The role of Quiescin Sulfhydryl Oxidase 1 (QSOX1) in glioblastoma cell behavior
Date
2019
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Publisher
University of Delaware
Abstract
Disulfide bonds are common post-translational modifications that impart stability and functionality onto proteins. Free thiols in reduced, unfolded proteins are oxidized to form disulfide bonds with the reduction of molecular oxygen to hydrogen peroxide. This process is known as oxidative protein folding and occurs primarily in the endoplasmic reticulum. Quiescin Sulfhydryl Oxidase 1 (QSOX1) is a facile disulfide bond generating enzyme that was discovered in our laboratory. The mechanism of oxidative protein folding in the endoplasmic reticulum with emphasis on QSOX1 is discussed in Chapter 1 of this dissertation. Also discussed in Chapter 1 are the biological roles of QSOX1 in normal and diseased tissues. ☐ QSOX1 has been upregulated in a number of cancers including prostate, pancreatic and breast cancer. Its overexpression is correlated to aggressive cancers and poor patient prognosis. Glioblastoma (GBM) is an aggressive, grade IV brain tumor. GBM is extremely difficult to treat as cells invade the brain very quickly and thus, escape surgery to lead to an often more aggressive recurrence. There is a continuing need to understand the mechanism of GBM cell migration and invasion. The role of QSOX1 in GBM is investigated in Chapter 2. We used GBM cell line T98G, to attenuate QSOX1 using lentivirally introduced short hairpin RNA (shRNA). The effect of QSOX1 attenuation on cell morphology, proliferation and migration was investigated in vitro. We also used the embryonic chick brain xenograft model to analyze GBM cell invasion in vivo. Our results indicated that the experimental reduction of QSOX1 expression in GBM cells led to decreased cell proliferation, in vitro migration and in vivo invasion.
Cell adhesion molecule L1CAM (L1, CD171) is another factor that affects GBM cell proliferation, motility and invasion. L1 is present on the surface of exosomes. In our final chapter, Chapter 3, we aimed to determine if L1-decorated exosomes were capable of stimulating GBM cell invasion in vivo. Exosomes from control GBM and L1-attenuated GBM cells were isolated and characterized. L1-decorated and L1-attenuated exosomes were combined with L1-attenuated cells and injected into embryonic chick brain. Our results showed that L1-decorated exosomes were able to increase invasion of L1-attenuated GBM cells in vivo. The increased invasion seemed to be initial and not sustained, thus, indicating a need for continuous L1 availability for prolonged invasion.
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Keywords
Disulfide bonds, Exosomes, Glioblastoma, L1CAM, Oxidative protein folding, QSOX1