E-CADHERIN-DEPENDENT GROWTH SUPPRESSION IS MEDIATED BY THE CYCLIN-DEPENDENT KINASE INHIBITOR P27(KIP1)

Recent studies have demonstrated the importance of E-cadherin, a hemop hilic cell-cell adhesion molecule, in contact inhibition of growth of normal epithelial cells. Many tumor cells also maintain strong interce llular adhesion, and are growth-inhibited by cell-cell contact, especi ally when grown in three-dimensional culture. To determine if E-cadher in could mediate contact-dependent growth inhibition of nonadherent EM T/6 mouse mammary carcinoma cells that lack E-cadherin, we transfected these cells with an exogenous E-cadherin expression vector. E-cadheri n expression in EMT/6 cells resulted in tighter adhesion of multicellu lar spheroids and a reduced proliferative fraction in three-dimensiona l culture. In addition to increased cell-cell adhesion, E-cadherin exp ression also resulted in dephosphorylation of the retinoblastoma prote in, 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-cd k2 complex, and a reduction in cyclin E-cdk2 activity, Exposure to E-c adherin-neutralizing antibodies in three-dimensional culture simultane ously prevented adhesion and stimulated proliferation of E-cadherin tr ansfectants as well as a panel of human colon, breast, and lung carcin oma cell lines that express functional E-cadherin. To test the importa nce of p27 in E-cadherin-dependent growth inhibition, we engineered E- cadherin-positive cells to express inducible p27, By forcing expressio n of p27 levels similar to those observed in aggregated cells, the sti mulatory effect of E-cadherin-neutralizing antibodies on proliferation could be inhibited. This study demonstrates that E-cadherin, classica lly described as an invasion suppressor, is also a major growth suppre ssor, and its ability to inhibit proliferation involves upregulation o f the cyclin-dependent kinase inhibitor p27.