Molecular Characterization of Mammalian Dicarbonyl/l-Xylulose Reductase and Its Localization in Kidney

Abstract

In this report, we first cloned a cDNA for a protein that is highly expressed in mouse kidney and then isolated its counterparts in human, rat hamster, and guinea pig by polymerase chain reaction-based cloning. The cDNAs of the five species encoded polypeptides of 244 amino acids, which shared more than 85% identity with each other and showed high identity with a human sperm 34-kDa protein, P34H, as well as a murine lungspecific carbonyl reductase of the short-chain dehydrogenase/reductase superfamily. In particular, the human protein is identical to P34H, except for one amino acid substitution. The purified recombinant proteins of the five species were about 100-kDa homotetramers with NADPH-linked reductase activity for ␣-dicarbonyl compounds, catalyzed the oxidoreduction between xylitol and L-xylulose, and were inhibited competitively by nbutyric acid. Therefore, the proteins are designated as dicarbonyl/L-xylulose reductases (DCXRs). The substrate specificity and kinetic constants of DCXRs for dicarbonyl compounds and sugars are similar to those of mammalian diacetyl reductase and L-xylulose reductase, respectively, and the identity of the DCXRs with these two enzymes was demonstrated by their co-purification from hamster and guinea pig livers and by protein sequencing of the hepatic enzymes. Both DCXR and its mRNA are highly expressed in kidney and liver of human and rodent tissues, and the protein was localized primarily to the inner membranes of the proximal renal tubules in murine kidneys. The results imply that P34H and diacetyl reductase (EC 1.1.1.5) are identical to Lxylulose reductase (EC 1.1.1.10), which is involved in the uronate cycle of glucose metabolism, and the unique localization of the enzyme in kidney suggests that it has a role other than in general carbohydrate metabolism.

Accumulation of Ubiquitin and Sequestosome-1 Implicate Protein Damage in Diacetyl-Induced Cytotoxicity

“…21,33,79 Because the reactive a-dicarbonyl group is implicated in diacetyl-induced protein damage, we originally hypothesized that DCXR would provide protection from protein damage through metabolism of diacetyl to acetoin, which does not have the reactive a-dicarbonyl group. 36 Consistent with this hypothesis, we did observe a significantly increased number of cells with ubiquitin puncta and K63-ubiquitin puncta in airway epithelium of DCXR knockout compared with wild-type mice in the 200 ppm exposure group in the dose-response experiment. There was a similar trend at this same exposure concentration in the molecular pathology experiment, although the effect did not consistently reach statistical significance, possibly as a result of the lower number of animals in that experiment.…”

“…36 The product of DCXRmediated diacetyl metabolism is acetoin, which contains an a-hydroxyketone in place of the reactive a-dicarbonyl group. In an acute inhalation toxicity mixed exposure study using ratios similar to those seen in workplaces, acetoin did not significantly alter diacetyl-induced changes in airway reactivity.…”

Dicarbonyl/l-Xylulose Reductase: A Potential Biomarker Identified by Laser-Capture Microdissection-Micro Serial Analysis of Gene Expression of Human Prostate Adenocarcinoma

“…We identified dicarbonyl/L-xylulose reductase (DCXR), an enzyme that catalyzes a-dicarbonyl and L-xylulose, as an up-regulated gene in prostate cancer cells. The dcxr gene, which is located on chromosome 17q25.3, encodes an f100-kDa homotetramer with NADPH-linked reductase activity for both a-dicarbonyl compounds and L-xylulose (14). The specificity of DCXR mRNA overexpression in prostate cancer tissue was confirmed by quantitative real-time reverse transcriptase-PCR (RT-PCR) and virtual Northern blot analysis.…”

Decreased expression of the human carbonyl reductase 2 gene HCR2 in hepatocellular carcinoma

“…In the course of these processes, HCR2 may play a role in detoxification by cleaning the reactive alpha-dicarbonyl compounds and excessive reactive oxygen species (ROS) generated in oxidative stress. This was demonstrated with two murine homologues of HCR2 [5]. It is believed that most HCC cases arise in the setting of chronic hepatitis virus infection; during persistent inflammation, sustained generation of ROS and the metabolic activations of dietary carcinogens such as aflatoxin B1 induce genetic mutations and chromosomal alterations that may eventually lead to the initiation of HCC [8,9].…”

“…AF139841. As a new member of the short chain dehydrogenase/reductase (SDR) superfamily, HCR2 encodes a homotetrameric cytosolic enzyme that is highly expressed in the human liver and kidney, showing NADPH-dependent oxidoreductase activity for alpha-dicarbonyl compounds and L-xylulose [5]. Reactive alpha-dicarbonyl compounds are generated by oxidative stress and prone to conversion into advanced glycation end products that accumulate in the plasma proteins and tissues, and interact with other long-lived proteins to cause renal failure, sclerotic disorders or retinopathy [6,7].…”