Up-regulation of EphA2 and down-regulation of EphrinA1 are associated with the aggressive phenotype and poor prognosis of malignant glioma

Abstract

Malignant gliomas display over-expression of the receptor tyrosine kinase EphA2. However, expression levels of the EphA2 ligand, EphrinA1, have not been fully elucidated. Seventy-eight patients with primary gliomas were included in this study who underwent surgical resection, radiation, and chemotherapy. The expression of EphA2 and EphrinA1 in tumors was assessed by immunohistochemistry and was statistically analyzed in combination with the follow-up data of patients. EphA2 was highly expressed in most malignant gliomas, but EphrinA1 was expressed at low levels in these tumors. The increased EphA2 expression is associated with higher-grade histology and poor patient prognosis. Contrary to this, the increased EphrinA1 expression is associated with lower-grade histology, but not associated with poor patient prognosis. Moreover, patients with tumors positive for EphA2 and negative for EphrinA1 had significantly shorter overall and progression-free survival than patients with tumors positive for both EphA2 and EphrinA1, negative for both EphA2 and EphrinA1, or negative for EphA2 and positive for EphrinA1. RNAi-mediated suppression of endogenous EphA2 in human glioblastoma multiforme cells resulted in increased EphrinA1 levels, as well as decreased cell viability, anchorage independence and in vitro invasion, and increased apoptosis. Furthermore, suppression of EphA2 resulted in delayed tumor growth in mice xenografts. Together, these data indicate that up-regulation of EphA2 and down-regulation of Ephrina1 may correlate with poor prognosis for patients with high-grade glioma. EphA2 suppression partially reversed the aggressive phenotypes of malignant gliomas, possibly through up-regulating EphrinA1 expression, which may help explain how EphA2 modulates the malignant progression of gliomas.