The Influence of ABCC1 Single Nucleotide Polymorphisms on the Cellular Export of the Human Carcinogen Arsenic

Abstract ID 91100 Poster Board 411 Arsenic is a naturally occurring metalloid found in the earth's crust. Arsenic causes cancers of the skin, bladder, and lung in humans, and is associated with numerous other adverse health effects such as cardiovascular and endocrine disease. Conservative estimates suggest that between 92 to 220 million people worldwide are exposed to unacceptable levels of arsenic (>10 ppb) in their drinking water, resulting in a massive global health concern. The Multidrug Resistance Protein 1 (MRP1, gene name ABCC1) is a member of the ATP-binding cassette (ABC) transporter superfamily. First identified in a doxorubicin-selected small cell lung cancer cell line, MRP1 exports a variety of substrates that differ from doxorubicin in terms of chemical structure and charge. MRP1 can transport certain arsenic metabolites, such as arsenic triglutathione [As(GS)₃], monomethylarsenic diglutathione, and dimethylarsinic acid. This, combined with the knowledge that MRP1 is localized to the basolateral surface of polarized epithelial cells and exports substrates into the blood, establishes a potential role for MRP1 in cellular arsenic defense. The ABCC1 gene is highly polymorphic, and numerous single nucleotide polymorphisms (SNPS) have been characterized for their transport of physiological conjugated organic anions such as leukotriene C₄ (LTC₄). However, the influence of genetic variability on arsenic metabolite transport has yet to be characterized. We hypothesized that 13 selected single nucleotide polymorphisms (SNPs) of ABCC1 would have decreased transport of As(GS)₃. These ABCC1 SNPs were transiently expressed in human embryonic kidney (HEK) 293 cells and MRP1-enriched membrane vesicles prepared. Immunoblots showed there was no significant difference in MRP1 levels between wild-type- and variant-MRP1-enriched membrane vesicles. The transport of radiolabelled As(GS)₃ by MRP1-enriched membrane vesicles was measured and showed that R230Q-, R433S- and A989T-MRP1 exhibited a 1.5, 2, and 10 ten-fold decrease in transport of As(GS)₃ relative to wild type-MRP1, respectively. We also found that transport of LTC₄ by R433S-MRP1 was reduced by two-fold, while it was unchanged for R230Q- and A989T-MRP1, suggesting that R433S-MRP1 reduced the general function of MRP1.These results show that naturally occurring mutations in ABCC1 can affect the ability of MRP1 to transport arsenic metabolites. Individuals carrying SNPs associated with decreased transport may retain more arsenic inside their cells, increasing their susceptibility to arsenic-induced diseases. This is especially relevant to SNP-carrying individuals in regions which are associated with higher probabilities of unacceptable arsenic exposure.