Prostatic secretory protein (PSP94) expression in human female reproductive tissues, breast and in endometrial cancer cell lines

Three-dimensional structures of avian beta-microseminoproteins: insight from the chicken egg-specific beta-microseminoprotein 3 paralog

Beta‐microseminoproteins (MSMBs) are small disulfide‐rich proteins that are conserved among vertebrates. These proteins exhibit diverse biological activities and were mainly reported to play a role in male fertility, immunity, and embryogenesis. In this work, we focused on the chicken MSMB3 protein that was previously depicted as an egg antibacterial protein. We report that MSMB3 protein is exclusively expressed in the reproductive tissues of laying hens (in contrast to chicken MSMB1 and MSMB2 paralogs), to be incorporated in the egg white during the process of egg formation. We also showed that chicken MSMB3 possesses highly conserved orthologs in bird species, including Neognathae and Palaeognathae. Chicken MSMB3 was purified from egg white using heparin affinity chromatography and was analyzed by top‐down and bottom‐up proteomics. Several proteoforms could be characterized, and a homodimer was further evidenced by NMR spectroscopy. The X‐ray structure of chicken MSMB3 was solved for the first time, revealing that this protein adopts a novel dimeric arrangement. The highly cationic MSMB3 protein exhibits a distinct electrostatic distribution compared with chicken MSMB1 and MSMB2 structural models, and with published mammalian MSMB structures. The specific incorporation of MSMB3 paralog in the egg, and its phylogenetic conservation in birds together with its peculiar homodimer arrangement and physicochemical properties, suggests that the MSMB3 protein has evolved to play a critical role during the embryonic development of avian species. These new data are likely to stimulate research to elucidate the structure/function relationships of MSMB paralogs and orthologs in the animal kingdom.

STAT6, PBX2, and PBRM1 Emerge as Predicted Regulators of 452 Differentially Expressed Genes Associated With Puberty in Brahman Heifers

The liver plays a central role in metabolism and produces important hormones. Hepatic estrogen receptors and the release of insulin-like growth factor 1 (IGF1) are critical links between liver function and the reproductive system. However, the role of liver in pubertal development is not fully understood. To explore this question, we applied transcriptomic analyses to liver samples of pre- and post-pubertal Brahman heifers and identified differentially expressed (DE) genes and genes encoding transcription factors (TFs). Differential expression of genes suggests potential biological mechanisms and pathways linking liver function to puberty. The analyses identified 452 DE genes and 82 TF with significant contribution to differential gene expression by using a regulatory impact factor metric. Brain-derived neurotrophic factor was observed as the most down-regulated gene (P = 0.003) in post-pubertal heifers and we propose this gene influences pubertal development in Brahman heifers. Additionally, co-expression network analysis provided evidence for three TF as key regulators of liver function during pubertal development: the signal transducer and activator of transcription 6, PBX homeobox 2, and polybromo 1. Pathway enrichment analysis identified transforming growth factor-beta and Wnt signaling pathways as significant annotation terms for the list of DE genes and TF in the co-expression network. Molecular information regarding genes and pathways described in this work are important to further our understanding of puberty onset in Brahman heifers.

PSP94, an upstream signaling mediator of prostasin found highly elevated in ovarian cancer

Ovarian cancer is a leading cause of cancer death as diagnosis is frequently delayed to an advanced stage. Effective biomarkers and screening strategies for early detection are urgently needed. In the current study, we identify PSP94 as a key upstream factor in mediating prostasin (a protein previously reported to be overexpressed in ovarian cancer) signaling that regulates prostasin expression and action in ovarian cancer cells. PSP94 is overexpressed in ovarian cancer cell lines and patients, and is significantly correlated with prostasin levels. Signaling pathway analysis demonstrated that both PSP94 and prostasin, as potential upstream regulators of the Lin28b/Let-7 pathway, regulate Lin28b and its downstream partner Let-7 in ovarian cancer cells. Expression of PSP94 and prostasin show a strong correlation with the expression levels of Lin28b/Let-7 in ovarian cancer patients. Thus, PSP94/prostasin axis appears to be linked to the Lin28b/Let-7 loop, a well-known signaling mechanism in oncogenesis in general that is also altered in ovarian cancer. The findings suggest that PSP94 and PSP94/prostasin axis are key factors and potential therapeutic targets or early biomarkers for ovarian cancer.

