Date of Award

6-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Program

Biomedical Sciences

Track

Cancer and Developmental Biology

Research Advisor

Lawrence M. Pfeffer, Ph.D.

Committee

Suzanne J. Baker, Ph.D. Andrew M. Davidoff, M.D. Meiyun Fan, M.D. Ph.D. Ronald N. Laribee, Ph.D. Martine F. Roussel, Ph.D.

Keywords

BRG1, Cancer, CSC, GBM, STAT3, SWI/SNF

Abstract

Glioblastoma Multiforme (GBM) is an aggressive brain tumor, characterized by high cellular heterogeneity, is refractory to treatment and has dismal prognosis. These characteristics of GBM have suggested the presence of stem-like cells that have the ability to initiate and maintain tumors of a heterogeneous nature, and bestow resistance to current therapeutic regimens. It is therefore imperative to identify the dysregulated molecular pathways which enable the maintenance of these cells in a stem-like state in order to inform strategies to therapeutically target them.

In this study, we investigated the role of the Y705 and S727 phosphorylation domains of STAT3, a multifunctional transcription factor that is constitutively activated in the glioma stem like cells or glioma-initiating cells (GIC). We demonstrate that STAT3 is critical for GIC tumorigenesis. Furthermore, we show that the Y705 phosphorylation of STAT3 is necessary for GIC-induced tumor formation. We demonstrate that in GICs Y705 and S727 phosphorylation of STAT3 is sequential, such that Y705 phosphorylation precedes S727 phosphorylation. In addition, we also observed that S727 phosphorylation is dependent on Y705 phosphorylation.

Furthermore, by targeted microarrays and RNA Sequencing we have identified ~160 genes that are STAT3-regulated. These genes are involved in several critical biological processes including the cell cycle, hypoxia, TGF- and the extracellular matrix. We further show that a subset of these STAT3-regulated genes are also associated with GBM disease stratification.

Additionally, we demonstrate that BRG1, the catalytic component of the chromatin remodeling complex SWI/SNF, plays a critical role in the maintenance of the GICs and in the drug resistance of these cells. We show that BRG1 promotes the expression of key stem cell markers, Oct4, Nanog and CD44, while loss of BRG1 led to upregulation of astrocyte differentiation marker GFAP and S100, as well as the oligodendroglial marker Olig2. These findings indicate that BRG1 loss in GICs resulted in a transition towards a more differentiated fate. Targeted microarrays identified several genes that are dependent on BRG1 in GICs. One of these genes is TXNIP, a major redox regulator that is also a negative regulator of glycolysis. We found that TXNIP expression in the GICs is regulated by both BRG1 and STAT3. Furthermore, using genetic and pharmacological means we demonstrate that BRG1 plays a critical role in the chemo sensitivity of the GICs.

ORCID

http://orcid.org/dgan-guly-@uth-sc.e-du

DOI

10.21007/etd.cghs.2018.0461

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