The major G-quadruplex formed in the human BCL-2 proximal promoter adopts a parallel structure with a 13-nt loop in K+ solution.
The human BCL-2 gene contains a 39-bp GC-rich region upstream of the P1 promoter that has been shown to be critically involved in the regulation of BCL-2 gene expression. Inhibition of BCL-2 expression can decrease cellular proliferation and enhance the efficacy of chemotherapy. Here we report the major G-quadruplex formed in the Pu39 G-rich strand in this BCL-2 promoter region. The 1245G4 quadruplex adopts a parallel structure with one 13-nt and two 1-nt chain-reversal loops. The 1245G4 quadruplex involves four nonsuccessive G-runs, I, II, IV, V, unlike the previously reported bcl2 MidG4 quadruplex formed on the central four G-runs. The parallel 1245G4 quadruplex with the 13-nt loop, unexpectedly, appears to be more stable than the mixed parallel/antiparallel MidG4. Parallel-stranded structures with two 1-nt loops and one variable-length middle loop are found to be prevalent in the promoter G-quadruplexes; the variable middle loop is suggested to determine the specific overall structure and potential ligand recognition site. A limit of 7 nt in loop length is used in all quadruplex-predicting software. Thus, the formation and high stability of the 1245G4 quadruplex with a 13-nt loop is significant. The presence of two distinct interchangeable G-quadruplexes in the overlapping region of the BCL-2 promoter is intriguing, suggesting a novel mechanism for gene transcriptional regulation and ligand modulation.
Department of Pharmacology and Toxicology, College of Pharmacy, †Department of Chemistry, §BIO5 Institute, ∥The Arizona Cancer Center, University of Arizona , 1703 East Mabel Street, Tucson, Arizona 85721, United States.
Prashansa
P
Agrawal
Clement
C
Lin
Raveendra I
RI
Mathad
Megan
M
Carver
Danzhou
D
Yang
D001483:Base Sequence; D054856:G-Quadruplexes; D019254:Genes, bcl-2; D006147:Guanine / Q000737:chemistry*; D006801:Humans; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D009690:Nucleic Acid Conformation; D011188:Potassium / Q000737:chemistry; D011401:Promoter Regions, Genetic; D017510:Protein Folding; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000737:chemistry* / Q000235:genetics; D012996:Solutions
D019253:Proto-Oncogene Proteins c-bcl-2; D012996:Solutions; D006147:Guanine; D011188:Potassium