The cAMP response element binding protein synergizes with other transcription factors to mediate cAMP responsiveness.
The cAMP responsiveness of the promoter for phosphoenolpyruvate carboxykinase (EC 4.1.1.32) is mediated by a synergistic interaction between a complex regulatory region, which binds liver-enriched transcription factors, and a typical cAMP response element (CRE). Although a role for the CRE-binding protein (CREB) in the cAMP-responsiveness of this promoter has been generally assumed, some uncertainty remains due to the observations that several C/EBP-related proteins bind with near equal affinity, relative to CREB, to this particular CRE. Thus, a detailed analysis of the involvement of CREB in this synergism was undertaken in HepG2 cells. Gel mobility shift assays demonstrate that a CRE probe is bound by CREB present in HepG2 cells. Furthermore, we show that a dominant repressor of CREB is able to significantly reduce the cAMP responsiveness of the PEPCK promoter in HepG2 cells. Finally, we demonstrate using a GAL4-CREB fusion protein that CREB is able to synergize with the liver-enriched factors bound upstream on the PEPCK promoter to mediate a liver-specific response to cAMP. Examination of several mutant forms of CREB allow us to conclude that the "synergy" domain of CREB resides within amino acid residues 83-203, and that residues 83-145 can mediate a partial synergistic response. This study establishes that CREB is able to synergize with liver-enriched transcription factors to mediate a tissue-specific response to cAMP.
Roesler
W J
WJ
Department of Biochemistry, College of Medicine, University of Saskatchewan, Saskatoon, Canada.
Graham
J G
JG
Kolen
R
R
Klemm
D J
DJ
McFie
P J
PJ
D000595:Amino Acid Sequence; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism*; D017362:Cyclic AMP Response Element-Binding Protein / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008099:Liver / Q000378:metabolism; D008969:Molecular Sequence Data; D010729:Phosphoenolpyruvate Carboxykinase (GTP) / Q000235:genetics; D011401:Promoter Regions, Genetic; D029701:Saccharomyces cerevisiae Proteins; D016415:Sequence Alignment; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
D017362:Cyclic AMP Response Element-Binding Protein; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; C052130:GAL4 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D000242:Cyclic AMP; D010729:Phosphoenolpyruvate Carboxykinase (GTP)