RESPONSE OF A NEIL1 DEFICIENT MURINE EPITHELIAL CELL LINE TO CHROMATE

DNA is constantly exposed to oxidants which can lead to nucleobase damage. Chromium is of particular interest as a DNA oxidant because of its abundance in the environment and the ease with which it can be taken into a cell. Chromate, Cr(VI), ions are taken up by a cell through relatively non-selective anion channels which normally regulate uptake of phosphate and sulfate ions. Once in the cell, chromate ions are reduced by intracellular reductants such as ascorbate and glutathione to Cr(III). Highly reactive Cr(V) and Cr(IV) species are created during this transition which are able to directly oxidize DNA, particularly guanine residues due to their low reduction potential relative to the other three bases, adenine, thymine, and cytosine. 7,8-dihydro-8-oxo-2’-deoxyguanosine (8-oxoG) has previously been viewed as the primary marker of oxidative stress but the reduction potential of 8-oxoG is even lower than that of the parent guanine residue making it a prime target for further oxidative events. Spiroiminodihydantoin (Sp) is one product of these further oxidative events. The NEIL1 base excision repair (BER) glycosylase has been shown to recognize and cleave the oxidative DNA lesion Sp. NEIL1 belongs to a family of three mammalian DNA glycosylases Neil1, Neil2, and Neil3. NEIL1 and NEIL2 are both able to recognize and cleave the oxidative lesion Sp in single stranded DNA in vitro. In duplex DNA, only NEIL1 is able to recognize and cleave the Sp lesion. A Neil1 -/- mouse model was recently developed and displayed a range of metabolic disorders that could be linked to oxidative DNA damage. These altered phenotypes included obesity, fatty liver, kidney vacuolization, hyperleptinemia, hyperinsulinemia, and increased mitochondrial DNA damage and deletions. Using kidney epithelial cells from the Neil1 -/- mouse model, we have shown that a NEIL1 glycosylase deficiency alters toxicity, cell cycle arrest and apoptosis patterns following exposure to chromate.