Development of an ELISA for sPSP94 and utility of the sPSP94/sPSA ratio as a diagnostic indicator to differentiate between benign prostatic hyperplasia and prostate cancer

BACKGROUND

The serum PSA (sPSA) test has low specificity for prostate cancer (PCa), since sPSA also rises in benign prostatic hyperplasia (BPH). Serum PSP94 (sPSP94), a major secreted prostate protein, is indicated as a PCa marker. The potential of sPSP94 and sPSA in conjunction with each other to improve specificity of diagnostic test for PCa needs to be evaluated.

METHODS

PCa patients (n=33), BPH patients (n=44) and healthy controls (n=50) were recruited. A serum-based sandwich ELISA was developed to measure sPSP94 concentrations. Utility of sPSP94 in improving specificity of sPSA test was evaluated by studying sPSP94/sPSA ratios of study participants.

RESULTS

Considerable decrease in overlap among sPSP94/sPSA ratio values of BPH and PCa patients was observed, as compared to sPSP94 or sPSA alone. For differentiating between BPH and PCa patients, this ratio had a maximum area under the curve (AUC) of 0.859 (P=0.0132) and had a comparable sensitivity (90.91%) to sPSA with an increased specificity of 70.45%. Further, decision curve analysis (DCA) showed that sPSP94/sPSA ratio had a superior net benefit in identifying PCa, in patients opting for biopsy.

CONCLUSION

The sPSP94/sPSA ratio can be a better differentiating marker between BPH and PCa, than sPSP94 or sPSA alone.

Prostate Secretory Protein of 94 amino acids (PSP94) binds to prostatic acid phosphatase (PAP) in human seminal plasma

Prostate Secretory Protein of 94 amino acids (PSP94) is one of the major proteins present in the human seminal plasma. Though several functions have been predicted for this protein, its exact role either in sperm function or in prostate pathophysiology has not been clearly defined. Attempts to understand the mechanism of action of PSP94 has led to the search for its probable binding partners. This has resulted in the identification of PSP94 binding proteins in plasma and seminal plasma from human. During the chromatographic separation step of proteins from human seminal plasma by reversed phase HPLC, we had observed that in addition to the main fraction of PSP94, other fractions containing higher molecular weight proteins also showed the presence of detectable amounts of PSP94. This prompted us to hypothesize that PSP94 could be present in the seminal plasma complexed with other protein/s of higher molecular weight. One such fraction containing a major protein of ~47 kDa, on characterization by mass spectrometric analysis, was identified to be Prostatic Acid Phosphatase (PAP). The ability of PAP present in this fraction to bind to PSP94 was demonstrated by affinity chromatography. Co-immunoprecipitation experiments confirmed the presence of PSP94-PAP complex both in the fraction studied and in the fresh seminal plasma. In silico molecular modeling of the PSP94-PAP complex suggests that β-strands 1 and 6 of PSP94 appear to interact with domain 2 of PAP, while β-strands 7 and 10 with domain 1 of PAP. This is the first report which suggests that PSP94 can bind to PAP and the PAP-bound PSP94 is present in human seminal plasma.

A novel MSMB-related microprotein in the postovulatory egg coats of marsupials

BACKGROUND

Early marsupial conceptuses differ markedly from those of eutherian mammals, especially during cleavage and early blastocyst stages of development. Additionally, in marsupials the zona pellucida is surrounded by two acellular layers, the mucoid coat and shell, which are formed from secretions from the reproductive tract.

RESULTS

We report the identification of a novel postovulatory coat component in marsupials, which we call uterinesecreted microprotein (USM). USM belongs to a family of disulfide-rich microproteins of unconfirmed function that is found throughout deuterostomes and in some protostomes, and includes β-microseminoprotein (MSMB) and prostate-associated microseminoprotein (MSMP). We describe the evolution of this family in detail, including USM-related sequences in other vertebrates. The orthologue of USM in the tammar wallaby, USM1, is expressed by the endometrium with a dynamic temporal profile, possibly under the control of progesterone.

