CAAT/enhancer binding protein activates an enhancer in the glutamine synthetase distal 5'-flanking sequence.
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/EBPalpha in NIH-3T3 cells. Thus, our data indicate that C/EBPalpha has the capacity to activate functional C/EBP sites in the GS gene distal 5'-flanking region.
Hadden
Timothy J
TJ
Research Service, The John D. Dingell VA Medical Center, 4646 John R., Detroit, Michigan 48201, USA. thadden@cmb.biosci.wayne.edu
Ryou
Chongsuk
C
Zhu
Liping
L
Miller
Richard E
RE
D016475:3T3 Cells; D017667:Adipocytes / Q000166:cytology*; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D022762:CCAAT-Enhancer-Binding Proteins / Q000378:metabolism*; D002454:Cell Differentiation; D004742:Enhancer Elements, Genetic; D015971:Gene Expression Regulation, Enzymologic; D017930:Genes, Reporter; D005974:Glutamate-Ammonia Ligase / Q000235:genetics*; D051379:Mice; D008969:Molecular Sequence Data; D018160:Receptors, Cytoplasmic and Nuclear / Q000096:biosynthesis; D014157:Transcription Factors / Q000096:biosynthesis
D022762:CCAAT-Enhancer-Binding Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors; D005974:Glutamate-Ammonia Ligase