Genetic determinants of NEIL2 transcription

The human genome is constantly damaged by reactive oxygen species (ROS) which produce a multitude of oxidative DNA lesions that can lead to mutations, genomic instability, and ultimately, to the development of cancer and other diseases. The DNA base excision repair (BER) pathway is initiated by a DNA glycosylase and subsequently, includes several other proteins that function in a step-wise fashion to repair the mutagenic site resulting from oxidative damage. The importance of maintaining the integrity of this pathway in order to reduce disease risk has been demonstrated by many studies. NEIL2 is a novel BER glycosylase that has been associated with transcription-coupled DNA repair and has a preference for oxidative products of cytosine. Because this enzyme is thought to be involved in transcription-coupled DNA repair, it could play a substantial role in maintaining genomic stability, not only in highly proliferating cells but also in non-dividing cells, such as nerve cells, that remain transcriptionally active. Thus, alterations in the expression levels of this gene could impact DNA repair capabilities and could contribute to disease risk, especially in individuals exposed to mutagenic agents at the beginning of the study. Genetic determinants that influence NEIL2 transcription, including cis-regulatory sequences and sequence polymorphisms, were unknown. We hypothesize that cis-regulatory sequences in the 5’ upstream region of NEIL2 regulate gene transcript levels and that SNPs proximal to these sequences impact gene regulation and thus affect DNA repair efficiency, especially in individuals exposed to environmental mutagens. Consistent with these hypothesizes, we found that individual NEIL2 transcription levels varied by 63 fold amongst individuals and that sequence variations in the promoter region of the NEIL2 gene influences gene transcription levels. These sequence variations were also associated with DNA repair capacity of the cell, indicating a role for NEIL2 in regulation of global DNA repair. By characterizing the underlying mechanisms that may, in part, be responsible for variations in NEIL2 expression, we have shown that the NEIL2 promoter contains both negative and positive regulatory regions. When exposed to oxidative stress, expression from the positive regulatory region is decreased. Site directed mutagenesis of an NF-kappaB/Sp-1 site in this region abolishes this transcriptional response to oxidative stress, indicating specific cis-elements were responsible for alterations in NEIL2 in the presence of oxidative stress. Taken together, this study provides the first in vivo and in vitro descriptions of the genetic mechanisms the govern NEIL2 expression. \r\n\r\n