title: Epidermal growth factor and insulin-induced deoxyribonucleic acid synthesis in primary rat hepatocytes is phosphatidylinositol 3-kinase dependent and dissociated from protooncogene induction.
abstract: The mitogenic response to insulin and epidermal growth factor (EGF) was studied in subconfluent and confluent cultures of primary rat hepatocytes. In subconfluent cultures, wortmannin, LY294002, and rapamycin reversed insulin- and EGF-induced [3H]thymidine incorporation into DNA. The mitogen-activated protein kinase (MAPK) kinase 1 (MEK1) inhibitor PD98059 was without significant effect on either insulin- or EGF-induced [3H]thymidine incorporation. Insulin treatment did not alter levels of messenger RNAs (mRNAs) for c-fos, c-jun, and c-myc. EGF induced an increase in c-myc, but not c-fos or c-jun, mRNA levels in subconfluent hepatocyte cultures. This increase in c-myc mRNA was abolished by PD98059. In confluent cells that could not be induced to synthesize DNA, EGF treatment also promoted an increase in c-myc mRNA to levels seen in subconfluent cultures. This increase was also abrogated by PD98059. These data indicate that in primary rat hepatocyte cultures, 1) the phosphoinositol 3-kinase pathway, perhaps through p70s6k activation, regulates DNA synthesis in response to insulin and EGF; 2) the MAPKpathway is not involved in insulin- and EGF-induced DNA synthesis; and 3) p44/42 MAPKs are involved the induction of c-myc mRNA levels, although this induction is not required for DNA synthesis. These studies define two distinct signal transduction pathways that independently mediate growth-related responses in a physiologically relevant, normal cell system.
authors.affiliation: Department of Medicine, McGill University, Montréal, Québec, Canada.
authors.forename: C J
authors.initials: CJ
authors.lastname: Band
authors.forename: C
authors.initials: C
authors.lastname: Mounier
authors.forename: B I
authors.initials: BI
authors.lastname: Posner
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis*; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D005419:Flavonoids / Q000494:pharmacology; D016259:Genes, myc / Q000235:genetics; D007328:Insulin / Q000494:pharmacology*; D008099:Liver / Q000187:drug effects* / Q000378:metabolism*; D008297:Male; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism; D011494:Protein Kinases; D011519:Proto-Oncogenes / Q000235:genetics*; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D058570:TOR Serine-Threonine Kinases
chemical_list: D004247:DNA; D004791:Enzyme Inhibitors; D004815:Epidermal Growth Factor; D005419:Flavonoids; D007328:Insulin; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D011494:Protein Kinases; D012333:RNA, Messenger; D058570:TOR Serine-Threonine Kinases; C546845:mTOR protein, rat; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one