title: An intramolecular G-quadruplex structure with mixed parallel/antiparallel G-strands formed in the human BCL-2 promoter region in solution.
abstract: We report the first G-quadruplex structure formed in the promoter region of the human bcl-2. Bcl-2 is a potent oncoprotein that functions as an inhibitor of cell apoptosis and has been found to be aberrantly overexpressed in a wide range of human tumors. A highly GC-rich region upstream of the P1 promoter plays an important role in the regulation of the transcriptional activity of the bcl-2 oncogene. The purine-rich strand of this region contains multiple runs of guanines and can form three distinct intramolecular G-quadruplexes in K+-containing solution. Of these, the G-quadruplex formed within the middle four consecutive guanine runs has been shown to be the most stable G-quadruplex structure, while it is also a mixture of loop isomers. The predominant G-quadruplex structure formed in this region was studied by NMR. Our results demonstrate a novel folding of a unique intramolecular G-quadruplex structure with mixed parallel/antiparallel G-strands. This G-quadruplex structure contains three G-tetrads connected with a single-nucleotide double-chain-reversal side loop and two lateral loops. The first three-nucleotide CGC loop in the bcl-2 promoter sequence forms a lateral loop, as opposed to a double-chain-reversal side loop observed in a similar sequence in the c-MYC promoter, which appears to largely determine the overall folding of the bcl-2 G-quadruplex. Furthermore, both the bcl-2 and c-MYC promoter sequences contain the G3NG3 sequence motif, which forms a stable double-chain-reversal, parallel-stranded structural motif. This predominant bcl-2 G-quadruplex represents an attractive novel target for the design of new anticancer drugs that specifically modulate bcl-2 gene expression.
authors.affiliation: College of Pharmacy, University of Arizona, Tucson, 85721, USA.
authors.forename: Jixun
authors.initials: J
authors.lastname: Dai
authors.forename: Thomas S
authors.initials: TS
authors.lastname: Dexheimer
authors.forename: Ding
authors.initials: D
authors.lastname: Chen
authors.forename: Megan
authors.initials: M
authors.lastname: Carver
authors.forename: Attila
authors.initials: A
authors.lastname: Ambrus
authors.forename: Roger A
authors.initials: RA
authors.lastname: Jones
authors.forename: Danzhou
authors.initials: D
authors.lastname: Yang
mesh_terms: D001483:Base Sequence; D002942:Circular Dichroism; D004247:DNA / Q000737:chemistry* / Q000235:genetics*; D054856:G-Quadruplexes; D019254:Genes, bcl-2; D006147:Guanine / Q000737:chemistry; D006801:Humans; D019906:Nuclear Magnetic Resonance, Biomolecular; D009690:Nucleic Acid Conformation; D011401:Promoter Regions, Genetic; D012996:Solutions
chemical_list: D012996:Solutions; D006147:Guanine; D004247:DNA