Tumor necrosis factor-alpha inhibits peroxisome proliferator-activated receptor gamma activity at a posttranslational level in hepatic stellate cells.
Diminished activity of peroxisome proliferator-activated receptor gamma (PPARgamma) is implicated in activation of hepatic stellate cells (HSC), a critical event in the development of liver fibrosis. In the present study, we investigated PPARgamma regulation by TNF-alpha in an HSC line designated as BSC. In BSC, TNF-alpha decreased both basal and ligand (GW1929)-induced PPARgamma mRNA levels without changing its protein expression. Nuclear extracts from BSC treated with TNF-alpha showed decreased binding of PPARgamma to PPAR-responsive element (PPRE) as determined by electrophoretic mobility shift assay. In BSC transiently transfected with a PPARgamma1 expression vector and a PPRE-luciferase reporter gene, TNF-alpha decreased both basal and GW1929-induced transactivation of the PPRE promoter. TNF-alpha increased activation of ERK1/2 and JNK, previously implicated in phosphorylation of Ser(82) of PPARgamma1 and resultant negative regulation of PPARgamma transactivity. In fact, TNF-alpha failed to inhibit transactivity of a Ser(82)Ala PPARgamma1 mutant in BSC. TNF-alpha-mediated inhibition of PPARgamma transactivity was not blocked with a Ser(32)Ala/Ser(36)Ala mutant of inhibitory NF-kappaBalpha (IkappaBalpha). These results suggest that TNF-alpha inhibits PPARgamma transactivity in cultured HSC, at least in part, by diminished PPARgamma-PPRE (DNA) binding and ERK1/2-mediated phosphorylation of Ser(82) of PPARgamma1, but not via the NF-kappaB pathway.
Sung
Chin K
CK
Dept. of Pathology, Keck School of Medicine of the Univ. of Southern California, 1333 San Pablo St., MMR 412, Los Angeles, CA 90089-9141, USA.
She
Hongyun
H
Xiong
Shigang
S
Tsukamoto
Hidekazu
H
D000818:Animals; D001577:Benzophenones / Q000494:pharmacology; D002460:Cell Line; D004247:DNA / Q000378:metabolism; D004789:Enzyme Activation; D048031:JNK Mitogen-Activated Protein Kinases; D008099:Liver / Q000378:metabolism*; D008297:Male; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009154:Mutation; D016328:NF-kappa B / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011499:Protein Processing, Post-Translational / Q000187:drug effects*; D012333:RNA, Messenger / Q000037:antagonists & inhibitors; D051381:Rats; D017208:Rats, Wistar; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors* / Q000235:genetics*; D020218:Response Elements; D014157:Transcription Factors / Q000037:antagonists & inhibitors* / Q000235:genetics*; D014158:Transcription, Genetic / Q000187:drug effects; D015533:Transcriptional Activation / Q000187:drug effects; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000494:pharmacology
D001577:Benzophenones; D016328:NF-kappa B; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors; D014409:Tumor Necrosis Factor-alpha; D014443:Tyrosine; D004247:DNA; D048031:JNK Mitogen-Activated Protein Kinases; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; C120099:GW 1929