131 research outputs found
Deletion of HOG1 leads to osmosensitivity in starvation-induced, but not rapamycin-dependent Atg8 degradation and proteolysis
No full textThe mechanisms of regulation of autophagy are still obscure. In mammalian liver, starvation-induced autophagic proteolysis is regulated by the cellular hydration state in a microtubule- and p38(MAPK)-dependent way. Recent work shows that in yeast, loss of Hog 1, the yeast orthologue of p38(MAPK), leads to osmosensitivity of starvation-induced autophagy (Prick et al., Biochem J 2006; 394:153-161), pointing to an evolutionarily conserved mechanism. In this addendum further experiments from hog 1 Delta yeast cells are shown, which support the hypothesis that starvation- and rapamycin-induced autophagy processes differ in their susceptibility to osmotic stress. The potential mechanisms are discussed
In yeast, loss of Hog1 leads to osmosensitivity of autophagy
No full textIn mammalian liver, protcolysis is regulated by the cellular hydration state in a microtubule- and p38(MAPK) (p38 mitogenactivated protein kinase)-dependent fashion. Osmosensing in liver cells towards proteolysis is achieved by activation of integrin receptors. The yeast orthologue of p38(MAPK) is Hog1 Delta (high-osmolarity glycerol 1), which is involved in the hyperosinotic-response pathway. Since it is not known whether starvation-induced autophagy in yeast is osmosensitive and whether Hog I is involved in this process, we performed fluorescence microscopy experiments. The hog1 Delta cells exhibited a visible decrease of autophagy in hypo-osmotic and hyperosinotic nitrogen-starvation medium as compared with normo-osmolarity, as determined by GFP (green fluorescent protein)-Atg8 (autophagy-related 8) fluorescence. Western blot analysis of GFP-Atg8 degradation showed that WT (wild-type) cells maintained a stable autophagic activity over a broad osmolarity range, whereas hog 1 cells showed,in impaired autophagic actitivity during hypo- and hyper-osmotic stress. In [H-3]leucine-pre-labelled yeast cells, the proteolysis rate was osmodependent only in hog1 Delta cells. Neither maturation of pro-aminopeptidase I nor vitality was affected by osmotic stress in either yeast strain. In contrast, rapamycin-dependent autophagy, as measured by degradation of GFP-Atg8, did not significantly respond to hypo-osmotic or hyperosmotic stress in hog1 Delta or WT cells. We conclude that Hog I plays a role in the stabilization machinery of nitrogen-deprivation-induced autophagy in yeast cells during ambient osmolarity changes. This could be an analogy to the p38(MAPK) pathway in mammalian liver, where osmosensing towards p38(MAPK) is required for autopliagy regulation by hypo-osmotic amino-acid- induced cell swelling. A phenotypic difference is observed in rapamycin-induced autophagy, which does not seem to respond to extracellular osmolarity changes in hog1 Delta cells
Predicting sustained virological responses in chronic hepatitis C patients treated with peginterferon alfa-2a (40 KD)/ribavirin
No full textBackground/Aims: Prediction of sustained virological response (SVR) during treatment would allow clinicians to identify patients most likely to benefit from therapy.
Methods: Retrospective analysis of data from 1121 adults with chronic hepatitis C treated for 48 weeks with peginterferon alfa-2a (40 KD) 180 mu g/week plus placebo or ribavirin (1000/1200 mg/day), or interferon alfa-2b 3 MIU three times/week plus ribavirin in a randomized, multinational, study.
Results: 67% of patients treated with peginterferon alfa-2a (40 KD)/ribavirin with early virological responses (HCV RNA negative or >= 2 log(10) decrease) at week 12 had SVRs at week 72 (HCV RNA 80 % of the planned ribavirin dose.
Conclusions: Early, sustained suppression of HCV replication portends an SVR. Cessation of treatment may be contemplated in patients without a >= 2 log(10) reduction in HCV RNA after 12 weeks. (c) 2005 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved
Liver disease in cystic fibrosis
No full textPURPOSE OF REVIEW: This review highlights recent developments in liver disease associated with cystic fibrosis. RECENT FINDINGS: The broad spectrum of hepatobiliary problems in cystic fibrosis includes specific alterations ascribable to the underlying defect as well as lesions of iatrogenic origin or that reflect the effects of a disease process occurring outside the liver. Focal biliary cirrhosis, resulting from biliary obstruction and progressive periportal fibrosis, is the most clinically relevant problem, because extension of the initially focal fibrogenic process may lead to multilobular biliary cirrhosis, portal hypertension and eventually liver failure. Cystic fibrosis associated liver disease is presently classified among genetic cholangiopathies and results from lack or dysfunction of the cystic fibrosis transmembrane regulator at the apical membrane of bile duct cells. Major advances have been achieved regarding characterization of natural history, risk factors, diagnostic modalities and treatment options. SUMMARY: Liver disease is a relatively frequent and early complication of cystic fibrosis. The pathogenesis is apparently multifactorial, with contributions from environmental and genetic determinants. Its impact on quality of life and survival will increase in future years, and its early detection and treatment will become increasingly important issues. Ursodeoxycholic acid is the only treatment currently available, but novel therapeutic options are being evaluated
Probing the dynamic stalk region of the ribosome using solution NMR
No full textWe describe an NMR approach based on the measurement of residual dipolar couplings (RDCs) to probe the structural and motional properties of the dynamic regions of the ribosome. Alignment of intact 70S ribosomes in filamentous bacteriophage enabled measurement of RDCs in the mobile C-terminal domain (CTD) of the stalk protein bL12. A structural refinement of this domain using the observed RDCs did not show large changes relative to the isolated protein in the absence of the ribosome, and we also found that alignment of the CTD was almost independent of the presence of the core ribosome particle, indicating that the inter-domain linker has significant flexibility. The nature of this linker was subsequently probed in more detail using a paramagnetic alignment strategy, which revealed partial propagation of alignment between neighbouring domains, providing direct experimental validation of a structural ensemble previously derived from SAXS and NMR relaxation measurements. Our results demonstrate the prospect of better characterising dynamical and functional regions of more challenging macromolecular machines and systems, for example ribosome–nascent chain complexes
Transient receptor potential channels in mechanosensing and cell volume regulation
No full textTransient receptor potential (TRP) channels are unique cellular sensors responding to a wide variety of extra- and intracellular signals, including mechanical and osmotic stress. In recent years, TRP channels from multiple subfamilies have been added to the list of mechano- and/or osmosensitive channels, and it is becoming increasingly apparent that Ca2+ influx via TRP channels plays a crucial role in the response to mechanical and osmotic perturbations in a wide range of cell types. Although the events translating mechanical and osmotic stimuli into regulation of TRP channels are still incompletely understood, the specific mechanisms employed vary between different TRIP isoforms, and probably include changes in the tension and/or curvature of the lipid bilayer, changes in the cortical cytoskeleton, and signaling events such as lipid metabolism and protein phosphorylation/ dephosphorylation. This chapter describes candidate mechanosensitive channels from mammalian TRP subfamilies, discusses inherent and technical issues potentially confounding evaluation of mechano- and/or osmosensitivity, and presents methods relevant to the study of TRP channel regulation by mechanical and osmotic stimuli and involvement in cell volume regulation.status: Publishe
- …
