Impaired Ras membrane association and activation in PPARα 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.

Blunted DNA synthesis and delayed S-phase entry following inhibition of Cdk2 activity in the regenerating rat liver

“…Ras might also provide a link between the cyclin D/Cdk4 and the cyclin E/Cdk2 complex in cycling hepatocytes. 34,35 Therefore, the observation of similar upregulation of ras in rats administered the active compound compared to controls constitutes an additional argument for normal early cell cycle progression underscoring that CYC202 specifically inhibits late G1-S-phase transition, blunting cell proliferation.…”

Impaired liver regeneration and increased oval cell numbers following T cell–mediated hepatitis

“…17 Animal Model of pHx. Male mice were anesthetized with 50 mg/kg sodium pentobarbital, and a 70% hepatectomy or sham surgery was performed as described 18 by the removal of the median and left lateral lobes. After 0, 6, 24, or 48 hours, the mice were euthanized, and serum and tissue were collected.…”

Effects of Insulin Replacements, Inhibitors of Angiotensin, and PKCβ's Actions to Normalize Cardiac Gene Expression and Fuel Metabolism in Diabetic Rats

“…Activity of peroxisome proliferatoractivated receptor (PPAR)␣ was measured by an electrophoretic mobility shift assay probe (5Ј-AAAAACTGGGCCAAAGGTCT-3Ј) using a kit commercially available from Panomics (Redwood City, CA) according to the manufacturer's instructions. This assay has been previously validated and described (18). Heart membrane PKC activity assay.…”