Differential regulation of growth-promoting signalling pathways by E-cadherin.
BACKGROUND
Despite the well-documented association between loss of E-cadherin and carcinogenesis, as well as the link between restoration of its expression and suppression of proliferation in carcinoma cells, the ability of E-cadherin to modulate growth-promoting cell signalling in normal epithelial cells is less well understood and frequently contradictory. The potential for E-cadherin to co-ordinate different proliferation-associated signalling pathways has yet to be fully explored.


RESULTS
Using a normal human urothelial (NHU) cell culture system and following a calcium-switch approach, we demonstrate that the stability of NHU cell-cell contacts differentially regulates the Epidermal Growth Factor Receptor (EGFR)/Extracellular Signal-Regulated Kinase (ERK) and Phosphatidylinositol 3-Kinase (PI3-K)/AKT pathways. We show that stable cell contacts down-modulate the EGFR/ERK pathway, whilst inducing PI3-K/AKT activity, which transiently enhances cell growth at low density. Functional inactivation of E-cadherin interferes with the capacity of NHU cells to form stable calcium-mediated contacts, attenuates E-cadherin-mediated PI3-K/AKT induction and enhances NHU cell proliferation by allowing de-repression of the EGFR/ERK pathway and constitutive activation of β-catenin-TCF signalling.


CONCLUSIONS
Our findings provide evidence that E-cadherin can differentially and concurrently regulate specific growth-related signalling pathways in a context-specific fashion, with direct, functional consequences for cell proliferation and population growth. Our observations not only reveal a novel, complex role for E-cadherin in normal epithelial cell homeostasis and tissue regeneration, but also provide the basis for a more complete understanding of the consequences of E-cadherin loss on malignant transformation.
Jack Birch Unit for Molecular Carcinogenesis, Department of Biology, University of York, York, United Kingdom.
Nikolaos T
NT
Georgopoulos
Lisa A
LA
Kirkwood
Dawn C
DC
Walker
Jennifer
J
Southgate
D015820:Cadherins / Q000378:metabolism*; D049109:Cell Proliferation; D002478:Cells, Cultured; D066246:ErbB Receptors / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D006801:Humans; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D015398:Signal Transduction; D051820:TCF Transcription Factors / Q000378:metabolism; D019459:Urothelium / Q000166:cytology / Q000201:enzymology / Q000378:metabolism; D051176:beta Catenin / Q000378:metabolism
D015820:Cadherins; D051820:TCF Transcription Factors; D051176:beta Catenin; D019869:Phosphatidylinositol 3-Kinases; D066246:ErbB Receptors; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases