The Notch intracellular domain is ubiquitinated and negatively regulated by the mammalian Sel-10 homolog

The Caenorhabditis elegans sel-10 protein is structurally similar to E3 ubiquitin ligases and is a negative regulator of Notch (lin-12) and presenilin signaling. In this report, we characterize the mammalian Sel-10 homolog (mSel-10) and analyze its effects on Notch signaling. We find that mSel-10 localizes to the cell nucleus, and that it physically interacts with the Notch 1 intracellular domain (IC) and reduces Notch 1 IC-mediated activation of the HES 1 promoter. Notch 1 IC is ubiquitinated by mSel-10, and ubiquitination requires the presence of the most carboxyl-terminal region of the Notch IC, including the PEST domain. In the presence of the proteasome inhibitor MG132, the amount of Notch 1 IC and its level of ubiquitination are increased. Interestingly, this accumulation of Notch 1 IC in the presence of MG132 is accompanied by decreased activation of the HES 1 promoter, suggesting that ubiquitinated Notch 1 IC is a less potent transactivator. Finally, we show that mSel-10 itself is ubiquitinated and degraded by the proteasome. In conclusion, these data reveal the importance of ubiquitination and proteasome-mediated degradation for the activity and turnover of Notch ICs, and demonstrate that mSel-10 plays a key role in this process.

The origin of the ankyrin repeat region in Notch intracellular domains is critical for regulation of HES promoter activity

Notch signal transduction is mediated by proteolysis of the receptor and translocation of the intracellular domain (IC) into the nucleus, where it functions as a regulator of HES gene expression after binding to the DNA-binding protein RBP-J kappa. The mammalian Notch receptors are structurally very similar, but have distinct functions. Most notably, Notch 1 IC is a potent activator of the HES promoter, while Notch 3 IC is a much weaker activator and can repress Notch 1 IC-mediated HES activation in certain contexts. In this report we explore the molecular basis for this functional difference between Notch 1 and Notch 3 IC. We find that Notch 3 IC, like Notch 1 IC, can bind the SKIP and PCAF proteins. Furthermore, both Notch 1 and Notch 3 ICs displace the co-repressor SMRT from the DNA-binding protein RBP-J kappa on the HES promoter. The latter observation suggests that both Notch 3 IC and Notch 1 IC can access RBP-J kappa in vivo, and that the difference in activation capacity instead stems from structural differences in the two ICs when positioned on RBP-J kappa. We show that two distinct regions in the Notch IC are critical for the difference between the Notch 1 and Notch 3 IC. First, the origin of the ankyrin repeat region is important, i.e. only chimeric ICs containing a Notch 1-derived ankyrin repeat region are potent activators. Second, we identify a novel important region in the Notch IC. This region, named the RE/AC region (for repression/activation), is located immediately C-terminal to the ankyrin repeat region, and is required for Notch 1 IC's ability to activate and for Notch 3 IC's ability to repress a HES promoter. The interplay between the RE/AC region and the ankyrin repeat region provides a basis to understand the difference in HES activation between structurally similar Notch receptors.

[Epidemiology of human hydatidosis in the IX Region of la Araucania, Chile 1991-1998]

In the region of la Araucania, located in the south of Chile (37 degrees 24'-39 degrees 34' South lat.), the economy is based in cattle raising and agriculture. The cases of human hydatidosis, mortality and notification registered in la Araucania 1991-1998 are reviewed. The rate for hydatid disease is 38.5 per 100,000 population. Liver (47.1%) and lung (40.7%) were the most affected viscera. Days in hospital, 11-20 the 56.1%. Disease in female is 51.1%. The mortality rate is 0.8 per 100,000, the most frequently affected county is Imperial. The age group 15-44 years is the most affected. The notification rate is 8.74 per 100,000 population. The rate for hydatid disease is higher than the rate of notification, then necessarily there exist a subnotification. We think that it is necessary to investigate the serological prevalence of hydatidosis in the population of the IX Region Araucania.

