Phorbol ester-induced activation of mitogen-activated protein kinase/extracellular-signal-regulated kinase kinase and extracellular-signal-regulated protein kinase decreases glucose-6-phosphatase gene expression.
Glucose-6-phosphatase (G6Pase) plays a central role in blood glucose homoeostasis, and insulin suppresses G6Pase gene expression by the activation of phosphoinositide 3-kinase (PI 3-kinase). Here, we show that the phorbol ester PMA decreases both basal and dexamethasone/cAMP-induced expression of a luciferase gene under the control of the G6Pase promoter in transiently transfected H4IIE hepatoma cells. This regulation was suppressed by the inhibitors of the mitogen-activated protein kinase/extracellular-signal-regulated kinase kinase (MEK), PD98059 and U0126, but not by the inhibitor of PI 3-kinase, LY294002. The co-expression of a constitutively active mutant of MEK mimicked the regulation of G6Pase promoter activity by PMA. The effect of PMA on both basal and induced G6Pase gene transcription was impaired by the overexpression of a dominant negative MEK construct, as well as by the expression of mitogen-activated protein kinase phosphatase-1. The mutation of the forkhead-binding sites within the insulin-response unit of the G6Pase promoter, which decreases the effect of insulin on G6Pase gene expression, did not alter the regulation of gene expression by PMA. The data show that PMA decreases G6Pase gene expression by the activation of MEK and extracellular-signal regulated protein kinase. With that, PMA mimics the effect of insulin on G6Pase gene expression by a different signalling pathway.
Schmoll
D
D
Department of Medical Biochemistry and Molecular Biology, University of Greifswald, Klinikum, Sauerbruchstrasse, D-17487 Greifswald, Germany. schmoll@mail.uni-greifswald.de
Grempler
R
R
Barthel
A
A
Joost
H G
HG
Walther
R
R
D000818:Animals; D018797:Cell Cycle Proteins; D054638:Dual Specificity Phosphatase 1; D004789:Enzyme Activation; D005419:Flavonoids / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects*; D005952:Glucose-6-Phosphatase / Q000235:genetics* / Q000378:metabolism; D017874:Immediate-Early Proteins / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases; D011401:Promoter Regions, Genetic / Q000187:drug effects / Q000235:genetics; D054645:Protein Phosphatase 1; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D018797:Cell Cycle Proteins; D005419:Flavonoids; D017874:Immediate-Early Proteins; D007328:Insulin; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D020928:Mitogen-Activated Protein Kinases; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D054638:Dual Specificity Phosphatase 1; C517021:Dusp1 protein, rat; D017027:Protein Tyrosine Phosphatases; D005952:Glucose-6-Phosphatase; D013755:Tetradecanoylphorbol Acetate; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one