title: ERK-associated changes in E2F4 phosphorylation, localization and transcriptional activity during mitogenic stimulation in human intestinal epithelial crypt cells.
abstract: BACKGROUND
  The transcription factor E2F4 controls proliferation of normal and cancerous intestinal epithelial cells. E2F4 localization in normal human intestinal epithelial cells (HIEC) is cell cycle-dependent, being cytoplasmic in quiescent differentiated cells but nuclear in proliferative cells. However, the intracellular signaling mechanisms regulating such E2F4 localization remain unknown.
  
  
  RESULTS
  Treatment of quiescent HIEC with serum induced ERK1/2 activation, E2F4 phosphorylation, E2F4 nuclear translocation and G1/S phase transition while inhibition of MEK/ERK signaling by U0126 prevented these events. Stimulation of HIEC with epidermal growth factor (EGF) also led to the activation of ERK1/2 but, in contrast to serum or lysophosphatidic acid (LPA), EGF failed to induce E2F4 phosphorylation, E2F4 nuclear translocation and G1/S phase transition. Furthermore, Akt and GSK3β phosphorylation levels were markedly enhanced in serum- or LPA-stimulated HIEC but not by EGF. Importantly, E2F4 phosphorylation, E2F4 nuclear translocation and G1/S phase transition were all observed in response to EGF when GSK3 activity was concomitantly inhibited by SB216763. Finally, E2F4 was found to be overexpressed, phosphorylated and nuclear localized in epithelial cells from human colorectal adenomas exhibiting mutations in APC and KRAS or BRAF genes, known to deregulate GSK3/β-catenin and MEK/ERK signaling, respectively.
  
  
  CONCLUSIONS
  The present results indicate that MEK/ERK activation and GSK3 inhibition are both required for E2F4 phosphorylation as well as its nuclear translocation and S phase entry in HIEC. This finding suggests that dysregulated E2F4 nuclear localization may be an instigating event leading to hyperproliferation and hence, of tumor initiation and promotion in the colon and rectum.
authors.affiliation: Département d'Anatomie et Biologie Cellulaire, Cancer Research Pavillon, Faculté de Médecine et des Sciences de la Santé, Université de Sherbrooke, 3201, Jean-Mignault, Sherbrooke, J1E4K8, QC, Canada.
authors.forename: Marie-Christine
authors.initials: MC
authors.lastname: Paquin
authors.forename: Sébastien
authors.initials: S
authors.lastname: Cagnol
authors.forename: Julie C
authors.initials: JC
authors.lastname: Carrier
authors.forename: Caroline
authors.initials: C
authors.lastname: Leblanc
authors.forename: Nathalie
authors.initials: N
authors.lastname: Rivard
mesh_terms: D000236:Adenoma / Q000378:metabolism / Q000473:pathology; D002070:Butadienes / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects*; D002478:Cells, Cultured; D015179:Colorectal Neoplasms / Q000378:metabolism / Q000473:pathology; D050704:E2F4 Transcription Factor / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000494:pharmacology; D038362:Glycogen Synthase Kinase 3 / Q000037:antagonists & inhibitors / Q000187:drug effects; D006801:Humans; D007413:Intestinal Mucosa / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology*; D008246:Lysophospholipids / Q000494:pharmacology; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology*; D008934:Mitogens / Q000494:pharmacology*; D009570:Nitriles / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects / Q000502:physiology; D014158:Transcription, Genetic / Q000187:drug effects* / Q000502:physiology
chemical_list: D002070:Butadienes; D050704:E2F4 Transcription Factor; C493762:E2F4 protein, human; D004791:Enzyme Inhibitors; D008246:Lysophospholipids; D008934:Mitogens; D009570:Nitriles; C113580:U 0126; D004815:Epidermal Growth Factor; D038362:Glycogen Synthase Kinase 3; C032881:lysophosphatidic acid
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