The notch 3 intracellular domain represses notch 1-mediated activation through Hairy/Enhancer of split (HES) promoters

The Notch signaling pathway is important for cellular differentiation. The current view is that the Notch receptor is cleaved intracellularly upon ligand activation. The intracellular Notch domain then translocates to the nucleus, binds to Suppressor of Hairless (RBP-Jk in mammals), and acts as a transactivator of Enhancer of Split (HES in mammals) gene expression. In this report we show that the Notch 3 intracellular domain (IC), in contrast to all other analysed Notch ICs, is a poor activator, and in fact acts as a repressor by blocking the ability of the Notch 1 IC to activate expression through the HES-1 and HES-5 promoters. We present a model in which Notch 3 IC interferes with Notch 1 IC-mediated activation at two levels. First, Notch 3 IC competes with Notch 1 IC for access to RBP-Jk and does not activate transcription when positioned close to a promoter. Second, Notch 3 IC appears to compete with Notch 1 IC for a common coactivator present in limiting amounts. In conclusion, this is the first example of a Notch IC that functions as a repressor in Enhancer of Split/HES upregulation, and shows that mammalian Notch receptors have acquired distinct functions during evolution.

Effects of the 3-hydroxyanthranilic acid analogue NCR-631 on anoxia-, IL-1 beta- and LPS-induced hippocampal pyramidal cell loss in vitro

The kynurenine pathway intermediate 3-hydroxyanthranilic acid (3-HANA) is converted by 3-HANA 3,4-dioxygenase (3-HAO) to the putative neuropathogen quinolinic acid (QUIN). In the present study, the neuroprotective effects of the 3-HANA analogue and 3-HAO inhibitor NCR-631 was investigated using organotypic cultures of rat hippocampus. An anoxic lesion was induced by exposing the cultures to 100% N2 for 150 min, resulting in a pronounced loss of pyramidal neurons, as identified using NMDA-R1 receptor subunit immunohistochemistry. NCR-631 provided a concentration-dependent protective effect against the anoxia. NCR-631 was also found to counteract the loss of pyramidal neurons in two models of neuroinflammatory-related damage; incubation with either LPS (10 ng/ml) or IL-1 beta (10 IU/ml). The findings suggest that NCR-631 has neuroprotective properties and that it may be a useful tool to study the role of kynurenines in neurodegeneration.

[Hygienic, chemical and ecotoxicological aspects of the disinfection of biologically treated waste water by ozone and UV light]

Biologically treated waste water from two different municipal treatment plants with mainly domestic waste water on the one hand and industrial influenced waste water on the other hand was disinfected by UV-irradiation and ozonation. Hygienic, chemical and eco-toxic effects of the disinfection step were examined. It was found that by ozonation as well as by UV-irradiation the required guide and imperative values for fecal and total coliform bacteria were fulfilled. The UV-irradiation induces no changes concerning chemical waste water quality and toxic effects. In contrast to these results ozonation can lead to alterations in chemistry and toxicity depending on the waste water composition.

Comparison of mRNA contents of interleukin-1 beta and nitric oxide synthase in pancreatic islets isolated from female and male nonobese diabetic mice

