The Single Nucleotide Substitution T → A rs2072580 Damages the CREB1 Binding Site in the Bidirectional SART3/ISCU Promoter.

Background/objectives: The regulatory SNPs (rSNPs) that disturb the binding of transcription factors (TFs) and alter the transcription levels of genes play a paramount role in the formation of different traits and are associated with many pathologies. The search for allele-specific events in RNA-seq and ChIP-seq data is a powerful genome-wide approach to detect rSNPs. Using this approach, we have identified the T → A rs2072580 substitution in the bidirectional SART3/ISCU promoter as a potential rSNP and demonstrated its association with colorectal cancer, relying on International Cancer Genome Consortium data. The goal of this work was to identify the TF binding site that is affected by the T → A substitution and to study the effect of this substitution on reporter gene expression in different plasmid constructs.

Methods: Electrophoretic mobility shift assay (EMSA), cross-competition analysis and supershift assay, plasmid construction, and dual luciferase reporter assay.

Results: The T → A rs2072580 substitution is shown to damage the binding site for ubiquitous TF CREB1 and to significantly decrease the activity of the heterologous promoter carrying the cassettes of two or three repeated CREB binding sites inserted upstream of it. However, the substitution disturbing the CREB1 binding site within the bidirectional promoter shared by SART3 and ISCU inhibits the promoter activity of only the SART3 gene but has no effect on the activity of the ISCU promoter.

Conclusions: The performed comprehensive functional analysis of the T → A rs2072580 in the bidirectional SART3/ISCU promoter unambiguously implies it is an rSNP. These results form the background for further studies of this rSNP and its potential significance for various pathologies.