Modulation of lipocalin-type prostaglandin D2 synthase expression in catfish seminal vesicles by thyroid disrupting agents and hormones

Thyroid hormones play crucial role in several biological processes including reproduction. Disruption of normal thyroid status by environmental contaminants can cause severe impairment in reproductive functions. In our previous study, we reported down-regulation of a protein in seminal vesicular fluid of air-breathing catfish, Clarias gariepinus during experimentally induced hyperthyroidism. N-terminal amino acid sequence analysis followed by search in sequence database denoted it to be lipocalin-type prostaglandin D2 synthase (ptgds-b). In the present study, we cloned full-length cDNA of ptgds-b based on the N-terminal amino acid sequence. Surprisingly, Northern blot as well as RT-PCR analysis demonstrated the presence of ptgds-b transcript predominantly in seminal vesicles and developing testis. Further, ptgds-b mRNA significantly decreased in seminal vesicles following L-thyroxine overdose while there was an increased expression of ptgds-b after depletion of thyroid hormone by thiourea and withdrawal of the treatments reverted this effect. Treatment of catfish with human chorionic gonadotropin and estradiol significantly reduced ptgds-b expression. Taken together, we report ptgds-b as a thyroid hormone regulated protein in the seminal vesicles in addition to gonadotropin and estradiol. Further studies might explain the exclusive presence of ptgds-b in seminal vesicles and developing testis yet present data evaluated it as a putative biomarker for thyroid hormone disruption.

Insights into the prostanoid pathway in the ovary development of the penaeid shrimp Penaeus monodon

The prostanoid pathway converts polyunsaturated fatty acids (PUFAs) into bioactive lipid mediators, including prostaglandins, thromboxanes and prostacyclins, all of which play vital roles in the immune and reproductive systems in most animal phyla. In crustaceans, PUFAs and prostaglandins have been detected and often associated with female reproductive maturation. However, the presence of prostanoid biosynthesis genes remained in question in these species. In this study, we outlined the prostanoid pathway in the black tiger shrimp Penaeus monodon based on the amplification of nine prostanoid biosynthesis genes: cytosolic phospholipase A2, hematopoietic prostaglandin D synthase, glutathione-dependent prostaglandin D synthase, prostaglandin E synthase 1, prostaglandin E synthase 2, prostaglandin E synthase 3, prostaglandin F synthase, thromboxane A synthase and cyclooxygenase. TBLASTX analysis confirmed the identities of these genes with 51-99% sequence identities to their closest homologs. In addition, prostaglandin F2α (PGF2α), which is a product of the prostaglandin F synthase enzyme, was detected for the first time in P. monodon ovaries along with the previously identified PUFAs and prostaglandin E2 (PGE2) using RP-HPLC and mass-spectrometry. The prostaglandin synthase activity was also observed in shrimp ovary homogenates using in vitro activity assay. When prostaglandin biosynthesis was examined in different stages of shrimp ovaries, we found that the amounts of prostaglandin F synthase gene transcripts and PGF2α decreased as the ovaries matured. These findings not only indicate the presence of a functional prostanoid pathway in penaeid shrimp, but also suggest a possible role of the PGF2α biosynthesis in shrimp ovarian development.

CYP74C3 and CYP74A1, plant cytochrome P450 enzymes whose activity is regulated by detergent micelle association, and proposed new rules for the classification of CYP74 enzymes

CYP74C3 (cytochrome P450 subfamily 74C3), an HPL (hydroperoxide lyase) from Medicago truncatula (barrel medic), and CYP74A1, an AOS (allene oxide synthase) from Arabidopsis thaliana, are key membrane-associated P450 enzymes in plant oxylipin metabolism. Both recombinant detergent-free enzymes are monomeric proteins with dual specificity and very low enzyme activity that can be massively activated with detergent. This effect is a result of the formation of a complex between the protein monomer and a single detergent micelle and, in the case of CYP74A1, has a major effect on the substrate specificity of the enzyme. Association with a detergent micelle without an effect on protein oligomeric state represents a new mechanism of activation for membrane-associated P450 enzymes. This may represent a second unifying feature of CYP74 enzymes, in addition to their known differences in reaction mechanism, which separates them functionally from more classical P450 enzymes. Highly concentrated and monodispersed samples of detergent-free CYP74C3 and CYP74A1 proteins should be suitable for structural resolution. On the basis of recent evidence for incorrect assignment of CYP74 function, using the current rules for CYP74 classification based on sequence relatedness, we propose an alternative based on substrate and product specificity for debate and discussion.

Evolution of the lipocalin family as inferred from a protein sequence phylogeny

The lipocalins constitute a family of proteins that have been found in eubacteria and a variety of eukaryotic cells, where they play diverse physiological roles. It is the primary goal of this review to examine the patterns of change followed by lipocalins through their complex history, in order to stimulate scientists in the field to experimentally contrast our phylogeny-derived hypotheses. We reexamine our previous work on lipocalin phylogeny and update the phylogenetic analysis of the family. Lipocalins separate into 14 monophyletic clades, some of which are grouped in well supported superclades. The lipocalin tree was rooted with the bacterial lipocalin genes under the assumption that they have evolved from a single common ancestor with the metazoan lipocalins, and not by horizontal transfer. The topology of the rooted tree and the species distribution of lipocalins suggest that the newly arising lipocalins show a higher rate of amino acid sequence divergence, a higher rate of gene duplication, and their internal pocket has evolved towards binding smaller hydrophobic ligands with more efficiency.

[New aspects on prostaglandin D synthases]

Prostaglandin (PG) D2 is a major prostanoid produced in the central nervous system and mast cells, acting as a neuromodulator and an allergic and inflammatory mediator. PGD2 is readily dehydrated to produce PGs of the J series, such as PGJ2, delta 12-PGJ2, and 15-deoxy-delta 12, 14-PGJ2. We identified two distinct types of PGD synthase: one is glutathione independent, the lipocalin-type enzyme; and the other is glutathione-dependent, the hematopoietic enzyme. Lipocalin-type PGD synthase is localized in the central nervous system and genital organs, dominantly produced in the leptomeninges of the brain and pigmented epithelium of the retina, and is actively secreted as beta-trace into the cerebrospinal fluid and interphotoreceptor matrix, respectively. Since the enzyme binds all-trans- or 9-cis-retinoic acid with Kd of about 100 nM, it is considered to be a bifunctional protein acting as a PGD2-producing enzyme and an extracellular retinoid-transporter. Alternatively, we recently cloned the cDNA for hematopoietic PGD synthase, crystallized the recombinant enzyme, and determined the three-dimensional structure. The enzyme is the first member of the sigma class glutathione S-transferase (GST) from vertebrates and possesses a prominent cleft as the active site, which is never seen among other members of the GST family.