title: Phosphorylation of transcriptional coactivator peroxisome proliferator-activated receptor (PPAR)-binding protein (PBP). Stimulation of transcriptional regulation by mitogen-activated protein kinase.
abstract: Peroxisome proliferator-activated receptor (PPAR)-binding protein (PBP) is an important coactivator for PPARgamma and other transcription factors. PBP is an integral component of a multiprotein thyroid hormone receptor-associated protein (TRAP)/vitamin D(3) receptor-interacting protein (DRIP)/activator-recruited cofactor (ARC) complex required for transcriptional activity. To study the regulation of PBP by cellular signaling pathways, we identified the phosphorylation sites of PBP. Using a combination of in vitro and in vivo approaches and mutagenesis of PBP phosphorylation sites, we identified six phosphorylation sites on PBP: one exclusive protein kinase A (PKA) phosphorylation site at serine 656, two protein kinase C (PKC) sites at serine 796 and serine 1345, a common PKA/PKC site at serine 756, and two extracellular signal-regulated kinase 2 sites of the mitogen-activated protein kinase (MAPK) family at threonine 1017 and threonine 1444. Binding of PBP to PPARgamma1 or retinoid-X-receptor for 9-cis-retinoic acid (RXR) is independent of their phosphorylation states, implying no changes in protein-protein interaction after modification by phosphorylation. Overexpression of RafBXB, an activated upstream kinase of the MAPK signal transduction pathway, exerts a significant additive inductive effect on PBP coactivator function. This effect is significantly diminished by overexpression of RafBXB301, a dominant negative mutant of RafBXB. These results identify phosphorylation as a regulatory modification event of PBP and demonstrate that PBP phosphorylation by Raf/MEK/MAPK cascade exerts a positive effect on PBP coactivator function. The functional role of PKA and PKC phosphorylation sites in PBP remains to be elucidated.
mesh_terms: D000818:Animals; D001483:Base Sequence; D019556:COS Cells; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D056913:Mediator Complex Subunit 1; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009838:Oligodeoxyribonucleotides; D010766:Phosphorylation; D011994:Recombinant Proteins / Q000378:metabolism; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors; D014158:Transcription, Genetic
chemical_list: D002352:Carrier Proteins; C538855:MED1 protein, human; D056913:Mediator Complex Subunit 1; D009838:Oligodeoxyribonucleotides; D011994:Recombinant Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D020928:Mitogen-Activated Protein Kinases