Expression profile of MODY3/HNF-1alpha protein in the developing mouse pancreas

AIMS/HYPOTHESIS

One subtype of MODY (MODY3) results from the heterozygous mutation of a hepatocyte nuclear factor (HNF)-1alpha. The pattern of HNF-1alpha expression in the normal pancreas has not been determined. This study aimed to clarify the profile of HNF-1alpha protein expression in the developing mouse pancreas.

METHODS

Double immunofluorescence staining was carried out for HNF-1alpha and pancreatic hormones or transcription factors (PDX-1, Pax6, Isl1, and Nkx2.2). The expression of these transcription factors was also studied in the beta cells of HNF-1 alpha mutant mice.

RESULTS

HNF-1alpha was expressed by both endocrine and exocrine cells of the pancreas. Double immunofluorescence staining showed that HNF-1alpha was expressed in the nuclei of alpha cells, beta cells, delta cells, and pancreatic polypeptide (PP) cells. HNF-1alpha was first detected in most pancreatic epithelial cells on embryonic day 10.5 (E10.5), and hormone-positive endocrine cells and amylase-positive cells expressed HNF-1alpha on E15.5. Most of the Pax6-, Isl1-, or PDX-1-positive cells showed co-expression of HNF-1alpha. However, HNF-1alpha immunoreactivity was not observed in 36.0% of Nkx2.2-positive cells. Expression of Nkx2.2, Isl1 and Pax6 seemed to be normal in the beta cells of transgenic mice with dominant negative overexpression of HNF-1alpha. Expression of PDX-1 did not change in the beta cells of pre-diabetic HNF-1 alpha (-/-) mice, but expression was markedly decreased in the diabetic stage.

CONCLUSION/INTERPRETATION

HNF-1alpha is expressed by both endocrine cells and exocrine cells of the pancreas from the foetal stage along with other transcription factors, so HNF-1alpha might play a role during development.

Overexpression of N-acetylglucosaminyltransferase III enhances the epidermal growth factor-induced phosphorylation of ERK in HeLaS3 cells by up-regulation of the internalization rate of the receptors

N-Acetylglucosaminyltransferase III (GnT-III) is a key enzyme that inhibits the extension of N-glycans by introducing a bisecting N-acetylglucosamine residue. In this study we investigated the effect of GnT-III on epidermal growth factor (EGF) signaling in HeLaS3 cells. Although the binding of EGF to the epidermal growth factor receptor (EGFR) was decreased in GnT-III transfectants to a level of about 60% of control cells, the EGF-induced activation of extracellular signal-regulated kinase (ERK) in GnT-III transfectants was enhanced to approximately 1.4-fold that of the control cells. A binding analysis revealed that only low affinity binding of EGF was decreased in the GnT-III transfectants, whereas high affinity binding, which is considered to be responsible for the downstream signaling, was not altered. EGF-induced autophosphorylation and dimerization of the EGFR in the GnT-III transfectants were the same levels as found in the controls. The internalization rate of EGFR was, however, enhanced in the GnT-III transfectants as judged by the uptake of (125)I-EGF and Oregon Green-labeled EGF. When the EGFR internalization was delayed by dansylcadaverine, the up-regulation of ERK phosphorylation in GnT-III transfectants was completely suppressed to the same level as control cells. These results suggest that GnT-III overexpression in HeLaS3 cells resulted in an enhancement of EGF-induced ERK phosphorylation at least in part by the up-regulation of the endocytosis of EGFR.

Redox capacity of cells affects inactivation of glutathione reductase by nitrosative stress

Glutathione reductase (GR) plays a pivotal role in maintaining glutathione (GSH) in its reduced form. We have isolated a cDNA for rat GR and constructed a baculovirus system to produce recombinant GR on a large scale. This protein was purified by simple, two-step chromatographic procedure using DE52 and 2',5'-ADP Sepharose. Tissue distributions of GR were examined by Northern and Western blotting with a rabbit antibody to purified GR. GR was expressed in the order of reactivity; kidney, colon, liver, stomach, etc. Western blot analysis showed that both the cytosolic and the mitochondrial fractions of liver homogenate gave immunoreactive bands of similar size. This indicates that the same gene products exist in these fractions. Since nitric oxide (NO) produced under inflammatory conditions causes nitrosative stress and affects the redox states of surrounding tissues, we investigated the effects of NO donors on the enzymatic activities of purified GR. S-nitrosoglutathione (GSNO), 3-morpholinosydnonimine N-ethylcarbamide (SIN-1), and S-nitroso-N-acetyl-D,L-penicillamine (SNAP) at 1 mM gave 39, 15, and 12% inhibitions, respectively. In RAW 264.7 cells the GR activity was reported to be inhibited by GSNO. In A549 cells, however, no such change in the activity, protein levels and mRNA of GR was noted. Since these cells have a much higher redox capacity than RAW 264.7 cells as judged by GR activity and thioredoxin reductase activity it wound minimize cellular damage, including inactivation of GR caused by nitrosative stress.

