The nucleocytoplasmic shuttling of E2F4 is involved in the regulation of human intestinal epithelial cell proliferation and differentiation.
The specific mechanisms controlling the transition from proliferation to terminal differentiation in human intestinal epithelial cells (HIEC) remain largely undefined. Herein, we analyzed the expression and localization of Rb and E2F proteins in well-established normal intestinal epithelial cell models which allow for the re-enactment of the crypt-villus axis in vitro as well as in intact epithelium and in colon cancer cells. We report that (1) expression of E2F1 is down-regulated while E2F4 protein is sequestered in the cytoplasm during G(0) arrest associated with serum deprivation, confluency, and terminal differentiation of intestinal cells; (2) concurrently, there is an accumulation of the hypophosphorylated form of the pocket proteins into the nucleus with an increased association of E2F4 with pRb and p130; (3) cells which expressed high levels of nuclear E2F4 are all positive for Ki67 staining in human fetal intestine; (4) activation of HIEC crypt cells by growth factors leads to an increase in the nuclear localization of E2F4 which may be attributable to a decrease in the serine/threonine phosphorylation of this transcription factor; (5) inhibition of p38 MAP kinase with alpha/beta inhibitor SB203580 induces E2F4 translocation into the nucleus and its transcriptional activity. In conclusion, our data suggest a key role for E2F4 in proliferation of human intestinal crypt cells and that its cytoplasmic retention as well as its sequestration by Rb proteins may represent a critical step in initiating cell-cycle exit.
Deschênes
Claude
C
CIHR Group on Functional Development and Physiopathology of the Digestive Tract, Département d'Anatomie et Biologie Cellulaire, Faculté de Médecine, Université de Sherbrooke, Sherbrooke, Québec, Canada.
Alvarez
Laetitia
L
Lizotte
Marie-Eve
ME
Vézina
Anne
A
Rivard
Nathalie
N
D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology*; D018797:Cell Cycle Proteins; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D050704:E2F4 Transcription Factor; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism*; D005333:Fetus; D005455:Fluorescent Antibody Technique; D006801:Humans; D015151:Immunoblotting; D007422:Intestines / Q000166:cytology / Q000502:physiology; D020928:Mitogen-Activated Protein Kinases / Q000187:drug effects / Q000378:metabolism; D021381:Protein Transport / Q000187:drug effects / Q000502:physiology*; D016160:Retinoblastoma Protein / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*; D014162:Transfection; D048051:p38 Mitogen-Activated Protein Kinases
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; D050704:E2F4 Transcription Factor; C493762:E2F4 protein, human; D004791:Enzyme Inhibitors; D016160:Retinoblastoma Protein; D014157:Transcription Factors; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases