title: Identification and characterization of a nucleolar phosphoprotein, Nopp140, as a transcription factor.
abstract: Expression of the alpha-1 acid glycoprotein (AGP) gene (agp) is activated by a key transcription factor, AGP/enhancer-binding protein (AGP/EBP, commonly called C/EBP beta), in the liver during the acute-phase response. In addition to this positive regulation, agp is negatively regulated by nucleolin (T. H. Yang et al., Mol. Cell. Biol. 14:6068-6074, 1994). Other factors involve in positive regulation of the agp gene are poorly characterized. In a systematic search for factors that may interact with AGP/EBP, we have identified Nopp 140, a phosphoprotein of 140 kDa, by immunoaffinity chromatography. Nopp 140 not only functions as a transcriptional activator per se but also interacts with AGP/EBP to synergistically activate the agp gene in an AGP/EBP-binding motif-dependent manner. In addition to interacting with AGP/EBP, Nopp140 interacts specifically with TFIIB. Distinct regions of Nopp140 that interact with AGP/EBP and TFIIB have been characterized. The sequence of Nopp140 contains several stretches of serine- and acidic amino acid-rich sequences which are also found in ICP4 of herpes simplex virus type 1, a known transcription factor that interacts with TFIIB. The physical interaction between TFIIB and wild-type Nopp140 or several deletion mutants of Nopp140 correlates with the ability of Nopp140 to activate the agp gene synergistically with AGP/EBP. Thus, the molecular mechanism for agp gene activation may involve the interaction of AGP/EBP and TFIIB mediated by coactivator Nopp140.
authors.affiliation: Institute of Biochemical Sciences, College of Science, National Taiwan University, Taipei.
authors.forename: L H
authors.initials: LH
authors.lastname: Miau
authors.forename: C J
authors.initials: CJ
authors.lastname: Chang
authors.forename: W H
authors.initials: WH
authors.lastname: Tsai
authors.forename: S C
authors.initials: SC
authors.lastname: Lee
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D022762:CCAAT-Enhancer-Binding Proteins; D002466:Cell Nucleolus / Q000378:metabolism*; D003001:Cloning, Molecular; D004268:DNA-Binding Proteins / Q000378:metabolism; D005786:Gene Expression Regulation / Q000502:physiology*; D008099:Liver; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D009961:Orosomucoid / Q000235:genetics; D010750:Phosphoproteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D011485:Protein Binding; D051381:Rats; D015534:Trans-Activators / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D035581:Transcription Factor TFIIB; D014157:Transcription Factors / Q000378:metabolism; D015533:Transcriptional Activation
chemical_list: D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; C075564:NOLC1 protein, human; C513067:Nolc1 protein, rat; D009687:Nuclear Proteins; D009961:Orosomucoid; D010750:Phosphoproteins; D015534:Trans-Activators; D035581:Transcription Factor TFIIB; D014157:Transcription Factors