Distinct physical and structural properties of the ovine uterine serpin

Proteomic analysis of amniotic and allantoic fluid from buffaloes during foetal development

The objective of this study was to describe the dynamic changes in protein composition and protein abundance in amniotic and allantoic fluids from buffaloes during gestation. Amniotic and allantoic fluids were collected during the first, second and third trimesters of gestation. The foetuses were measured and weighed. Fluid samples were centrifuged at 800 g for 10 min and then at 10,000 g for 60 min at 4°C. The supernatant was collected to determine the total protein concentration. Based on total protein concentration, an aliquot (50 μg) was used for in-solution tryptic digestion, and mass spectrometry analysis (nano-LC-MS/MS) was performed. A multivariate statistical analysis of the proteomic data was conducted. Across the different stages of buffalo gestation, fifty-one proteins were found in the amniotic fluid, and twenty-one were found in the allantoic fluid. A total of twelve proteins were common among the stages, and four presented significant differences (VIP score α > 1). Fibronectin and alpha-1-antiproteinase were more abundant in the amniotic fluid than in the allantoic fluid. Alpha-2-macroglobulin and alpha-2-HS-glycoprotein were more abundant in the allantoic fluid than in the amniotic fluid. Alpha-2-macroglobulin participates in remodelling and growth of the uterus at beginning of the gestation (first trimester), and these findings indicate that can serve as a potential tool for the early diagnosis of pregnancy in buffaloes.

Expression and Properties of Recombinant Ovine Uterine Serpin

Ovine uterine serpin (OvUS) is produced in the uterus of sheep under the influence of progesterone. It weakly inhibits pepsin and reduces proliferation of lymphocytes, tumor cell lines, and preimplantation embryos. When purified from uterine fluid, the concentration required for its antiproliferative effect in vitro is ~0.25–1 mg/ml. Here we show that recombinant (r) OvUS is a more potent regulator of cell proliferation than native (n) OvUS purified from uterine fluid. To produce rOvUS, RNA was extracted from endometrium from a pregnant ewe and cDNA was amplified by reverse transcription-polymerase chain reaction using gene-specific primers. The purified OvUS cDNA was inserted into the ampicillin-resistant plasmid vector pcDNA3.1/V5-His-TOPO. The plasmid was introduced into the TOP10 Escherichia coli strain, purified, and used for transfection of Freestyle 293-F cells. Digestion of rOvUS with protein N-glycosidase F confirmed that rOvUS was N-glycosylated. Both rOvUS and nOvUS inhibited proliferation of phytohemagglutin-activated sheep lymphocytes and the P388D1 mouse lymphoma and PC-3 prostate cell lines. Inhibition was greater for rOvUS than for nOvUS, and concentrations as low as 15 μg/ml rOvUS were effective at reducing lymphocyte proliferation. Addition of rOvUS to fertilized bovine embryos reduced the cleavage rate and the percentage of embryos that became blastocysts. Native OvUS did not affect cleavage rate and had a smaller effect on development to the blastocyst stage. Experiments demonstrate that OvUS is a more potent inhibitor of cell proliferation and embryonic development than previously believed and add credence to the putative role for the protein in regulating cell proliferation.

Evolution and function of the uterine serpins (SERPINA14)

Uterine serpins (recently designated as SERPINA14) are hormonally induced proteins secreted in large quantities by the endometrial epithelium during pregnancy. The SERPINA14 proteins belong to the serine proteinase inhibitor (serpin) superfamily, but their apparent lack of inhibitory activity toward serine proteinases suggests that these proteins evolved a different function from the anti-proteinase activity typically found in most members of the serpin superfamily. The gene is present in a limited group of mammals in the Laurasiatheria superorder (ruminants, horses, pigs, dolphins and some carnivores) while being absent in primates, rodents, lagomorphs and marsupials. Thus, the gene is likely to have evolved by gene duplication after divergence of Laurasiatheria and to play an important role in pregnancy. That role may vary between species. In sheep, SERPINA14 probably serves an immunoregulatory role to prevent rejection of the fetal allograft. It is inhibitory to lymphocyte proliferation and natural killer cell function. In the pig, SERPINA14 is involved in iron transport to the fetus by binding to and stabilizing the iron-binding protein uteroferrin. It is possible that SERPINA14 has undergone divergence in function since the original emergence of the gene in a common ancestor of species possessing SERPINA14.

