Glucagon induces the gene expression of aquaporin-8 but not that of aquaporin-9 water channels in the rat hepatocyte

2009 ◽  
Vol 296 (4) ◽  
pp. R1274-R1281 ◽  
Author(s):  
Leandro R. Soria ◽  
Sergio A. Gradilone ◽  
M. Cecilia Larocca ◽  
Raúl A. Marinelli
Keyword(s):  
Gene Expression ◽  
Rna Polymerase Ii ◽  
Rat Hepatocytes ◽  
Water Channels ◽  
Bile Secretion ◽  
Signal Pathways ◽  
Rat Hepatocyte ◽  
Confocal Immunofluorescence Microscopy ◽  
Aquaporin 9 ◽  
Additional Support

Glucagon stimulates the vesicle trafficking of aquaporin-8 (AQP8) water channels to the rat hepatocyte canalicular membranes, a process thought to be relevant to glucagon-induced bile secretion. In this study, we investigated whether glucagon is able to modulate the gene expression of hepatocyte AQP8. Glucagon was administered to rats at 0.2 mg/100 g body wt ip in 2, 3, or 6 equally spaced doses for 8, 16, and 36 h, respectively. Immunoblotting analysis showed that hepatic 34-kDa AQP8 was significantly increased by 79 and 107% at 16 and 36 h, respectively. Hepatic AQP9 protein expression remained unaltered. AQP8 mRNA expression, assessed by real-time PCR, was not modified over time, suggesting a posttranscriptional mechanism of AQP8 protein increase. Glucagon effects on AQP8 were directly studied in primary cultured rat hepatocytes. Immunoblotting and confocal immunofluorescence microscopy confirmed the specific glucagon-induced AQP8 upregulation. The RNA polymerase II inhibitor actinomycin D was unable to prevent glucagon effect, providing additional support to the nontranscriptional upregulation of AQP8. Cycloheximide also showed no effect, suggesting that glucagon-induced AQP8 expression does not depend on protein synthesis but rather on protein degradation. Inhibitory experiments suggest that a reduced calpain-mediated AQP8 proteolysis could be involved. The action of glucagon on hepatocyte AQP8 was mimicked by dibutyryl cAMP and suppressed by PKA or phosphatidylinositol-3-kinase (PI3K) inhibitors. In conclusion, our data suggest that glucagon induces the gene expression of rat hepatocyte AQP8 by reducing its degradation, a process that involves cAMP-PKA and PI3K signal pathways.

Altered expression and distribution of aquaporin-9 in the liver of rat with obstructive extrahepatic cholestasis

2008 ◽  
Vol 295 (4) ◽  
pp. G682-G690 ◽  
Author(s):  
Giuseppe Calamita ◽  
Domenico Ferri ◽  
Patrizia Gena ◽  
Flavia I. Carreras ◽  
Giuseppa E. Liquori ◽  
...  
Keyword(s):  
Basolateral Membrane ◽  
Rat Hepatocytes ◽  
Bile Secretion ◽  
Simultaneous Increase ◽  
Immunogold Electron Microscopy ◽  
Transcriptional Level ◽  
Extrahepatic Cholestasis ◽  
Altered Expression ◽  
Aquaporin 9 ◽  
Duct Ligation

Rat hepatocytes express aquaporin-9 (AQP9), a basolateral channel permeable to water, glycerol, and other small neutral solutes. Although liver AQP9 is known for mediating the uptake of sinusoidal blood glycerol, its relevance in bile secretion physiology and pathophysiology remains elusive. Here, we evaluated whether defective expression of AQP9 is associated to secretory dysfunction of rat hepatocytes following bile duct ligation (BDL). By immunoblotting, 1-day BDL resulted in a slight decrease of AQP9 protein in basolateral membranes and a simultaneous increase of AQP9 in intracellular membranes. This pattern was steadily accentuated in the subsequent days of BDL since at 7 days BDL basolateral membrane AQP9 decreased by 85% whereas intracellular AQP9 increased by 115%. However, the AQP9 immunoreactivity of the total liver membranes from day 7 of BDL rats was reduced by 49% compared with the sham counterpart. Results were confirmed by immunofluorescence and immunogold electron microscopy and consistent with biophysical studies showing considerable decrease of the basolateral membrane water and glycerol permeabilities of cholestatic hepatocytes. The AQP9 mRNA was slightly reduced only at day 7 of BDL, indicating that the dysregulation was mainly occurring at a posttranslational level. The altered expression of liver AQP9 during BDL was not dependent on insulin, a hormone known to negatively regulate AQP9 at a transcriptional level, since insulinemia was unchanged in 7-day BDL rats. Overall, these results suggest that extrahepatic cholestasis leads to downregulation of AQP9 in the hepatocyte basolateral plasma membrane and dysregulated aquaporin channels contribute to bile flow dysfunction of cholestatic hepatocyte.

