Search PubMed⌕ Search

Biomedical subjects

S Justice

Publications and source records attributed to S Justice.

9 recordsLinked to original sources
PubMed2000

Stimulation of endogenous GH and interleukin-6 receptors selectively activates different Jaks and Stats, with a Stat5 specific synergistic effect of dexamethasone.

The interaction of GH, interleukin (IL)-6 and glucocorticoids is likely to be important in regulating the GH-insulin-like growth factor (IGF)-I axis. The signalling cascades activated by GH and IL-6 appear to be very similar, as demonstrated by studies using overexpression of the receptor and other components of the Jak-Stat and mitogen-activated protein (MAP) kinase pathways. Here we show that the human embryonic kidney cell line 293 (HEK293) expresses GH and IL-6 receptors endogenously. To determine which specific pathways might be activated by the two cytokines, at physiological levels of all components, we studied GH and IL-6 mediated signal transduction both under basal conditions and in the presence of overexpressed receptors and Stat proteins. Our results suggest a receptor specificity of Jak2 for GH receptors, and Jak1 for IL-6 receptors. Stat activation in response to GH and IL-6 was determined by reporter gene induction. Both GH and IL-6 were able to induce the reporter gene containing the Stat5 responsive element (LHRE) but the IL-6 response appeared to be mediated mainly through Stat3 activation. In contrast, the reporter gene containing the Stat3 responsive element (SIE) was IL-6 specific. The levels of gene induction by GH and IL-6 were not altered by the co-stimulation with GH and IL-6, suggesting that there is little cross-talk at the Jak-Stat activation level between the two cytokines. Neither GH nor IL-6 activated the MAP-kinase responsive serum response element (SRE), unless GH receptors or gp130 were overexpressed. Transfection of Stat3 or Stat5 expression vectors enhanced the response to GH and IL-6. Stimulation with dexamethasone synergistically enhanced GH activation of the LHRE reporter gene but had no effect on the IL-6 activation of the same reporter or on the SIE reporter gene. Thus, our studies suggest that while each cytokine, GH and IL-6, may activate various members of the Jak-Stat pathway in overexpression studies, specific activation of Stat3 by IL-6 and of Jak2 and Stat5 by GH can be observed in HEK293 cells and that in this system the synergistic effect of dexamethasone appears specific for Stat5.

Cell Line↗
PubMed1999

Studies with a growth hormone antagonist and dual-fluorescent confocal microscopy demonstrate that the full-length human growth hormone receptor, but not the truncated isoform, is very rapidly internalized independent of Jak2-Stat5 signaling.

UNLABELLED: We have investigated trafficking of two negative regulators of growth hormone receptor (GHR) signaling: a human, truncated receptor, GHR1-279, and a GH antagonist, B2036. Fluorescent-labeled growth hormone (GH) was rapidly internalized by the full-length GHR, with >80% of the hormone internalized within 5 min of exposure to GH. In contrast, <5% of labeled GH was internalized by cells expressing truncated GHR1-279. Using another truncated receptor, GHR1-317 fused to enhanced green fluorescent protein (EGFP), we have exploited fluorescence energy transfer to monitor the trafficking of ligand-receptor complexes. The data confirmed that internalization of this truncated receptor is very inefficient. It was possible to visualize the truncated GHR1-317-EGFP packaged in the endoplasmic reticulum, its rapid movement in membrane bound vesicles to the Golgi apparatus, and subsequent transport to the cell membrane. The GH antagonist, B2036, blocked Jak2-Stat5-mediated GHR signaling but was internalized with a similar time course to native GH. THE RESULTS: 1) demonstrate the rapid internalization of GH when studied under physiological conditions; 2) confirm the hypothesis that internalization of cytoplasmic domain truncated human GHRs is very inefficient, which explains their dominant negative action; and 3) show that the antagonist action of B2036 is independent of receptor internalization.

Golgi Apparatus↗
PubMed1999

Bacterial cell division.

Formation of the bacterial division septum is catalyzed by a number of essential proteins that assemble into a ring structure at the future division site. Assembly of proteins into the cytokinetic ring appears to occur in a hierarchial order that is initiated by the FtsZ protein, a structural and functional analog of eukaryotic tubulins. Placement of the division site at its correct location in Escherichia coli requires a division inhibitor (MinC), that is responsible for preventing septation at unwanted sites near the cell poles, and a topological specificity protein (MinE), that forms a ring at midcell and protects the midcell site from the division inhibitor. However, the mechanism responsible for identifying the position of the midcell site or the polar sites used for spore septum formation is still unclear. Regulation of the division process and its coordination with other cell cycle events, such as chromosome replication, are poorly understood. However, a protein has been identified in Caulobacter (CtrA) that regulates both the initiation of chromosome regulation and the transcription of ftsZ, and that may play an important role in the coordination process.

