Identification of novel genes with important functions in glioblastoma multiforme and acute myeloid leukemia

Abstract

Glioblastoma multiforme (GBM) is one of the most common and aggressive brain tumors. The cancer stem cells of GBM (GSCs) are notorious for being invasive as well as resistant to radiation and chemotherapy. The current treatment options for GBM lack specificity and result in severe side effects. Therefore, the need for finding novel and efficient treatments with high specificity in GBM has become paramount.

In study I, to assess the role of various cytoskeletal regulators as potential biomarkers for prognosis and treatment design in GBM, we analyzed gene expression through a bioinformatics approach. Using this method, we identified six genes having a potential value as biomarkers. In combination, we performed a small molecule screen using various Food and Drug Administration (FDA) approved oncology drugs and compared the effects of these compounds, on GBM cytoskeleton, to the conventional chemotherapeutic temozolomide (TMZ). Our results show the importance of cytoskeletal regulators in GBM and the need for combinatorial therapies.

In study II, to identify novel genes required for the growth of acute myeloid leukemia (AML), we performed a large scale short hairpin RNA (shRNA) screen in AML cells and non-transformed bone marrow (BM) cells. We identified the chromatin remodeler, CHD4, as essential for leukemic growth and validated its role in-vitro and in-vivo using RNA interference and CRISPR-Cas9 approaches. More importantly, we found that CHD4 was not required for the growth of normal hematopoietic cells. The study suggests CHD4 as a novel therapeutic target in childhood AML.

To identify genes that are required for the growth of GCSs, in studies III and IV, we performed an unbiased functional shRNA screen. Using this approach, in study III, we identified ubiquitin C-terminal hydrolase-L1 (UCHL1) as being selectively essential for the growth of GSCs. Inhibition of UCHL1 was detrimental to GBM cells, caused cell cycle arrest at G0 phase and induced apoptosis. Small molecule inhibitors of UCHL1 effectively and specifically reduced viability of GBM cells and did not affect viability or function of mature neurons.

In study IV, we also developed a new shRNA/CRISPR-Cas9 modular vector system for efficient and multiplex validation of genes. From the screening data, we identified Ariadne RBR E3 Ubiquitin Protein Ligase 1 (ARIH1) and Ariadne RBR E3 Ubiquitin Protein Ligase 2 (ARIH2) to be specifically required for the growth of GBM cells. Inhibition of ARIH1 and ARIH2 effectively reduced cell growth of various GBM cell lines, and loss of ARIH2 specifically induced cell cycle arrest and sensitivity to DNA damage. Our data from studies III and IV suggests UCHL1, ARIH1 and ARIH2 as novel targets for future GBM therapies.