Abstract 5134: G-Quadruplex structure formation in the proximal promoter region of the human vascular endothelial growth factor gene

Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL The human vascular endothelial growth factor gene, VEGF, is a key regulator of angiogenesis. It plays an important role in tumor survival, growth and metastasis. It is over-expressed in many types of human cancers including glioma and renal cell carcinoma, ovarian and pancreatic cell carcinomas. The VEGF proximal promoter region contains a poly G/poly C rich tract that is essential for basal and inducible VEGF expression. The guanine-rich (G-rich) strand on this tract is shown to form a specific secondary structure, the G-quadruplex. Here we have elucidated the solution structure of the major intramolecular G-quadruplex formed on the G-rich strand of this region in K+ solution by proton Nuclear Magnetic Resonance (NMR) spectroscopy followed by the structural calculation of the G-quadruplex using Distance Geometry Simulated Annealing (DGSA) module of XPLOR-NIH software. It is inferred that this strand adopts a well-defined parallel-stranded G-quadruplex structure, which contains three G-tetrads stabilized by Hoogsteen hydrogen bonding, as well as three double-chain reversal loops containing 1:4:1 bases, a feature important for the formation of the most thermodynamically stable conformation. The size of the 4-base loop plays a critical role in determining the most favored folded pattern of a G-quadruplex. These 4-base loop residues interact with the residues of the 3’ flanking region of VEGF sequence; also, the 1-base double-chain reversal loop on two edges of the tetrad are very stable, which overall contribute in stabilizing the 1:4:1 conformer. We have found that the two cytosines in this central 4-base loop are involved in hydrogen bonding with the 3’ terminal end residues of VEGF, which is a salient feature as this interaction is sequence-specific and differs from that in other parallel-stranded structures, e.g. c-myc, significantly. These results are also supported by the DMS footprinting results by Guo et al. (2008) which show that the guanines involved in the tetrad formation in this major G-quadruplex loop isomer 1:4:1 are well-protected against DMS methylation. Therefore, the knowledge about the secondary structure of this non B-DNA conformation of the VEGF promoter region is essential for using the G- quadruplex as a target for anticancer drugs, which could be a novel approach to anti-angiogenesis drug discovery in cancer therapy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5134. doi:10.1158/1538-7445.AM2011-5134