Heterogeneous Nuclear Ribonucleoprotein K Binds to the Cytosine-Rich Sequence of the Hypoxia Inducible Factor 1 Alpha Proximal Promoter that forms a Stable i-motif at Neutral pH
Diana J Uribe, Yoon-Joo Shin, Eric Lau, Scot W Ebbinghaus and Daekyu Sun*
Pharmacology and Toxicology Department, Cancer Biology Graduate Interdisciplinary Program, University of Arizona, Tucson, AZ, USA
- *Corresponding Author:
- Daekyu Sun
Pharmacology and Toxicology Department
Cancer Biology Graduate Interdisciplinary Program
University of Arizona, Room 419
BIO5 Institute, 1657 E. Helen St.
Tucson, Arizona 85721, USA
E-mail: [email protected]
Received December 14, 2012; Accepted December 26, 2012; Published December 28, 2012
Citation: Uribe DJ, Shin YJ, Lau E, Ebbinghaus SW, Sun D (2013) Heterogeneous Nuclear Ribonucleoprotein K Binds to the Cytosine-Rich Sequence of the Hypoxia Inducible Factor 1 Alpha Proximal Promoter that forms a Stable i-motif at Neutral pH. J Phys Chem Biophys S5:001. doi: 10.4172/2161-0398.S5-001
Copyright: © 2013 Uribe DJ, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
The proximal promoter of the hypoxia inducible factor 1 alpha (HIF-1α) gene contains a poly-purine/poly-pyrimidine (pPu/pPy) tract, which has been shown to affect 90% of its transcriptional control. The guanine-rich sequence of this pPu/pPy tract has been known to be structurally dynamic, easily forming a G-quadruplex structure with a 1:6:1 folding pattern. In present study, we demonstrated that the cytosine-rich (C-rich) sequence within the pPu/pPy tract of the HIF-1α promoter is able to form two major intramolecular i-motif structures with 3:3:3 or 3:4:2 folding patterns near physiological pH using circular dichroism, bromine footprinting and site-directed mutational analysis. These structures are the first known i-motifs that form at neutral pH, with a transitional pH at 6.9, which have been discovered to form within the proximal promoter sequence of oncogenes. Additionally, electrophoretic mobility shift assays (EMSA) combined with bromine footprinting revealed that heterogeneous nuclear ribonucleoprotein K (hnRNP K) is able to bind to the unfolded state of C-rich sequence in a sequence specific manner. Taken together, our results demonstrate that the i-motif structures that form within the C-rich sequence of the HIF-1α promoter can form under physiological conditions and that hnRNP K can bind to this C-rich sequence.