Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.3.1.28 (chloramphenicol acetyltransferase)
 5,100 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Transcription of the phosphoenolpyruvate carboxykinase (PEPCK) and PEPCK-chloramphenicol acetyltransferase (CAT) genes is induced by cAMP and glucocorticoids and is inhibited by insulin in H4IIE cells, as it is in liver. In contrast, PEPCK-CAT expression in HepG2 cells is not affected by insulin but is induced by cAMP, which in turn is repressed by glucocorticoids. Mutations were introduced into well defined transcription factor binding sites to investigate possible interactions between the cAMP regulatory element (CRE) binding protein (CREB) and glucocorticoid response unit (GRU) binding proteins. H4IIE rat hepatoma cells were transfected with PEPCK-CAT plasmids with or without an expression vector for protein kinase A (PKA). Glucocorticoid-induced CAT activity was dependent upon the GRU and was decreased in plasmids lacking the CRE. To determine the direct effects of CREB, the DNA binding and dimerization domain of GAL4 was substituted for that of CREB (CRG), and the PEPCK CRE was replaced with a GAL4 binding site (G4PEPCK-CAT). CRG elevated basal and glucocorticoid-induced activities of G4PEPCK-CAT equally and restored responsiveness to PKA. The basal activity of CRG was not diminished by concomitant treatment with PKA plus its inhibitor peptide, PKI, or by mutation of the PKA phosphorylation. Deletion of C-terminal regions of the CREB activation domain from CRG diminished basal activation without affecting induction by PKA. The glucocorticoid-induced level of CAT activity decreased in proportion to the reduced ability of CREB to activate basal transcription. Induction by glucocorticoid, in the absence or presence of PKA, was not affected by CRG, indicating that interaction of GRU-bound factors with CREB is not required for glucocorticoid induction of PEPCK. These results indicate that CREB is directly involved in basal and PKA-induced expression of PEPCK, and that CREB supports glucocorticoid-induced PEPCK expression through its positive effect on basal transcription.
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PMID:Involvement of 3',5'-cyclic adenosine monophosphate regulatory element binding protein (CREB) in both basal and hormone-mediated expression of the phosphoenolpyruvate carboxykinase (PEPCK) gene. 811 62

Our previous finding that insulin induces apolipoprotein AI (apoAI) transcription points to the participation of intracellular signaling. This finding prompted us to ask whether two classical G-protein-coupled signaling pathways requiring activated protein kinase A (PKA) or kinase C (PKC) may also regulate apoAI. Therefore, human hepatoma, Hep G2 cells stably transfected with pAI.474-CAT, a reporter construct spanning -474 to -7 of apoAI DNA fused to chloramphenicol acetyltransferase (CAT) were treated with 10 microm forskolin (FSK) or 50 nm phorbol dibutyrate (PDBu) to activate PKA and PKC, respectively. Results showed that the apoAI promoter activity increased 4-5-fold following 24 h of treatment with either FSK or PDBu. Induction by either agent was blocked with actinomycin D but not the protein synthesis inhibitor, cycloheximide. The PKA inhibitor, PKI 14-22 amide, abrogated induction by FSK, 100 microm 8-bromo-cAMP, or 100 ng/ml cholera toxin, but it had no effect on activation via PKC. Similarly, PDBu induction was attenuated by 2 microm of the PKC inhibitor, GF109203X, but it did not affect FSK activity. Next we used deletional constructs to show that the actions of FSK and PDBu required the insulin-responsive core element (IRCE). This motif matched the consensus binding site for the transcription factor, Sp1. The binding of Sp1 to the IRCE was confirmed by gel-retardation and supershift analysis. Site-directed mutagenesis of the IRCE eliminated Sp1 action and induction by FSK or PDBu. Whereas overexpression of Sp1 enhanced basal and FSK or PDBu induced promoter activity, transfection of an antisense oligomer against Sp1 mRNA attenuated both parameters. In summary, activation of PKA or PKC increases apoAI promoter activity. The activity of both signaling pathways is mediated by the IRCE, a motif that binds the transcription factor, Sp1.
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PMID:Activation of apolipoprotein AI gene expression by protein kinase A and kinase C through transcription factor, Sp1. 1082 13