The three insulin response sequences in the glucose-6-phosphatase catalytic subunit gene promoter are functionally distinct.

Vander Kooi BT, Streeper RS, Svitek CA, Oeser JK, Powell DR, O'Brien RM
J Biol Chem. 2003 278 (14): 11782-93

PMID: 12556524 · DOI:10.1074/jbc.M212570200

Glucose-6-phosphatase catalyzes the terminal step in the gluconeogenic and glycogenolytic pathways. In HepG2 cells, the maximum repression of basal glucose-6-phosphatase catalytic subunit (G6Pase) gene transcription by insulin requires two distinct promoter regions, designated A (located between -231 and -199) and B (located between -198 and -159), that together form an insulin response unit. Region A binds hepatocyte nuclear factor-1, which acts as an accessory factor to enhance the effect of insulin, mediated through region B, on G6Pase gene transcription. We have previously shown that region B binds the transcriptional activator FKHR (FOXO1a) in vitro. Chromatin immunoprecipitation assays demonstrate that FKHR also binds the G6Pase promoter in situ and that insulin inhibits this binding. Region B contains three insulin response sequences (IRSs), designated IRS 1, 2, and 3, that share the core sequence T(G/A)TTTT. However, detailed analyses reveal that these three G6Pase IRSs are functionally distinct. Thus, FKHR binds IRS 1 with high affinity and IRS 2 with low affinity but it does not bind IRS 3. Moreover, in the context of the G6Pase promoter, IRS 1 and 2, but not IRS 3, are required for the insulin response. Surprisingly, IRS 3, as well as IRS 1 and IRS 2, can each confer an inhibitory effect of insulin on the expression of a heterologous fusion gene, indicating that, in this context, a transcription factor other than FKHR, or its orthologs, can also mediate an insulin response through the T(G/A)TTTT motif.

MeSH Terms (22)

Animals Base Sequence Carcinoma, Hepatocellular Catalytic Domain Chloramphenicol O-Acetyltransferase DNA-Binding Proteins Forkhead Box Protein O1 Forkhead Transcription Factors Gene Expression Regulation, Enzymologic Glucose-6-Phosphatase Humans Hypoglycemic Agents Insulin Insulin-Like Growth Factor Binding Protein 1 Mice Nerve Tissue Proteins Promoter Regions, Genetic Rats Recombinant Fusion Proteins Transcriptional Activation Transcription Factors Tumor Cells, Cultured

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