Fujii K, Furukawa F, Matsuyoshi N
Department of Dermatology, Kobe City General Hospital, Kobe, Japan.
Exp Cell Res. 1996 Feb 25;223(1):50-62. doi: 10.1006/excr.1996.0057.
Various types of tumors show aberrant expression and overexpression of epidermal growth factor (EGF) receptor and the degree of receptor expression correlates with a malignant phenotype in many epithelial tumors. However, in vitro evidence supporting the advantageous role of receptor overexpression is deficient. In this study, we compared the effects of exogenous EGF on the cell colony morphology in monolayer and collagen gel culture between HSC-1 squamous carcinoma cells overexpressing EGF receptor and their revertant subline cells. These cells formed coherent cell colonies under routine culture conditions, but addition of EGF induced dissociation of cell colonies within 24 h in the parent HSC-1 cells, though not in the subline cells. Since the colony dissociation apparently involved loss of cell-cell adhesion, we also studied the effects of EGF on E-cadherin expression and its function. Cell aggregation assays showed that EGF reduced E-cadherin function dose-dependently in the parent cells, but not in the subline cells. However, immunoblotting analysis and ELISA showed the absence of downregulation or degradation of E-cadherin. Instead, EGF tyrosine phosphorylated cadherin/catenin complex components including beta-catenin and increased the detergent solubility of E-cadherin in the parent cells. These results suggest that EGF modified the functional association between E-cadherin and actin filament through tyrosine phosphorylation of the cadherin/catenin complex and thereby made the adhesion molecule incompetent. Our results indicate that the ligand activation of overexpressed EGF receptor impairs E-cadherin-mediated cell-cell adhesion and causes dissociation of the squamous carcinoma cell colonies, which facilitates tumor cell invasion in vivo. This might be relevant to the advantageous role of EGF receptor overexpression in malignant phenotype of epithelial tumor cells.
多种类型的肿瘤表现出表皮生长因子（EGF）受体的异常表达和过表达，并且受体表达程度与许多上皮性肿瘤的恶性表型相关。然而，支持受体过表达具有有利作用的体外证据并不充分。在本研究中，我们比较了外源性EGF对过表达EGF受体的HSC-1鳞状癌细胞及其回复亚系细胞在单层培养和胶原凝胶培养中细胞集落形态的影响。这些细胞在常规培养条件下形成连贯的细胞集落，但添加EGF后，亲代HSC-1细胞中的细胞集落在24小时内发生解离，而亚系细胞则未出现这种情况。由于集落解离明显涉及细胞间黏附的丧失，我们还研究了EGF对E-钙黏蛋白表达及其功能的影响。细胞聚集试验表明，EGF在亲代细胞中剂量依赖性地降低E-钙黏蛋白功能，但在亚系细胞中则无此作用。然而，免疫印迹分析和酶联免疫吸附测定显示E-钙黏蛋白没有下调或降解。相反，EGF使包括β-连环蛋白在内的钙黏蛋白/连环蛋白复合体组分发生酪氨酸磷酸化，并增加了亲代细胞中E-钙黏蛋白的去污剂溶解性。这些结果表明，EGF通过钙黏蛋白/连环蛋白复合体的酪氨酸磷酸化修饰了E-钙黏蛋白与肌动蛋白丝之间的功能关联，从而使黏附分子失去功能。我们的结果表明，过表达的EGF受体的配体激活损害了E-钙黏蛋白介导的细胞间黏附，并导致鳞状癌细胞集落解离，这有利于体内肿瘤细胞的侵袭。这可能与EGF受体过表达在上皮性肿瘤细胞恶性表型中的有利作用相关。
