Serum components and activated Ha-ras antagonize expression of perivenous marker genes stimulated by beta-catenin signaling in mouse hepatocytes.
Hepatocytes of the periportal and perivenous zones of the liver lobule show marked differences in the contents and activities of many enzymes and other proteins. Previous studies from our and other groups have pointed towards an important role of beta-catenin-dependent signaling in the regulation of expression of genes encoding proteins with preferential perivenous localization, whereas, in contrast, signaling through Ras-dependent pathway(s) may induce a 'periportal' phenotype. We have now conducted a series of experiments to further investigate this hypothesis. In transgenic mice with scattered expression of an activated Ha-ras (Ha-ras(G12V)) mutant in liver, expression of the perivenous markers glutamine synthetase and two cytochrome P450 isoforms was completely abolished in those hepatocytes demonstrating constitutively activated extracellular signal-regulated kinase activity, even though they were located directly adjacent to central veins. Similarly, incubation of primary hepatocytes or hepatoma cells with increasing amounts of serum caused a concentration-dependent attenuation of expression of perivenous marker mRNAs, whereas the expression of periportal markers was increased. The inhibitory effect of high amounts of serum on the expression of perivenous markers was also observed if their expression was stimulated by activation of beta-catenin signaling, and comparable inhibitory effects were seen in cells stably transfected with a T-cell factor/lymphoid-enhancing factor-driven luciferase reporter. Epidermal growth factor could partly mimic serum effects in hepatoma cells, and its effect could be blocked by an inhibitor of extracellular signal-regulated kinase activity. These data suggest that activation of the Ras/mitogen-activated protein kinase (extracellular signal-regulated kinase) pathway favors periportal gene expression while simultaneously antagonizing a perivenous phenotype of hepatocytes.
Braeuning
Albert
A
Institute of Pharmacology und Toxicology, Department of Toxicology, University of Tuebingen, Germany.
Menzel
Moritz
M
Kleinschnitz
Eva-Maria
EM
Harada
Naomoto
N
Tamai
Yoshitaka
Y
Köhle
Christoph
C
Buchmann
Albrecht
A
Schwarz
Michael
M
D000818:Animals; D060466:Axin Protein; D015415:Biomarkers; D006528:Carcinoma, Hepatocellular / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics; D003598:Cytoskeletal Proteins / Q000235:genetics; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects*; D005974:Glutamate-Ammonia Ligase / Q000235:genetics; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D015689:Oncogene Protein p21(ras) / Q000235:genetics / Q000378:metabolism*; D044967:Serum / Q000737:chemistry*; D015398:Signal Transduction; D051820:TCF Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects; D051176:beta Catenin / Q000378:metabolism*
D060466:Axin Protein; C111729:Axin2 protein, mouse; D015415:Biomarkers; D003598:Cytoskeletal Proteins; D051820:TCF Transcription Factors; D051176:beta Catenin; D003577:Cytochrome P-450 Enzyme System; D048049:Extracellular Signal-Regulated MAP Kinases; D015689:Oncogene Protein p21(ras); D005974:Glutamate-Ammonia Ligase