Identification of binding proteins for PSP94 in human prostate adenocarcinoma cell lines LNCaP and PC-3

Growth inhibition mediated by PSP94 or CRISP-3 is prostate cancer cell line specific

The prostate secretory protein of 94 amino acids (PSP94) has been shown to interact with cysteine-rich secretory protein 3 (CRISP-3) in human seminal plasma. Interestingly, PSP94 expression is reduced or lost in the majority of the prostate tumours, whereas CRISP-3 expression is upregulated in prostate cancer compared with normal prostate tissue. To obtain a better understanding of the individual roles these proteins have in prostate tumourigenesis and the functional relevance of their interaction, we ectopically expressed either PSP94 or CRISP-3 alone or PSP94 along with CRISP-3 in three prostate cell lines (PC3, WPE1-NB26 and LNCaP) and performed growth inhibition assays. Reverse transcription-polymerase chain reaction and Western blot analysis were used to screen prostate cell lines for PSP94 and CRISP-3 expression. Mammalian expression constructs for human PSP94 and CRISP-3 were also generated and the expression, localization and secretion of recombinant protein were assayed by transfection followed by Western blot analysis and immunofluorescence assay. The effect that ectopic expression of PSP94 or CRISP-3 had on cell growth was studied by clonogenic survival assay following transfection. To evaluate the effects of co-expression of the two proteins, stable clones of PC3 that expressed PSP94 were generated. They were subsequently transfected with a CRISP-3 expression construct and subjected to clonogenic survival assay. Our results showed that PSP94 and CRISP-3 could each induce growth inhibition in a cell line specific manner. Although the growth of CRISP-3-positive cell lines was inhibited by PSP94, growth inhibition mediated by CRISP-3 was not affected by the presence or absence of PSP94. This suggests that CRISP-3 may participate in PSP94-independent activities during prostate tumourigenesis.

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 cotton-top tamarin (Saguinus oedipus) has five beta-microseminoprotein genes, two of which are pseudogenes

beta-Microseminoprotein (MSP) is one of the most abundant proteins in human seminal plasma and is secreted from the prostate gland. Its evolution can be traced from primates down to nonvertebrate species such as amphioxus, despite substantial differences in the primary structure. Most mammals are known to have one single MSP gene, but we have previously shown that the cotton-top tamarin and the common marmoset-two New World monkeys-carry several MSP genes. In this study we continue our characterization of MSP genes in the cotton-top tamarin by presenting the full nucleotide sequence of the three previously identified genes, mspA, mspE, and mspJ. A promoter analysis using the luciferase reporter showed that mspE is as transcriptionally active as the single human MSP gene, whereas mspA and mspJ display no activity with this assay. Two novel MSP genes were also identified, mspB and mspH, both of which are pseudogenes. MspB has a frameshift mutation in the third exon resulting in a new C-terminus and premature stop of translation. MspH has the features of a processed pseudogene, originating from a transcript of mspE. It is integrated into the genome together with another processed pseudogene originating from a transcript of the nucleoporin gene NUP88. The MSP genes described in this study probably arose by phylogenetically rather late duplication or retrotransposition, suggesting that they are confined to a limited number of New World monkeys.

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.

Prostate secretory protein of 94 amino acids (PSP-94) and its peptide (PCK3145) as potential therapeutic modalities for prostate cancer

This review focuses on the promising roles of prostate secretory protein of 94 amino acids (PSP-94) and one of its derived peptides (PCK3145) as potential therapeutic modalities for prostate cancer and its associated complications. Evaluation of these compounds was carried out in vitro and in vivo using syngeneic models of rat prostate cancer. Overproduction of parathyroid hormone-related protein (PTHrP) results in the development of hypercalcemia of malignancy in several malignancies including prostate cancer. In order to evaluate the effect of PSP-94 and PCK3145 on prostate cancer progression, the rat Dunning R3227 MatLyLu cell line transfected with full-length cDNA encoding PTHrP (MatLyLu-PTHrP) was used. As the main pathogenetic factor of hypercalcemia of malignancy, overexpression of PTHrP was aimed at mimicking the hypercalcemic nature seen in patients suffering from late-stage cancer. In vitro studies showed that PSP-94 and PCK3145 can cause a dose-dependent inhibition in the growth of MatLyLu-PTHrP cells. For in vivo studies, male Copenhagen rats were inoculated either s.c. into the right flank or directly into the left ventricle via intracardiac (i.c.) inoculation with MatLyLu-PTHrP cells. In these models, s.c. injection of MatLyLu cells results in the development of primary tumor growth, whereas i.c. inoculation routinely results in the development of experimental skeletal metastases in the lumbar vertebrae causing hind-limb paralysis. Administration of PSP-94 and PCK3145 into tumor-bearing animals resulted in a dose-dependent inhibition of primary tumor growth, and tumoral and plasma PTHrP levels, and in the reduction of plasma calcium levels. Additionally, treatment with PSP-94 or PCK3145 caused an inhibition of skeletal metastases resulting in a significant delay in the development of hind-limb paralysis. Interestingly, equimolar concentrations of PCK3145 were shown to be more effective in delaying the development of experimental skeletal metastases as compared to PSP-94. One of the possible mechanisms of action of these modalities is through the induction of apoptosis which was observed by both in-vitro and in-vivo analyses of MatLyLu-PTHrP cells and tumors. Several intracellular mechanisms can also be involved in inhibiting PTHrP production and anti-tumor effects of PSP-94 and PCK3145. Collectively, these studies warrant the continued clinical development of these agents as therapeutic agents for patients with hormone-refractory 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.

Prostate secretory protein (PSP94) suppresses the growth of androgen-independent prostate cancer cell line (PC3) and xenografts by inducing apoptosis

BACKGROUND

PSP94 (prostate secretory protein of 94 aa; also called PIP), one of the predominant proteins secreted into the seminal fluid, was proposed as an independent diagnostic/prognostic marker for prostate cancers. It was also shown to inhibit rat prostate cancer growth. In this study, we investigated the effect of purified PSP94 on the growth of androgen-independent human prostate cancer cells (PC3) and its potential mechanism of action.

METHODS AND RESULTS

PSP94, in a dose- and time-dependent manner, inhibited the growth of PC3 cells. The protein demonstrated a stronger inhibitory effect on the colony-forming ability of PC3 cells in soft agar. A daily injection of PSP94 at 5 microg/kg/body weight resulted in a 50-60% inhibition in the growth of PC3 xenografts in athymic mice. PC3 cell growth inhibition by PSP94 resulted from cell death characteristic of morphological apoptosis, which was confirmed by dual fluorescence microscopy, electron microscopy, and DNA fragmentation assays. Mechanistic studies indicated that PSP94 enhanced the expression of proapoptotic protein Bax without affecting Bcl-2 levels.

CONCLUSIONS

This study suggests that PSP94 may represent a novel, apoptosis-based, antitumor agent applicable to the treatment of hormone-refractory human prostate cancers.