A novel G-quadruplex-forming GGA repeat region in the c-myb promoter is a critical regulator of promoter activity

Abstract

The c-myb promoter contains multiple GGA repeats beginning 17 bp downstream of the transcription initiation site. GGA repeats have been previously shown to form unusual DNA structures in solution. Results from chemical footprinting, circular dichroism and RNA and DNA polymerase arrest assays on oligonucleotides representing the GGA repeat region of the c-myb promoter demonstrate that the element is able to form tetrad:heptad:heptad:tetrad (T:H:H:T) G-quadruplex structures by stacking two tetrad:heptad G-quadruplexes formed by two of the three (GGA)4 repeats. Deletion of one or two (GGA)4 motifs destabilizes this secondary structure and increases c-myb promoter activity, indicating that the G-quadruplexes formed in the c-myb GGA repeat region may act as a negative regulator of the c-myb promoter. Complete deletion of the c-myb GGA repeat region abolishes c-myb promoter activity, indicating dual roles of the c-myb GGA repeat element as both a transcriptional repressor and an activator. Furthermore, we demonstrated that Myc-associated zinc finger protein (MAZ) represses c-myb promoter activity and binds to the c-myb T:H:H:T G-quadruplexes. Our findings show that the T:H:H:T G-quadruplex-forming region in the c-myb promoter is a critical cis-acting element and may repress c-myb promoter activity through MAZ interaction with G-quadruplexes in the c-myb promoter.

An RNA-binding Protein, Lin28, Recognizes and Remodels G-quartets in the MicroRNAs (miRNAs) and mRNAs It Regulates

“…G-quadruplexes are found within DNAs in eukaryotic telomeres (66); the promoter regions of some cancer-related genes, including BCL2 (67), KIT (68), MYB (69), MYC (70), HIF1A (71), hTERT (72), KRAS (73), RB (74), and VEGF (75); immunoglobulin gene switch regions (76); and ribosomal genes (77). G4-intercalating agents have been assessed for anticancer ther-apy (57,50,51).…”

Cellular uptake and binding of guanidine-modified phthalocyanines to KRAS/HRASG-quadruplexes

“…VEGF, 7 c-myb 8 and ILPR (insulin gene). 9 Due to its potential as a cancer-specific target, there is considerable interest in developing small ligands that stabilize G4-DNA.…”

Targeting G-Quadruplex DNA with Small Molecules

“…[48] These sequences are also highly susceptible to S1 nuclease cleavage, [49] DNA repair, [50] and can fold into stable non-duplex structures in vitro. [48,51,52] In the case of a 14-nucleotide repeated sequence [20][21][22][23][24][25][26][27] Alternatively, two-, three-, or four DNA strands can associate in intermolecular G-quadruplex structures.…”

“…Recently, a trinucleotide repeat (GGA) capable of forming G-quadruplex structure(s) was shown to have both transcriptional activation and repressor activities in the context of the c-MYB promoter. [52] Another early example of a putative G-quadruplex-containing promoter is the non-repetitive nuclease hypersensitive element 'NHEIII 1 ' located 142 bp upstream of the P1 promoter of the c-MYC gene. By using a combination of DNA point mutations and small molecule binding interactions, a correlation between G-quadruplex stabilization and the suppression of promoter activity was established by the Hurley Lab.…”