Journal of Biochemistry Advance Access originally published online on March 2, 2009
Journal of Biochemistry 2009 145(6):771-781; doi:10.1093/jb/mvp035
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Simvastatin Suppresses Leptin Expression in 3T3-L1 Adipocytes via Activation of the Cyclic AMP–PKA Pathway Induced by Inhibition of Protein Prenylation
Section of Biochemistry, Department of Oral Function and Molecular Biology, Ohu University School of Dentistry, Koriyama 963-8611, Japan
*To whom correspondence should be addressed. Tel/Fax: +81-24-938-9192, E-mail: n-horiuchi{at}den.ohu-u.ac.jp
Received February 8, 2009; Accepted February 23, 2009
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Abstract |
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Simvastatin inhibits 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, which catalyses conversion of HMG-CoA to mevalonate, a rate-limiting step in cholesterol synthesis. We demonstrated that simvastatin at 1 µM markedly inhibited adipocyte differentiation measured by Oil Red O staining in preadipocyte cells (3T3-L1), while expression of leptin, a marker of adipocyte differentiation, was suppressed by 1 µM simvastatin for up to 12 days of culture. Next, to elucidate mechanisms underlying the reduction of leptin expression induced by simvastatin, differentiated 3T3-L1 adipocytes were treated with various inhibitors with mevalonate or its metabolite in the presence or absence of simvastatin. Simvastatin time- and dose-dependently suppressed leptin mRNA expression. Heterogeneous nuclear RNA related to leptin mRNA was inhibited by 10 µM simvastatin, while stability of the mRNA was not changed by treatment with simvastatin in transcription-arrested 3T3-L1 cells. Simvastatin inhibition of leptin gene transcription was not abrogated by pre-treatment with cycloheximide, an inhibitor of protein synthesis. Addition of mevalonate or geranylgeranyl pyrophosphate (GGPP), a mevalonate metabolite, abolished simvastatin-induced inhibition of leptin expression in 3T3-L1 cells. Suppression of expression was observed upon addition of GGTI-298, a geranylgeranyl transferase I inhibitor, but not FTI-277, a farnesyl transferase inhibitor. Expression was suppressed by treatment with hydroxyfasudil, a protein prenylation inhibitor. Treatment with phosphatidylinositol 3-kinase (PI3K) inhibitors, LY294002 and wortmannin, reduced leptin expression in 3T3-L1 cells. Simvastatin dose-dependently increased intra-cellular cyclic AMP (cAMP) concentrations in 3T3-L1 cells, with maximal stimulation obtained at 10 µM. Addition of GGPP abolished simvastatin-induced stimulation of cAMP accumulation and protein kinase A (PKA) activity. H89, an inhibitor of PKA, completely abolished simvastatin-induced suppression of leptin expression. These results suggested that simvastatin reduced geranylgeranylprotein prenylation followed by deactivation of PI3K, leading to cAMP accumulation and subsequent activation of PKA in differentiated 3T3-L1 adipocytes. Finally, PKA inhibited leptin gene transcription without new protein synthesis.
Key Words: statins, leptin, adipocyte differentiation, HMG-CoA reductase, prenylation, protein kinase A
Abbreviations:
aP2, adipocyte-specific protein 2; BMP-2, bone morphogenetic protein-2; cAMP, cyclic AMP; C/EBPβ, CCAAT/enhancer-binding protein β; CREB, cAMP responsive element binding protein; DMEM medium, Dulbecco's; modified Eagle's; medium; DRB, 5,6-dichlorobenzimidazole riboside; ELISA, enzyme-linked immunosorbent assay; FBS, fetal bovine serum; FPP, farnesyl pyrophosphate; GGPP, geranylgeranyl pyrophosphate; Glut4, glucose transporter 4; HMG-CoA, 3-hydroxy-3-methylglutaryl-coenzyme A; hnRNA, heterogeneous nuclear RNA; IBMX, 3-isobutyl-1-methylxanthine; LPL, lipoprotein lipase; MAPK, mitogen activated kinase; ob/ob, leptin deficient; PDE3B, phosphodiesterase 3B; PI3K, phosphatidylinositol 3-kinase; PKA, protein kinase A; PPAR
, peroxisome proliferation-activator receptor ; RT-PCR, reverse transcriptase-polymerase chain reactions; Runx2, Runt-related transcription factor 2; TG, triglycerides