Abstract 2136: Nuclear trafficking of Tie2 is associated with radioresistance of gliomas

Abstract

Abstract Resistance and relapse are still primary causes that result in poor effectiveness of chemo- and radiotherapy in glioblastoma multiforme (GBMs), the most frequent subtype of primary brain tumors in adults. Patients suffering from this disease exhibit a median survival that ranges from 9 to 15 month, and the disease invariably recur after therapy due to the presence of cells exhibiting a multidrug-resistance phenotype. Aberrant DNA repair pathways can enable tumor cells to survive DNA damage that is induced after chemotherapy and radiotherapy. Therefore, development of new therapeutic strategies requires the identification of key molecular pathways regulating the resistant phenotype of these tumors. Previous work from our laboratory showed that Tie2, a previously considered specific vascular tyrosine kinase receptor, was expressed in glioma tumors and in brain tumor stem cells. The degree of expression of Tie2 was related to the malignancy of these tumors, and played an essential role in the multidrug resistance phenotype of gliomas. Our current research is focused on deciphering the mechanisms underlying this critical function. We found that density of Tie2 receptors in the membrane decreased upon exposure to both ligand (angiopoietin 1, Ang1) and ionizing irradiation (IR). Immunoflurorescence studies using confocal microscope and subcellular fractionation followed by Western blot showed that Tie2 traffics from the cellular membrane to the nucleus upon both stimuli. Western blot analysis using antibodies against N- and C-terminus, and against phosphorylated-Tie2, indicated that the nuclear Tie2 is a full-length protein, and importantly that is phosphorylated at Tyr992. Of biological importance, to find the role of Tie2 in the nucleus, we irradiated the glioma cells, U251.Tie2, and found that ionizing radiation also helps Tie2 to move to the nucleus and importantly it binds with γH2AX one of the key DNA repair protein complex. By using confocal microscopy we found that Tie2 makes foci with γH2AX after DNA damage. We also found that after genotoxic stress like ionizing radiation or DNA-damaging drugs, Tie2-expressing cells were more resistant to DNA damaging effect, as assessed by cell viability assay and comet assay. Collectively, the nuclear Tie2 plays important role in the DNA repair which will result in the design of Tie2-targeting combinational therapies for patients with glioblastomas. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2136. doi:1538-7445.AM2012-2136