CONCLUSIONS

USM appears to have evolved in a mammalian ancestor specifically as a component of the postovulatory coats. By analogy with the known properties of MSMB, it may have roles in regulating sperm motility/survival or in the immune system. However, its C-terminal domain is greatly truncated compared with MSMB, suggesting a divergent function.

The rs10993994 risk allele for prostate cancer results in clinically relevant changes in microseminoprotein-beta expression in tissue and urine

Background

Microseminoprotein-beta (MSMB) regulates apoptosis and using genome-wide association studies the rs10993994 single nucleotide polymorphism in the MSMB promoter has been linked to an increased risk of developing prostate cancer. The promoter location of the risk allele, and its ability to reduce promoter activity, suggested that the rs10993994 risk allele could result in lowered MSMB in benign tissue leading to increased prostate cancer risk.

Methodology/Principal Findings

MSMB expression in benign and malignant prostate tissue was examined using immunohistochemistry and compared with the rs10993994 genotype. Urinary MSMB concentrations were determined by ELISA and correlated with urinary PSA, the presence or absence of cancer, rs10993994 genotype and age of onset. MSMB levels in prostate tissue and urine were greatly reduced with tumourigenesis. Urinary MSMB was better than urinary PSA at differentiating men with prostate cancer at all Gleason grades. The high risk allele was associated with heterogeneity of MSMB staining and loss of MSMB in both tissue and urine in benign prostate.

Conclusions

These data show that some high risk alleles discovered using genome-wide association studies produce phenotypic effects with potential clinical utility. We provide the first link between a low penetrance polymorphism for prostate cancer and a potential test in human tissue and bodily fluids. There is potential to develop tissue and urinary MSMB for a biomarker of prostate cancer risk, diagnosis and disease monitoring.

High-affinity binding of seminal plasma PSP94 to human immunoglobulin is through the Fab domain

Prostate secretory protein of 94 amino acids (PSP94) is one of the major proteins present in human seminal plasma. We had earlier reported that PSP94 has the ability to bind to human IgG. The aims of the present study were to further delineate the PSP94-IgG interaction and to understand whether this could have any significance in sperm function. Direct binding of IgG fragments to PSP94 showed maximal binding with F(ab')(2) followed by Fab, while Fc displayed least binding in ELISA. Binding kinetics of PSP94-IgG interaction using surface plasmon resonance (SPR) revealed high-affinity binding of IgG to PSP94 with a dissociation constant (K(D)) of 8.8 x 10(-)(11)M. PSP94-IgG interaction was found to be through the Fab domains of IgG. Real-time interaction kinetics revealed association constants for binding of IgG, Fab, and F(ab')(2) towards PSP94 to be of the same order but with altered dissociation constants. IgG and its F(ab')(2) fragment once complexed to PSP94 demonstrated negligible dissociation, while dissociation rate of Fab fragment was 6.6 x 10(-)(4). In silico molecular modeling of PSP94-IgG complex identified N- and C-terminal beta-strands of PSP94 to be the most plausible region involved in IgG interaction. Immunofluorescence studies revealed that IgG bound to human spermatozoa predominantly in the tail region, which could be prevented when IgG was preincubated with PSP94. This study reports for the first time that IgG forms a high-affinity complex with PSP94 through its F(ab')(2) domain and reveals the ability of PSP94 to prevent binding of IgG to spermatozoa.

Crystal structure of prostate secretory protein PSP94 shows an edge-to-edge association of two monomers to form a homodimer

