Biophysical Analysis Of Mutagenic DNA Structures In The Human PKD1 Gene
Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a severe but relatively common (1/500) renal disease. It results from an inherited mutation in one PKD1 gene, followed by a "second hit" mutation in the other normal gene leading to a cellular recessive mechanism. The PKD1 gene is prone to these somatic inactivation events, but the mutagenic mechanisms remain largely unknown. Bioinformatic analysis of PKD1 has revealed guanine repeat sequences capable of forming four-stranded structures known as G-quadruplex (G4) DNA, motifs involved with oncogenic translocations at other loci. We therefore tested the ability of these sequences to form G4 structures under physiological conditions. Circular Dichroism confirmed that guanine repeats within the human PKD1 gene fold into G4 DNA structures in vitro. This structure was abolished in control DNAs where the guanine repeats were disrupted via thymine substitution. G4 formation was observed for repeats located within large tandem arrays and also for more isolated G4 sequences. One G4 motif overlaps with a cataloged pathogenic deletion and analysis confirms that this sequence supports G4 formation. Our findings support the model that DNA structure formation within the human PKD1 gene contributes to an increase in genetic instability and the emergence of ADPKD. This work contributes to the discovery of suitable molecular markers that may be clinically useful in the diagnosis and prevention of polycystic kidney disease.