Differential regulation of mRNAs encoding three protein-tyrosine phosphatases by insulin and activation of protein kinase C

Approaches to Decrease Hyperglycemia by Targeting Impaired Hepatic Glucose Homeostasis Using Medicinal Plants

Liver plays a pivotal role in maintaining blood glucose levels through complex processes which involve the disposal, storage, and endogenous production of this carbohydrate. Insulin is the hormone responsible for regulating hepatic glucose production and glucose storage as glycogen, thus abnormalities in its function lead to hyperglycemia in obese or diabetic patients because of higher production rates and lower capacity to store glucose. In this context, two different but complementary therapeutic approaches can be highlighted to avoid the hyperglycemia generated by the hepatic insulin resistance: 1) enhancing insulin function by inhibiting the protein tyrosine phosphatase 1B, one of the main enzymes that disrupt the insulin signal, and 2) direct regulation of key enzymes involved in hepatic glucose production and glycogen synthesis/breakdown. It is recognized that medicinal plants are a valuable source of molecules with special properties and a wide range of scaffolds that can improve hepatic glucose metabolism. Some molecules, especially phenolic compounds and terpenoids, exhibit a powerful inhibitory capacity on protein tyrosine phosphatase 1B and decrease the expression or activity of the key enzymes involved in the gluconeogenic pathway, such as phosphoenolpyruvate carboxykinase or glucose 6-phosphatase. This review shed light on the progress made in the past 7 years in medicinal plants capable of improving hepatic glucose homeostasis through the two proposed approaches. We suggest that Coreopsis tinctoria, Lithocarpus polystachyus, and Panax ginseng can be good candidates for developing herbal medicines or phytomedicines that target inhibition of hepatic glucose output as they can modulate the activity of PTP-1B, the expression of gluconeogenic enzymes, and the glycogen content.

Glucose enhances protein tyrosine phosphatase 1B gene transcription in hepatocytes

Protein tyrosine phosphatase 1B (PTP1B) is a negative regulator of the insulin receptor signal transduction pathway. We investigated the effects of glucose on PTP1B transcription in the human hepatocyte cell line Huh7. Using a reporter gene assay, we found that D-glucose dose-dependently enhanced the PTP1B promoter activity. Real-time PCR demonstrated that D-glucose also increased PTP1B mRNA expression. Protein kinase C (PKC) inhibitors partially but significantly inhibited the transactivation by D-glucose. Mithramycin, a Sp1 inhibitor, completely abrogated this transactivation. The deletion of three possible Sp1 sites in the promoter region of PTP1B significantly reduced the basal promoter activity and transactivation by D-glucose. Sp1 activation by PKC is one of the key mechanisms in the regulation of several gene expressions. Our data suggested that glucose enhanced PTP1B transcription through Sp1 activation by PKC. Increased hepatic PTP1B expression may partly explain glucose toxicity in diabetes.

Molecular genetics of human hypertension

EH (essential hypertension) is a major public health problem in many countries due to its high prevalence and its association with coronary heart disease, stroke, renal disease, peripheral vascular disease and other disorders. Epidemiological studies have demonstrated that EH is heritable. Owing to the fact that blood pressure is controlled by cardiac output and total peripheral resistance, many molecular pathways are believed to be involved in the disease. In this review, recent genetic studies investigating the molecular basis of EH, including different molecular pathways, will be highlighted.

Association of 20q13.2 copy number changes with the advanced stage of ovarian cancer—tissue microarray analysis

Overrepresentations in 20q have been reported in a number of ovarian cancers by comparative genomic hybridization. In order to study the relation of the increased copy number of 20q13.2 with tumor phenotype in ovarian cancer, we applied FISH on a tissue microarray. The TMA technology enables us to analyze a large number of different malignancy, histology, stage and grade tumors. Overall, the frequency of 20q13.2 alterations in epithelial ovarian cancer was 25.50% (10.74% gains and 14.76% amplifications). There was not statistically significant difference between the frequencies of 20q13.2 copy number changes in different grade tumors. The frequency of gains and amplifications increased significantly from stage I to stage II to stage III tumors. Our results showed strong association between increases 20q13.2 copies and advanced tumor stage. We concluded that genetic alterations in 20q13.2 may be of prognostic significance for stage progression of the ovarian cancer.

