title: Peroxisome proliferator-activated receptor-gamma1 is dephosphorylated and degraded during BAY 11-7085-induced synovial fibroblast apoptosis.
abstract: Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) plays a central role in whole body metabolism by regulating adipocyte differentiation and energy storage. Recently, however, PPAR-gamma has also been demonstrated to affect proliferation, differentiation, and apoptosis of different cell types. As we have previously shown that BAY 11-7085-induced synovial fibroblast apoptosis is prevented by PPAR-gamma agonist 15d-PGJ2; the expression of PPAR-gamma in these cells was studied. Both PPAR-gamma1 and PPAR-gamma2 isoforms were cloned from synovial fibroblast RNA, but only PPAR-gamma1 was detected by Western blot, showing constitutive nuclear expression. Within minutes of BAY 11-7085 treatment, a PPAR-gamma1-specific band was shifted into a form of higher mobility, suggesting dephosphorylation, as confirmed by phosphatase treatment of cell extracts. Of interest, BAY 11-7085-induced PPAR-gamma1 dephosphorylation was followed by PARP and caspase-8 cleavage as well as by PPAR-gamma1 protein degradation. PPAR-gamma1 dephosphorylation was followed by the loss of PPAR-DNA binding activity ubiquitously present in synovial fibroblast nuclear extracts. Unlike the phosphorylated form, dephosphorylated PPAR-gamma1 was found in insoluble membrane cell fraction and was not ubiquitinated before degradation. PPAR-gamma1 dephosphorylation coincided with ERK1/2 phosphorylation that accompanies BAY 11-7085-induced synovial fibroblasts apoptosis. 15d-PGJ2, PGD2, and partially UO126, down-regulated ERK1/2 phosphorylation, protected cells from BAY 11-7085-induced apoptosis, and reversed both PPAR-gamma dephosphorylation and degradation. Furthermore, PPAR-gamma antagonist BADGE induced PPAR-gamma1 degradation, ERK1/2 phosphorylation, and synovial fibroblasts apoptosis. The results presented suggest an anti-apoptotic role for PPAR-gamma1 in synovial fibroblasts. Since apoptotic marker PARP is cleaved after PPAR-gamma1 dephosphorylation but before PPAR-gamma1 degradation, dephosphorylation event might be enough to mediate BAY 11-7085-induced apoptosis in synovial fibroblasts.
authors.affiliation: Center for Biomedical Integrative Genoproteomics (CBIG), Department of Rheumatology, Department of Medical Chemistry and Human Genetics and Department of Orthopedic Surgery, University of Liège, 4000 Liège, Belgium.
authors.forename: Biserka
authors.initials: B
authors.lastname: Relic
authors.forename: Valérie
authors.initials: V
authors.lastname: Benoit
authors.forename: Nathalie
authors.initials: N
authors.lastname: Franchimont
authors.forename: Marie-Joelle
authors.initials: MJ
authors.lastname: Kaiser
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Hauzeur
authors.forename: Philippe
authors.initials: P
authors.lastname: Gillet
authors.forename: Marie-Paule
authors.initials: MP
authors.lastname: Merville
authors.forename: Vincent
authors.initials: V
authors.lastname: Bours
authors.forename: Michel G
authors.initials: MG
authors.lastname: Malaise
mesh_terms: D017209:Apoptosis; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism / Q000473:pathology*; D015870:Gene Expression; D006801:Humans; D009570:Nitriles / Q000494:pharmacology*; D010003:Osteoarthritis / Q000378:metabolism; D047495:PPAR gamma / Q000737:chemistry* / Q000378:metabolism; D010766:Phosphorylation; D015230:Prostaglandin D2 / Q000031:analogs & derivatives / Q000378:metabolism; D013450:Sulfones / Q000494:pharmacology*; D013583:Synovial Membrane / Q000473:pathology; D014162:Transfection
chemical_list: C477819:15-deoxyprostaglandin J2; C416282:BAY 11-7085; D009570:Nitriles; D047495:PPAR gamma; D013450:Sulfones; D015230:Prostaglandin D2