One of the common features of malignant human gliomas is the intrinsic ability of single tumor cells to disperse throughout the brain, rendering the virtual failure of all existing therapies to alter the growth of these deadly tumors. Currently, the mechanisms underlying the perilous invasiveness of glioma cells are poorly understood. Acquisition of malignant growth and insidious invasiveness by glioma cells involves multiple genetic alterations including mutations of epidermal growth factor receptor (EGFR) and PTEN. Genetic studies showed that the most common form of EGFR mutants, EGFRvIII and PTEN loss promote glioma cell invasion in the brain. Recently, we identified an up-regulation of engulfment and cell motility 1 (ELMO1) in invasive glioma cell lines. ELMO1 and its binding partner, dedicator of cytokinesis 1 (Dock180) function as a bipartite guanine nucleotide exchange factor (GEF) that activates Rac1 and promotes cell migration of C. elegans, Drosophila and mammalian cells. Using various model systems including analysis of a large number of primary human glioma specimens, we reported that this bipartite Rac1 GEF, ELMO1-Dock180 promotes glioma cell migration and invasion in vitro and ex vivo (brain slice model). Our preliminary studies reveal expression of EGFRvIII with ELMO1-Dock180 and loss of PTEN in invasive areas but not in central regions on these clinical glioma specimens. Exogenous expression of EGFRvIII by human glioma cell lines and short-term cultured primary human glioma cells with endogenous EGFRvIII displayed increases in Rac1 activity, tyrosine phosphorylation of ELMO1 and Dock180, and glioma cell motility. Inhibition of this GEF attenuated EGFRvIII-promoted cell motility. Additionally, knockdown of PTEN in EGFRvIII-expressing glioma cells resulted in induced tyrosine phosphorylation of endogenous ELMO1 and Dock180 and further enhanced cell motility. The goal of this proposal is to investigate the mechanisms by which EGFRvIII and PTEN modulate glioma cell invasion through the ELMO1-Dock180-Rac1 pathway and establish ELMO1-Dock180 as a therapeutic target for glioma treatment. Our central hypothesis is that EGFRvIII stimulates glioma cell invasion through ELMO1-Dock180 and loss of PTEN in EGFRvIII-expressing cells further enhances glioma cell invasion. We will address our hypotheses with three Specific Aims.
In Specific Aim 1, we will test our hypothesis by determining the role of ELMO1-Dock180 in EGFRvIII-stimulated glioma cell motility.
In Specific Aim 2, we will test our hypothesis by evaluating the effect of PTEN in EGFRvIII-ELMO1-Dock180-induced glioma cell motility.
In Specific Aim 3, we will test our hypothesis by determining the impact of inhibition of ELMO1, Dock180, PTEN and their effectors on glioma cell invasion in the brain in invasive gliomas expressing EGFRvIII with known PTEN status. We have excellent model systems in place to test our hypotheses, extensive experience in characterization of glioma cell invasion and all of the necessary resources. The proposed studies could advance our understanding of the inherent ability of glioma cell infiltration and provide important strategies to limit the infiltration of glioma cells in the brain. This project has translational significance in providing new insights into intrinsic invasiveness of glioma cells and exploring approaches that impact the response to existing glioma therapies.
A hallmark of malignant gliomas is the intrinsic ability of single tumor cells to infiltrate throughout the brain, rendering these tumors virtually incurable by all existing therapies and also underlies their great propensity for recurrence. Therefore, further understanding of mechanisms underlying the aberrant cell motility during glioma invasion is imperative because it could lead to developing new strategies to treat malignant diffuse gliomas. In this proposal, we plan to determine the novel role of a bipartite guanine nucleotide exchange factor (GEF) composed of engulfment and cell motility 1 (ELMO1) and dedicator of cytokinesis 1 (Dock180) in glioma cell invasion and investigate the molecular mechanisms by which ELMO1-Dock180 mediate aberrant glioma cell infiltration into the brain. The proposed work has translational significance in providing new insights into intrinsic invasiveness of glioma cells and exploring approaches that impact the response to existing glioma therapies.
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