c-Fos accelerates hepatocyte conversion to a fibroblastoid phenotype through ERK-mediated upregulation of paxillin-Serine178 phosphorylation.
Transforming growth factor beta (TGF-beta) exerts an important role in the late steps of carcinogenesis by cooperating with Ras to induce cell motility and tumor invasion. The transcription complex AP-1 has been implicated in the regulation of genes involved in motility and invasion, by mechanisms not yet delineated. We utilized a model of immortalized human hepatocytes (IHH) overexpressing c-Fos (IHH-Fos) or not (IHH-C) to investigate the role of c-Fos on cell motility in response to a prolonged treatment with TGF-beta, EGF or a combination of both. Cotreatment with EGF and TGF-beta, but neither cytokine alone, induced the conversion of hepatocytes to a fibroblastoid phenotype and increased their motility in Boyden chambers. EGF/TGF-beta cotreatment induced a higher effect on ERK phosphorylation compared to TGF-beta treatment alone. It also induced an increase in total and phosphorylated Ser(178) paxillin, a protein previously implicated in cell motility. This response was inhibited by two specific MEK inhibitors, indicating the involvement of the ERK pathway in paxillin activation. Overexpression of c-Fos correlated with increased cell scattering and motility, higher levels of ERK activation and phospho Ser(178) paxillin, increased levels of EGF receptor (EGF-R) mRNA and higher EGF-R phosphorylation levels following EGF/TGF-beta cotreatment. Conversely, siRNA-mediated invalidation of c-Fos delayed the appearance of fibroblastoid cells, decreased EGF-R mRNA and downregulated ERK and Ser(178) paxillin phosphorylations, indicating that c-Fos activates hepatocyte motility through an EGF-R/ERK/paxillin pathway. Since c-Fos is frequently overexpressed in hepatocarcinomas, this newly identified mechanism might be involved in the progression of hepatic tumors in vivo.
Güller
Meryem C
MC
INSERM U697, Université Paris 7 Denis Diderot, Paris, France.
André
Jocelyne
J
Legrand
Agnès
A
Setterblad
Niclas
N
Mauviel
Alain
A
Verrecchia
Franck
F
Daniel
Fanny
F
Bernuau
Dominique
D
D001483:Base Sequence; D002461:Cell Line, Transformed; D017931:DNA Primers; D004789:Enzyme Activation; D004815:Epidermal Growth Factor / Q000494:pharmacology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D005347:Fibroblasts / Q000166:cytology; D022781:Hepatocytes / Q000166:cytology*; D006801:Humans; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D051419:Paxillin / Q000737:chemistry / Q000378:metabolism*; D010766:Phosphorylation; D016133:Polymerase Chain Reaction; D016760:Proto-Oncogene Proteins c-fos / Q000502:physiology*; D012694:Serine / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D016212:Transforming Growth Factor beta / Q000494:pharmacology; D015854:Up-Regulation
D017931:DNA Primers; D051419:Paxillin; D016760:Proto-Oncogene Proteins c-fos; D016212:Transforming Growth Factor beta; D012694:Serine; D004815:Epidermal Growth Factor; D048049:Extracellular Signal-Regulated MAP Kinases