Haemonchus contortus: cloning and characterization of serpin

The serpin gene of Haemonchus contortus (hc-serpin) was cloned and characterized in this study. Specific primers for rapid amplification cDNA ends (RACE) were designed based on the expression sequence tag (EST, BM173953) to amplify the 3'- and 5'-ends of hc-serpin. The full length of the cDNA of this gene was obtained by overlapping the sequences of 3'- and 5'-extremities and amplification by reverse transcription-PCR. The biochemical activities of the recombinant protein (rHc-Serpin), which was expressed in prokaryotic cells and purified by affinity chromatography and size-exclusion chromatography, were analyzed by assays of trypsin inhibition, anti-coagulation activity, and stability to temperature and pH. The results showed that the cloned full-length cDNA comprised 1317bp and encoded a peptide with 367 amino acid residues which showed sequence similarity to several known serpins. The rHc-Serpin inhibited trypsin activity effectively and prolonged the coagulation time of rabbit blood in vitro. The rHc-Serpin was stable from pH 2.0-10.0 and kept activity at high temperature until 75 degrees C. Optimal pH of rHc-Serpin protein to inhibit trypsin activity was at pH 7.6. The natural serpin of H. contortus detected by immunoblot assay was about 63kDa, and the rHc-Serpin was recognized strongly by serum from naturally infected goats. By immunohistochemistry, the serpin was localised exclusively in the epithelial cells of gastrointestinal tract in adult H. contortus. The results indicated that the cloned gene was serpin and that the protein may play important roles in the biological functions of H. contortus.

Cytokine production by peripheral blood mononuclear cells of women with a history of preterm birth

Preterm birth is associated with elevated production of pro-inflammatory cytokines such as TNFalpha at the maternal-fetal interface. Previous studies have suggested that women with a history of preterm birth produce aberrantly strong inflammatory responses to bacterial lipopolysaccharide (LPS). However many intrauterine infections in women are associated with pathogens including Ureaplasma urealyticum, Mycoplasma hominis and Streptococcus agalactiae (group B streptococcus) that contain pro-inflammatory factors other than LPS. We evaluated whether peripheral blood leukocytes from women with a history of preterm birth produce elevated amounts of TNFalpha upon stimulation with pathogens associated with preterm birth and if pre-treatment with aspirin, an anti-inflammatory medication, decreases the ex vivo production of this cytokine. Heat-killed bacteria elicited increased TNFalpha production from leukocytes in a dose-dependent manner, but no differences in TNFalpha production between leukocytes from women with preterm birth and control women with term birth were detected. In women who consumed aspirin each day for one week, TNFalpha production was increased in leukocytes from control women stimulated with Escherichia coli and U. urealyticum, but was reduced or unchanged in leukocytes from women with preterm birth. Similar trends were observed for a subset of samples stimulated with U. urealyticum and assayed for IL-6, IL-10, IL-1beta and TNFalpha by bead array. We conclude that leukocytes from women with a history of preterm birth do not have elevated pro-inflammatory responses to pathogens, and that reproductive history is associated with different effects of aspirin on pro-inflammatory cytokine production.

Regulation of DNA synthesis and the cell cycle in human prostate cancer cells and lymphocytes by ovine uterine serpin

Background

Uterine serpins are members of the serine proteinase inhibitor superfamily. Like some other serpins, these proteins do not appear to be functional proteinase inhibitors. The most studied member of the group, ovine uterine serpin (OvUS), inhibits proliferation of several cell types including activated lymphocytes, bovine preimplantation embryos, and cell lines for lymphoma, canine primary osteosarcoma and human prostate cancer (PC-3) cells. The goal for the present study was to evaluate the mechanism by which OvUS inhibits cell proliferation. In particular, it was tested whether inhibition of DNA synthesis in PC-3 cells involves cytotoxic actions of OvUS or the induction of apoptosis. The effect of OvUS in the production of the autocrine and angiogenic cytokine interleukin (IL)-8 by PC-3 cells was also determined. Finally, it was tested whether OvUS blocks specific steps in the cell cycle using both PC-3 cells and lymphocytes.

Results

Recombinant OvUS blocked proliferation of PC-3 cells at concentrations as low as 8 μg/ml as determined by measurements of [³H]thymidine incorporation or ATP content per well. Treatment of PC-3 cells with OvUS did not cause cytotoxicity or apoptosis or alter interleukin-8 secretion into medium. Results from flow cytometry experiments showed that OvUS blocked the entry of PC-3 cells into S phase and the exit from G₂/M phase. In addition, OvUS blocked entry of lymphocytes into S phase following activation of proliferation with phytohemagglutinin.

Conclusion

Results indicate that OvUS acts to block cell proliferation through disruption of the cell cycle dynamics rather than induction of cytotoxicity or apoptosis. The finding that OvUS can regulate cell proliferation makes this one of only a few serpins that function to inhibit cell growth.

