Document Type

Dissertation

Degree

Doctor of Philosophy (PhD)

Major/Program

Biomedical Sciences

First Advisor's Name

Jeremy W. Chambers

First Advisor's Committee Title

Committee chair

Second Advisor's Name

Ralph DeBerardinis

Second Advisor's Committee Title

Committee member

Third Advisor's Name

Lidia Kos

Third Advisor's Committee Title

Committee member

Fourth Advisor's Name

Nazira El-Hage

Fourth Advisor's Committee Title

Committee member

Fifth Advisor's Name

Helen Tempest

Fifth Advisor's Committee Title

Committee member

Keywords

Sab, Mitochondria, Metabolism, Glioblastoma, Neuroblastoma

Date of Defense

6-22-2018

Abstract

Glioblastoma (GBM) is the most common and aggressive type of brain cancer, with an average life expectancy of 15 months. The standard of care for GBM, surgery accompanied by radiation and chemotherapy (temozolomide-TMZ), has not changed in over 10 years illustrating the need for new and efficacious treatments. Therefore, it is imperative to improve our knowledge of GBM physiology to understand the mechanisms driving recurrence and chemoresistance so that more effective therapeutic options can be developed. Mitochondria-cell communication is key to monitor and maintain both mitochondrial and cellular health, and signaling events on the outer mitochondrial membrane (OMM) have emerged as a crucial signal integration site for cellular responses. Consequently, proteins on the OMM are crucial to determining cellular survival and dictating organelle physiology. Thus, the goal of our current study is to evaluate OMM proteins to determine how alterations in organelle regulation may impact CNS tumor biology. We first measured the concentrations of Bcl-2 family proteins on mitochondria from ten continuous GBM cell lines and correlated the protein levels to IC50values of genotoxic agents TMZ and irinotecan. We found that Bcl-2 levels corresponded to chemoresistance, while increased Bim concentrations promoted chemosensitivity. In contrast to our studies in gynecological cancers, the concentrations of the pro-dysfunction OMM scaffold protein Sab had no impact on chemosensitivity of the GBM cell lines, despite diminished Sab expression in GBM patients. However, we identified a novel truncated variant of Sab in the GBM cell lines. We found that GBM cells expressing only full-length Sab had a slower proliferation rate than those with the variant, which could be attributed to increased glycolysis in GBM cells expressing the Sab variant. To determine if the lack of Sab-mediated apoptosis was consistent across CNS tumors, we analyzed publicly-available patient data and found that Sab expression is down-regulated in neuroblastoma patients, a pediatric malignancy responsible for 12% of childhood cancer deaths. We found that that inhibiting Sab-mediated signaling in human neuroblastoma (SH-SY5Y cells) enhanced oxidative phosphorylation in a pyruvate dehydrogenase-dependent manner, increased BCl-2 levels (pro-survival), decreased Bim concentrations (pro-apoptotic), and promoted chemoresistance. Furthermore, examination of additional neuroblastoma cells derived from CNS tumors revealed that Sab levels correspond to proliferation rate, metabolic phenotype, and chemosensitivity. Our studies demonstrate the importance of OMM signaling in CNS tumor physiology and emphasizes the importance of cellular context to the outcomes of OMM signaling events.

Identifier

FIDC006885

Available for download on Saturday, July 18, 2020

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