G-quadruplex formation within the promoter region of HSPB2 and its effect on transcription

G -rich sequences in DNA and RNA tend to fold into stable secondary structures called G-quadruplexes. Except for the telomere region, G-quadruplex-forming sequences are widely present in gene promoters and have been implicated in transcriptional regulation. Single nucleotide polymorphisms (SNPs) can disrupt the G-quadruplex structure of a gene promoter. In this study, we confirmed the promoter of HSPB2, a cancer -related gene, tends to form an unusual DNA secondary structure. The dual luciferase assay revealed that the SNP rs2234704 in the HSPB2 promoter with a single G > A mutation increased the transcriptional activity of the HSPB2 promoter. Circular dichroism and native PAGE revealed that the G -rich strand of the DNA in this promoter preferred to form a parallel G-quadruplex, which could be destabilized by the SNP rs2234704 (G > A) mutation. Furthermore, we found that the SNP rs2234704 (G > A) greatly increased and influenced the overexpression of HSPB2 in breast cancer samples. These results suggest SNP rs2234704 (G > A) may play a role in the occurrence of breast cancer by destroying the Gquadruplex structure and promoting the expression of HSPB2.