Expression of a novel alternatively spliced variant of NADP(H)-dependent retinol dehydrogenase/reductase with deletion of exon 3 in cervical squamous carcinoma

NRDR inhibits estradiol synthesis and is associated with changes in reproductive traits in pigs

Cumulus cells secreting steroid hormones have important functions in oocyte development. Several members of the short-chain dehydrogenase/reductase (SDR) family are critical to the biosynthesis of steroid hormones. NADPH-dependent retinol dehydrogenase/reductase ( NRDR), a member of the SDR superfamily, is overexpressed in pig breeds that also show high levels of androstenone. However, the potential functions and regulatory mechanisms of NRDR in pig ovaries have not been reported to date. The present study demonstrated that NRDR is highly expressed in pig ovaries and is specifically located in cumulus granulosa cells. Functional studies showed that NRDR inhibition increased estradiol synthesis. Both pregnant mare serum gonadotropin and human chorionic gonadotropin downregulated the expression of NRDR in pig cumulus granulosa cells. When the relationship between reproductive traits and single-nucleotide polymorphisms (SNPs) of the NRDR gene was examined, we found that two SNPs affected reproductive traits. SNP rs701332503 was significantly associated with a decrease in the total number of piglets born during multiparity, and rs326982309 was significantly associated with an increase in the average birth weight during primiparity. Thus, NRDR has an important role in steroid hormone biosynthesis in cumulus granulosa cells, and NRDR SNPs are associated with changes in porcine reproduction traits.

Crystal structure and catalytic characterization of the dehydrogenase/reductase SDR family member 4 (DHRS4) from Caenorhabditis elegans

The human dehydrogenase/reductase SDR family member 4 (DHRS4) is a tetrameric protein that is involved in the metabolism of several aromatic carbonyl compounds, steroids, and bile acids. The only invertebrate DHRS4 that has been characterized to date is that from the model organism Caenorhabditis elegans. We have previously cloned and initially characterized this protein that was recently annotated as DHRS4_CAEEL in the UniProtKB database. Crystallization and X-ray diffraction studies of the full-length DHRS4_CAEEL protein in complex with diacetyl revealed its tetrameric structure and showed that two subunits are connected via an intermolecular disulfide bridge that is formed by N-terminal cysteine residues (Cys5) of each protein chain, which increases the enzymatic activity. A more detailed biochemical and catalytic characterization shows that DHRS4_CAEEL shares some properties with human DHRS4 such as relatively low substrate affinities with aliphatic α-diketones and a preference for aromatic dicarbonyls such as isatin, with a 30-fold lower Km value compared with the human enzyme. Moreover, DHRS4_CAEEL is active with aliphatic aldehydes (e.g. hexanal), while human DHRS4 is not. Dehydrogenase activity with alcohols was only observed with aromatic alcohols. Protein thermal shift assay revealed a stabilizing effect of phosphate buffer that was accompanied by an increase in catalytic activity of more than two-fold. The study of DHRS4 homologs in simple lineages such as C. elegans may contribute to our understanding of the original function of this protein that has been shaped by evolutionary processes in the course of the development from invertebrates to higher mammalian species.

DATABASE

Structural data are available in the PDB under the accession numbers 5OJG and 5OJI.

Alcohol dehydrogenase and aldehyde dehydrogenase in malignant neoplasms

According to International Agency for Research on Cancer, ethanol and acetaldehyde belong to group 1 of human carcinogens. The accurate mechanism by which alcohol consumption enhances carcinogenesis is still unexplained. Alcohol is oxidized primarily by alcohol dehydrogenase (ADH) to acetaldehyde, a substance capable of initiating carcinogenesis by forming adducts with proteins and DNA and causing mutations. Next, acetaldehyde is metabolized by aldehyde dehydrogenase (ALDH) to acetate. In tissues of many cancers, we can observe significantly higher activity of total alcohol dehydrogenase with any change in aldehyde dehydrogenase activity in comparison with healthy cells. Moreover, in malignant diseases of digestive system, significantly increased activity of ADH isoenzymes class I, III and IV was found. The gynecological, brain and renal cancers exhibit increased activity of class I ADH. ADH and ALDH can play also a crucial regulatory role in initiation and progression of malignant diseases by participation in retinoic acid synthesis and elimination of toxic acetaldehyde. Besides, changes of enzymes activities in tumor cells are reflected in serum of cancer patients, which create the possibilities of application ADH isoenzymes as cancer markers.