Role of SRC homology 2-containing tyrosine phosphatase 2 on proliferation of rat smooth muscle cells

OBJECTIVE

Src homology 2-containing phosphotyrosine phosphatase 2 (SHP2) is ubiquitously expressed and believed to function as part of a positive signaling pathway mediating growth factor-induced protein tyrosine phosphorylation. Proliferation of aortic vascular smooth muscle cells (SMCs) is an important contributor to atherosclerosis. We examined the effect of SHP2 expression on SMC proliferative activity.

METHODS AND RESULTS

SHP2 was abundant in cultured aortic SMCs, and SHP2 staining was markedly increased in the thickened aortic intima in rats with balloon-induced injury. We obtained several SMC clones by using geneticin screening. Endogenous SHP2 expression varied among individual clones. Significant positive relationships were observed between SHP2 expression and bromodeoxyuridine uptake in SMCs stimulated by FBS, platelet-derived growth factor, or insulin-like growth factor-1. In SMCs transiently transfected with SHP2, FBS stimulation significantly increased bromodeoxyuridine uptake beyond the uptake by control SMCs.

CONCLUSIONS

Increased SHP2 expression in SMCs may accelerate aortic atherosclerosis by increasing cell growth.

Analysis of genetic alterations in salivary gland tumors by comparative genomic hybridization

In order to define and map chromosomal copy number alterations in salivary gland tumors (SGTs), a comparative genomic hybridization (CGH) technique was applied to two pleomorphic adenomas (PAs), one adenoid cystic carcinoma (ACC), and one basal cell adenocarcinoma (BCAC). The PAs exhibited regional copy number losses at 5q12.4-q14.1, 9q12-q21.13, and 16q11.2, as well as a gain at 20p12.1; among these, the losses at the 9q12-q21.11 and 16q11.2 regions were common to both PAs. The ACC showed overrepresentations of the entire regions of chromosomes 16 and 20, a regional gain at 22q12.3-q13.1, and no losses. In the BCAC, regional gains at 9p21.1-pter, 18q21.1-q22.3, and 22q11.23-q13.31 as well as losses at 2q24.2 and 4q25-q27 were seen; the gain at 22q12.3-q13.1 was common in both the ACC and the BCAC. These CGH data indicate that different genetic alterations are present in the different types of SGTs, and that the alterations involve several chromosomes. The discovery of common alterations in the same and/or different types of tumors might be important in the understanding of the development and progression of the SGTs.

Novel genomic imbalances in B-cell splenic marginal zone lymphomas revealed by comparative genomic hybridization and cytogenetics

Splenic marginal zone lymphoma (SMZL) has recently been recognized in the World Health Organization classification of hematological diseases as distinct type of non-Hodgkin's lymphoma. In contrast to the well-established chromosomal changes associated with other B-cell non-Hodgkin's lymphoma, few genetic alterations have been found associated with SMZL. The aim of our study was to analyze by comparative genomic hybridization (CGH) the chromosomal imbalances in 29 patients with SMZL and to correlate these findings with clinical and biological characteristics and patient outcome. In 21 cases, cytogenetic studies were simultaneously performed. Most of the patients (83%) displayed genomic imbalances. A total of 111 DNA copy number changes were detected with a median of four abnormalities per case (range, 1 to 12). Gains (n = 92) were more frequent than losses (n = 16), while three high-level amplifications (3q26-q29, 5p11-p15, and 17q22-q25) were observed. The most frequent gains involved 3q (31%), 5q (28%), 12q and 20q (24% each), 9q (21%), and 4q (17%). Losses were observed in 7q (14%) and 17p (10%). SMZL patients with genetic losses had a shorter survival than the remaining SMZL patients (P < 0.05). In summary, chromosomal imbalances in regions 3q, 4q, 5q, 7q, 9q, 12q, and 20q have been detected by CGH in SMZL. Patients with SMZL displaying genetic losses by CGH had a short survival.

