Role of EphA3 receptor mutations in lung cancer
Initial Award Abstract
Prolonged exposure to the carcinogens in tobacco smoke causes gene mutations that drive the transformation of epithelial cells into malignant cancer cells. Particularly affected are the epithelial cells of the lungs, which receive the greatest exposure to the carcinogens. Recent gene sequencing projects have identified a large number of somatic mutations in functional domains of the EphA3 receptor tyrosine kinase in human lung cancer specimens and cell lines, strongly suggesting that mutations in this Eph receptor play a causal role in the oncogenic transformation of lung epithelial cells. The Eph family is the largest family of receptor tyrosine kinases, and members of this family are highly expressed in many tumor types. Furthermore, increasing evidence suggests that the Eph receptors play important roles in cancer pathogenesis, but these roles appear to be complex and are not well understood. Both tumor suppressor and tumor promoting activities have been reported for the Eph receptors, which may depend on whether these receptors are activated by their ligands, the ephrins, or engaged in crosstalk with oncogenic growth factor receptors. The cellular context may also influence the outcome of Eph/ephrin signaling.
EphA3 is one of the Eph receptors found to be the most frequently mutated in cancer cells, but its role in cancer has not yet been extensively investigated. Seventeen different EphA3 missense mutations have been identified so far in lung cancer, many of which would be expected to interfere with EphA3 function. Some of these mutations are in the ephrin-binding domain, suggesting that they could affect the ligand-binding ability of EphA3. Others are in the kinase domain, suggesting that they could modulate kinase activity. However, the functional consequences of the mutations remain to be demonstrated. We propose to investigate the role of EphA3 in lung cancer and elucidate how EphA3 mutations affect the behavior of lung cancer cells. In our work with other Eph receptors, we found that Eph receptor activation by their ephrin ligands inhibits major oncogenic signaling pathways and the malignant properties of cancer cells. We therefore hypothesize that some of the EphA3 mutations that have been identified in lung cancer may contribute to lung cancer progression by inhibiting ephrin binding. On the other hand, if we find that the mutations identified in the EphA3 kinase domain increase kinase activity, as would be predicted from the nature of the mutations, this will suggest the importance of kinase activity in the tumor promoting (possibly ephrinindependent) effects EphA3.
Here we propose to generate those EphA3 mutants identified in lung cancer that are most likely to affect receptor function. We will then examine whether the mutations affect the ability of EphA3 to bind ephrin ligands and its kinase activity. We will also examine how EphA3 expression and activation by ephrin ligands affects oncogenic intracellular signaling pathways and lung cancer cell growth and migration/invasion. Finally, we will assess the in vivo effects of EphA3 expression and of mutations that affect EphA3 ligand binding or kinase activity using a lung cancer xenograft model. Our long-term objective is to elucidate the importance of EphA3 function in lung cancer
pathogenesis. This information will establish whether EphA3 could be a useful therapeutic target in lung cancer and identify the strategies to modulate EphA3 function that would be most effective for anti-cancer treatment. |