Several recent genome-wide association studies have linked the human MSMB gene, encoding prostate secretory protein of 94 residues (PSP94), with prostate cancer susceptibility. PSP94 is one of the most abundant proteins from prostatic secretions and a primary constituent of human semen. PSP94 suppresses tumor growth and metastasis, and its expression gradually decreases during progression of the prostate cancer. It is a rapidly evolving protein with homologues present in several species with 10 conserved cysteine residues. PSP94 homologues show high-affinity binding with different proteins from the cysteine-rich secretory protein family, some of which have been shown to be ion channel blockers. Here, we report the crystal structure of human PSP94 at 2.3 A resolution. The structure shows that the amino and the carboxyl ends of the polypeptide chain are held in close proximity facing each other. A strong hydrogen bond between these ends, which are located respectively on the first and the last beta-strands, leads to formation of an almost straight edge in PSP94 structure. Crystal structure shows that these edges from two PSP94 monomers associate in antiparallel fashion, leading to formation of a dimer. Our studies further show that dimers dissociate into monomers at acidic pH, possibly through distortion of the straight edge. Further, based on several observations, we propose that PSP94 binds to cysteine-rich secretory proteins and immunoglobulin G through the same edge, which is involved in the formation of PSP94 dimeric interface.

The potential value of microseminoprotein-beta as a prostate cancer biomarker and therapeutic target

BACKGROUND

Recent genome-wide association studies have shown an association of a SNP two base pairs upstream of the 5' UTR of the microseminoprotein-beta (MSMB) gene with an increased risk of developing the prostate cancer, re-igniting interest in its protein product, MSMB.

METHODS

As one of the most abundant prostatic proteins, MSMB can be reliably detected in tissue and serum.

RESULTS

It has been consistently shown that MSMB expression is high in normal and benign prostate tissue and lowered or lost in prostate cancer suggesting that it might be a useful tissue biomarker for prostate cancer diagnosis and its levels in serum may be useful as a marker for prognosis. Members of the cysteine-rich secretory protein family and laminin receptors have been shown to bind MSMB at the cell surface and in serum thereby regulating apoptosis. Thus, in the benign prostate, MSMB regulates cell growth, but when MSMB is lost during tumourigenesis, cells are able to grow in a more uncontrolled manner. Both full length MSMB and a short peptide comprised of amino acids 31-45 have been tested for potential therapeutic benefit in mouse models and humans.

CONCLUSIONS

MSMB has potential as a biomarker of prostate cancer development, progression and recurrence and potentially as a target for therapeutic intervention.

The Ccr4-NOT deadenylase subunits CNOT7 and CNOT8 have overlapping roles and modulate cell proliferation

Accurate gene expression requires the precise control of mRNA levels, which are determined by the relative rates of nuclear (pre-)mRNA synthesis and processing, and cytoplasmic mRNA turnover. A key step in mRNA degradation is the removal of the poly(A) tail, which involves several deadenylases including components of the Ccr4-Not complex. Here, we focused on the role of the human paralogues CNOT7 (hCaf1/Caf1a) and CNOT8 (hPop2/Caf1b/Calif), which possess deadenylase activity mediated by DEDD nuclease domains. We show that efficient proliferation requires both subunits, although combined knockdown of CNOT7 and CNOT8 further reduces cell proliferation indicating partial redundancy between these proteins. Interestingly, the function of CNOT7 in cell proliferation partly depends on its catalytic activity. On the other hand, the interaction between CNOT7 and BTG2, a member of the antiproliferative BTG/Tob family involved in transcription and mRNA decay appears less important for proliferation of MCF7 cells, suggesting that CNOT7 does not function solely in conjunction with BTG2. Further analysis of gene expression profiles of CNOT7 and/or CNOT8 knockdown cells underscores the partial redundancy between these subunits and suggests that regulation of several genes, including repression of the antiproliferative genes MSMB and PMP22, by the Ccr4-Not complex contributes to cell proliferation.

Crystallization and preliminary X-ray diffraction analysis of human seminal plasma protein PSP94

The human seminal plasma protein PSP94 is a small protein of 94 residues that contains ten cysteines. Since its discovery about 25 years ago, several potential biological functions have been reported for this protein. Many PSP94 homologues have also been identified since then from various species, but no crystal structure has been determined to date. PSP94 has been purified from human seminal plasma and crystallized. These crystals diffracted to approximately 2.3 A resolution and belonged to space group P4(1)2(1)2, with unit-cell parameters a = 107.9, b = 107.9, c = 92.1 A. There are four molecules in the asymmetric unit. Structure solution by the heavy-atom method is currently in progress.