Interleukin-1 beta (IL-1 beta) has been suggested to mediate beta-cell destruction in insulin-dependent diabetes mellitus (IDDM) by inducing nitric oxide production. In this study, we assessed the levels of IL-1 beta and the inducible form of nitric oxide synthase (iNOS), using a semi-quantitative polymerase chain reaction assay, and performed determinations of nitrite accumulation and IL-1 beta bioactivity, on pancreatic islets isolated from 5- and 16-week-old female and male nonobese diabetic (NOD) mice and from nondiabetes prone NMRI mice. NOD mouse islets contained notable amounts of IL-1 beta mRNA. At 5 weeks of age, but not at 16 weeks, the values were higher in islets isolated from NOD females compared to males. The IL-1 beta bioactivity showed differences roughly reflecting the mRNA levels in the NOD mouse islets. In the NMRI mouse islets the IL-1 beta bioactivity was very low. The expression of iNOS mRNA increased in both male and female islets between 5 and 16 weeks of age. Immunocytochemistry of pancreatic sections indicated the presence of macrophages especially in the peri-insular area of the NOD mice which suggests that IL-1 beta was produced by macrophages. The levels of IL-1 beta activity and mRNA in freshly isolated islets from NOD 5-weeks-old females did not correlate to the iNOS mRNA content or to the nitrite production. However, after incubation with IL-1 beta in vitro, both NOD and NMRI islets responded with a marked increase in nitric oxide production.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of protein tyrosine kinases in islet cells: possible role of the Flk-1 receptor for beta-cell maturation from duct cells

To elucidate the expression of genes of importance for beta-cell replication and the production of insulin, single-stranded cDNAs from different preparations of insulin producing cells were used as template for the polymerase chain reaction (PCR) using primers specific for protein tyrosine kinases (PTKs). In RINm5F cells, as well as in fetal rat islets, the receptor PTK fetal liver kinase-1 (Flk-1) was expressed among other receptor and cytoplasmic tyrosine kinases. To elucidate the putative effects of stimulation of the Flk-1 receptor, fetal rat islet-like structures were cultured in the presence of the ligand for this receptor, vascular endothelial growth factor (VEGF). VEGF was found to stimulate both the insulin content/islet DNA ratio and the accumulation of insulin in the culture medium without affecting the rates of beta-cell replication. To investigate the localization of expression of the Flk-1 receptor in the pancreas, serial sections of fetal pancreata were immunostained for Flk-1 and insulin. Expression of Flk-1 was detected in endothelial-like cells and cells lining pancreatic ducts. The latter are considered to contain precursor cells for the endocrine pancreas. In conclusion, specific protein tyrosine kinases are expressed in islet cells, and are presumably participating in the regulation of islet function. Specifically, the receptor PTK Flk-1 may play a role of beta-cell maturation from pancreatic duct cells.

[Blastocystis infection in symptomatic patients at the Regional Hospital of Temuco, Chile]

At the Regional Hospital of Temuco, 670 adult and children patients, with intestinal complaints, were studied to determine the prevalence of infection by enteroparasites or commensals in a general way, and by Blastocystis hominis in a particular attempt. A coproparasitological study was carried out using a modified Telemann method. Infection by parasites and/or commensals was demonstrated in 446 (66.6%) patients. The most frequent agent was B. hominis (35.8%) followed by Giardia intestinalis (22.5%) among the protozoa. The frequencies of helminths and commensals were 7.7 and 42.5% respectively. The endemic characteristics of intestinal infections by parasites was ratified and the prevalence of infection by B. hominis was proved to be higher in comparison to other zones of the country.

[Intestinal parasites in the riverside population of Villarrica Lake, Chile]

The prevalence of intestinal parasites in 200 persons of bank side Lake was studied. Age, sex and environmental sanitary conditions were considered in each case. A modified Telemann method was performed for examining stool samples from each individual. Infection by pathogenic or commensal helminths and protozoa was detected in 55.6% of samples. Correlation with sex and environmental sanitary conditions was observed. Infection by Diphyllobothrium sp. was not found.

[Hydatidosis in the IXth Region of Chile. A regional problem and challenge]

Infection by Echinococcus granulosus is the main zoonosis affecting the human population of the IXth Region in southern Chile. Prevalence rates vary from 18.2 to 48 per 100,000. Animals are affected with prevalence rates of 40% for bovines, 39.5% for sheep and 14.8% for pork as estimated at the central meat processing plant in the city of Temuco. A cost of approximately $300,000 is estimated to treat affected individuals. Much greater losses may be estimated from unnotified meat processing in rural areas and from reduced yield of animal products such as wool an milk. Accordingly, a regional program for control of this zoonosis is urgently required.

