AdvisorHurley, Laurence H
Committee ChairHurley, Laurence H
MetadataShow full item record
PublisherThe University of Arizona.
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.
AbstractAberrant expression of Platelet-derived growth factor A (PDGF-A) and PDGF receptor-β (PDGFR-β) play critical roles in the angiogenesis and proliferation of several malignancies. In this dissertation I explore the transcriptional regulatory role of the Gquadruplex- forming regions in the promoters of human PDGF-A and PDGFR-β, and identify new targets for developing small molecules to modulate their expression in tumors. For PDGF-A promoter, our studies focus on two essential nuclease hypersensitive elements, NHE(PDGF-A) and 5´-end far upstream 5´-SHS. The structural aspects of the intramolecular G-quadruplexes formed in NHE(PDGF-A) and the ligands to stabilize these secondary DNA structures have been investigated by using singlestranded and duplex DNA of the NHE(PDGF-A). We demonstrate that the G-quadruplexinteractive compound, TMPyP4, can selectively inhibit the basal promoter activity of PDGF-A, suggesting that the NHE(PDGF-A) G-quadruplex acts as a repressor in PDGF-A transcription. We also found that the 5´-SHS G-rich strand oligomer can invade the NHE(PDGF-A) and form a unique three-stranded complex in supercoiled plasmids, which is facilitated by potassium ions and TMPyP4. Therefore, we propose a novel molecular mechanism for transcriptional silencing of the NHE(PDGF-A) by 5´-SHS in the PDGF-A promoter, in that the formation of G-quadruplex in the NHE(PDGF-A) provides a platform for the G-rich strand of 5´-SHS to invade and form a partial duplex DNA with the C-rich strand of the NHE(PDGF-A), resulting in displacement of hnRNP K and thus transcription silencing. Prior to the studies describe here, the promoter of human PDGFR-β had not been identified. Herein, we have cloned and characterized the first functional promoter of human PDGFR-β gene. A crucial highly GC-rich region (NHE(PDGFR-β)) in the human PDGFR-β promoter has been identified by its hypersensitivity to the S1 nuclease. Further studies demonstrate that stable G-quadruplex structures can form in the G-rich strand of NHE(PDGFR-β). The G-quadruplex-interactive molecule, telomestatin, can selectively stabilize G-quadruplexes formed in the human PDGFR-β promoter and inhibit its expression in Daoy cells. On the basis of these results, we propose that ligandmediated stabilization of the G-quadruplex structure in the proximal promoter region of human PDGF-A or PDGFR-β can be used to modulate the expression of these protooncogenes.
Degree ProgramPharmaceutical Sciences