Evidence for the presence of a guanine quadruplex forming region within a polypurine tract of the hypoxia inducible factor 1α promoter

The promoter of the hypoxia inducible factor 1 alpha (HIF-1 alpha) gene has a polvpurine/polypyrimidine tract (-65 to -85) overlapping or adjacent to several putative transcription facto;binding sites, and we found that mutagenesis of this region diminished basal HIF-1 alpha expression. Oligonucleotides representing this region of the HIF-1 alpha promoter were analyzed by electrophoretic mobility shift, chemical probing, circular dichroism, and DNA polymerase arrest assays. The guanine-rich strand was found to form a parallel, unimolecular quadruplex in the presence of potassium that was further stabilized by two known quadruplex binding compounds, the cationic porphyrin TmPyP4 and the natural product telomestatin, while TmPyP2, a positional isomer of TmPyP4, did not stabilize quadruplex formation. These data suggest that a quadruplex structure may form in a region of the HIF-1 alpha promoter that regulates basal HIF-1 alpha expression.