Characterization of the major single nucleotide polymorphic variants of aldo-keto reductase 1C3 (type 5 17β-hydroxysteroid dehydrogenase).

Aldo-keto reductase (AKR) 1C3, also known as type 5 17β-hydroxysteroid dehydrogenase and prostaglandin F synthase, is a member of the AKR superfamily that reduces aldehydes and ketones to primary and secondary alcohols. It plays an essential role in the peripheral formation of androgens and is implicated in several steroid hormone dependent diseases including prostate cancer, breast cancer, and polycystic ovary syndrome (PCOS). AKR1C3 has 14 nonsynonymous single nucleotide polymorphisms (nsSNPs) with different global frequencies and ethnic distributions. Association studies support their role in disease, but a detailed functional genomic analysis of these variants is lacking. One study examined five AKR1C3 nsSNPs for their ability to reduce exemestane, an aromatase inhibitor used to treat breast cancer, to 17β-dihydroexemestane, and reported a 17-250-fold reduction in catalytic efficiency of H5Q, E77G, K104D, and R258C variants compared to wild type (WT). This observation provided the impetus to examine the impact of these variants on AKR1C3 function. Here, we purified AKR1C3 WT, and the top four most frequently occurring nsSNPs, H5Q, E77G, K104D, and R258C, from E. coli to expand upon their characterization and illuminate functional differences that could affect disease outcome and treatment. While we found negligible deviations in steady state kinetics, the K104D variant showed reduced thermal stability compared to WT. The presence of NAD(P) restored the stability of the variant. As it is unlikely that the apoenzyme will exist within the cell without cofactor bound the K104D is not expected to manifest a phenotype.