CAAT/Enhancer Binding Protein Activates an Enhancer in the Glutamine Synthetase Distal 5′-Flanking Sequence

• Published in: Archives of biochemistry and biophysics Vol. 397; no. 2; pp. 258 - 261
• Main Authors: Hadden, Timothy J., Ryou, Chongsuk, Zhu, Liping, Miller, Richard E.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15-01-2002
• Subjects: 3T3 Cells; adipocytes; Adipocytes - cytology; Animals; Base Sequence; Binding Sites; CAAT/enhancer binding proteins; CCAAT-Enhancer-Binding Proteins - metabolism; Cell Differentiation; diabetes mellitus; Enhancer Elements, Genetic; gene expression; Gene Expression Regulation, Enzymologic; Genes, Reporter; Glutamate-Ammonia Ligase - genetics; glutamine synthetase; Mice; Molecular Sequence Data; obesity; Receptors, Cytoplasmic and Nuclear - biosynthesis; Transcription Factors - biosynthesis; diabetes mellitus; CAAT/enhancer binding proteins; glutamine synthetase; adipocytes; gene expression; obesity
• ISSN: 0003-9861; 1096-0384
• DOI: 10.1006/abbi.2001.2666

The glutamine synthetase (GS) gene is expressed at high levels in several cell types, including astrocytes, pericentral hepatocytes, and adipocytes. During hormone-mediated adipocyte differentiation of 3T3-L1 cells, GS gene expression increases several hundred fold. We previously reported that elements in the distal 5′-flanking sequence and intron-1 participate in establishing the temporal pattern of GS transcription during adipocyte differentiation. To examine the role of the distal 5′-flanking region in regulating adipocyte-specific GS expression, GS–CAT fusion genes were constructed and analyzed in transiently transfected 3T3-L1 cells. In this way, adipocyte differentiation-responsive enhancer activity was localized to a 422-bp sequence that occurs about 3.5 kb upstream from the transcription start site. This sequence includes several putative C/EBP binding sites and is activated by ectopic expression of C/EBPα in NIH-3T3 cells. Thus, our data indicate that C/EBPα has the capacity to activate functional C/EBP sites in the GS gene distal 5′-flanking region.