Expanding the Halohydrin Dehalogenase Enzyme Family: Identification of Novel Enzymes by Database Mining

Halohydrin dehalogenases are very rare enzymes that are naturally involved in the mineralization of halogenated xenobiotics. Due to their catalytic potential and promiscuity, many biocatalytic reactions have been described that have led to several interesting and industrially important applications. Nevertheless, only a few of these enzymes have been made available through recombinant techniques; hence, it is of general interest to expand the repertoire of these enzymes so as to enable novel biocatalytic applications. After the identification of specific sequence motifs, 37 novel enzyme sequences were readily identified in public sequence databases. All enzymes that could be heterologously expressed also catalyzed typical halohydrin dehalogenase reactions. Phylogenetic inference for enzymes of the halohydrin dehalogenase enzyme family confirmed that all enzymes form a distinct monophyletic clade within the short-chain dehydrogenase/reductase superfamily. In addition, the majority of novel enzymes are substantially different from previously known phylogenetic subtypes. Consequently, four additional phylogenetic subtypes were defined, greatly expanding the halohydrin dehalogenase enzyme family. We show that the enormous wealth of environmental and genome sequences present in public databases can be tapped for in silico identification of very rare but biotechnologically important biocatalysts. Our findings help to readily identify halohydrin dehalogenases in ever-growing sequence databases and, as a consequence, make even more members of this interesting enzyme family available to the scientific and industrial community.

Identification of a novel isoform of DHRS4 protein with a nuclear localization signal

The DHRS4 gene encodes an NADP(H)-dependent retinol dehydrogenase/reductase (NRDR) and plays an important role in regulating the synthesis of retinoic acid. In the present study, we identified a novel splice RNA variant, designated NRDRA2, of the human DHRS4 gene by RT-PCR, 3' RACE, and 5' RACE. NRDRA2 mRNA lacked exons 4 and 6, and had a shift in the reading frame when compared to DHRS4 mRNA, resulting in loss of the peroxisomal targeting signal of NRDR and gain of a nuclear localization signal in the predicted NRDRA2 protein. Endogenous NRDRA2 protein was identified in the human cervical carcinoma cell line HeLa by immunoprecipitation and mass spectrometric assay. A green fluorescent protein reporter assay showed that NRDRA2 protein mainly localized to the nuclei, confirming the sequence at its C-terminus as a legitimate nuclear localization signal sequence. This study identifies the alternative transcript variant NRDRA2 encoding a subcellular nuclear localized NRDRA2 protein.

The activity of class I, II, III and IV alcohol dehydrogenase isoenzymes and aldehyde dehydrogenase in cervical cancer

OBJECTIVE

The aim of this study was to compare the metabolism of cervical cancer cells and normal cervical cells by measurement of ADH isoenzymes and ALDH activities.

METHODS

The study material consisted of 40 cancerous cervical tissues. Class III, IV of ADH and total ADH activity was measured by the photometric method and class I, II ADH and ALDH activity by the fluorometric method with class-specific fluorogenic substrates.

RESULTS

The activity of the class I ADH isoenzyme and the total ADH were significantly higher in cervical cancer as compared to healthy tissues. Class I of ADH and total ADH activity are significantly higher in every stage of cancer as compared to the control. There are no significant differences between planoepitheliale and adenocarcinoma.

CONCLUSION

The increased activity of total ADH in cervical cancer may be the cause of some metabolic disorders in cancer cells, which may intensify carcinogenesis in this organ.

Bioinformatic analysis of the human DHRS4 gene cluster and a proposed mechanism for its transcriptional regulation

BACKGROUND

The human DHRS4 gene cluster consists of three genes, DHRS4, DHRS4L2 and DHRS4L1. Among them, DHRS4 encodes NADP(H)-dependent retinol dehydrogenase/reductase. In a previous study, we investigated the alternative splicing of DHRS4 and DHRS4L2. DHRS4L1 was added to the gene cluster recently, but little is known about its structure and expression. To reveal the regulatory mechanism of the DHRS4 gene cluster expression, we studied the structure and transcription of DHRS4L1 in the context of the transcriptional behaviors of the human DHRS4 gene cluster. Based on the results of bioinformatics analysis, we propose a possible mechanism for the transcriptional regulation of the human DHRS4 gene cluster.

RESULTS

The homologous comparison analysis suggests that DHRS4, DHRS4L2 and DHRS4L1 are three homologous genes in human. DHRS4L1 and DHRS4L2 are paralogues of DHRS4, and DHRS4L2 is the most recent member of the DHRS4 gene cluster. In the minus strand of the human DHRS4 gene cluster, a gene transcribed in an antisense direction was found containing a 5' sequence overlapping the region of exon 1 and promoter of DHRS4. By cloning the full length of RNA variants through 5'RACE and 3'RACE, we identified two transcription start sites, within exon a2 and exon 1, of this newly named gene DHRS4L1 using neuroblastoma cell line BE(2)-M17. Analysis of exon composition in the transcripts of DHRS4 gene cluster revealed that exon 1 was absent in all the transcripts initiated from exon a1 of DHRS4L2 and exon a2 of DHRS4L1.

