title: Interaction and cooperation of the CCAAT-box enhancer-binding protein β (C/EBPβ) with the homeodomain-interacting protein kinase 2 (Hipk2).
abstract: CCAAT box/enhancer-binding protein β (C/EBPβ) is a bZip transcription factor that plays crucial roles in important cellular processes such as differentiation and proliferation of specific cell types. Previously, we showed that C/EBPβ cooperates with the coactivator p300 through a novel mechanism that involves the C/EBPβ-induced phosphorylation of multiple sites in the carboxyl-terminal domain of p300 by protein kinase Hipk2. We have now examined the interaction and cooperation of C/EBPβ, p300, and Hipk2 in more detail. We show that Hipk2 and C/EBPβ are direct physical binding partners whose interaction is mediated by sequences located in the amino-terminal and central domains of Hipk2 and the amino-terminal part of C/EBPβ. In addition to phosphorylating p300 recruited to C/EBPβ, Hipk2 also phosphorylates C/EBPβ at sites that have previously been shown to plays key roles in the regulation of C/EBPβ activity. Silencing of Hipk2 expression disrupts adipocyte differentiation of 3T3-L1 cells, a physiological C/EBPβ-dependent differentiation process indicating that the cooperation of C/EBPβ and Hipk2 is functionally relevant. Finally, we demonstrate that C/EBPα, a related C/EBP family member whose amino-terminal sequences differ significantly from that of C/EBPβ, is unable to interact and cooperate with Hipk2. Instead, our data suggest that C/EBPα cooperates with the protein kinase Jnk to induce phosphorylation of p300. Overall, our data identify Hipk2 as a novel regulator of C/EBPβ and implicate different protein kinases in the cooperation of p300 with C/EBPβ and C/EBPα.
authors.affiliation: Institut für Biochemie, Westfälische-Wilhelms-Universität Münster, Wilhelm-Klemm-Strasse 2, D-48149 Münster, Germany.
authors.forename: Simone
authors.initials: S
authors.lastname: Steinmann
authors.forename: Anna
authors.initials: A
authors.lastname: Coulibaly
authors.forename: Johanna
authors.initials: J
authors.lastname: Ohnheiser
authors.forename: Anke
authors.initials: A
authors.lastname: Jakobs
authors.forename: Karl-Heinz
authors.initials: KH
authors.lastname: Klempnauer
mesh_terms: D041721:3T3-L1 Cells; D000595:Amino Acid Sequence; D000818:Animals; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000737:chemistry / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D002454:Cell Differentiation; D002460:Cell Line; D051379:Mice; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid
chemical_list: D022782:CCAAT-Enhancer-Binding Protein-beta; D002352:Carrier Proteins; C492003:Hipk2 protein, mouse; D017346:Protein Serine-Threonine Kinases
keywords: C/EBPβ; Hipk2; Phosphorylation; Protein Kinases; Protein-Protein Interactions; Transcription; p300