Functional Analyses of Single Nucleotide Polymorphic Variants of the DNA Glycosylase NEIL1 Present in sub-Saharan African Populations
Jamie Zuckerman, Irina Minko, Melis Kant, Pawel Jaruga, Miral M. Dizdar, Amanda McCullough, R. Stephen Lloyd
Nei-like glycosylase 1 (NEIL1) is a DNA repair enzyme that initiates the base excision repair (BER) pathway to cleanse the human genome of damage. Its substrate specificity includes several common base modifications formed under oxidative stress conditions as well as the imidazole ring open adducts that are induced by alkylating agents, following initial modification at N7 guanine. An example of the latter is the persistent and mutagenic 8,9-dihydro-8-(2,6-diamino-4-oxo-3,4-dihydropyrimid-5-yl-formamido)-9-hydroxyaflatoxin B1 (AFB1-FapyGua) adduct, resulting from the alkylating agent aflatoxin B1 (AFB1) exo-8-9-epoxide. Naturally occurring single nucleotide polymorphic (SNP) variants of NEIL1 are hypothesized to be associated with increased risk for development of early-onset hepatocellular carcinoma (HCC), especially in environments with high exposures to aflatoxins and chronic inflammation from viral infections and alcohol consumption. Given that AFB1 exposure and hepatitis B viral (HBV) infections present a major problem in the developing countries of sub-Saharan Africa, it has become pertinent to characterize SNP NEIL1 variants present in this geographic region. In this study, we characterized the three most common variants found in this region: P321A, R323G, and I182M. Biochemical analyses were conducted to determine the proficiencies of these variants in initiating the repair of DNA lesions. Data from these in vitro investigations show that damage recognition and incision activities of P321A and R323G were near that of wild-type (WT) NEIL1 on both thymine glycol (ThyGly) and AFB1-FapyGua. The substrate specificity of these variants with respect to various oxidatively-induced base lesions were also similar to that of WT. In contrast, the I182M variant was unstable, such that it precipitated under a variety of conditions and underwent rapid inactivation at a biologically relevant temperature, with partial stabilization being observed in the presence of undamaged DNA. This study provides insight regarding the potential increased risk for early-onset HCC in human populations carrying the NEIL1 I182M variant.
, Minko, I.
, Kant, M.
, Jaruga, P.
, Dizdar, M.
, McCullough, A.
and Lloyd, R.
Functional Analyses of Single Nucleotide Polymorphic Variants of the DNA Glycosylase NEIL1 Present in sub-Saharan African Populations, Dna Repair, [online], https://doi.org/10.1016/j.dnarep.2023.103544, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=936784
(Accessed December 11, 2023)