In vivo RNAi screen identifies NLK as a negative regulator of mesenchymal activity in glioblastoma.

Jason K Sa,Suji Han,Yong Jae Shin,Hee Jin Cho,Yeup Yoon,Yeonghwan Kim,Tohru Ishitani,Do-Hyun Nam,Gi-Soo Kim,Kyeung Min Joo,Woon Jin Kim,Jin-Ku Lee,Patrick J Paddison,Misuk Kim,Jeongwu Lee

doi:10.18632/oncotarget.3980

Abstract

Glioblastoma (GBM) is the most lethal brain cancer with profound genomic alterations. While the bona fide tumor suppressor genes such as PTEN, NF1, and TP53 have high frequency of inactivating mutations, there may be the genes with GBM-suppressive roles for which genomic mutation is not a primary cause for inactivation. To identify such genes, we employed in vivo RNAi screening approach using the patient-derived GBM xenograft models. We found that Nemo-Like Kinase (NLK) negatively regulates mesenchymal activities, a characteristic of aggressive GBM, in part via inhibition of WNT/β-catenin signaling. Consistent with this, we found that NLK expression is especially low in a subset of GBMs that harbors high WNT/mesenchymal activities. Restoration of NLK inhibited WNT and mesenchymal activities, decreased clonogenic growth and survival, and impeded tumor growth in vivo. These data unravel a tumor suppressive role of NLK and support the feasibility of combining oncogenomics with in vivo RNAi screen.

Highlights

Glioblastoma (GBM) is the most common and lethal primary brain tumor [1]
As we found that Nemo-Like Kinase (NLK) overexpression impeded GBM proliferation and clonogenic growth, we further evaluated the effects of NLK on cell cycle kinetics and apoptosis
We presented a systemic approach for identifying and validating a candidate putative tumor suppressor in GBM, which consists of the candidate gene selection based on genomic copy number alterations and mRNA expression levels of GBM specimen, in vivo loss-of-function screening, and subsequent validation in patient-derived primary GBM models

Summary

Introduction

Glioblastoma (GBM) is the most common and lethal primary brain tumor [1]. The current standard-of-care for GBM patients provides only palliation with a median survival of 14.6 months in spite of surgery, chemotherapy, and radiation [2, 3]. Molecular circuits and factors behind its aggressive behaviors and malignant characteristics remain incompletely understood. One of the key components for GBM malignancy is the loss of functional tumor suppressor genes. Tumor suppressors act in signaling networks that restrict cellular proliferation and present barriers to malignant transformation. Even though tumor suppressor genes per se may not be considered optimal as drug targets, their loss of function could create cellular dependency which could be exploited therapeutically [4]

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