the expression of mutant GLUT5 protein.

Alleles↗
PubMed1996

Overexpression of an osteogenic morphogen in fibrodysplasia ossificans progressiva.

BACKGROUND: Fibrodysplasia ossificans progressiva is a heritable disorder of connective tissue characterized by congenital malformation of the great toes and postnatal formation of ectopic bone. Although the disorder was first described more than 300 years ago, the genetic defect and pathophysiology remain unknown. Bone morphogenetic proteins are potent bone-inducing morphogens that participate in the developmental organization of the skeleton, and increased production of one or more of these proteins has been proposed as the cause of fibrodysplasia ossificans progressiva. METHODS: We studied lymphoblastoid cell lines established from peripheral-blood mononuclear cells of patients with fibrodysplasia ossificans progressiva and fibroblast-like cell lines derived from lesional and nonlesional tissue. We used Northern blot analysis and ribonuclease protection assays to measure the expression of messenger RNA (mRNA) of bone morphogenetic proteins 1 to 7 and immunohistochemical analysis to examine protein expression. RESULTS: Among the bone morphogenetic proteins and mRNAs examined, only bone morphogenetic protein 4 and its mRNA were present in increased levels in cells derived from an early fibroproliferative lesion in a patient with fibrodysplasia ossificans progressiva. Bone morphogenetic protein 4 mRNA was expressed in lymphoblastoid cell lines from 26 of 32 patients with fibrodysplasia ossificans progressiva but from only 1 of 12 normal subjects (P<0.001). Bone morphogenetic protein 4 and its mRNA were detected in the lymphoblastoid cell lines from a man with fibrodysplasia ossificans progressiva and his three affected children (two girls and a boy), but not from the children's unaffected mother. No other bone morphogenetic proteins were detected. CONCLUSIONS: Overexpression of a potent bone-inducing morphogen (bone morphogenetic protein 4) in lymphocytes is associated with the disabling ectopic osteogenesis of fibrodysplasia ossificans progressiva.

Bone Morphogenetic Proteins↗
PubMed1996

Variable gene expression within human tyrosinemia type 1 liver may reflect region-specific dysplasia.

Patients with hereditary tyrosinemia type 1 have a deficiency of fumarylacetoacetate hydrolase (FAH) and develop progressive hepatocellular dysfunction with a high risk of malignant transformation. Serum alpha-fetoprotein levels are frequently elevated in these patients; therefore, this commonly used marker of tumorigenesis is inadequate. To date, no literature exists describing the hepatic gene alterations in patients with this disease. We analyzed the expression of a panel of proliferation associated and liver-specific genes in the liver of a 33 month-old girl at the time of orthotopic liver transplantation. This study provides information that may be useful in developing markers for malignancy and understanding the pathogenesis of this disease. Gene expression patterns of two regenerating nodules and total liver from the patient with FAH deficiency were compared with control donor liver. Liver-specific and growth-induced genes with altered expression in the tyrosinemic liver included several functional classes: structural proteins (actin, thrombospondin), transcription factors (c-fos, egr-1, C/EBPalpha), liver-specific enzymes (glucose-6-phosphatase [G6Phase], and secreted factors (insulin-like growth factor binding protein 1 [GFBP-1]. Isolated macronodules demonstrated varied patterns of expression, suggesting that they do not form a homogeneous cellular environment. In the tyrosinemic liver, IGFBP-1 messenger RNA expression was high and G6Phase messenger RNA was not detectable. Although G6Phase and IGFBP-1 are coexpressed in regenerating liver, immunohistochemistry in the tyrosinemic liver demonstrated a mutually exclusive distribution for the two proteins in a tissue section with features of dysplasia. We propose that cells in these areas may have an aberrant transcription factor and growth factor "milieu" that leads to altered gene and protein expression. These molecular alterations are reflected in dysplastic histologic changes and may ultimately predispose to the development of malignancy.

Amino Acid Metabolism, Inborn Errors↗
PubMed1996

Association of interleukin-1-induced, NF kappa B DNA-binding activity with collagenase gene expression in human gingival fibroblasts.

