Camacho-Leal Pilar, Zhai Alexander B, Stanners Clifford P
Department of Biochemistry and McGill Cancer Centre, McGill University, Quebec, Canada.
J Cell Physiol. 2007 Jun;211(3):791-802. doi: 10.1002/jcp.20989.
CEA functions as an intercellular adhesion molecule and is up-regulated in a wide variety of human cancers, including colon, breast and lung. Its over-expression inhibits cellular differentiation, blocks cell polarization, distorts tissue architecture, and inhibits anoikis of many different cell types. Here we report results concerning the molecular mechanism involved in these biological effects, where relatively rapid molecular changes not requiring alterations in gene expression were emphasized. Confocal microscopy experiments showed that antibody-mediated clustering of a deletion mutant of CEA (DeltaNCEA), normally incapable of self binding and clustering, led to the co-localization of integrin alpha5beta1 with patches of DeltaNCEA on the cell surface. Activation of alpha5, as defined by an anti-alpha5 mAb-sensitive increase in cell adhesion to immobilized fibronectin, and an increased binding of soluble fibronectin to cells, was also observed. This was accompanied by the recruitment of integrin-linked kinase (ILK), protein kinase B (PKB/Akt), and the mitogen-activated protein kinase (MAPK) to membrane microdomains and the phosphorylation of Akt and MAPK. Inhibition of PI3-K and ILK, but not MAPK, prevented the alpha5beta1 integrin activation. Conversely, anti-alpha5 antibody inhibited the PI3-K-mediated activation of Akt, implying the involvement of outside-in and inside-out signaling in integrin activation. Therefore we propose that CEA-mediated signaling involves clustering of CEA and co-clustering and activation of the alpha5beta1 and associated specific signaling elements on the internal surfaces of membrane microdomains. These changes may represent a molecular mechanism for the biological effects of CEA.
癌胚抗原（CEA）作为一种细胞间粘附分子，在多种人类癌症中上调，包括结肠癌、乳腺癌和肺癌。其过表达抑制细胞分化、阻碍细胞极化、扭曲组织结构，并抑制多种不同细胞类型的失巢凋亡。在此我们报告了有关这些生物学效应所涉及分子机制的结果，其中强调了相对快速的分子变化，这些变化无需基因表达的改变。共聚焦显微镜实验表明，抗体介导的通常无法自我结合和聚集的CEA缺失突变体（DeltaNCEA）聚集，导致整合素α5β1与细胞表面的DeltaNCEA斑块共定位。还观察到α5的激活，这是由抗α5单克隆抗体敏感的对固定化纤连蛋白的细胞粘附增加以及可溶性纤连蛋白与细胞的结合增加所定义的。这伴随着整合素连接激酶（ILK）、蛋白激酶B（PKB/Akt）和丝裂原活化蛋白激酶（MAPK）募集到膜微区以及Akt和MAPK的磷酸化。抑制PI3 - K和ILK，但不抑制MAPK，可阻止α5β1整合素的激活。相反，抗α5抗体抑制PI3 - K介导的Akt激活，这意味着外向内和内向内信号传导参与整合素激活。因此我们提出，CEA介导的信号传导涉及CEA的聚集以及α5β1在膜微区内表面的共聚集和激活以及相关的特定信号元件。这些变化可能代表了CEA生物学效应的分子机制。