Cell Division↗
PubMed1998

Cirrhotic liver expresses low levels of the full-length and truncated growth hormone receptors.

In cirrhosis, as in other conditions of protein catabolism, there is a state of acquired GH resistance, as defined by high circulating GH levels with low insulin-like growth factor I levels. However, patients with end-stage liver failure respond to supraphysiological doses of GH with an increase in circulating insulin-like growth factor I levels. The present study represents a detailed analysis of GH receptor (GHR) expression in cirrhotic liver from 17 patients with end-stage liver disease. Specific binding of labeled GH was identified in all cirrhotic livers studied. The binding affinity for the GHR was similar in cirrhotic and normal livers, but the number of binding sites per mg protein of liver membrane was variable in both normal and cirrhotic liver, although it were generally lower in cirrhotic liver. GHR expression was identified in cirrhotic liver by Northern blotting, RT-PCR, and ribonuclease protection assay. On Northern blotting, a single transcript of 4.8 kb was identified in normal and cirrhotic tissues. RT-PCR identified expression of both full-length GHR and a truncated form of the GHR; this was confirmed by ribonuclease protection assay. In situ hybridization and immunohistochemistry confirmed the expression of GHR in regenerating hepatocytes and isolated cells in fibrous tissue. In conclusion, 1) the low level of GHR in cirrhotic liver may contribute to the acquired GH resistance found in cirrhotic patients; 2) the reduced expression of both full-length and truncated GHR is compatible with the low level of GH-binding protein found in cirrhosis, as this truncated receptor has previously been reported to generate large amounts of GH-binding protein; and 3) the demonstration of GH binding to cirrhotic liver explains why these patients with GH resistance may still respond to supraphysiological doses of GH.

Adult↗
PubMed1994

Export and trimerization pathways of maltoporin overlap in the inner membrane of Escherichia coli.

The production of functional porins involves multiple steps including: export of precursor polypeptides from the cytoplasm, assembly of monomers into trimers, and stabilization of trimers by association with lipopolysaccharide. In this report, a late export/assembly intermediate of the maltoporin (LamB) is found in the inner membrane of Escherichia coli using cell fractionation studies. This processed intermediate is transiently associated with a unique Triton X-100-insoluble subfraction of the inner membrane. The kinetics of appearance and solubility characteristics of this intermediate correspond to those of the metastable trimer form of LamB, suggesting that the export and assembly pathways overlap in the inner membrane prior to final localization in the bulk outer membrane.

Bacterial Outer Membrane Proteins↗
PubMed1991

Interleukin-6 secreting human pituitary adenomas in vitro.

Interleukin-6 was found to be secreted from seven out of ten human pituitary tumours cultured in vitro. These tumours included prolactin-secreting, growth hormone-secreting and clinically non-functioning adenomas. The amount of Interleukin-6 secreted was variable from 58 to 10,000 units per ml. in medium removed after a four-day incubation under basal conditions. Four tumours secreted IL-6 in excess of 500U/ml, three of which were clinically non-functioning, but each secreted follicle stimulating hormone in vitro. This is the first report of a cytokine growth factor being released basally by human pituitary tumours.

Adenoma↗
PubMed1990

The secretory characteristics of epidermal growth factor in human saliva.

A series of unstimulated and stimulated saliva samples from healthy volunteers was tested for EGF by radioimmunoassay. Salivary EGF, like other salivary constituents, was secreted in a diurnal pattern. On stimulation the rate of EGF secretion doubled but the concentration fell by 70% because of dilution by salivary fluid. EGF secretion was positively related to saliva flow (p = 0.00001) but the coefficient of correlation was low (r = 0.47). Over a period of 30 min continual salivary stimulation, EGF was released in a bimodal pattern with peaks occurring at 3 and 12 min. Subsequently, EGF secretion remained stable at a rate of release that was approx. 80% of the initial peak value (7.4 ng/min). Chromatography indicated that both high and low molecular-weight forms of EGF were present in unstimulated and stimulated saliva and that the low-weight form predominated. However, the proportion of high molecular-weight EGF increased from 18 to 38% of the total on short-term (3 min) stimulation.

Adolescent↗