Mitochondria: A Crossroads for Oxidative Stress and Apoptosis Resistance in Lymphoma

Persistent Link:
http://hdl.handle.net/10150/195161
Title:
Mitochondria: A Crossroads for Oxidative Stress and Apoptosis Resistance in Lymphoma
Author:
Wilkinson, Sarah Thomas
Issue Date:
2008
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
Non-Hodgkin lymphoma is commonly associated with chronic infection and inflammation. Such conditions are characterized by chronic oxidative stress. Because apoptosis signaling is often mediated by reactive oxygen species, lymphoma arising in the context of oxidative stress may become resistant to these apoptosis signals. Resistance to oxidative stress could contribute to tumorigenesis and limit response to chemotherapy, as apoptosis induced by many drugs involves reactive oxygen species. We used a cell culture model to understand how changes in the ability to handle oxidative stress contribute to apoptosis resistance. WEHI7.2 murine thymic lymphoma cells transfected with catalase or selected for resistance to hydrogen peroxide acquire a concomitant resistance to apoptosis induced by glucocorticoids. Cytochrome c release is delayed in these variants, demonstrating that apoptosis resistance lies upstream, in the signaling phase, or in the mitochondria themselves. By comparing the apoptosis-sensitive WEHI7.2 parental cells with the oxidative stress- and apoptosis-resistant variant cells, we investigated the contribution of cytosolic and mitochondrial changes to glucocorticoid-induced apoptosis. We showed that neither JNK kinase signaling, nor GSTπ, a redox sensor protein which regulates JNK, is activated during glucocorticoid-induced apoptosis. Our work using isolated mitochondria and recombinant tBid protein in cell-free apoptosis assays showed that the apoptosisresistant variants are intrinsically resistant to the release of cytochrome c and other intermembrane space proteins. The resistance was mediated upstream and within the mitochondria, and occurred at both steps controlling cytochrome c release. Given that the resistant variants demonstrated alterations in mitochondrial apoptotic function, we investigated mitochondrial protein changes that could explain these differences. An increased expression of cytochrome c was observed in the resistant variants, but selective reduction of cytochrome c expression showed that this change alone was not sufficient to affect sensitivity. The balance of pro- and anti-apoptotic Bcl-2 family members in untreated cells also did not explain intrinsic resistance. Alterations in Bcl-2 protein levels following treatment could contribute to glucocorticoid resistance, but additional work to test Bcl-2 family interactions will be required. We have identified points of resistance that are important in glucocorticoid-induced apoptosis and may also contribute to resistance to novel mitochondrial-targeting drugs.
Type:
text; Electronic Dissertation
Keywords:
Mitochondria; Apoptosis; Oxidative stress; Cytochrome c; Lymphoma
Degree Name:
PhD
Degree Level:
doctoral
Degree Program:
Cancer Biology; Graduate College
Degree Grantor:
University of Arizona
Advisor:
Briehl, Margaret M
Committee Chair:
Briehl, Margaret M

Full metadata record

DC FieldValue Language
dc.language.isoENen_US
dc.titleMitochondria: A Crossroads for Oxidative Stress and Apoptosis Resistance in Lymphomaen_US
dc.creatorWilkinson, Sarah Thomasen_US
dc.contributor.authorWilkinson, Sarah Thomasen_US
dc.date.issued2008en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractNon-Hodgkin lymphoma is commonly associated with chronic infection and inflammation. Such conditions are characterized by chronic oxidative stress. Because apoptosis signaling is often mediated by reactive oxygen species, lymphoma arising in the context of oxidative stress may become resistant to these apoptosis signals. Resistance to oxidative stress could contribute to tumorigenesis and limit response to chemotherapy, as apoptosis induced by many drugs involves reactive oxygen species. We used a cell culture model to understand how changes in the ability to handle oxidative stress contribute to apoptosis resistance. WEHI7.2 murine thymic lymphoma cells transfected with catalase or selected for resistance to hydrogen peroxide acquire a concomitant resistance to apoptosis induced by glucocorticoids. Cytochrome c release is delayed in these variants, demonstrating that apoptosis resistance lies upstream, in the signaling phase, or in the mitochondria themselves. By comparing the apoptosis-sensitive WEHI7.2 parental cells with the oxidative stress- and apoptosis-resistant variant cells, we investigated the contribution of cytosolic and mitochondrial changes to glucocorticoid-induced apoptosis. We showed that neither JNK kinase signaling, nor GSTπ, a redox sensor protein which regulates JNK, is activated during glucocorticoid-induced apoptosis. Our work using isolated mitochondria and recombinant tBid protein in cell-free apoptosis assays showed that the apoptosisresistant variants are intrinsically resistant to the release of cytochrome c and other intermembrane space proteins. The resistance was mediated upstream and within the mitochondria, and occurred at both steps controlling cytochrome c release. Given that the resistant variants demonstrated alterations in mitochondrial apoptotic function, we investigated mitochondrial protein changes that could explain these differences. An increased expression of cytochrome c was observed in the resistant variants, but selective reduction of cytochrome c expression showed that this change alone was not sufficient to affect sensitivity. The balance of pro- and anti-apoptotic Bcl-2 family members in untreated cells also did not explain intrinsic resistance. Alterations in Bcl-2 protein levels following treatment could contribute to glucocorticoid resistance, but additional work to test Bcl-2 family interactions will be required. We have identified points of resistance that are important in glucocorticoid-induced apoptosis and may also contribute to resistance to novel mitochondrial-targeting drugs.en_US
dc.typetexten_US
dc.typeElectronic Dissertationen_US
dc.subjectMitochondriaen_US
dc.subjectApoptosisen_US
dc.subjectOxidative stressen_US
dc.subjectCytochrome cen_US
dc.subjectLymphomaen_US
thesis.degree.namePhDen_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineCancer Biologyen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorBriehl, Margaret Men_US
dc.contributor.chairBriehl, Margaret Men_US
dc.contributor.committeememberBernstein, Harrisen_US
dc.contributor.committeememberBowden, G. Timen_US
dc.contributor.committeememberJacobson, Elaineen_US
dc.contributor.committeememberMonks, Terrenceen_US
dc.identifier.proquest2783en_US
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