St Croix B, Sheehan C, Rak J W, Flørenes V A, Slingerland J M, Kerbel R S
Division of Cancer Biology Research, Sunnybrook Health Science Center, University of Toronto, Toronto-Sunnybrook Regional Cancer Center, Toronto, Ontario, Canada M4N 3M5.
J Cell Biol. 1998 Jul 27;142(2):557-71. doi: 10.1083/jcb.142.2.557.
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.
近期研究已证明，E-钙黏蛋白（一种同源性细胞间黏附分子）在正常上皮细胞生长的接触抑制中具有重要作用。许多肿瘤细胞也保持着较强的细胞间黏附，并且受到细胞间接触的生长抑制，尤其是在三维培养中生长时。为了确定E-钙黏蛋白是否能介导缺乏E-钙黏蛋白的非贴壁EMT/6小鼠乳腺癌细胞的接触依赖性生长抑制，我们用外源性E-钙黏蛋白表达载体转染了这些细胞。EMT/6细胞中E-钙黏蛋白的表达导致多细胞球体的黏附更紧密，并且在三维培养中增殖分数降低。除了细胞间黏附增加外，E-钙黏蛋白的表达还导致视网膜母细胞瘤蛋白去磷酸化、细胞周期蛋白依赖性激酶抑制剂p27（kip1）水平升高以及细胞周期蛋白D1蛋白后期减少。紧密黏附的球体还显示与细胞周期蛋白E-cdk2复合物结合的p27水平升高，以及细胞周期蛋白E-cdk2活性降低。在三维培养中暴露于E-钙黏蛋白中和抗体同时阻止了E-钙黏蛋白转染细胞以及一组表达功能性E-钙黏蛋白的人结肠、乳腺和肺癌细胞系的黏附并刺激了其增殖。为了测试p27在E-钙黏蛋白依赖性生长抑制中的重要性，我们构建了E-钙黏蛋白阳性细胞以表达可诱导的p27。通过强制表达与聚集细胞中观察到的水平相似的p27水平，E-钙黏蛋白中和抗体对增殖的刺激作用可被抑制。这项研究表明，传统上被描述为侵袭抑制因子的E-钙黏蛋白也是一种主要的生长抑制因子，其抑制增殖的能力涉及细胞周期蛋白依赖性激酶抑制剂p27的上调。
