Acute Promyelocytic Leukemia (APL) results from an accumulation of undifferentiated promyelocyte progenitors. Complete clinical remission of APL can be achieved through therapy with retinoic acid (RA). However, patients treated with RA alone almost invariably develop resistance to RA. We have found that tumor necrosis factor (TNF) and RA can synergize to induce differentiation of RA sensitive APL cells in a much shorter period of time than RA alone. In addition, this combination can also overcome the maturation block of RA resistant APL cells and the non-APL leukemia cell line U937 leading to differentiation. Correlating with this, we found synergistic induction of several genes at early and late time points in both the RA sensitive and resistant cell lines. Through use of neutralization antibodies, we found the protein product of one of these genes, the receptor for the macrophage colony stimulating factor, was important in mediating the differentiation effects of TNF and RA. / To better understand transcriptional activation with RA and TNF we used the promoter of a gene synergistically induced by RA and TNF, Dif-2, as a model to investigate the mechanism whereby the two agents interact on the level of transcription at early time periods. We used ChIP analysis to study the accessibility of the promoter to binding by various transcription factors and the recruitment of cofactors in response to RA and TNF. We found that upon RA treatment, there was a release of corepressors and a decrease in histone methylation. This was accompanied by a subsequent increase in binding of the transcription factor PU.1, a recruitment of coactivators, as well as Snf5 (a component of the Swi/Snf complex), and an increase in histone acetylation. Interestingly, TNF could only stimulate NF-kappaB (downstream effectors of TNF) binding to the Dif-2 promoter when cells were cotreated with RA. Furthermore, TNF and RA lead to a heightened level of active, phosphorylated RNA Pol II at the Dif-2 promoter. Correlating with this was heightened recruitment of TFIIH, a known Pol II kinase. This may represent a mechanism whereby RA and TNF act in synergy to activate Pol II. These data suggest a novel mechanism for synergy between signaling pathways where RA can trigger a conformation change in a target promoter/enhancer region resulting in a more open conformation that is conducive to transcription factor binding in response to other stimuli.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.85103 |
| Date | January 2004 |
| Creators | Witcher, Michael Robert Ralph |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Division of Experimental Medicine.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 002166416, proquestno: AAINR06350, Theses scanned by UMI/ProQuest. |
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