CONCLUSIONS

Alternatively spliced RNA variants are prevalent in the human DHRS4 gene cluster. Based on the analysis of gene transcripts and bioinformatic prediction, we propose here that antisense transcription may be involved in the transcriptional initiation regulation of DHRS4 and in the posttranscriptional splicing of DHRS4L2 and DRHS4L1 for the homologous identity of DHRS4 gene cluster. Beside the alternative transcriptional start sites, the antisense RNA is novel possible factor serving to remove exon 1 from the transcripts initiated from exon a1 and exon a2.

Alternative transcription initiation and splicing variants of the DHRS4 gene cluster

The DHRS4 (short-chain dehydrogenase/reductase superfamily member 4) gene cluster, consisting of DHRS4 and its copy gene DHRS4L2, is localized on 14q11.2. The DHRS4 gene product NADP(H)-dependent retinol oxidoreductase participates in the metabolism of retinoids. The expression patterns of the DHRS4 gene cluster were investigated in human neuroblastoma cells. Transcript analysis of the DHRS4 gene cluster using 3'- and 5'-RACE (rapid amplification of cDNA ends), reverse transcription-PCR and bioinformatics approaches showed an alternative transcription start site in the copy gene DHRS4L2 which generates two transcripts, DHRS4A1 (GenBank(R) nucleotide sequence database accession number AY616183) and DHRS4A2 (AY943857), together with at least six alternative splicing variants (DHRS4A_v1-6) (AY920361, AY920362, DN237886, DN237887, DN237890 and DN237892 respectively), resulted from alternative splicing. DHRS4A1 and DHRS4A2 were specifically transcribed in neuroblastoma cells. RNA structural analysis of DHRS4A1 and DHRS4A2 suggested that they are non-coding RNAs. Expression analysis of DHRS4 by quantitative real-time PCR and Western blotting showed a lack of correlation between the levels of transcription and translation in the tissues examined. Bisulfite genomic sequencing PCR experiments indicated that the expression of DHRS4L2 was regulated by methylation of its CpG islands.

[Structure and function of peroxisomal tetrameric carbonyl reductase]

In this paper, the structure and function of a new tetrameric carbonyl reductase (TCR) is reviewed. TCRs were purified from rabbit and pig heart, using 4-benzoylpyridine as a substrate. Partial peptide sequencing and cDNA cloning of rabbit and pig TCRs revealed that both enzymes belonged to the short-chain dehydrogenase/reductase family and that their subunits consisted of 260 amino acid residues. Rabbit and pig TCRs catalyzed the reduction of alkyl phenyl ketones, alpha-dicarbonyl compounds, quinones and retinals. Both enzymes were potently inhibited by flavonoids and fatty acids. 9,10-Phenanthrenequinone, which is efficiently reduced by rabbit and pig TCRs, mediated the formation of superoxide radical through its redox cycling in pig heart. The C-terminal sequences of rabbit and pig TCRs comprised a type 1 peroxisomal targeting signal (PTS1) Ser-Arg-Leu, suggesting that the enzymes are localized in the peroxisome. In fact, pig TCR was targeted into the peroxisomal matrix, in the case of transfection of HeLa cells with vectors expressing the enzyme. However, when the recombinant pig TCR was directly introduced into HeLa cells, the enzyme was not targeted into the peroxisomal matrix. The crystal structure of recombinant pig TCR demonstrated that the C-terminal PTS1 of each subunit of the enzyme was buried in the interior of the tetrameric molecule. These findings indicate that pig TCR is imported into the peroxisome as a monomer and then forms an active tetramer within this organelle.

Characterization of human DHRS4: an inducible short-chain dehydrogenase/reductase enzyme with 3beta-hydroxysteroid dehydrogenase activity

Human DHRS4 is a peroxisomal member of the short-chain dehydrogenase/reductase superfamily, but its enzymatic properties, except for displaying NADP(H)-dependent retinol dehydrogenase/reductase activity, are unknown. We show that the human enzyme, a tetramer composed of 27kDa subunits, is inactivated at low temperature without dissociation into subunits. The cold inactivation was prevented by a mutation of Thr177 with the corresponding residue, Asn, in cold-stable pig DHRS4, where this residue is hydrogen-bonded to Asn165 in a substrate-binding loop of other subunit. Human DHRS4 reduced various aromatic ketones and alpha-dicarbonyl compounds including cytotoxic 9,10-phenanthrenequinone. The overexpression of the peroxisomal enzyme in cultured cells did not increase the cytotoxicity of 9,10-phenanthrenequinone. While its activity towards all-trans-retinal was low, human DHRS4 efficiently reduced 3-keto-C(19)/C(21)-steroids into 3beta-hydroxysteroids. The stereospecific conversion to 3beta-hydroxysteroids was observed in endothelial cells transfected with vectors expressing the enzyme. The mRNA for the enzyme was ubiquitously expressed in human tissues and several cancer cells, and the enzyme in HepG2 cells was induced by peroxisome-proliferator-activated receptor alpha ligands. The results suggest a novel mechanism of cold inactivation and role of the inducible human DHRS4 in 3beta-hydroxysteroid synthesis and xenobiotic carbonyl metabolism.