Identification of intermediate filament protein vimentin as an interacting protein of PPARγ
Date Issued
2008
Date
2008
Author(s)
Tsai, Yun-Chih
Abstract
Peroxisome proliferators activated receptor gamma (PPARγ) is a ligand activated transcription factor of the nuclear receptor family that regulates genes involved in differentiation, metabolism and immunity. Upon ligand binding, PPARγ releases bound corepressors and recruits coactivators for transcriptional activation. As a central signaling component, the activity of PPARγ is well regulated under various cellular processes. Mitogenic stimulation exerts negative regulation that suppresses PPARγ’s genomic activity. This downregulation is mediated largely by the extracellular signal regulated kinase 1/2 (ERKs)/mitogen activated protein kinases (MAPKs) signaling cascade. Upon mitogen and ligand stimulation, MEKs and ERKs rapidly translocate into the nucleus followed by ERK-mediated PPARγ phosphorylation on Serine 82/112. Upon binding onto the phosphorylated PPARγ, the NES in the MEKs then mediated the export of phosphorylated PPARγ out of the nucleus. This massive nuclear export reduces the ability of PPARγ to transactivate nuclear target genes and thereby inhibits its genomic function. However, the exact mechanism of nuclear export of PPARγ and the subsequent fate of cytoplasmic PPARγ remain further elucidated.ith advent of LC/MS/MS technique, we have identified a protein vimentin which was associated with PPARγ from the cell extracts of 3T3-L1 adipocytes upon induction of differentiation. During adipocyte differentiation, the expression of vimentin was increased in parallel of the increases of PPARγ. We confirmed the association of vimentin and PPARγ in the cytoplasmic compartment of 3T3-L1 adipocytes with immunoprecipitation-western blot and immunocytochemistry studies. Interestingly, vimentin was preferentially associated with the phospho-PPARγ especially after treatment of PPARγ ligand. ur data also suggest that phosphorylation of PPARγ appears after ligand treatment which leads to subsequent export of phosphorylated PPARγ to cytoplasm, at a leptomycin B-sensitive exportin 1/CRM1 dependent pathway, where interaction with vimentin occurs. Further detailed studies showed that the interaction of vimentin and pPPARγ may take place in mitochondria and ER in addition to the expected cytoskeleton in the insoluble portion of cell extracts.
Subjects
nuclear export
cellular compartment
nongenomic signaling
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