Comparative genomic hybridization reveals complex genetic changes in primary breast cancer tumors and their cell lines

DNA copy number changes were characterized by comparative genomic hybridization (CGH) in 18 breast cancer cell lines. In 5 of these, the results were comparable with those from the primary tumors of which the cell lines were established. All of the cell lines showed extensive DNA copy number changes, with a mean of 16.3 +/- 1.1 aberrations per sample (range 7-26). All of the cell lines had a gain at 8q22-qter. Other common gains of DNA sequences occurred at 1q31-32 (89%), 20q12-q13.2 (83%), 8q13 (72%), 3q26.1-qter (67%), 17q21-qter (67%) 5p14 (61%), 6p22 (56%), and 22pter-qter (50%). High-level amplifications were observed in all cell lines; the most frequent minimal common regions were 8q24.1 (89%), 20q12 (61%), 1q41 (39%), and 20p11.2 (28%). Losses were observed less frequently than gains and the minimal common regions of the most frequent losses were Xq11-q12 (56%), Xp11.2-pter (50%), 13q21 (50%), 8p12-pter (44%), 4p13-p14 (39%), 6q15-q22 (39%), and 18q11.2-qter (33%). Although the cell lines showed more DNA copy number changes than the primary tumors, all aberrations, except one found in a primary tumor, were always present in the corresponding cell line. High-level amplifications found both in primary tumors and cell lines were at 1q, 8q, 17q, and 20q. The DNA copy number changes detected in these cell lines can be valuable in investigation of tumor progression in vitro and for a more detailed mapping and isolation of genes implicated in breast cancer.

Increased activity and expression of MAP kinase in HCC model rats induced by 3'-methyl-4-dimethylamino-azobenzene

BACKGROUND/AIMS

The ras-mitogen-activated protein kinase (MAPK) cascade plays an important role not only in the mitogenic signal transduction pathway but also in the development of cancer, and it is believed to be one of the important regulators in normal hepatocytes and hepatocellular carcinoma. The aim of this study was to determine the role of insulin receptor substrate-1 and the MAPK cascade in rats with hepatocellular carcinoma induced by 3'-methyl-4-dimethylamino-azobenzene (3'-MeDAB).

METHODS

Liver cancer was induced in rats by feeding 3'-MeDAB, and the changes in expression of IRS-1 and MAPK were analyzed in tumorous, non-tumorous and control liver.

RESULTS

Expression of insulin receptor substrate-1 (IRS-1) showed a 1.4-fold increase at protein level in the tumors (p<0.01), but the tyrosine phosphorylation of IRS-1 did not differ between the tumor and control liver. Expression of MAPK and its activity were elevated 4.5-7.5-fold (p<0.01) and 4.6-fold (p<0.01) in the tumor compared with control liver. In non-tumorous lesions from rats fed with 3'-MeDAB, expression of MAPK, but not IRS-1, increased significantly (p<0.01). Between tumorous and adjacent non-tumorous lesions, there was a significant difference in MAPK expression (p<0.05) and activities (p<0.05).

CONCLUSIONS

The increased expression of MAPK may play an important role in the progression or initiation of HCC in this rat model.

Alterations in skeletal muscle protein-tyrosine phosphatase activity and expression in insulin-resistant human obesity and diabetes

Obese human subjects have increased protein-tyrosine phosphatase (PTPase) activity in adipose tissue that can dephosphorylate and inactivate the insulin receptor kinase. To extend these findings to skeletal muscle, we measured PTPase activity in the skeletal muscle particulate fraction and cytosol from a series of lean controls, insulin-resistant obese (body mass index > 30) nondiabetic subjects, and obese individuals with non-insulin-dependent diabetes. PTPase activities in subcellular fractions from the nondiabetic obese subjects were increased to 140-170% of the level in lean controls (P < 0.05). In contrast, PTPase activity in both fractions from the obese subjects with non-insulin-dependent diabetes was significantly decreased to 39% of the level in controls (P < 0.05). By immunoblot analysis, leukocyte antigen related (LAR) and protein-tyrosine phosphatase 1B had the greatest increase (threefold) in the particulate fraction from obese, nondiabetic subjects, and immunodepletion of this fraction using an affinity-purified antibody directed at the cytoplasmic domain of leukocyte antigen related normalized the PTPase activity when compared to the activity from control subjects. These findings provide further support for negative regulation of insulin action by specific PTPases in the pathogenesis of insulin resistance in human obesity, while other regulatory mechanisms may be operative in the diabetic state.