scholarly journals The Water Channel Aquaporin-8 Is Mainly Intracellular in Rat Hepatocytes, and Its Plasma Membrane Insertion Is Stimulated by Cyclic AMP

2001 ◽  
Vol 276 (15) ◽  
pp. 12147-12152 ◽  
Author(s):  
Fabiana Garcı́a ◽  
Arlinet Kierbel ◽  
M. Cecilia Larocca ◽  
Sergio A. Gradilone ◽  
Patrick Splinter ◽  
...  
Keyword(s):  
Water Transport ◽  
Water Permeability ◽  
Plasma Membranes ◽  
Water Channel ◽  
Rat Hepatocytes ◽  
Immunoblot Analysis ◽  
Subcellular Fractionation ◽  
Bile Secretion ◽  
Confocal Immunofluorescence Microscopy ◽  
Microsomal Membranes

We previously found that water transport across hepatocyte plasma membranes occurs mainly via a non-channel mediated pathway. Recently, it has been reported that mRNA for the water channel, aquaporin-8 (AQP8), is present in hepatocytes. To further explore this issue, we studied protein expression, subcellular localization, and regulation of AQP8 in rat hepatocytes. By subcellular fractionation and immunoblot analysis, we detected anN-glycosylated band of ∼34 kDa corresponding to AQP8 in hepatocyte plasma and intracellular microsomal membranes. Confocal immunofluorescence microscopy for AQP8 in cultured hepatocytes showed a predominant intracellular vesicular localization. Dibutyryl cAMP (Bt2cAMP) stimulated the redistribution of AQP8 to plasma membranes. Bt2cAMP also significantly increased hepatocyte membrane water permeability, an effect that was prevented by the water channel blocker dimethyl sulfoxide. The microtubule blocker colchicine but not its inactive analog lumicolchicine inhibited the Bt2cAMP effect on both AQP8 redistribution to cell surface and hepatocyte membrane water permeability. Our data suggest that in rat hepatocytes AQP8 is localized largely in intracellular vesicles and can be redistributed to plasma membranes via a microtubule-depending, cAMP-stimulated mechanism. These studies also suggest that aquaporins contribute to water transport in cAMP-stimulated hepatocytes, a process that could be relevant to regulated hepatocyte bile secretion.

scholarly journals IL-1β and IL-6 modulate apolipoprotein E gene expression in rat hepatocyte primary culture

1992 ◽  
Vol 1 (5) ◽  
pp. 329-333 ◽  
Author(s):  
Agnes Ribeiro ◽  
Marise Mangeney ◽  
Isabelle Bernard ◽  
Jean Chambaz ◽  
Francisco Delers
Keyword(s):  
Gene Expression ◽  
Primary Culture ◽  
Inflammatory Cytokines ◽  
Acute Phase Response ◽  
Rat Hepatocytes ◽  
Rat Hepatocyte ◽  
Apolipoprotein E Gene ◽  
Cultured Rat Hepatocytes ◽  
Apoe Mrna ◽  
Hepatocyte Primary Culture

Incubation of rat hepatocytes in primary culture with IL-1β at a concentration of 2.5 units/ml resulted in an increase (+80%) in the amount of apoE mRNA without any effect upon apoE synthesis. IL-6 at a low concentration (10 units/ml) induced a decrease (−35%) in the amount of apoE mRNA, but increased apoE synthesis (+28%). No effect was observed with higher concentrations of IL-1β (10 units/ml) or IL-6 (100 units/ml). These results suggest that inflammatory cytokines IL-1β and IL-6 modulate the expression of apoE gene in cultured rat hepatocytes, at a concentration that does not induce the acute phase response.

Linking transcription, RNA polymerase II elongation and alternative splicing

2020 ◽  
Vol 477 (16) ◽  
pp. 3091-3104 ◽  
Author(s):  
Luciana E. Giono ◽  
Alberto R. Kornblihtt
Keyword(s):  
Gene Expression ◽  
Alternative Splicing ◽  
Rna Polymerase Ii ◽  
Environmental Changes ◽  
Transcription Elongation ◽  
Single Gene ◽  
Regulation Of Gene Expression ◽  
Regulation Of Transcription ◽  
Stepping Stones ◽  
Eukaryotic Transcription

Gene expression is an intricately regulated process that is at the basis of cell differentiation, the maintenance of cell identity and the cellular responses to environmental changes. Alternative splicing, the process by which multiple functionally distinct transcripts are generated from a single gene, is one of the main mechanisms that contribute to expand the coding capacity of genomes and help explain the level of complexity achieved by higher organisms. Eukaryotic transcription is subject to multiple layers of regulation both intrinsic — such as promoter structure — and dynamic, allowing the cell to respond to internal and external signals. Similarly, alternative splicing choices are affected by all of these aspects, mainly through the regulation of transcription elongation, making it a regulatory knob on a par with the regulation of gene expression levels. This review aims to recapitulate some of the history and stepping-stones that led to the paradigms held today about transcription and splicing regulation, with major focus on transcription elongation and its effect on alternative splicing.

