Soluble ephrin a1 is necessary for the growth of HeLa and SK-BR3 cells

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.The Eph receptors are the largest family of receptor tyrosine kinases. They are activated by protein ligands, known as ephrins, which are attached to the cell membrane by either a membrane-spanning protein domain (B-type) or by a glycosylphosphatidylinositol (GPI) anchor (A-type). The receptors are also divided into A and B classes according to the type of ephrin they bind and their sequence similarity. Typically, the Eph A receptors bind to A-type ephrins, and Eph B receptors bind to B-type ephrins. However, binding between classes does occur with certain family members [1,2]. The functions regulated by Eph receptors and their ephrin ligands are diverse and cell-type dependent. They control a large number of physiological and developmental processes, and have also been implicated in both the suppression and advancement of cancer (reviewed in [3]).Perhaps the best characterized, in terms of its pro- and anti-oncogenic roles, is EPHA2. EPHA2 confers tumorigenic and metastatic potential to non-transformed breast and skin epithelial cells, as well as mouse fibroblasts,