Protein-tyrosine phosphatase 1B is a negative regulator of insulin- and insulin-like growth factor-I-stimulated signaling

To understand the physiological role of protein-tyrosine phosphatase 1B (PTPase 1B) in insulin and insulin-like growth factor-I (IGF-I) signaling, we established clonal cell lines overexpressing wild type or inactive mutant (C215S) PTPase 1B in cells overexpressing insulin (Hirc) or IGF-I (CIGFR) receptors. PTPase 1B overexpression in transfected cells was verified by immunoblot analysis with a monoclonal PTPase 1B antibody. Subfractionation of parental cells demonstrated that greater than 90% of PTPase activity was localized in the Triton X-100-soluble particulate (P1) cell fraction. PTPase activity in the P1 fraction of cells overexpressing wild type PTPase 1B was 3-6-fold higher than parental cells but was unaltered in all fractions from C215S PTPase 1B-containing cells. The overexpression of wild type and C215S PTPase 1B had no effects on intrinsic receptor kinase activity, growth rate, or general cell morphology. The effects of PTPase 1B overexpression on cellular protein tyrosine phosphorylation were examined by anti-phosphotyrosine immunoblot analysis. No differences were apparent under basal conditions, but hormone-stimulated receptor autophosphorylation and/or insulin receptor substrate tyrosine phosphorylation were inhibited in cells overexpressing wild type PTPase 1B and increased in cells expressing mutant PTPase 1B, in comparison with parental cells. Metabolic signaling, assessed by ligand-stimulated [14C]glucose incorporation into glycogen, was also inhibited in cells overexpressing active PTPase 1B and enhanced in cells containing C215S PTPase 1B. These data strongly suggest that PTPase 1B acts as a negative regulator of insulin and IGF-I signaling.

Phosphotyrosine protein phosphatases and diabetic pregnancy: an association between low molecular weight acid phosphatase and degree of glycemic control

Low molecular weight acid phosphatase encoded by the highly polymorphic locus ACP1 is a member of the protein-tyrosin phosphatase family (PTPases) which plays an essential role in the control of receptor signalling through phosphotyrosine pathways. Recent experiments have shown that purified rat liver ACP, corresponding to human ACP1, is able to hydrolyze a phosphotyrosine-containing synthetic peptide corresponding to the 1146-1158 sequence of the human insulin receptor, and shows a high affinity for it. This prompted us to analyze the degree of glycemic control in relation to ACP1 genetic variability in a sample of 214 diabetic pregnant women including IDDM, NIDDM and gestational diabetes. The ACP1 genotype was also determined in 482 non-diabetic pregnant women. In diabetic women glycemic levels in the last trimester of pregnancy appear to be significantly associated with the ACP1 genotype, and correlate positively with ACP1 enzymatic activity. The data suggest that quantitative variations of ACP1 may influence the clinical manifestations of diabetic disorders, and call for further studies on the role of this enzyme in the modulation of insulin-receptor phosphotyrosine pathways.

Insulin resistance is associated with abnormal dephosphorylation of a synthetic phosphopeptide corresponding to the major autophosphorylation sites of the insulin receptor