Molecular description of a 3D in vitro model for the study of epithelial ovarian cancer (EOC)

Epithelial ovarian cancer (EOC) cell lines are useful tools for the molecular and biological characterization of ovarian cancer. The use of an in vitro multidimensional (3-D) culture model recapitulates some of the growth conditions encountered by tumor cells in vivo. Here we describe a molecular comparison of spheroid based 3D EOC models versus monolayer cultures and xenografts using cell lines from malignant ovarian tumors (TOV-21G and TOV-112D) and ascites (OV-90) previously established and characterized in our laboratory. Gene expression analyses of the three models were performed using the Affymetrix HG-U133A high density DNA array. Cluster analysis identified a set of genes that stratified expression profiles from the EOC cell lines grown as spheroids and xenografts from that of monolayer cultures. The gene expression analysis results were validated by Q-PCR analyses on an independent set of RNAs. Differential expression observed for the S100A6 gene between the monolayer, spheroid cultures and xenografts was confirmed at the protein level by immunohistochemistry. The analysis was extended to various ovarian tumor tissues using an EOC tissue array. This result represents an example of a gene that, if studied in vitro, is more representative of the in vivo disease in a 3D model rather than the monolayer culture. Identification of genes in spheroid models that mimic the in vivo tumor gene expression patterns may allow a better understanding of the community effect observed in human disease that is determined by direct or indirect interactions of cells with their environment or other surrounding cells.

Cloning, expression, purification and functional characterization of recombinant human PSP94

Human PSP94 (prostate secretory protein of 94 amino acids) is a major protein synthesized by the prostate gland and secreted in large quantities in seminal fluid. Previous studies have suggested a potential biomedical utility of PSP94 in applications such as diagnosis/prognosis and in treatment of human prostate cancer (PCa). This study was designed to produce a recombinant human PSP94 (rPSP94) to evaluate its clinical and functional role in PCa. We cloned PSP94 cDNA and successfully expressed an active recombinant protein in yeast using Pichia pastoris expression system. A simple purification strategy was established that incorporated combination of membrane ultrafiltration (Pellicon tangential-flow system) and anion exchange chromatography using DE52 resin. The method minimized the technical level of expertise for the production of high quality functional protein. The purified rPSP94 (>98% purity) showed a single band with SDS-PAGE analysis and a peak with a molecular mass (M(r)) of 11,495 kDa using MALDI TOF mass spectrometry (MS). The in vitro competitive binding assays indicated high functional similarity of the rPSP94 with that of its native counterpart. Furthermore, in vivo administration of rPSP94 caused a significant growth inhibition of hormone refractory Mat LyLu tumors in Dunning rat model. Taken together, our data provides evidence for high suitability of the purified rPSP94 for evaluation of its potential diagnostic and therapeutic role in PCa and as a valuable analytical reference standard for clinical studies.

Rat PSP94 inhibits the growth and viability of the rat adenocarcinoma cell line PAIII in vitro

Previous studies have shown that human PSP94 can inhibit the growth of prostate cancer cells both in vitro and in vivo. To further validate this potential and investigate the protein within a homologous setting, we examined the effects of rat PSP94 on the growth of the rat prostate adenocarcinoma cell line PAIII in vitro. To generate rat PSP94, we used both a plasmid-based expression system and a recombinant rat PSP molecule. Rat PSP was shown to inhibit the growth and survival of PAIII cells in a dose-dependent manner with > 90 percent reductions in both observed. TUNEL and Annexin-V assays confirmed PAIII cell death to be via apoptosis.

Identification and expression of amphioxus beta-microseminoprotein (MSP)-like gene encoding an ancient and rapidly evolving protein in chordates

The cDNA encoding beta-microseminoprotein-like (beta-MSPL) was identified from the gut cDNA library of amphioxus. It contains a 336 bp open reading frame corresponding to a deduced protein of 111 amino acids and has eight cysteines conserved and located at the same positions as those in the vertebrate beta-MSPs. At amino acid level, it shares 12-20% similarity to the vertebrate beta-MSPs, and seems lacking the signal peptide at the N-terminus. This not only confirms that beta-MSP is a rapidly evolving protein during phylogeny, but also provides further data on the degree of diversity between species of this protein. RT-PCR and Northern blotting show that amphioxus beta-MSPL is expressed in all tissues examined, suggesting that beta-MSPL plays a fundamental role. However, in situ hybridization reveals that positive hybridization signals were present in all blastomeres of the embryos from 4-cell to gastrula stages, while its expression is restricted exclusively to notochord, somites and primitive gut in neurulae and larvae, and disappears in the ectoderm including the neural tube differentiated from the ectoderm. This suggests that beta-MSPL is possibly involved in the differentiation of ectoderm during embryonic development of cephalochordate amphioxus though it is ubiquitously expressed in embryos prior to gastrula stage and in the adult animal.

