Activation of the zymogen form of prostate-specific antigen by human glandular kallikrein 2

Role and Application of Biocatalysts in Cancer Drug Discovery

A biocatalyst is an enzyme that speeds up or slows down the rate at which a chemical reaction occurs and speeds up certain processes by 108 times. It is used as an anticancer agent because it targets drug activation inside the tumor microenvironment while limiting damage to healthy cells. Biocatalysts have been used for the synthesis of different heterocyclic compounds and is also used in the nano drug delivery systems. The use of nano-biocatalysts for tumor-targeted delivery not only aids in tumor invasion, angiogenesis, and mutagenesis, but also provides information on the expression and activity of many markers related to the microenvironment. Iosmapinol, moclobemide, cinepazide, lysine dioxygenase, epothilone, 1-homophenylalanine, and many more are only some of the anticancer medicines that have been synthesised using biocatalysts. In this review, we have highlighted the application of biocatalysts in cancer therapies as well as the use of biocatalysts in the synthesis of drugs and drug-delivery systems in the tumor microenvironment.

Precision Medicine Approach in Prostate Cancer

Prostate cancer is the most prevalent type of cancer and the second cause of death in men worldwide. Various diagnostic and treatment procedures are available for this type of malignancy, but High-grade or locally advanced prostate cancers showed the potential to develop to lethal phase that can be causing dead. Therefore, new approaches are needed to prolong patients' survival and to improve their quality of life. Precision medicine is a novel emerging field that plays an essential role in identifying new sub-classifications of diseases and in providing guidance in treatment that is based on individual multi-omics data. Multi-omics approaches include the use of genomics, transcriptomics, proteomics, metabolomics, epigenomics and phenomics data to unravel the complexity of a disease-associated biological network, to predict prognostic biomarkers, and to identify new targeted drugs for individual cancer patients. We review the impact of multi-omics data in the framework of systems biology in the era of precision medicine, emphasising the combination of molecular imaging modalities with highthroughput techniques and the new treatments that target metabolic pathways involved in prostate cancer.

Mechanism of semen liquefaction and its potential for a novel non-hormonal contraception†

Semen liquefaction is a proteolytic process where a gel-like ejaculated semen becomes watery due to the enzymatic activity of prostate-derived serine proteases in the female reproductive tract. The liquefaction process is crucial for the sperm to gain their motility and successful transport to the fertilization site in Fallopian tubes (or oviducts in animals). Hyperviscous semen or failure in liquefaction is one of the causes of male infertility. Therefore, the biochemical inhibition of serine proteases in the female reproductive tract after ejaculation is a prime target for novel contraceptive development. Herein, we will discuss protein components in the ejaculates responsible for semen liquefaction and any developments of contraceptive methods in the past that involve the liquefaction process.

Protease propeptide structures, mechanisms of activation, and functions

Proteases are a diverse group of hydrolytic enzymes, ranging from single-domain catalytic molecules to sophisticated multi-functional macromolecules. Human proteases are divided into five mechanistic classes: aspartate, cysteine, metallo, serine and threonine proteases, based on the catalytic mechanism of hydrolysis. As a protective mechanism against uncontrolled proteolysis, proteases are often produced and secreted as inactive precursors, called zymogens, containing inhibitory N-terminal propeptides. Protease propeptide structures vary considerably in length, ranging from dipeptides and propeptides of about 10 amino acids to complex multifunctional prodomains with hundreds of residues. Interestingly, sequence analysis of the different protease domains has demonstrated that propeptide sequences present higher heterogeneity compared with their catalytic domains. Therefore, we suggest that protease inhibition targeting propeptides might be more specific and have less off-target effects than classical inhibitors. The roles of propeptides, besides keeping protease latency, include correct folding of proteases, compartmentalization, liganding, and functional modulation. Changes in the propeptide sequence, thus, have a tremendous impact on the cognate enzymes. Small modifications of the propeptide sequences modulate the activity of the enzymes, which may be useful as a therapeutic strategy. This review provides an overview of known human proteases, with a focus on the role of their propeptides. We review propeptide functions, activation mechanisms, and possible therapeutic applications.