Nutrient-regulated gene expression in eukaryotes

2006 ◽  
Vol 73 ◽  
pp. 85-96 ◽  
Author(s):  
Richard J. Reece ◽  
Laila Beynon ◽  
Stacey Holden ◽  
Amanda D. Hughes ◽  
Karine Rébora ◽  
...  
Keyword(s):  
Gene Expression ◽  
Rna Polymerase ◽  
Rna Polymerase Ii ◽  
Transcriptional Control ◽  
Direct Interaction ◽  
Signalling Pathways ◽  
A Cell ◽  
One Step ◽  
Higher Eukaryotes ◽  
Regulated Gene Expression

The recognition of changes in environmental conditions, and the ability to adapt to these changes, is essential for the viability of cells. There are numerous well characterized systems by which the presence or absence of an individual metabolite may be recognized by a cell. However, the recognition of a metabolite is just one step in a process that often results in changes in the expression of whole sets of genes required to respond to that metabolite. In higher eukaryotes, the signalling pathway between metabolite recognition and transcriptional control can be complex. Recent evidence from the relatively simple eukaryote yeast suggests that complex signalling pathways may be circumvented through the direct interaction between individual metabolites and regulators of RNA polymerase II-mediated transcription. Biochemical and structural analyses are beginning to unravel these elegant genetic control elements.

GLIOBLASTOMA MULTIFORME: PATHOGENESIS AND MOLECULAR MARKERS

2017 ◽  
Vol 63 (5) ◽  
pp. 695-702
Author(s):  
Oleg Kit ◽  
Dmitriy Vodolazhskiy ◽  
Yelena Frantsiyants ◽  
Svetlana Panina ◽  
E. Rastorguev ◽  
...  
Keyword(s):  
Gene Expression ◽  
Brain Tumor ◽  
Molecular Markers ◽  
Glioblastoma Multiforme ◽  
Somatic Mutations ◽  
Web Of Science ◽  
Molecular Subtypes ◽  
Regulation Of Gene Expression ◽  
Signal Pathways ◽  
Poorly Differentiated

Glioblastoma multiforme (GBM) is the most common and invasive poorly differentiated brain tumor with nearly 100 % rate of recurrence and unfavorable prognosis. The aim of the present review is to analyze recent studies and experimental results (Scopus, Web of Science, PubMed) concerning somatic mutations in glioblastoma, aberrant regulation of gene expression of signal pathways including EGFR, TGFß, etc. and markers for GBM progression. Particularly the molecular subtypes of glioblastoma and NGS results are considered in this review.

scholarly journals Commuting to Work: Nucleolar Long Non-Coding RNA Control Ribosome Biogenesis from Near and Far

2021 ◽  
Vol 7 (3) ◽  
pp. 42
Author(s):  
Victoria Mamontova ◽  
Barbara Trifault ◽  
Lea Boten ◽  
Kaspar Burger
Keyword(s):  
Gene Expression ◽  
Rna Polymerase Ii ◽  
Ribosome Biogenesis ◽  
Intergenic Spacer ◽  
Cellular Growth ◽  
Rrna Synthesis ◽  
Protein Coding ◽  
Non Coding Rna ◽  
And Function ◽  
In Cis

Gene expression is an essential process for cellular growth, proliferation, and differentiation. The transcription of protein-coding genes and non-coding loci depends on RNA polymerases. Interestingly, numerous loci encode long non-coding (lnc)RNA transcripts that are transcribed by RNA polymerase II (RNAPII) and fine-tune the RNA metabolism. The nucleolus is a prime example of how different lncRNA species concomitantly regulate gene expression by facilitating the production and processing of ribosomal (r)RNA for ribosome biogenesis. Here, we summarise the current findings on how RNAPII influences nucleolar structure and function. We describe how RNAPII-dependent lncRNA can both promote nucleolar integrity and inhibit ribosomal (r)RNA synthesis by modulating the availability of rRNA synthesis factors in trans. Surprisingly, some lncRNA transcripts can directly originate from nucleolar loci and function in cis. The nucleolar intergenic spacer (IGS), for example, encodes nucleolar transcripts that counteract spurious rRNA synthesis in unperturbed cells. In response to DNA damage, RNAPII-dependent lncRNA originates directly at broken ribosomal (r)DNA loci and is processed into small ncRNA, possibly to modulate DNA repair. Thus, lncRNA-mediated regulation of nucleolar biology occurs by several modes of action and is more direct than anticipated, pointing to an intimate crosstalk of RNA metabolic events.

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