During earlier examination of interleukin-1 (IL-1)-induced matrix metalloproteinase gene expression in human gingival fibroblasts a highly induced immediate early gene, I kappa B-alpha, a NF kappa B DNA-binding inhibitor, was identified. The aim now was to investigate whether recombinant (r)IL-1 beta induces the stimulation of NF kappa B and its inhibitor proteins in human gingival fibroblasts and to understand if inhibition of its activity affects collagenase gene expression. Primary gingival fibroblasts (human) were treated with rIL-1 beta to determine the effect on NF kappa B-like DNA-binding activity. IL-1 induced the production of steady-state mRNA levels of I kappa B-alpha in the cultured fibroblasts. Nuclear run-on transcription studies demonstrated that rIL-1 induction of I kappa B-alpha may be transcriptionally regulated. Using electrophoretic mobility gel-shift assays it was shown that rIL-1 activates NF kappa B-like, DNA-binding activity in these fibroblasts. NF kappa B-like DNA-binding activity was rapidly induced and turned over in gingival fibroblasts with peak activity at 30 min after rIL-1 treatment. Further, treatment with chymotrypsin protease inhibitor and antioxidant inhibitor prevented IL-1-induced, NF kappa B-like, DNA-binding activity and collagenase mRNA production. When coupled with the existence of NF kappa B consensus DNA-binding sites on the collagenase gene promoter, these findings suggest that the stimulation of NF kappa B in gingival fibroblasts by rIL-1 could play an important part in the regulation of their collagenase gene expression. The ability of IL-1 to stimulate this expression may define a pivotal role for this cytokine in the pathogenesis of periodontitis.

Cells, Cultured↗
PubMed1996

Expression of PRL-1 nuclear PTPase is associated with proliferation in liver but with differentiation in intestine.

Mechanisms controlling the tyrosine phosphorylation of cellular proteins are important in the regulation of cellular processes including growth and differentiation. It has become clear that a number of protein tyrosine phosphatases (PTPases) that dephosphorylate tyrosyl residues may play a role in the growth response, both in growth-promoting and growth-inhibiting capacities. We identified PRL-1, a unique nuclear PTPase that is an immediate-early gene in liver regeneration and is positively associated with growth, including fetal and neoplastic hepatic growth and anchorage-independent growth after overexpression in fibroblasts. In this study, we show that PRL-1 nuclear protein levels in regenerating liver parallel those of its mRNA, although the peak occurs later, just before the onset of DNA synthesis. We further show that PRL-1 is significantly expressed in intestinal epithelia and that, in contrast to the expression pattern of PRL-1 in liver, its expression is associated with cellular differentiation in intestine. Specifically, PRL-1 is expressed in villus but not crypt enterocytes and in confluent differentiated but not undifferentiated proliferating Caco-2 colon carcinoma cells. The expression of PRL-1 in intestine shows inverse correlation with proliferating cell nuclear antigen expression, a marker for S-phase cells. These results suggest that PRL-1 may play different roles in these two digestive tissues. Such a dichotomy of roles has previously been described for some protein tyrosine kinases and might be due to the availability of alternate substrates in different tissues.

3T3 Cells↗
PubMed1996

Increased expression of cytokine-induced neutrophil chemoattractant in septic rat liver.

Hepatocellular dysfunction in sepsis may be neutrophil mediated. We therefore tested the hypothesis that sepsis-induced neutrophil accumulation is associated with increased expression of the chemokine, cytokine-induced neutrophil chemoattractant (CINC). In Sprague-Dawley rats made septic by cecal ligation and puncture, we demonstrate a time-dependent increase in CINC mRNA, which returns to baseline by 48 h. By in situ hybridization, this mRNA is present in hepatocytes and nonparenchymal cells. CINC protein levels in septic animals parallel mRNA levels and resolve by 48 h. Because CINC expression is induced by cytokines including tumor necrosis factor-alpha (TNF- alpha), we show, by immunohistochemistry, that sepsis elevates intrahepatic TNF-alpha. Finally, because the CINC promoter is transactivated by the transcription factor, nuclear factor kappa B (NF-kappa B), we determined that hepatic NF-kappa B DNA binding increases dramatically, peaking 16 h after cecal ligation and puncture. Thus activated NF-kappa B may mediate CINC induction in sepsis. This constellation of findings suggests a mechanism by which sepsis may induce neutrophil accumulation in the liver and may have implications regarding sepsis-induced hepatic dysfunction.

