Abstract
Glioblastoma, the most common malignant tumor in the brain, lacks effective treatments and is currently incurable. To identify novel drug targets for this deadly cancer, the publicly available results of RNA interference screens from the Project Achilles database were analyzed. Ten candidate genes were identified as survival genes in 15 glioblastoma cell lines. RAN, member RAS oncogene family (RAN) was expressed in glioblastoma at the highest level among all candidates based upon cDNA microarray data. However, Kaplan-Meier survival analysis did not show any correlation between RAN mRNA levels and patient survival. Because RAN is a small GTPase that regulates nuclear transport controlled by karyopherin subunit beta 1 (KPNB1), RAN was further analyzed together with KPNB1. Indeed, GBM patients with high levels of RAN also had more KPNB1 and levels of KPNB1 alone did not relate to patient prognosis. Through a Cox multivariate analysis, GBM patients with high levels of RAN and KPNB1 showed significantly shorter life expectancy when temozolomide and promoter methylation of O6-methylguanine DNA methyltransferase were used as covariates. These results indicate that RAN and KPNB1 together are associated with drug resistance and GBM poor prognosis. Furthermore, the functional blockade of RAN and KPNB1 by importazole remarkably suppressed cell viability and activated apoptosis in GBM cells expressing high levels of RAN, while having a limited effect on astrocytes and GBM cells with undetectable RAN. Together, our results demonstrate that RAN activity is important for GBM survival and the functional blockade of RAN/KPNB1 is an appealing therapeutic approach.
Highlights
Glioblastoma (GBM) is an aggressive tumor generally found in the cerebral hemispheres of the brain
To identify survival genes from RNA interference (RNAi) screens in 15 GBM cell lines, we followed the following criteria: [1] Candidate genes should be targeted by two different short hairpin RNAs (shRNAs); [2] The fold change of shRNA loss should be
These results suggest that GBM cells expressing RAS oncogene family (RAN) have a high-index of proliferation, indicative of a detectable activity of RAN
Summary
Glioblastoma (GBM) is an aggressive tumor generally found in the cerebral hemispheres of the brain. RAN in Glioblastoma live longer than 5 years after diagnosis and aggressive treatments, such as chemotherapy, radiation therapy, and surgical resection [1, 3,4,5]. Surgery is not sufficient for a clean and complete resection of the tumor mass due to the infiltration of tumor cells into the normal brain parenchyma. The remaining tumor cells are often refractory to chemo drugs and radiation, thereby contributing to the high incidence of tumor recurrence that is robustly associated with a poor prognosis of GBM [6,7,8,9].
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