Takafumi Ishii

Abstract 3951: EphA10 exhibits anti-apoptotic activity through its dominant-negative role for EphA signaling in cancer cells

Eph receptors are members of receptor tyrosine kinase family. They are activated by binding of their ligands, ephrins, which regulate numerous physiological responses, including axon guidance, and pattern formation during development. In addition to their important roles during development, several members of the Eph receptor family have been reported to function in carcinogenesis. Recently EphA10 was isolated as the 16th member of the Eph receptor family. EphA10 is expressed in normal testis and binds to ephrin-A. However, biological functions of EphA10 remain unclear. We demonstrate here that EphA10 functions as a dominant-negative receptor for EphA signaling. Our results show that EphA10 is over-expressed in cancer tissues, especially breast and lung cancer tissues as compared with patient-matched adjacent normal tissues. EphA10 binds to ephrin-A2, 3, 4, and 5. Analysis of the amino acid sequence of EphA10 revealed that EphA10 does not have Lys and Asp in the kinase domain, which are necessary for kinase activity nor two Tyr in the juxtamembrane domain, which are necessary for phosphorylation. As expected from the amino acid sequence, no intrinsic tyrosine kinase activity of EphA10 was detected despite its interaction with ephrin-A. To further investigate the mechanism of EphA10 signaling, we tested the role of EphA10 in modulating ephrin-A4 activity. In our experiment, ephrin-A4 suppressed phosphorylation of ERK1/2 in HEK293 cells. EphA10 over-expression in HEK293 cells reduced the effect of ephrin-A4 on ERK1/2. Conversely, reduction of EphA10 expression by antisense oligonucleotides induced apoptosis in the breast cancer cell line ZR-75-1. In addition to its role in shunting ephrin-A response through binding to ephrin-A directly, we found that EphA10 formed a hetero-complex with functional EphA7, suggesting that EphA10 may block EphA signaling by forming non-functional hetero complexes with other functional EphA receptors. Our studies demonstrated that EphA10 has anti-apoptotic function in cancer cells by blocking EphA signaling through its dominant-negative activity. Thus, EphA10 potentially plays an important role in cancer cell survival. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3951.