A synthetic 15-mer peptide (PCK3145) derived from prostate secretory protein can reduce tumor growth, experimental skeletal metastases, and malignancy-associated hypercalcemia

In previous studies, we have shown that prostate secretory protein (PSP-94) can reduce prostate cancer growth in vivo. In the current study, we identified the amino acid sequence of PSP-94 that is required for eliciting this response. For these studies, we used rat prostate cancer Mat Ly Lu cells overexpressing parathyroid hormone-related protein (PTHrP), which is the main pathogenetic factor responsible for hypercalcemia of malignancy. Synthetic peptides corresponding to amino acids 7-21 (PCK721), 31-45 (PCK3145), and 76-94 (PCK7694) of PSP-94 were synthesized. Only PCK3145 showed a significant reduction in tumor cell proliferation. For in vivo studies, syngenic male Copenhagen rats were inoculated s.c. with Mat Ly Lu cells overexpressing PTHrP into the right flank or into the left ventricle via intracardiac injection, which results in experimental metastases to the lumbar vertebrae causing hind-limb paralysis. Animals were infused with different doses (1, 10, and 100 microg/kg/day) of peptides for 15 days, and the effect of these treatments on tumor volume, skeletal metastases, or development of hind-limb paralysis was determined. Treatment with PCK3145 resulted in a dose-dependent decrease in tumor volume and delay in the development of skeletal metastases. Bone histomorphometry showed that after intracardiac inoculation of tumor cells, the highest dose of PCK3145 (100 microg/kg/day) resulted in reducing skeletal tumor burden, which delayed the development of hind-limb paralysis. Treatment with PCK3145 led to reduction of plasma calcium and PTHrP levels and a significant decrease in PTHrP levels in the primary tumors and in vertebrae of experimental animals. These effects of PCK3145 were due to its ability to promote tumor cell apoptosis. Collectively, the results of these studies have demonstrated the ability of a small peptide derived from PSP-94 to reduce tumor volume and experimental skeletal metastases-results that will be highly beneficial in the continued development of this peptide as a novel therapeutic agent for patients with hormone refractory, late-stage prostate cancer.

Characterization of ostrich (Struthio camelus) beta-microseminoprotein (MSP): identification of homologous sequences in EST databases and analysis of their evolution during speciation

Beta-microseminoprotein, alternatively called prostatic secretory protein of 94 amino acids, is a hydrophilic, unglycosylated, small protein rich in conserved half-cystine residues. Originally found in human seminal plasma and prostatic fluids, its presence was later shown in numerous secretions and its homologs were described in many vertebrate species. These studies showed that this protein had rapidly evolved, but they failed to unambiguously identify its biological role. Here, we show that a protein isolated from ostrich pituitary gland is closely related to a similar one isolated from chicken serum and that the two are structurally related to the mammalian beta-microseminoprotein. The complete 90-amino acid sequence of the ostrich molecule was established through a combination of automated Edman degradation and matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometric procedures, including postsource decay (PSD) and ladder sequencing analyses. This study documents for the first time that beta-microseminoprotein is present in aves. It is also the first report of a C-terminal amidated form for a member of this protein family and the first in which the disulfide linkages are established. Database searches using the herein-described amino acid sequence allowed identification of related proteins in numerous species such as cow, African clawed frog, zebrafish, and Japanese flounder. These small proteins show a strikingly high rate of amino acid substitutions, especially across phyla boundaries. Noticeably, no beta-microseminoprotein-related gene could be found in the recently completed fruit fly genome, indicating that if such a gene exists in arthropods, it must have extensively diverged from the vertebrate ones.