Glycation of apolipoprotein E impairs its binding to heparin: identification of the major glycation site

The increased glycation of plasma apolipoproteins represents a possible major factor for lipid disturbances and accelerated atherogenesis in diabetic patients. The glycation of apolipoprotein E (apoE), a key lipid-transport protein in plasma, was studied both in vivo and in vitro. ApoE was shown to be glycated in plasma very low density lipoproteins of both normal subjects and hyperglycemic, diabetic patients. However, diabetic patients with hyperglycemia showed a 2-3-fold increased level of apoE glycation. ApoE from diabetic plasma showed decreased binding to heparin compared to normal plasma apoE. The rate of Amadori product formation in apoE in vitro was similar to that for albumin and apolipoproteins A-I and A-II. The glycation of apoE in vitro significantly decreased its ability to bind to heparin, a critical process in the sequestration and uptake of apoE-containing lipoproteins by cells. Diethylenetriaminepentaacetic acid, a transition metal chelator, had no effect on the loss of apoE heparin-binding activity, suggesting that glycation rather than glycoxidation is responsible for this effect. In contrast, glycation had no effect on the interaction of apoE with amyloid beta-peptide. ApoE glycation was demonstrated to be isoform-specific. ApoE(2) showed a higher glycation rate and the following order was observed: apoE(2)>apoE(4)>apoE(3). The major glycated site of apoE was found to be Lys-75. These findings suggest that apoE is glycated in an isoform-specific manner and that the glycation, in turn, significantly decreases apoE heparin-binding activity. We propose that apoE glycation impairs lipoprotein-cell interactions, which are mediated via heparan sulfate proteoglycans and may result in the enhancement of lipid abnormalities in hyperglycemic, diabetic patients.

The structural organization of the human aldehyde reductase gene, AKR1A1, and mapping to chromosome 1p33-->p32

Genomic DNA encoding for human aldehyde reductase (AKR1A1), a member of the aldo-keto reductase superfamily, was isolated and characterized. The genomic DNA is approximately 16 kb in length and contains eight exons which encode the entire coding region and the 3'-untranslated sequences. AKR1A1 was localized on chromosome 1p33-->p32 by fluorescence in situ hybridization.

Overexpression of the aldose reductase gene induces apoptosis in pancreatic beta-cells by causing a redox imbalance

To determine the role of the polyol metabolizing pathway under hyperglycemic conditions, the effects of aldose reductase (AR) on the cellular functions of pancreatic beta-cells were examined. Stable transfectants of rat AR cDNA were obtained with a pancreatic beta-cell line, HIT, in which a negligible amount of AR was originally expressed. Overproduction of AR triggered DNA fragmentation, as judged with the TUNEL method and agarose gel electrophoresis. Morphological analysis by electron microscopy also clearly showed apoptosis of the AR-overexpressing HIT cells. Induction by interleukin-1beta of gene expression such as those of an inducible form of nitric oxide synthase (NOS-II) and Mn-superoxide dismutase (Mn-SOD), was much lower in the transfectants than in the control cells, while the expression of constitutively expressed genes such as those for Cu,Zn-superoxide dismutase and insulin was not changed. The susceptibility to interleukin-1beta stimulation of the expression of the NOS II and Mn-SOD genes was due to suppressed NF-kappaB activity, which is essential for the expression of these genes. In addition, the intracellular NADPH/NADP+ ratio was considerably lower in the AR-transfected cells than in control cells. Thus, the overexpression of AR in pancreatic beta-cells induced apoptosis that may be caused by a redox imbalance.

Different expression patterns of nitric oxide synthase isozymes in various gynecological cancers

The expression of nitric oxide synthase (NOS) in human gynecological cancers, including ovarian cancers, uterocervical cancers, and endometrial cancers for example, was examined by the reverse transcriptase/polymerase chain reaction, coupled with Southern hybridization and by immunohistochemistry. Nitric oxide synthase II (NOS II), an inducible form, was expressed in more than 90% of the cancers. Nitric oxide synthase I (NOS I), a neuronal form, was expressed in 58% of all the ovarian cancers, in which the serous type is found more frequently (5 out of 7) than the mucinous type (2 out of 6), and in all clear-cell cancers. The frequency of NOS I expression in uterocervical cancers and endometrial cancers was relatively low. Nitric oxide synthase III (NOS III), an endothelial form, was detected in 25% of ovarian and 33% of endometrial cancers, while no expression was detected in uterocervical cancers. In terms of cancer types, all clear-cell adenocarcinomas and most of the serous-type adenocarcinomas expressed both NOS I and NOS II, while most uterine squamous carcinomas and endometrial adenocarcinomas expressed only NOS II. However, there was no correlation between the frequency of NOS expression and patients' age or the clinical stage of the disease. Since NO increases vascular permeability and blood flow, the high frequency of NOS expression in gynecological cancers may serve to stimulate and promote tumor growth.