Insulin resistance in the ob/ob mouse model is associated with a reduction in insulin-induced protein-tyrosine phosphorylation in tissues such as liver. To ascertain whether this decrease in phosphorylation may be due to increased phosphatase activity, protein-tyrosine phosphatase (PTPase) activity was determined in particulate and soluble fractions from livers of 5- to 23-week-old ob/ob mice and age-matched lean littermates. PTPase activity was measured using a synthetic phosphopeptide, TRDIY(P)ETDY(P)Y(P)RK, as the substrate, corresponding to residues 1142 to 1153 of the insulin receptor and containing the major autophosphorylation sites of the regulatory domain. The ob/ob mice were hyperinsulinemic across all age groups, but only the youngest mice (aged 5 to 7 weeks) were hyperglycemic. Most PTPase activity was present in the liver particulate fraction and was 19% to 114% greater in ob/ob mice as compared with controls. PTPase activity in the liver soluble fraction was 26% less than control values in the youngest ob/ob mice (5 to 7 weeks), but increased with age and was 41% and 131% above control values at 21 to 23 and 25 to 27 weeks of age, respectively. Oral administration of the PTPase inhibitor sodium orthovanadate (0.6 mg/mL in drinking water for 2 weeks) to young ob/ob mice caused a significant reduction in the elevated particulate PTPase activity, with concomitant decreases in plasma insulin and plasma glucose. Assessment of PTPase activity with a monophosphate form of the same synthetic peptide, TRDIY(P)ETDYYRK, showed lower PTPase activities as compared with the triphosphate form and no significant differences between ob/ob and control preparations.(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations in specific protein-tyrosine phosphatases accompany insulin resistance of streptozotocin diabetes

To test whether protein tyrosine phosphatases (PTPases) may play a role in the insulin resistance of insulinopenic diabetes, we assessed PTPase activity as well as the protein and mRNA abundance of three major candidate PTPases in subcellular fractions of liver and skeletal muscle of streptozotocin-diabetic rats before and after insulin treatment. PTPase activity against the insulin receptor in liver and muscle cytosol increased to 120-125% of control in the diabetic animals and by an additional 5-10% after insulin treatment. In the particulate fraction, PTPase activity decreased to 65-70% of control in diabetic liver and muscle and increased to 115-120% of control after insulin treatment. Protein for the leukocyte common antigen-related PTPase paralleled the changes in the PTPase activity in the particulate fraction. SH-PTP2/syp and PTPase 1B were both significantly increased in diabetes. SH-PTP2/syp also exhibited an increased ratio of particulate to cytosol distribution in diabetic tissues (1.8-1.9) that was reversed after insulin treatment (0.79-0.95). Northern analysis suggested that the PTPases were regulated at a pretranslational level. These changes in the abundance and distribution of specific PTPases may be involved in the pathogenesis of insulin resistance in insulinopenic diabetes.

Thiazolidine derivatives ameliorate high glucose-induced insulin resistance via the normalization of protein-tyrosine phosphatase activities

The mechanisms for the insulin resistance induced by hyperglycemia were investigated by studying the effect of high glucose concentration (HG) and its modulation by thiazolidine derivatives, on insulin signaling using Rat 1 fibroblasts expressing human insulin receptors (HIRc). Incubating HIRc cells in 27 mM D-glucose for 4 days impaired the insulin-stimulated phosphorylation of pp185 and receptor beta-subunits. Both protein kinase C activities and phorbol dibutyrate binding to intact cells were unchanged; however, cytosolic protein-tyrosine phosphatase (PTPase) activity increased within 1 h prior to the impairment of insulin receptor kinase in HG cells (Maegawa, H., Tachikawa-Ide, R., Ugi, S., Iwanishi, M., Egawa, K., Kikkawa, R., Shigeta, Y., and Kashiwagi, A. (1993) Biochem. Biophys. Res. Commun. 197, 1078-1082). Increased PTPase activity was consistent with a 2-fold increase in the amount of PTP1B, and anti-PTP1B antibody inhibited this increment of cytosolic PTPase activity in HG cells. Co-incubating cells with pioglitazone prevented these abnormalities in cytosolic PTPase, the PTP1B content and the impaired phosphorylation of pp185 and receptor beta subunits in HG cells. Finally, HG cells had impaired insulin-stimulated alpha-amino-isobutyric acid uptake, which was ameliorated by exposure to thiazolidine derivatives. In conclusion, exposing cells to high glucose levels desensitizes insulin receptor function, and thiazolidine derivatives can reverse the process via the normalization of cytosolic PTPase, but not of protein kinase C.

