Department of Biochemistry and Microbiology, University of Victoria, P,O, Box 3055 Station CSC Victoria, British Columbia, V8W 3P6, Canada.
Cancer Cell Int. 2010 Oct 27;10:41. doi: 10.1186/1475-2867-10-41.
Ephrin A1 (EFNA1) is a member of the A-type ephrin family of cell surface proteins that function as ligands for the A-type Eph receptor tyrosine kinase family. In malignancy, the precise role of EFNA1 and its preferred receptor, EPHA2, is controversial. Several studies have found that EFNA1 may suppress EPHA2-mediated oncogenesis, or enhance it, depending on cell type and context. However, little is known about the conditions that influence whether EFNA1 promotes or suppresses tumorigenicity. EFNA1 exists in a soluble form as well as a glycophosphatidylinositol (GPI) membrane attached form. We investigated whether the contradictory roles of EFNA1 in malignancy might in part be related to the existence of both soluble and membrane attached forms of EFNA1 and potential differences in the manner in which they interact with EPHA2.
Using a RNAi strategy to reduce the expression of endogenous EFNA1 and EPHA2, we found that both EFNA1 and EPHA2 are required for growth of HeLa and SK-BR3 cells. The growth defects could be rescued by conditioned media from cells overexpressing soluble EFNA1. Interestingly, we found that overexpression of the membrane attached form of EFNA1 suppresses growth of HeLa cells in 3D but not 2D. Knockdown of endogenous EFNA1, or overexpression of full-length EFNA1, resulted in relocalization of EPHA2 from the cell surface to sites of cell-cell contact. Overexpression of soluble EFNA1 however resulted in more EPHA2 distributed on the cell surface, away from cell-cell contacts, and promoted the growth of HeLa cells.
We conclude that soluble EFNA1 is necessary for the transformation of HeLa and SK-BR3 cells and participates in the relocalization of EPHA2 away from sites of cell-cell contact during transformation.
Ephrin A1（EFNA1）是细胞表面蛋白 A 型 Ephrin 家族的成员，作为 A 型 Eph 受体酪氨酸激酶家族的配体发挥作用。在恶性肿瘤中，EFNA1 及其首选受体 EPHA2 的精确作用存在争议。一些研究发现，EFNA1 可能抑制 EphA2 介导的致癌作用，也可能增强其作用，具体取决于细胞类型和背景。然而，对于影响 EFNA1 促进或抑制肿瘤发生的条件知之甚少。EFNA1 以可溶性形式和糖磷脂酰肌醇（GPI）膜结合形式存在。我们研究了 EFNA1 在恶性肿瘤中的矛盾作用是否部分与 EFNA1 的可溶性和膜结合形式的存在以及它们与 EphA2 相互作用的方式的潜在差异有关。
使用 RNAi 策略降低内源性 EFNA1 和 EPHA2 的表达，我们发现 EFNA1 和 EPHA2 均是 HeLa 和 SK-BR3 细胞生长所必需的。过表达可溶性 EFNA1 的条件培养基可挽救生长缺陷。有趣的是，我们发现过表达膜结合形式的 EFNA1 可抑制 HeLa 细胞在 3D 而非 2D 中的生长。内源性 EFNA1 的敲低或全长 EFNA1 的过表达导致 EphA2 从细胞膜重新定位到细胞-细胞接触部位。然而，可溶性 EFNA1 的过表达导致更多的 EphA2 分布在细胞膜上，远离细胞-细胞接触部位，并促进 HeLa 细胞的生长。
我们得出结论，可溶性 EFNA1 是 HeLa 和 SK-BR3 细胞转化所必需的，并且在转化过程中参与 EphA2 从细胞-细胞接触部位的重新定位。