Identification and cloning of caprine uterine serpin

The uterine serpins have been described in sheep, cattle, and pigs as a highly diverged group of the large superfamily of serpin proteins that typically function as serine proteinase inhibitors. Here, the range of species that possess and express a uterine serpin gene is extended to the goat. Sequencing of cDNA amplified from total RNA from a pregnant goat at day 25 of pregnancy resulted in a 1,292 bp full-length consensus cDNA sequence for caprine uterine serpin (CaUS). The predicted amino acid sequence of the caprine precursor showed 96%, 82%, 55%, and 56% identity to OvUS, BoUS, PoUS1, and PoUS2, respectively. The signal peptide extends from amino acids 1 to 25, resulting in a secreted protein of 404 amino acids and 46,227 Mr (excluding carbohydrate). Both the goat and sheep uterine serpins have a nine amino acid insert in the Helix I region that is not found in bovine or porcine uterine serpins. A total of 13 amino acids in CaUS are different than those for the nearest homologue, ovine uterine serpin. One of these is in the site of cleavage of the signal sequence, where a single nucleotide substitution (G --> C) changed the cysteine for the sheep, bovine, and porcine genes to a serine. In addition, the amino acid at the putative P1-P1' site (the scissile bond for antiproteinase activity) is a valine for CaUS, BoUS, PoUS1, and PoUS2 versus an alanine for OvUS. The hinge region of all five of the uterine serpins (P17-P9) is distinct from the consensus pattern for inhibitory sequences and it is unlikely, therefore, that the uterine serpins possess prototypical proteinase inhibitory activity. The goat uterine serpin was immunolocalized to the glandular epithelium of the endometrium from a pregnant nanny at day 25 of pregnancy. There was also immunoreactive product in scattered luminal epithelial cells. No immunoreaction product was detected in endometrium from a nanny at day 5 of the estrous cycle. Western blotting of uterine fluid collected from the pregnant uterine horn of a unilaterally-pregnant goat revealed the presence of a protein band at Mr approximately 56,000 that reacted with monoclonal antibody to OvUS. In conclusion, the range of species in which uterine serpins are present and expressed in the uterus includes the goat in addition to the previously described sheep, cow, and pig. In all of these species, the uterine serpin is derived primarily from glandular epithelium, is secreted into the uterine lumen, and contains sequence characteristics suggesting it is not an inhibitory serpin.

Antiproliferative Actions of Ovine Uterine Serpin

PROBLEM

Ovine uterine serpin (OvUS) is a member of the serine proteinase inhibitor superfamily and is the major protein produced by luminal and glandular epithelium of the sheep endometrium during mid to late pregnancy. The protein does not have prototypical proteinase inhibitory activity but can inhibit a wide variety of lymphocyte functions such as mitogen-induced proliferation and natural killer cell cytotoxicity.

METHOD OF STUDY

The antiproliferative actions of OvUS were studied.

RESULTS

It was demonstrated that, in addition to inhibiting lymphocyte proliferation, OvUS inhibits growth of two tumor cell lines (D17 and PC-3). The protein also interrupts development of pre-implantation embryos. Inhibition of cell proliferation is not universal, however, as OvUS did not inhibit growth of two non-tumorigenic cell lines (MDBK and BEND). The mechanism of action of inhibitory effects of OvUS is not known although experiments with inhibitors of protein kinase A indicate that the protein does not inhibit lymphocyte proliferation through this pathway. Moreover, the protein does not induce apoptosis.

CONCLUSIONS

The finding that OvUS has antiproliferative activity is demonstrative of the wide range of functions exerted by members of the serpin superfamily. The antiproliferative property of OvUS may reflect the role of the protein during pregnancy and may be exploitable for design of new antiproliferative drugs.

Linkage between the hormone binding site and the reactive center loop of thyroxine binding globulin

Thyroxine binding globulin (TBG) is the major carrier of the thyroid hormones triiodothyronine (T3) and thyroxine (T4) in plasma. TBG is member of the serpin family of proteins although it has no proteinase inhibitory activity. In this study we show that TBG has properties typical of a metastable serpin and provide evidence that occupancy of the hormone binding site alters the conformation of the reactive center loop. After reactive center loop cleavage by endoproteinase Asp-N or neutrophil elastase the protein became more stable to guanidine hydrochloride denaturation compared to the native protein, as a result of loop insertion. In addition, incubation of the native protein with a reactive center loop peptide, caused a change in mobility on a native gel. This is consistent with the idea that thyroxine binding globulin is able to form a binary complex with the peptide as a result of beta-sheet A expansion. To assess the effect of cleavage and loop insertion on the hormone binding site we used the specific binding of a fluorophore, 1,8-anilinonaphthalene sulfonic acid (ANS). Loop insertion itself had no effect on ANS affinity, but cleavage with elastase at the P4'-P5' bond caused a reduction in affinity, presumably because this cleavage site is located within the hormone binding site. These data support the concept that cleavage of TBG by proteinases released in inflammation is a mechanism to deliver thyroid hormones to target tissues. A linkage between the occupancy state of the hormone binding site and the conformation of the reactive center loop was indicated by the observation that binding of T3 to native TBG reduced proteolytic susceptibility by both endoproteinase Asp-N and elastase.