GTP-binding proteins may stimulate insulin biosynthesis in rat pancreatic islets by enhancing the signal-recognition-particle-dependent translocation of the insulin mRNA poly-/mono-some complex to the endoplasmic reticulum

We aimed to elucidate the putative role of GTP-binding proteins in the regulation of insulin biosynthesis. For this purpose, freshly isolated rat islets were incubated in the presence of liposomes containing GDP, guanosine 5'-[beta-thio]diphosphate (GDP[S]), GTP, guanosine 5'-[gamma-thio]triphosphate (GTP[S]), guanosine 5'-[beta gamma-methylene]triphosphate (p[CH2]ppG), guanosine 5'[beta gamma-imido]triphosphate (p[NH]ppG) and ATP, and the effects of the liposomal delivery of these substances on rates of biosynthesis of insulin and total protein were determined. Insulin biosynthesis during a 1 h incubation at 1.67 mM-glucose was stimulated by ATP- and GTP[S]-containing liposomes as compared with control liposomes. At 16.7 mM-glucose, only the GTP[S]-containing liposomes stimulated insulin biosynthesis. No inhibition of islet protein and insulin synthesis was observed with GDP-, GDP[S]-, p[CH2]ppG- and p[NH]ppG-containing liposomes. By determining the subcellular distribution of insulin mRNA, it was found that the mRNA content associated with microsomes was increased and that associated with the cytosolic mono-/poly-somes decreased when the islets were incubated with GTP[S]-containing liposomes, resulting in an approximate doubling of the ratio of microsomal to polysomal-associated insulin mRNA. ATP-containing liposomes produced no effects on the association of insulin mRNA with microsomes. By using photoaffinity labelling and immunoprecipitation techniques, specific binding of GTP[35S] to the alpha-subunit of the signal-recognition particle (SRP) receptor in islet homogenates containing physiological concentrations of GTP and GDP was demonstrated. These findings suggest that the GTP-binding subunit(s) of the SRP receptor, and possibly also of other GTP-binding proteins involved in this process, may regulate insulin biosynthesis by stimulating the translocation of insulin mRNA to the endoplasmic reticulum and by increasing preproinsulin-peptide translocation into the lumen of the reticulum.

Nonspecific delivery of substances into pancreatic islet cells by pH-sensitive liposomes in vitro

The aim of this study was to evaluate the suitability of different liposome preparations for translocation of substances into the pancreatic islet cell in vitro. For this purpose, isolated islets, either fresh or cultured or dispersed islet cells from the rat were incubated with different liposome preparations containing 6-carboxyfluorescein. The composition of the liposomes was either phosphatidylcholine/ganglioside (pH-insensitive) or phosphatidylethanolamine/oleic acid (pH-sensitive). Non-specific immunoglobulin was attached to the liposome membrane by means of covalent conjugation or by dialysis. Following incubation with the different liposomes, the islets were dispersed and examined in a fluorescence microscope for assessment of intracellular fluorescence emitted by the liposome-delivered fluorescein. It was found that the delivery of liposomal contents into islet cells was the least when using the pH-insensitive liposomes. The delivery could be slightly increased if immunoglobulin was conjugated to these liposomes. Intracellular fluorescence arising from pH-sensitive liposomes was clearly stronger than that from pH-insensitive liposomes. The use of pH-sensitive liposomes with conjugated IgG, however, failed to improve the delivery. When the proportions of fluorescent cells in the different islet preparations were compared, there was a higher percentage of such cells in the freshly isolated islets and in the dispersed islet cells than in the cultured islet cells. To quantitate the liposome mediated delivery of substances, cells in suspension, from a insulin producing tumor cell line (RINm5F) of from dispersed rat islets, were incubated with carboxyfluorescein containing liposomes and the intracellular release of the fluorescein was followed spectrofluorometrically.(ABSTRACT TRUNCATED AT 250 WORDS)