Activation and activity of glycosylated KLKs 3, 4 and 11

Human kallikrein-related peptidases 3, 4, 11, and KLK2, the activator of KLK3/PSA, belong to the prostatic group of the KLKs, whose major physiological function is semen liquefaction during the fertilization process. Notably, these KLKs are upregulated in prostate cancer and are used as clinical biomarkers or have been proposed as therapeutic targets. However, this potential awaits a detailed characterization of these proteases. In order to study glycosylated prostatic KLKs resembling the natural proteases, we used Leishmania (LEXSY) and HEK293 cells for secretory expression. Both systems allowed the subsequent purification of soluble pro-KLK zymogens with correct propeptides and of the mature forms. Periodic acid-Schiff reaction, enzymatic deglycosylation assays, and mass spectrometry confirmed the glycosylation of these KLKs. Activation of glycosylated pro-KLKs 4 and 11 turned out to be most efficient by glycosylated KLK2 and KLK4, respectively. By comparing the glycosylated prostatic KLKs with their non-glycosylated counterparts from Escherichia coli, it was observed that the N-glycans stabilize the KLK proteases and change their activation profiles and their enzymatic activity to some extent. The functional role of glycosylation in prostate-specific KLKs could pave the way to a deeper understanding of their biology and to medical applications.

A novel prostate cancer immunotherapy using prostate-specific antigen peptides and Candida skin test reagent as an adjuvant

OBJECTIVES

Our group developed the use of the Candida skin test reagent as an adjuvant of cell-mediated immunity in designing a human papillomavirus therapeutic vaccine. Here, this technology is being applied for designing a prostate cancer immunotherapy.

METHODS

Peptides based on the prostate-specific antigen amino acid sequences were selected, synthesized, and evaluated in terms of their (1) solubility, (2) maturation effects on Langerhans cells by fluorescence-activated cell sorter analysis, and (3) recognition by peripheral immune cells from prostate cancer patients using interferon-γ enzyme-linked immunospot assay.

RESULTS

The peptides were soluble in 10 mM succinate at pH of 5 with 5% glycine, and they demonstrated no maturation effects on Langerhans cells from healthy donors. On the other hand, peripheral immune cells from 4 of 10 prostate cancer patients examined had positive responses in enzyme-linked immunospot assay to one or more prostate-specific antigen peptides.

CONCLUSION

In summary, a design and a formulation of a novel prostate cancer immunotherapy are described. The immunogenicity of prostate-specific antigen peptides in some prostate cancer patients supports further development of this immunotherapy.

Biochemical characterization of human tissue kallikrein 15 and examination of its potential role in cancer

OBJECTIVE

Human tissue kallikrein 15 (KLK15) is the last cloned member of the KLK-related gene family. Despite being implicated in multiple cancers, its pathophysiological role remains unknown. We aimed to biochemically characterize KLK15 and preliminarily study its role in cancer.

DESIGN & METHODS

Recombinant KLK15 protein was produced, purified to homogeneity and quantified by mass spectrometry (parallel reaction monitoring analysis). We profiled the enzymatic activity of KLK15 using fluorogenic peptide substrates, and performed kinetic analysis to discover the cleavage sites. As KLK15 has mainly been associated with prostate cancer, we used a degradomic approach and subsequent KEGG pathway analysis to identify a number of putative protein substrates in the KLK15-treated prostate cancer cell line PC3.

RESULTS

We discovered trypsin-like activity in KLK15, finding that it cleaves preferentially after arginine (R). The enzymatic activity of KLK15 was regulated by different factors such as pH, cations and serine protease inhibitors. Notably, we revealed that KLK15 most likely interacts with the extracellular matrix (ECM) receptor group.

CONCLUSION

To our knowledge, this is the first study that experimentally verifies the trypsin-like activity of KLK15. We show here for the first time that KLK15 may be able to cleave many ECM components, similar to several members of the KLK family. Thus the protease could potentially be linked to tumorigenesis by promoting metastasis via this mechanism.

