Mouse Akr1cl gene product is a prostaglandin D₂ 11-ketoreductase with strict substrate specificity

A mouse gene, Akr1cl, encodes a member of the aldo-keto reductase 1C subfamily (AKR1CL), whose function, however, remains unknown. Here, we show that the recombinant AKR1CL is an NADPH-dependent reductase of prostaglandin (PG) D₂ (K_m 3.2 μM, k_cat 5.6 min^-1) and oxidizes 9α,11β-PGF₂ (K_m 30 μM, k_cat 3.3 min^-1) in the reverse reaction. In contrast, it did not exhibit oxidoreductase activity towards other PGs (E₂, A₁, B₂ and F_2α), steroids and nonsteroidal carbonyls and alcohols, which are substrates of other mammalian AKR1C subfamily enzymes. The enzyme activity was inhibited by estradiol, quercetin, benzbromarone, ethacrynic acid and flufenamic acid, of which estradiol was the most potent competitive inhibitor (K_i 3.2 μM). The mRNA for AKR1CL was expressed abundantly in mouse testis, ovary and adrenal gland, and at low levels in the brain, lung, small intestine and prostate. Thus, AKR1CL is the first PGD₂ 11-ketoreductase with strict substrate specificity in mammals. The site-directed mutagenesis of P85 in AKR1CL to the corresponding residue, W, in other mammalian AKR1C subfamily enzymes resulted in broad substrate specificity for nonsteroidal carbonyls and alcohols, suggesting that P85 plays a critical role in the strict specificity for PGD₂ and 9α,11β-PGF₂.