title: Impaired Ras membrane association and activation in PPARalpha knockout mice after partial hepatectomy.
abstract: Liver regeneration after partial hepatectomy (PH) involves several signaling mechanisms including activation of the small GTPases Ras and RhoA in response to mitogens leading to DNA synthesis and cell proliferation. Peroxisome proliferator-activated receptor-alpha (PPARalpha) regulates the expression of several key enzymes in isoprenoid synthesis, which are key events for membrane association of Ras and RhoA. Thus the role of PPARalpha in cell proliferation after PH was tested. After PH, an increase in PPARalpha DNA binding was observed in wild-type mice, correlating with an increase in the PPARalpha-regulated enzyme acyl-CoA oxidase. In addition, the PPARalpha-regulated genes farnesyl pyrophosphate synthase and 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) synthase were significantly increased in wild-type mice. However, these increases were not observed in PPARalpha knockout (PPARalpha -/-) mice. The peak in DNA synthesis observed 42 h after PH was reduced by approximately 60% in PPARalpha -/- mice, despite increases in TNF-alpha and IL-1. Also, under these conditions, membrane association of Ras was high in wild-type mice after PH but was impaired in PPARalpha -/- mice. Accordingly, Ras was significantly elevated in the cytosol in PPARalpha -/- mice. This observation correlated with lower levels of active GTP-bound Ras after PH in PPARalpha -/- mice compared with wild-type mice. Similar observations were made for RhoA. Moreover, deletion of PPARalpha blunted the activation of cyclin-dependent kinase (cdk)2/cyclin E and cdk4/cyclin D complexes. Collectively, these results support the hypothesis that PPARalpha is necessary for cell cycle progression in regenerating mouse liver via mechanisms involving prenylation of small GTPases Ras and RhoA.
authors.affiliation: Laboratory of Hepatobiology and Toxicology, Department of Pharmacology, Curriculum in Toxicology, School of Medicine, University of North Carolina, Chapel Hill, North Carolina 27599, USA. wheelmi@med.unc.edu
authors.forename: Michael D
authors.initials: MD
authors.lastname: Wheeler
authors.forename: Olivia M
authors.initials: OM
authors.lastname: Smutney
authors.forename: Jennifer F
authors.initials: JF
authors.lastname: Check
authors.forename: Ivan
authors.initials: I
authors.lastname: Rusyn
authors.forename: R
authors.initials: R
authors.lastname: Schulte-Hermann
authors.forename: Ronald G
authors.initials: RG
authors.lastname: Thurman
mesh_terms: D000214:Acyl Coenzyme A / Q000378:metabolism; D000818:Animals; D000963:Antimetabolites; D015153:Blotting, Western; D001973:Bromodeoxyuridine; D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology; D002462:Cell Membrane / Q000378:metabolism; D016207:Cytokines / Q000096:biosynthesis; D003600:Cytosol / Q000378:metabolism; D004247:DNA / Q000096:biosynthesis; D024202:Electrophoretic Mobility Shift Assay; D004797:Enzyme-Linked Immunosorbent Assay; D006498:Hepatectomy; D008115:Liver Regeneration / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D023282:Nuclease Protection Assays; D011233:Precipitin Tests; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics*; D012260:Ribonucleases / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics*; D018631:ras Proteins / Q000378:metabolism*; D020742:rhoA GTP-Binding Protein / Q000378:metabolism
chemical_list: D000214:Acyl Coenzyme A; D000963:Antimetabolites; D016207:Cytokines; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors; D004247:DNA; D012260:Ribonucleases; D018631:ras Proteins; D020742:rhoA GTP-Binding Protein; D001973:Bromodeoxyuridine