Insulin and IGF-1 stimulate the beta-catenin pathway through two signalling cascades involving GSK-3beta inhibition and Ras activation.
We examined the interplay between the insulin/IGF-1- and beta-catenin-regulated pathways, both of which are suspected to play a role in hepatocarcinogenesis. Insulin and IGF-1 stimulated the transcription of a Lef/Tcf-dependent luciferase reporter gene by 3-4-fold in HepG2 cells. This stimulation was mediated through the activation of phosphatidylinositol 3-kinase (PI 3-K)/Akt and the inhibition of glycogen synthase kinase-3beta (GSK-3beta) since the effects of insulin and IGF-1 were inhibited by dominant-negative mutants of PI 3-K or Akt and an uninhibitable GSK-3beta. Together with inhibiting GSK-3beta, insulin and IGF-1 increased the cytoplasmic levels of beta-catenin. The PI 3-K/Akt/GSK-3beta pathway was not the sole to mediate insulin and IGF-1 stimulation of Lef/Tcf-dependent transcription. The Ras signalling pathway was also required as (i) the stimulatory effects of insulin and IGF-1 were inhibited by dominant-negative Ras or the MEK1 inhibitor PD98059 and (ii) activated Ha-Ras or constitutively active MEK1 synergized with catalytically inactive GSK-3beta to stimulate Lef/Tcf-dependent transcription. This study provides the first evidence that insulin and IGF-1 stimulate the beta-catenin pathway through two signalling cascades bifurcating downstream of PI 3-K and involving GSK-3beta inhibition and Ras activation. These findings demonstrate for the first time the ability of insulin and IGF-1 to activate the beta-catenin pathway in hepatoma cells and thereby provide new insights into the role of these factors in hepatocarcinogenesis.
Desbois-Mouthon
C
C
INSERM U.402, Faculté de Médecine Saint-Antoine, Paris, France.
Cadoret
A
A
Blivet-Van Eggelpoël
M J
MJ
Bertrand
F
F
Cherqui
G
G
Perret
C
C
Capeau
J
J
D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D006528:Carcinoma, Hepatocellular / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects; D003598:Cytoskeletal Proteins / Q000187:drug effects / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D017930:Genes, Reporter; D011905:Genes, ras; D038362:Glycogen Synthase Kinase 3; D038341:Glycogen Synthase Kinases; D006801:Humans; D007328:Insulin / Q000378:metabolism* / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000378:metabolism* / Q000494:pharmacology; D051821:Lymphoid Enhancer-Binding Factor 1; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D009154:Mutation; D019869:Phosphatidylinositol 3-Kinases / Q000187:drug effects / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000187:drug effects / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D015398:Signal Transduction; D015534:Trans-Activators; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured; D051176:beta Catenin
D017871:Calcium-Calmodulin-Dependent Protein Kinases; D003598:Cytoskeletal Proteins; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D005419:Flavonoids; D038362:Glycogen Synthase Kinase 3; D038341:Glycogen Synthase Kinases; D007328:Insulin; D007334:Insulin-Like Growth Factor I; D051821:Lymphoid Enhancer-Binding Factor 1; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D015534:Trans-Activators; D014157:Transcription Factors; D051176:beta Catenin; C495270:CTNNB1 protein, human; C494918:AKT1 protein, human; C482125:MAP2K1 protein, human; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one