A role for Akt in epidermal growth factor-stimulated cell cycle progression in cultured hepatocytes: generation of a hyperproliferative window after adenoviral expression of constitutively active Akt.
Epidermal growth factor (EGF) stimulation of cell cycle progression in cultured primary hepatocytes has previously been reported to be dependent on the mammalian target of rapamycin (mTOR) elements of the phosphoinositide 3-kinase (PI3K) signaling cascade and not the Akt pathway. Here we have established conditions of combined treatment of rat hepatocytes with insulin and EGF that favor cell cycle progression. The resulting cell population expresses albumin and retains receptor regulation of the signaling pathways leading to glycogen phosphorylase activation. We then investigated the hypothesis that the Akt limb of the PI3K pathway plays a central role in this insulin/EGF enhancement of cell cycle progression. The phosphorylation of Akt, central to the PI3K pathway, was increased by both insulin (sustained) and EGF (transient). The stimulation of Akt phosphorylation was inhibited in a concentration-dependent manner by the PI3K inhibitor, 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002). Cell cycle progression in these cultures was reduced, but not abolished, by this inhibitor. The mTOR inhibitor, rapamycin, also inhibited entry into S phase. The novel Akt inhibitor A-443654 [(S)-1-(1H-indol-3-ylmethyl)-2-[5-(3-methyl-1H-indazol-5-yl)-pyridin-3-yloxy]-ethylamine] blocked both EGF-stimulated cell cycle progression and phosphorylation of the Akt substrate glycogen synthase kinase-3. Infection of cells with an adenoviral vector expressing a constitutively active form of Akt but not a kinase-dead form increased hepatocyte proliferation probably through enhanced cell cycle progression and reduced apoptosis. These results show that the Akt element of the PI3K cascade is necessary for EGF-stimulated cell cycle progression and provide evidence that the sustained elevation of Akt alone generates a hyperproliferative window in hepatocyte cultures.
Luo
Yi
Y
The Cell Signaling Laboratory, The Hawthorn Building, Leicester School of Pharmacy, De Montfort University, Leicester LE1 9BH, UK.
Dixon
C Jane
CJ
Hall
John F
JF
White
Pamela J
PJ
Boarder
Michael R
MR
D000244:Adenosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology*; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D024981:Glycogen Phosphorylase / Q000378:metabolism; D022781:Hepatocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D007295:Inositol Phosphates / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology; D008297:Male; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011494:Protein Kinases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D016196:S Phase / Q000187:drug effects; D058570:TOR Serine-Threonine Kinases; D013873:Thionucleotides / Q000494:pharmacology; D014162:Transfection; D014530:Uridine Diphosphate / Q000494:pharmacology; D014544:Uridine Triphosphate / Q000494:pharmacology
D007295:Inositol Phosphates; D007328:Insulin; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors; D013873:Thionucleotides; C002480:methylthio-ADP; D014530:Uridine Diphosphate; D000244:Adenosine Diphosphate; D004815:Epidermal Growth Factor; D000255:Adenosine Triphosphate; D024981:Glycogen Phosphorylase; D011494:Protein Kinases; C546845:mTOR protein, rat; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D014544:Uridine Triphosphate