title: Phosphorylation prevents C/EBPβ from the calpain-dependent degradation.
abstract: CCAAT/enhancer-binding protein (C/EBP) β plays an important role in proliferation and differentiation of 3T3-L1 preadipocytes. C/EBPβ is sequentially phosphorylated during the 3T3-L1 adipocyte differentiation program, first by MAPK/Cyclin A/cdk2 on Thr(188) and subsequently by GSK3β on Ser(184) or Thr(179). Dual phosphorylation is critical for the gain of DNA binding activity of C/EBPβ. In this manuscript, we found that phosphorylation also contributed to the stability of C/EBPβ. Both ex vivo and in vitro experiments showed that phosphorylation by MAPK/Cyclin A/cdk2 and GSK3β protected C/EBPβ from μ-calpain-mediated proteolysis, while phosphorylation on Thr(188) by MAPK/Cyclin A/cdk2 contributed more to the stabilization of C/EBPβ, Further studies indicated that phosphorylation mimic C/EBPβ was insensitive to both calpain accelerator and calpain inhibitor. Thus, phosphorylation might contribute to the stability as well as the gain of DNA binding activity of C/EBPβ.
authors.affiliation: Key Laboratory of Molecular Medicine, The Ministry of Education, Department of Biochemistry and Molecular Biology, Fudan University, Shanghai Medical College, PR China.
authors.forename: Yuan-yuan
authors.initials: YY
authors.lastname: Zhang
authors.forename: Shu-fen
authors.initials: SF
authors.lastname: Li
authors.forename: Shu-wen
authors.initials: SW
authors.lastname: Qian
authors.forename: You-you
authors.initials: YY
authors.lastname: Zhang
authors.forename: Yuan
authors.initials: Y
authors.lastname: Liu
authors.forename: Qi-Qun
authors.initials: QQ
authors.lastname: Tang
authors.forename: Xi
authors.initials: X
authors.lastname: Li
mesh_terms: D041721:3T3-L1 Cells; D017667:Adipocytes / Q000378:metabolism; D000818:Animals; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000235:genetics / Q000378:metabolism*; D002154:Calpain / Q000378:metabolism*; D019925:Cyclin A / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2 / Q000235:genetics / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D051379:Mice; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D010766:Phosphorylation; D055550:Protein Stability; D059748:Proteolysis
chemical_list: D022782:CCAAT-Enhancer-Binding Protein-beta; C545013:Cebpb protein, mouse; D019925:Cyclin A; D051357:Cyclin-Dependent Kinase 2; D020929:Mitogen-Activated Protein Kinase Kinases; D002154:Calpain; C449002:mu-calpain