Human erythrocyte bisphosphoglycerate mutase: inactivation by glycation in vivo and in vitro

2,3-Bisphosphoglycerate mutase (BPGM) [EC 5.4.2.4] is a multifunctional enzyme that catalyzes both the synthesis and the degradation of 2,3-diphosphoglycerate (2,3-DPG) and contains three types of activities in that it functions as a 2,3-DPG synthetase, a phosphoglycerate mutase and a 2,3-DPG phosphatase. In humans, BPGM occurs only in erythrocytes and plays a pivotal role in the dissociation of oxygen from hemoglobin via 2,3-DPG. The present study shows that the specific activity of BPGM in erythrocytes of diabetic patients is decreased, compared to normal controls as judged by 2,3-DPG synthetase activity and immunoreactive contents. To understand the mechanism by which the enzyme is inactivated, the enzyme was purified from pooled erythrocytes from diabetic patients and subjected to a boronate affinity column. The flow through fraction was active while the bound fraction was completely inactive. The bound fraction was reactive to an anti-hexitollysine antibody, indicating that the enzyme had undergone glycation and inactivation. The primary glycated site of the enzyme was found to be Lys158 as judged by amino acid sequencing and the reactivity with an anti-hexitollysine IgG, after reverse-phase HPLC of the lysyl-endopeptidase-digested peptides. Extensive glycation of recombinant BPGM in vitro indicated that the glycation sites were Lys2, Lys4, Lys17, Lys42, Lys158, and Lys196. From these results, the loss of enzymatic activity appears to be due to the glycation of Lys158 which may be located in the vicinity of the substrate binding site.

Immunological detection of fructated proteins in vitro and in vivo

An antibody has been raised against fructated lysine in proteins by immunizing fructated lysine-conjugated ovalbumin in rabbits. The affinity-purified antibody specifically recognized proteins incubated with fructose but not with other reducing sugars such as glucose, galactose or ribose, as judged by immunoblotting and ELISA techniques. Competitive binding to this antibody was observed specifically by fructated lysine but not by glucated lysine, glucose, fructose or lysine. The antibody binds specifically to fructated lysine residues in the protein but not to borohydride-reduced material or advanced glycation end products, indicating that the antibody recognizes only the reducing, carbonyl-containing forms produced in the early stage of the fructation reaction. When BSA was incubated with various concentrations of fructose, the reactivity of the antibody increased in a dose- and time-dependent manner. When soluble proteins prepared from either normal or streptozotocin-induced diabetic rat eyes were analysed by ELISA with this antibody, an increase in the reactive components was observed as a function of aging as well as under diabetic conditions. Western blotting analysis showed that lens crystallin reacted highly with this antibody. Because fructose is biosynthesized largely through the polyol pathway, which is enhanced under diabetic conditions, and lens is known to have a high activity of enzymes in this pathway, this antibody is capable of recognizing fructated proteins in vivo. Thus it is a potentially useful tool for investigating two major issues that seem to be involved in diabetic complications, namely the glycation reaction and the polyol pathway.

Overexpression of aldehyde reductase protects PC12 cells from the cytotoxicity of methylglyoxal or 3-deoxyglucosone

The glycation reaction (Maillard reaction) plays a major role in diabetic complications, since some reaction intermediates are responsible for the modification and cross-linking of long-lived proteins, resulting, in turn, in a deterioration of normal cell function. The reaction intermediates include methylglyoxal (MG) and 3-deoxyglucosone (3-DG), both of which are cytotoxic dicarbonyl compounds and are elevated during hyperglycemia. Aldehyde reductase (ALR) catalyzes the reduction of both compounds. To examine the intracellular role of ALR in the diabetic complications of neural cells, its gene was overexpressed in rat pheochromocytoma PC12 cells, which normally express a low level of ALR. Western blot analysis showed that ALR protein in the ALR gene-transfected cells was more than twice as much as in the control cells. In the parental cells, cytotoxicity, including apoptotic cell death, which was determined by fluorescent microscopy using the fluorescent DNA binding dye Hoechst 33258, was observed at 100 microM MG. In the ALR gene-transfected cells, the cytotoxicity of both MG and 3-DG and apoptotic cell death were decreased. This suggests that intracellular ALR protects neural cells from the cytotoxicity of 3-DG or MG, and that neural cells, which normally express a low level of ALR, might be susceptible to diabetic complications caused by intermediate products of the Maillard reaction, such as 3-DG and MG.

[Low-dose cytarabine ocfosfate therapy in an elderly acute myelogenous leukemia]

A 71-year-old man was admitted for severe anemia. Bone marrow puncture revealed 48% of blast cells. A diagnosis of acute myelogenous leukemia (AML-M 4) was made. As the patient was old, we administered 300mg of cytarabine ocfosfate (SPAC) for 21 days. Blast cells in bone marrow decreased 5.6%, and SPAC was considered effective. We treated him with the same dose of SPAC for 14 days after a 21-day interval from the end of the first treatment. Although leukemic cells were still seen in bone marrow after two treatments, we considered him in partial remission, and he was discharged. After discharge, the hematological findings remain almost normal with intermittent treatment of 150 mg of SPAC for over one year. Thus, cytarabine ocfosfate might be useful in elderly AML patients.