title: CHOP, a novel developmentally regulated nuclear protein that dimerizes with transcription factors C/EBP and LAP and functions as a dominant-negative inhibitor of gene transcription.
abstract: We report on the identification of a nuclear protein that serves as a dominant-negative inhibitor of the transcription factors C/EBP and LAP. A 32P-labeled LAP DNA-binding and dimerization domain "zipper probe" was used to isolate a clone that encodes a new C/EBP-homologous protein: CHOP-10. CHOP-10 has strong sequence similarity to C/EBP-like proteins within the bZIP region corresponding to the DNA-binding domain consisting of a leucine zipper and a basic region. Notably, however, CHOP-10 contains 2 prolines substituting for 2 residues in the basic region, critical for binding to DNA. Thus, heterodimers of CHOP-10 and C/EBP-like proteins are unable to bind their cognate DNA enhancer element. CHOP-10 mRNA is expressed in many different rat tissues. Antisera raised against CHOP-10 recognize a nuclear protein with an apparent molecular mass of 29 kD. CHOP-10 is induced upon differentiation of 3T3-L1 fibroblasts to adipocytes, and cytokine-induced dedifferentiation of adipocytes is preceded by the loss of nuclear CHOP-10. Coimmunoprecipitation of CHOP-10 and LAP from transfected COS-1 cells demonstrated a direct interaction between the two proteins, in vivo. Consistent with the structure of its defective basic region, bacterially expressed CHOP-10 inhibits the DNA-binding activity of C/EBP and LAP by forming heterodimers that cannot bind DNA. In transfected HepG2 cells, expression of CHOP-10 attenuates activation of C/EBP- and LAP-driven promoters. We suggest that CHOP-10 is a negative modulator of the activity of C/EBP-like proteins in certain terminally differentiated cells, similar to the regulatory function of Id on the activity of MyoD and MyoD-related proteins important in the development of muscle cells.
authors.affiliation: Laboratory of Molecular Endocrinology, Massachusetts General Hospital, Boston.
authors.forename: D
authors.initials: D
authors.lastname: Ron
authors.forename: J F
authors.initials: JF
authors.lastname: Habener
mesh_terms: D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D022762:CCAAT-Enhancer-Binding Proteins; D002455:Cell Division; D004247:DNA / Q000235:genetics; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D007150:Immunohistochemistry; D016350:Leucine Zippers; D051379:Mice; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D010957:Plasmids; D011233:Precipitin Tests; D012333:RNA, Messenger / Q000235:genetics; D016415:Sequence Alignment; D051742:Transcription Factor CHOP; D014157:Transcription Factors / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection
chemical_list: D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; C497250:Ddit3 protein, mouse; D009687:Nuclear Proteins; D012333:RNA, Messenger; D014157:Transcription Factors; D051742:Transcription Factor CHOP; D004247:DNA