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E-Cadherin-dependent growth suppression is mediated by the cyclin-dependent kinase inhibitor p27(KIP1)
B St Croix1, C Sheehan, J W Rak
1Division of Cancer Biology Research, Sunnybrook Health Science Center, University of Toronto, Toronto-Sunnybrook Regional Cancer Center, Toronto, Ontario, Canada M4N 3M5.
Abstract:
Recent studies have demonstrated the importance of E-cadherin, a homophilic cell-cell adhesion molecule, in contact inhibition of growth of normal epithelial cells. Many tumor cells also maintain strong intercellular adhesion, and are growth-inhibited by cell- cell contact, especially when grown in three-dimensional culture. To determine if E-cadherin could mediate contact-dependent growth inhibition of nonadherent EMT/6 mouse mammary carcinoma cells that lack E-cadherin, we transfected these cells with an exogenous E-cadherin expression vector. E-cadherin expression in EMT/6 cells resulted in tighter adhesion of multicellular spheroids and a reduced proliferative fraction in three-dimensional culture. In addition to increased cell-cell adhesion, E-cadherin expression also resulted in dephosphorylation of the retinoblastoma protein, an increase in the level of the cyclin-dependent kinase inhibitor p27(kip1) and a late reduction in cyclin D1 protein. Tightly adherent spheroids also showed increased levels of p27 bound to the cyclin E-cdk2 complex, and a reduction in cyclin E-cdk2 activity. Exposure to E-cadherin-neutralizing antibodies in three-dimensional culture simultaneously prevented adhesion and stimulated proliferation of E-cadherin transfectants as well as a panel of human colon, breast, and lung carcinoma cell lines that express functional E-cadherin. To test the importance of p27 in E-cadherin-dependent growth inhibition, we engineered E-cadherin-positive cells to express inducible p27. By forcing expression of p27 levels similar to those observed in aggregated cells, the stimulatory effect of E-cadherin-neutralizing antibodies on proliferation could be inhibited. This study demonstrates that E-cadherin, classically described as an invasion suppressor, is also a major growth suppressor, and its ability to inhibit proliferation involves upregulation of the cyclin-dependent kinase inhibitor p27.
Insights
E-cadherin, a cell adhesion molecule, suppresses tumor growth by increasing cell-cell adhesion and upregulating the p27 protein, which inhibits cell proliferation. This finding highlights E-cadherin
Area of Science:
- Cell Biology
- Molecular Oncology
- Cancer Research
Background:
- E-cadherin is crucial for contact inhibition of normal epithelial cells.
- Tumor cells often exhibit strong intercellular adhesion and growth inhibition via cell contact.
- The role of E-cadherin in growth inhibition of E-cadherin-deficient tumor cells requires further investigation.
Purpose of the Study:
- To investigate if E-cadherin can mediate contact-dependent growth inhibition in E-cadherin-null EMT/6 mouse mammary carcinoma cells.
- To elucidate the molecular mechanisms underlying E-cadherin-mediated growth suppression.
- To assess the role of p27 in E-cadherin-dependent growth inhibition.
Main Methods:
- Transfection of EMT/6 cells with an E-cadherin expression vector.
- Culture of cells in three-dimensional systems to observe spheroid formation and proliferation.
- Analysis of cell cycle regulatory proteins, including retinoblastoma protein, p27(kip1), cyclin D1, and cyclin E-cdk2 complex.
- Use of E-cadherin-neutralizing antibodies to block adhesion and assess proliferation.
- Engineering E-cadherin-positive cells for inducible p27 expression.
Main Results:
- E-cadherin expression in EMT/6 cells led to tighter spheroid adhesion and reduced proliferation in 3D culture.
- E-cadherin expression induced retinoblastoma protein dephosphorylation, increased p27(kip1) levels, and decreased cyclin D1.
- Adherent spheroids showed increased p27 bound to cyclin E-cdk2, reducing its activity.
- Blocking E-cadherin function with antibodies stimulated proliferation in various cancer cell lines.
- Inducible p27 expression in E-cadherin-positive cells counteracted the proliferative effect of antibody treatment.
Conclusions:
- E-cadherin acts as a significant growth suppressor, in addition to its role as an invasion suppressor.
- E-cadherin-mediated growth inhibition involves the upregulation of the cyclin-dependent kinase inhibitor p27.
- Targeting E-cadherin or modulating p27 levels could be potential therapeutic strategies for cancer treatment.