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.
| Identifer | oai:union.ndltd.org:arizona.edu/oai:arizona.openrepository.com:10150/195161 |
| Date | January 2008 |
| Creators | Wilkinson, Sarah Thomas |
| Contributors | Briehl, Margaret M, Briehl, Margaret M, Bernstein, Harris, Bowden, G. Tim, Jacobson, Elaine, Monks, Terrence |
| Publisher | The University of Arizona. |
| Source Sets | University of Arizona |
| Language | English |
| Detected Language | English |
| Type | text, Electronic Dissertation |
| 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. |
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