Animals↗
PubMed1996

Rapid activation of latent transcription factor complexes reflects initiating signals in liver regeneration.

Liver regeneration following partial hepatectomy represents a physiologic response to a growth stimulus occurring in the intact animal. Understanding what growth factors and cytokines trigger liver regeneration will provide insights into recovery from hepatic injury mediated by viruses and toxins, and promote an understanding of normal cellular growth control. The modification of pre-existing latent transcription factors in the remnant liver by extracellular signals immediately post-hepatectomy provides a mechanism for the transcriptional activation of primary or immediate early growth response genes, thereby establishing a transcriptional cascade. Two factors activated within minutes to hours post-hepatectomy in a protein synthesis-independent fashion include PHF/NF-kappaB and Stat3. Interestingly, these factors are commonly activated by cytokines such as TNFalpha, IL-1 and IL-6 suggesting that there may be a connection between cytokine release and the onset of liver regeneration. In addition to these known transcription factor complexes, we have used a reporter gene assay in transgenic mice to attempt to identify promoter sequences that are responsible for the transcriptional activation of the liver-restricted IGFBP-1 immediate early gene within minutes posthepatectomy. Studies so far indicate that an upstream region of 800 bp is able to confer both tissue-restricted expression and induction during liver regeneration. Identification of the transcriptional activators or liver regeneration factors responsible for this induction will result in further dissection of the initiating signals.

Journal Article↗
PubMed1996

Comparison of gallium-67-citrate and thallium-201 scintigraphy in peripheral and intrathoracic lymphoma.

UNLABELLED: We performed this study in an attempt to reconcile the differences with respect to 67Ga uptake as a function of tumor grade and type in the literature, as well as to determine the sensitivity of 201Tl uptake in both Hodgkin's and non-Hodgkin's lymphoma. METHODS: Thirty-six (9 with low-grade lymphoma, 11 with intermediate-grade lymphoma, 4 with high-grade lymphoma and 12 with Hodgkin's lymphoma) patients underwent both 67Ga and 201Tl scintigraphy. Biopsies were done on all patients. A semiquantitative rating system was used to make statistical comparisons for thallium versus gallium in all lymphoma subgroups, as well as comparisons of thallium and gallium to themselves in all subgroups. RESULTS: Patient sensitivity was only 56% and site sensitivity was 32% in patients with low-grade lymphoma. Conversely, 201Tl sensitivity was 100%, respectively, for patients and sites. The difference between 201Tl and 67Ga sensitivity in patients with low-grade lymphoma on a site basis was statistically significant. When compared to itself in lymphoma subgroups, 201Tl was found to be statistically more avid for low-grade lymphoma than for intermediate, high or Hodgkin's lymphoma. Gallium-67 sensitivity for low-grade lymphoma was significantly less than for Hodgkin's and intermediate grade lymphomas. No significant differences were found when 201Tl and 67Ga were compared in the intermediate, high or Hodgkin's lymphoma groups. CONCLUSION: Thallium-201 demonstrates significantly greater tumor avidity in the low-grade lymphoma group compared to 67Ga citrate. Gallium-67-citrate appears relatively nonavid for low-grade lymphoma compared to 201Tl and is statistically inferior in detecting low-grade lymphoma in comparison to its ability to detect intermediate or high-grade lymphomas. Gallium-67-citrate should not be considered dependable in evaluating patients with low-grade lymphoma. Neither 201Tl or 67Ga is dependable in the evaluation of low-grade lymphoma within the abdomen, since gallium avidity for low-grade lymphoma is low and gastrointestinal excretion of 201Tl is poorly controlled.

Biopsy↗