Insulin receptor signaling is augmented by antisense inhibition of the protein tyrosine phosphatase LAR

Considerable evidence has shown that most physiologic responses to insulin require activation of the intrinsic tyrosine kinase of the insulin receptor. Biochemical studies have also supported the hypothesis that receptor kinase activity can be modulated by cellular protein tyrosine phosphatases (PTPases), which have not yet been identified. To test the hypothesis that the transmembrane PTPase LAR can modulate insulin receptor signaling in vivo, antisense RNA expression was used to specifically suppress LAR protein levels by 63% in the rat hepatoma cell line, McA-RH7777. Hormone-dependent autophosphorylation of the insulin receptor was increased by approximately 150% in the antisense-expressing cells at all insulin concentrations tested. This increase in autophosphorylation was paralleled by a 35% increase in insulin receptor tyrosine kinase activity. Reduced LAR levels did not alter non-hormone-dependent tyrosine phosphorylation nor basal insulin receptor tyrosine phosphorylation and kinase activity. Most significantly, reduced LAR levels resulted in a 350% increase in insulin-dependent phosphatidylinositol 3-kinase activity. These studies provide unique in vivo evidence that LAR is involved in the modulation of insulin receptor signaling in intact cells.

Overexpression of the tyrosine phosphatase PTP1B is associated with human ovarian carcinomas

OBJECTIVE

Our purpose was to determine whether protein tyrosine phosphatase 1B is overexpressed in ovarian cancers, possibly altering the balance of intracellular tyrosine phosphorylation.

STUDY DESIGN

The expression of protein tyrosine phosphatase 1B was assayed in frozen sections from 54 human ovarian carcinomas and seven normal ovaries by immunochemical staining with monoclonal antibody AE4-2J, which is specific for protein tyrosine phosphatase 1B. The expression of protein tyrosine phosphatase 1B-specific messenger ribonucleic acid in tumors was determined by Northern analysis. The results were analyzed statistically by means of Fisher's exact test.

RESULTS

Minimal staining was observed in normal ovarian epithelium. In contrast, 43 of 54 (79.6%) tumors displayed increased protein tyrosine phosphatase 1B expression, which is statistically associated with malignancy. Overexpression was associated with the expression of the p185c-erbB-2, p170EGFR, and p165mCSFR growth factor receptor protein tyrosine kinases. Protein tyrosine phosphatase 1B messenger ribonucleic acid expression was inconsistently increased in tumor cells.

CONCLUSION

Increased expression of protein tyrosine phosphatase 1B in ovarian cancers that also express protein tyrosine kinases suggests that protein tyrosine phosphatase 1B may play a role in the growth regulation of ovarian cancers.

T cell receptor V beta gene bias in rheumatoid arthritis

Polymerase chain reaction (PCR) technology was employed to examine peripheral blood and synovial T cells in patients with rheumatoid arthritis (RA) for biased utilization of T cell receptor (TCR) variable region (V) genes. Oligonucleotide primers specific for individual TCR V beta gene families were used to amplify TCR gene products in a semiquantitative assay of their relative utilization in unselected T cell populations. Mean V beta expression in 24 RA peripheral blood samples was very similar to that in a panel of 15 normal subjects, except for a slight decrease in V beta 13.2 expression. V beta utilization in 8 RA synovial tissue samples and 13 synovial fluid samples was compared to simultaneously obtained blood samples. Although heterogeneous patterns of skewed V beta utilization were observed, several significant trends emerged. By a number of approaches to data analysis, a statistically significant increase in expression of V beta 6 and V beta 15 in synovial T cells was documented. In addition, increased synovial expression of V beta 14 was found, but only in the synovial fluid samples. Reduced expression of V beta 1, V beta 4, V beta 5.1, V beta 10, V beta 16, and V beta 19 was also observed in synovial T cells. These results indicate that biased V beta gene utilization in different peripheral compartments of RA patients can be observed in unselected T cell populations, and are consistent with the conclusion that populations of T cells expressing these V beta gene products may be involved in the pathogenesis of the disease.