Discovery of novel transcripts of the human tissue kallikrein (KLK1) and kallikrein-related peptidase 2 (KLK2) in human cancer cells, exploiting Next-Generation Sequencing technology

Tissue kallikrein, kallikrein-related peptidases (KLKs), and plasma kallikrein form the largest group of serine proteases in the human genome, sharing many structural and functional properties. Several KLK transcripts have been found aberrantly expressed in numerous human malignancies, confirming their prognostic or/and diagnostic values. However, the process of alternative splicing can now be studied in-depth due to the development of Next-Generation Sequencing (NGS). In the present study, we used NGS to discover novel transcripts of the KLK1 and KLK2 genes, after nested touchdown PCR. Bioinformatics analysis and PCR experiments revealed a total of eleven novel KLK transcripts (two KLK1 and nine KLK2 transcripts). In addition, the expression profiles of each novel transcript were investigated with nested PCR experiments using variant-specific primers. Since KLKs are implicated in human malignancies, qualifying as potential biomarkers, the quantification of the presented novel transcripts in human samples may have clinical applications in different types of cancer.

New biomarkers for diagnosis and prognosis of localized prostate cancer

The diagnostics and management of localized prostate cancer is complicated because of cancer heterogeneity and differentiated progression in various subgroups of patients. As a prostate cancer biomarker, FDA-approved detection assay for serum prostate specific antigen (PSA) and its derivatives are not potent enough to diagnose prostate cancer, especially high-grade disease (Gleason ≥7). To date, a collection of new biomarkers was developed. Some of these markers are superior for primary screening while others are particularly helpful for cancer risk stratification, detection of high-grade cancer, and prediction of adverse events. Two of those markers such as proPSA (a part of the Prostate Health Index (PHI)) and prostate specific antigen 3 (PCA3) (a part of the PCA3 Progensa test) were recently approved by FDA for clinical use. Other markers are not PDA-approved yet but are available from Clinical Laboratory Improvement Amendment (CLIA)-certified clinical laboratories. In this review, we characterize diagnostic performance of these markers and their diagnostic and prognostic utility for prostate cancer.

Mutational Analysis of Prostate-Specific Antigen Defines the Intrinsic Proteolytic Activity of the proPSA Zymogen

BACKGROUND

Prostate-specific antigen (PSA) is an important prostate cancer biomarker. It is also a protease expressed at high concentrations by the normal and malignant prostate. PSA is secreted as a zymogen (proPSA) with an inhibitory prodomain that must be removed for full activity. ProPSA variants, assumed to be inactive, are found in the blood of prostate cancer patients, and are indicative of poor clinical outcome. Despite the abundance of clinical reports, our understanding of PSA's enzymology is limited, in part due to a lack of appropriate experimental systems. We sought to develop a series of PSA-derived mutants that would help to enhance our understanding of the gene.

METHODS

Sixteen rPSA variants were generated and characterized by a variety of biochemical methods.

RESULTS

The wildtype cDNA (WT) provided the template for generating a panel of recombinants. These included variants that abolished removal of the prodomain (R24A), disabled its enzymatic activity (S213A), and/or facilitated a cell-based conversion to the active conformation (FR). The purified variants' proteolytic activity was examined using a fluorogenic substrate, known PSA-cleavable proteins, and physiologically relevant inhibitors. Upon demonstrating our successful generation and purification of the PSA variants, we characterized proPSA activity, describing cleavage of synthetic and biologic substrates, but not serum protease inhibitors. This finding was exploited in the development of a self-activating mutant (PSA_QY) that exhibited the greatest enzymatic activity of all the variants.

CONCLUSIONS

The system described herein will prove useful for varied applications. ProPSA is partially functional with relatively high activity compared to the mature enzyme. In demonstrating the zymogen's intrinsic activity, we suggest that the proPSA in prostate cancer patient serum is not inert. This may have implications for our understanding of the disease. Prostate 76:1203-1217, 2016. © 2016 Wiley Periodicals, Inc.

