EphA2 Receptor Tyrosine Kinase in Malignant Tumor Cell

描述(申请人提供)：EphA2受体是最近克隆的Eph受体酪氨酸激酶(RTK)家族的成员，在多种恶性肿瘤中过表达。EphA2受体的表达水平与肿瘤的恶性程度一致。EphA2在未转化的乳腺上皮细胞系中过表达可导致裸鼠成瘤。然而，EphA2在肿瘤恶性中过表达的机制尚不清楚。我们的初步数据显示，EphA2在未转化的乳腺上皮细胞MCF10A中的过度表达破坏了它们在三维培养中形成腺泡样球的能力。此外，E-钙粘蛋白在过度表达EphA2受体的MCF10A细胞中的表达存在错误定位。这些数据表明，高水平的EphA2可能通过细胞间黏附的不稳定而促进恶性行为。相反，阻断恶性肿瘤细胞中EphA2受体的激活会抑制RhoA GTPase的激活、细胞迁移和体内的肿瘤生长，表明EphA2受体信号转导是肿瘤恶性所必需的。基于这些数据，我们假设EphA2过表达(1)通过修饰连接复合体破坏细胞与细胞的黏附，(2)通过调节Vav3介导的RhoA GTPase活性促进细胞运动，(3)增强体内肿瘤的侵袭和转移。为了验证这些假说，我们特别建议：(1)确定EphA2过表达破坏细胞间黏附的机制；(2)研究EphA2过表达细胞中细胞运动能力的增加是否由Vav3依赖的RhoA GTPase激活所介导；以及(3)在多阶段转基因肿瘤模型中，确定EphA2过表达是否必要且足以促进肿瘤的形成和转移。该项目的成功不仅将为EphA2诱导的细胞侵袭和转移提供分子基础，也将为EphA2缺乏或过表达对肿瘤进展和转移的影响提供体内的临床前数据。

DESCRIPTION (provided by applicant): EphA2 receptor is a member of the recently cloned Eph family receptor tyrosine kinases (RTKs) that overexpressed in a variety of malignant tumors. The level of EphA2 receptor expression consistently correlates with the degree of malignancy. Overexpression of EphA2 in non-transformed breast epithelial line has led to tumor formation in nude mice. However, the mechanism by which EphA2 overexpression in tumor malignancy remains unclear. Our preliminary data show that overexpression of EphA2 in non-transformed breast epithelial cells MCF10A disrupts their ability to form acini-like spheroids in a three-dimentional culture. In addition, E-cadherin expression is mis-localized in MCF10A cells overexpressing EphA2 receptor. These data suggest high levels of EphA2 may promote malignant behavior through destabilization of cell-cell adhesion. Conversely, blocking EphA2 receptor activation in malignant tumor cells inhibits RhoA GTPase activation, cell migration, and tumor growth in vivo, indicating that EphA2 receptor signaling is required for tumor malignancy. Based on these data, we hypothesize that EphA2 overexpression (1) disrupts cell-cell adhesion through modifying junctional complexes, (2) promotes cell motility by modulation of Vav3-mediated RhoA GTPase activity, and (3) enhances tumor invasion and metastasis in vivo. To test these hypotheses, we specifically propose to:(1) identify mechanisms by which EphA2 overexpression disrupts cell-cell adhesion; (2) investigate whether increased cell motility in EphA2 overexpressing cells is mediated by Vav3- dependent activation of RhoA GTPase; and (3) determine if EphA2 overexpression is necessary and sufficient to promote tumor formation and metastasis in multi-stage transgenic tumor models. The success of this project will not only provide molecular basis of EphA2-induced cell invasion and metastasis, but also provide in vivo pre-clinical data on the effect of EphA2-deficiency or EphA2 overexpression on tumor progression and metastasis.