Characterization of Secondary DNA Structures Formed in the c-myb and hTERT Promoters and Their Potential Role in the Regulation of Transcription
AuthorPalumbo, SunMi Lee
AdvisorHurley, Laurence H
Ebbinghaus, Scot W
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.
AbstractIn this dissertation, the formation of unusual G-quadruplexes in the critical regions of the c-myb and hTERT promoters for control of promoter activity was investigated.The c-myb promoter contains three copies of an almost perfect (GGA)4 sequence. We demonstrate that the each (GGA)4 repeat forms a tetrad:heptad G-quadruplex and any two of the three can intramolecularly dimerize to form T:H:H:T G-quadruplexes. The three T:H:H:T G-quadruplex combinations are of differing degrees of stability and can be further stabilized by G-quadruplex interactive compounds. We also demonstrate that the c-myb G-quadruplex forming region is a critical transcriptional regulatory element and interacts with various nuclear proteins including MAZ (Myc Associated Zinc finger protein). The data from luciferase reporter assay show that the c-myb GGA repeat region plays dual roles as a transcriptional activator and an inhibitor by serving as binding sites for the activators and by forming G-quadruplex structures in the region, respectively. Furthermore, we show that MAZ is a transcriptional repressor of the c-myb promoter and binds to both the double-stranded and T:H:H:T G-quadruplex-folded conformations of the GGA repeat region of the c-myb promoter.The hTERT core promoter contains a G-rich region of 12 consecutive G-tracts, which includes three critical Sp1 binding sites. Although this G-rich region has the potential to form multiple G-quadruplexes, our investigation on the full-length G-rich sequence demonstrate that the G-rich region forms a unique G-quadruplex structure in which two tandem intramolecular G-quadruplex structures are present, consisted of one G-quadruplex formed by the G-tracts 1-4 and the other formed by the G-tracts 5, 6, 11, and 12. We also demonstrate that the latter unusual structure contains a 26-base middle loop that likely forms a hairpin structure and is more stable than the other conventional G-quadruplex. Significantly, the formation of this unusual tandem G-quadruplex structure in the full-length will disable all three critical Sp1 binding sites, which will dramatically downregulate hTERT expression. G-quadruplex formation in the hTERT promoter suggests that the effect of G-quadruplex interactive ligands on telomerase inhibition and telomere shortening may be exerted by the direct interaction between the hTERT G-quadruplex structure and the ligands.
Degree ProgramCancer Biology