A Single Glycan at the 99-Loop of Human Kallikrein-related Peptidase 2 Regulates Activation and Enzymatic Activity

Human kallikrein-related peptidase 2 (KLK2) is a key serine protease in semen liquefaction and prostate cancer together with KLK3/prostate-specific antigen. In order to decipher the function of its potential N-glycosylation site, we produced pro-KLK2 in Leishmania tarentolae cells and compared it with its non-glycosylated counterpart from Escherichia coli expression. Mass spectrometry revealed that Asn-95 carries a core glycan, consisting of two GlcNAc and three hexoses. Autocatalytic activation was retarded in glyco-pro-KLK2, whereas the activated glyco-form exhibited an increased proteolytic resistance. The specificity patterns obtained by the PICS (proteomic identification of protease cleavage sites) method are similar for both KLK2 variants, with a major preference for P1-Arg. However, glycosylation changes the enzymatic activity of KLK2 in a drastically substrate-dependent manner. Although glyco-KLK2 has a considerably lower catalytic efficiency than glycan-free KLK2 toward peptidic substrates with P2-Phe, the situation was reverted toward protein substrates, such as glyco-pro-KLK2 itself. These findings can be rationalized by the glycan-carrying 99-loop that prefers to cover the active site like a lid. By contrast, the non-glycosylated 99-loop seems to favor a wide open conformation, which mostly increases the apparent affinity for the substrates (i.e. by a reduction of K_m). Also, the cleavage pattern and kinetics in autolytic inactivation of both KLK2 variants can be explained by a shift of the target sites due to the presence of the glycan. These striking effects of glycosylation pave the way to a deeper understanding of kallikrein-related peptidase biology and pathology.

Adaptive Evolution Favoring KLK4 Downregulation in East Asians

The human kallikrein (KLK) cluster, located at chromosome 19q13.3-13.4, encodes 15 serine proteases, including neighboring genes (KLK3, KLK2, KLK4, and KLK5) with key roles in the cascades of semen liquefaction, tooth enamel maturation, and skin desquamation. KLK2 and KLK3 were previously identified as targets of adaptive evolution in primates through different mechanisms linked to reproductive biology and, in humans, genome-wide scans of positive selection captured, a yet unexplored, evidence for KLK neutrality departure in East Asians. We perform a detailed evaluation of KLK3-KLK5 variability in the 1000 Genomes samples from East Asia, Europe, and Africa, which was sustained by our own sequencing. In East Asians, we singled out a 70-kb region surrounding KLK4 that combined unusual low levels of diversity, high frequency variants with significant levels of population differentiation (FST > 0.5) and fairly homogenous haplotypes given the large local recombination rates. Among these variants, rs1654556_G, rs198968_T, and rs17800874_A stand out for their location on putative regulatory regions and predicted functional effects, namely the introduction of several microRNA binding sites and a repressor motif. Our functional assays carried out in different cellular models showed that rs198968_T and rs17800874_A operate synergistically to reduce KLK4 expression and could be further assisted by rs1654556_G. Considering the previous findings that KLK4 inactivation causes enamel malformations in humans and mice, and that this gene is coexpressed in epidermal layers along with several substrates involved in either cell adhesion or keratinocyte differentiation, we propose KLK4 as another target of selection in East Asians correlated to tooth and epidermal morphological traits.

Generation and application of polyclonal IgY antibodies specific for full-length and nicked prostate-specific antigen

BACKGROUND

The prostate-specific antigen (PSA) is considered an important serum marker for prostate cancer detection, monitoring and staging. The purpose of this study was to generate IgY class antibodies that recognize native PSA and selected epitopes.

METHODOLOGY

Hens immunized with either full-length human PSA or its peptidyl fragment-conjugates produced specific antibodies that were isolated from egg yolks. We developed a monoclonal/IgY sandwich ELISA with a PSA detection limit of 50 pg/ml and a linear range of 0.05-1.0 ng/ml.

CONCLUSION

Because the signal observed for the PSA-specific IgY antibodies by ELISA and the reactivity profile of the epitope-derived IgYs were comparable to those of mouse monoclonal IgG antibodies, avian antibodies may be a cost-effective alternative to mammalian antibodies for prostate cancer diagnostics.

