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The 3.0-resolution x-ray structure of rat liver 3a-hydroxysteroid dehydrogenase/dihydrodiol dehydrogenase (3a-HSD, EC 1.1.1.50) was determined by molecular replacement using human placental aldose reductase as the search model. The protein folds into an a/ or triose-phosphate Isomerase barrel and lacks a coI Rossmann fold for bnding pyridine nucleotide. The structure contains a concentration of hydrophobic amino adds that lie in a cavity near the top ofthe barrel and that are presumed to be involved in binding hydrophobic substrates (steroids, prostaglandins, and polycyclic aromatic hydrocarbons) and inhibitors (nonsteroidal antdinflammatory drugs). At the distal end of this cavity lie three residues in close proximity that have been implicated in catalysis by site-directed mutagens-Tyr-55, Tyr-55 is postulated to act as the general acid. 3a-HSD shares significant sequence identity with other HSDs that belong to the aldo-keto reductase superfamily and these may show similar architecture. Other members of this family include prostaglandin F synthase and p-crystallin. By contast, 3a-HSD shares no sequence identity with HSDs that are members ofthe short-chain alcohol dehydrogenase family but does contain the Tyr-XaaXaa-Xaa-Lys consensus sequence imlated in catalysis in this family. In the 3a-HSD structure these residues are on the periphery of the barrel and are unlikely to participate in catalysis.3a-Hydroxysteroid dehydrogenase [3a-HSD; 3a-hydroxysteroid:NAD(P)+ oxidoreductase, EC 1.1.1.50] from rat liver cytosol is a monomeric NAD(P)+-linked oxidoreductase with a molecular mass of 37,029 daltons deduced from its cDNA clone (1). The enzyme reduces biologically important 3-oxo steroids of the androstane (C19), pregnane (C21), and cholane (C24) series, in which the A/B ring fusion may be in the cis or trans configuration (2). These reactions lead to the inactivation of circulating androgens, progestins, and glucocorticoids as well as the biosynthesis of bile acids (3). The enzyme functions as a dihydrodiol dehydrogenase and, by oxidizing trans-dihydrodiols of polycyclic aromatic hydrocarbons, can suppress the formation of the ultimate carcinogens: the anti-diol epoxides (4). The enzyme also displays 9-, 11-, and 15-hydroxyprostaglandin dehydrogenase activity (5). This multifunctional enzyme is potently inhibited by nonsteroidal antiinflammatory drugs and can be used to screen the antuinflammatory potency of unknowns (6). Structural information is required to understand how this enzyme recognizes its diverse ligands. 3a-HSD shares high amino acid sequence identity with bovine lung prostaglandin F synthase (69%), human chlordecone reductase (66%), and frog lens p-crystallin (55%), which are members of the aldo-keto reductase superfamily. Included in this family are human placental, bovine, and rat lens aldose reductase, which share 58% sequence identity with 3a-HSD (ref. 1 and references therein). Two newly sequenced HSDs which belong to this family include 20a-HSD from rabbit ovary (7) and bovine testis (8)...

No abstract

Specific mRNA destabilization represents an important and novel site of action for the cytokine suppressive effects of p38 inhibitors.

A yeast two-hybrid assay was employed to identify androgen receptor (AR) protein partners in gonadotropin-releasing hormone neuronal cells. By using an AR deletion construct (AR-(⌬371-485)) as a bait, ␤-catenin was identified as an AR-interacting protein from a gonadotropin-releasing hormone neuronal cell library. Immunolocalization of co-transfected AR and FLAG-␤-catenin demonstrated that FLAG-␤-catenin was predominantly cytoplasmic in the absence of androgen. In the presence of 5␣-dihydrotestosterone, FLAG-␤-catenin completely co-localized to the nucleus with AR. This effect was specific to AR because liganded progesterone, glucocorticoid, or estrogen ␣ receptors did not translocate FLAG-␤-catenin to the nucleus. Agonist-bound AR was required because the AR antagonists casodex and hydroxyflutamide failed to translocate ␤-catenin. Time course experiments demonstrated that co-translocation occurred with similar kinetics. Nuclear co-localization was independent of the glycogen synthase kinase-3␤, p42/44 ERK mitogen-activated protein kinase, and phosphatidylinositol 3-kinase pathways because inhibitors of these pathways had no effect. Transcription assays demonstrated that liganded AR repressed ␤-catenin/T cell factor-responsive reporter gene activity. Conversely, co-expression of ␤-catenin/T cell factor repressed AR stimulation of AR-responsive reporter gene activity. Our data suggest that liganded AR shuttles ␤-catenin to the nucleus and that nuclear interaction of AR with ␤-catenin may modulate transcriptional activity in androgen target tissues.