title: Distinct functions of H-Ras and K-Ras in proliferation and survival of primary hepatocytes due to selective activation of ERK and PI3K.
abstract: Ras proteins mediate signals both via extracellular signal-regulated kinase 1 and 2 (ERK), and phosphoinositide 3-kinase (PI3K). These signals are key events in cell protection and compensatory cell growth after exposure to cell damaging and pro-apoptotic stimuli, thus maintaining homeostasis. By transfection techniques, we found that both H-Ras and K-Ras were expressed and appeared functionally active in primary hepatocytes. We compared the ability of H-Ras and K-Ras homologues to preferentially activate one of the two pathways, thereby differentially controlling cell survival and growth. We found that ectopic expression of dominant negative (DN) H-RasN17, but not DN K-RasN17, efficiently inhibited both phosphorylation and translocation of ERK to the nuclear compartment, which are prerequisites for cell cycle progression. Furthermore, ectopic expression of constitutive active (CA) H-RasV12, but not CA K-RasV12, potentiated EGF-induced proliferation. We also found that expression of CA mutants of either H-Ras or K-Ras protected hepatocytes from transforming growth factor-beta1 (TGF-beta1)-induced apoptosis. However, H-Ras-induced survival was mediated by ERK/RSK as well as by PI3K, whereas K-Ras-induced survival was mediated by PI3K only. In conclusion, H-Ras and K-Ras had differential functions in proliferation and survival of primary hepatocytes. H-Ras was the major mediator of ERK-induced proliferation and survival, whereas H-Ras and K-Ras both mediated PI3K-induced survival.
authors.affiliation: Laboratory for Toxicopathology, Institute of Pathology, Rikshospitalet-Radiumhospitalet Medical Centre, University of Oslo, Norway. carola.rosseland@labmed.uio.no
authors.forename: Carola M
authors.initials: CM
authors.lastname: Rosseland
authors.forename: Lene
authors.initials: L
authors.lastname: Wierød
authors.forename: Liv I
authors.initials: LI
authors.lastname: Flinder
authors.forename: Morten P
authors.initials: MP
authors.lastname: Oksvold
authors.forename: Ellen
authors.initials: E
authors.lastname: Skarpen
authors.forename: Henrik S
authors.initials: HS
authors.lastname: Huitfeldt
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002467:Cell Nucleus / Q000187:drug effects / Q000201:enzymology; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000187:drug effects; D004815:Epidermal Growth Factor / Q000494:pharmacology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D005799:Genes, Dominant; D022781:Hepatocytes / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology*; D006801:Humans; D008297:Male; D051379:Mice; D015513:Oncogene Proteins / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D016283:Proto-Oncogene Proteins p21(ras) / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D053773:Transforming Growth Factor beta1 / Q000494:pharmacology; D018631:ras Proteins / Q000378:metabolism*
chemical_list: C528429:Hras protein, rat; C528430:Kras protein, rat; D015513:Oncogene Proteins; D053773:Transforming Growth Factor beta1; D004815:Epidermal Growth Factor; D019869:Phosphatidylinositol 3-Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins