Brantley-Sieders Dana M, Fang Wei Bin, Hwang Yoonha, Hicks Donna, Chen Jin
Division of Rheumatology and Immunology, Department of Medicin, Vanderbilt University School of Medicine, Nashville, TN 37232-2363, USA.
Cancer Res. 2006 Nov 1;66(21):10315-24. doi: 10.1158/0008-5472.CAN-06-1560.
Ephrin-A1, the prototypic ligand for EphA receptor tyrosine kinases, is overexpressed in vascularized tumors relative to normal tissue. Moreover, ephrin-A1-Fc fusion proteins induce endothelial cell sprouting, migration, and assembly in vitro, and s.c. vascular remodeling in vivo. Based on these data, we hypothesized that native, membrane-bound ephrin-A1 regulates tumor angiogenesis and progression. We tested this hypothesis using a transplantable mouse mammary tumor model. Small interfering RNA-mediated ephrin-A1 knockdown in metastatic mammary tumor cells significantly diminishes lung metastasis without affecting tumor volume, invasion, intravasation, or lung colonization upon i.v. injection in vivo. Ephrin-A1 knockdown reduced tumor-induced endothelial cell migration in vitro and microvascular density in vivo. Conversely, overexpression of ephrin-A1 in nonmetastatic mammary tumor cells elevated microvascular density and vascular recruitment. Overexpression of ephrin-A1 elevated wild-type but not EphA2-deficient endothelial cell migration toward tumor cells, suggesting that activation of EphA2 on endothelial cells is one mechanism by which ephrin-A1 regulates angiogenesis. Furthermore, ephrin-A1 knockdown diminished, whereas overexpression of ephrin-A1 elevated, vascular endothelial growth factor (VEGF) levels in tumor cell-conditioned medium, suggesting that ephrin-A1-mediated modulation of the VEGF pathway is another mechanism by which membrane-tethered ephrin-A1 regulates angiogenic responses from initially distant host endothelium. These data suggest that ephrin-A1 is a proangiogenic signal, regulating VEGF expression and facilitating angiogenesis-dependent metastatic spread.
Ephrin-A1是EphA受体酪氨酸激酶的典型配体，相对于正常组织，其在血管化肿瘤中过表达。此外，ephrin-A1-Fc融合蛋白在体外可诱导内皮细胞发芽、迁移和组装，并在体内诱导皮下血管重塑。基于这些数据，我们推测天然的、膜结合的ephrin-A1可调节肿瘤血管生成和进展。我们使用可移植的小鼠乳腺肿瘤模型对这一假设进行了测试。在转移性乳腺肿瘤细胞中，小干扰RNA介导的ephrin-A1敲低显著减少了肺转移，而不影响肿瘤体积、侵袭、血管内渗或体内静脉注射后的肺定植。Ephrin-A1敲低降低了体外肿瘤诱导的内皮细胞迁移和体内微血管密度。相反，在非转移性乳腺肿瘤细胞中过表达ephrin-A1可提高微血管密度和血管募集。Ephrin-A1的过表达提高了野生型内皮细胞而非EphA2缺陷型内皮细胞向肿瘤细胞的迁移，这表明内皮细胞上EphA2的激活是ephrin-A1调节血管生成的一种机制。此外，Ephrin-A1敲低减少了肿瘤细胞条件培养基中的血管内皮生长因子（VEGF）水平，而ephrin-A1的过表达则提高了该水平，这表明ephrin-A1介导的VEGF途径调节是膜结合的ephrin-A1调节最初远处宿主内皮细胞血管生成反应的另一种机制。这些数据表明，ephrin-A1是一种促血管生成信号，可调节VEGF表达并促进依赖血管生成的转移扩散。