Structure-function analyses of human kallikrein-related peptidase 2 establish the 99-loop as master regulator of activity

Human kallikrein-related peptidase 2 (KLK2) is a tryptic serine protease predominantly expressed in prostatic tissue and secreted into prostatic fluid, a major component of seminal fluid. Most likely it activates and complements chymotryptic KLK3 (prostate-specific antigen) in cleaving seminal clotting proteins, resulting in sperm liquefaction. KLK2 belongs to the “classical” KLKs 1–3, which share an extended 99- or kallikrein loop near their non-primed substrate binding site. Here, we report the 1.9 Å crystal structures of two KLK2-small molecule inhibitor complexes. In both structures discontinuous electron density for the 99-loop indicates that this loop is largely disordered. We provide evidence that the 99-loop is responsible for two biochemical peculiarities of KLK2, i.e. reversible inhibition by micromolar Zn²⁺ concentrations and permanent inactivation by autocatalytic cleavage. Indeed, several 99-loop mutants of KLK2 displayed an altered susceptibility to Zn²⁺, which located the Zn²⁺ binding site at the 99-loop/active site interface. In addition, we identified an autolysis site between residues 95e and 95f in the 99-loop, whose elimination prevented the mature enzyme from limited autolysis and irreversible inactivation. An exhaustive comparison of KLK2 with related structures revealed that in the KLK family the 99-, 148-, and 220-loop exist in open and closed conformations, allowing or preventing substrate access, which extends the concept of conformational selection in trypsin-related proteases. Taken together, our novel biochemical and structural data on KLK2 identify its 99-loop as a key player in activity regulation.

Activation profiles of human kallikrein-related peptidases by matrix metalloproteinases

The 15 human kallikrein-related peptidases (KLKs) are clinically important biomarkers and therapeutic targets of interest in inflammation, cancer, and neurodegenerative disease. KLKs are secreted as inactive pro-forms (pro-KLKs) that are activated extracellularly by specific proteolytic release of their amino-terminal pro-peptide, and this is a key step in their functional regulation. Physiologically relevant KLK regulatory cascades of activation have been described in skin desquamation and semen liquefaction, and work by a large number of investigators has elucidated pairwise and autolytic activation relationships among the KLKs with the potential for more extensive activation cascades. More recent work has asked whether functional intersection of KLKs with other types of regulatory proteases exists. Such studies show a capacity for members of the thrombostasis axis to act as broad activators of pro-KLKs. In the present report, we ask whether such functional intersection is possible between the KLKs and the members of the matrix metalloproteinase (MMP) family by evaluating the ability of the MMPs to activate pro-KLKs. The results identify MMP-20 as a broad activator of pro-KLKs, suggesting the potential for intersection of the KLK and MMP axes under pathological dysregulation of MMP-20 expression.

Clinical use of [-2]proPSA (p2PSA) and its derivatives (%p2PSA and Prostate Health Index) for the detection of prostate cancer: a review of the literature

Prostate-specific antigen (PSA) is recognized as an organ-specific marker with low specificity and sensitivity in discriminating prostate cancer (PCa) from other benign conditions, such as prostatic hyperplasia or chronic prostatitis. Thus, in the case of clinical suspicion, a PCa diagnosis cannot be made without a prostate biopsy. [-2]proPSA (p2PSA), a precursor of PSA, has been investigated as a new marker to accurately detect PCa. The aim of this systematic review was to discuss the available literature regarding the clinical validity and utility of p2PSA and its derivatives, p2PSA/fPSA (%p2PSA) and the Prostate Health Index (PHI). A systematic search of the PubMed and Scopus electronic databases was performed in accordance with the PRISMA statement (http://www.prisma-statement.org), considering the time period from January 1990 to January 2014 and using the following search terms: proprostate specific antigen, proenzyme PSA, proPSA, [-2]proPSA, p2PSA, Prostate Health Index, and PHI. To date, 115 studies have been published, but only 35 were considered for the qualitative analysis. These studies suggested that p2PSA is the most cancer-specific form of PSA, being preferentially expressed in PCa tissue and being significantly elevated in the serum of men with PCa. It is now evident that p2PSA, %p2PSA, and PHI measurements improve the specificity of the available tests (PSA and derivatives) in detecting PCa. Moreover, increasing PHI values seem to correlate with more aggressive disease. Some studies have compared p2PSA and its derivatives with other new biomarkers and found p2PSA to be significantly more accurate. Indeed, the implementation of these tests in clinical practice has the potential to significantly increase the physician's ability to detect PCa and avoid unnecessary biopsies, while also having an effective impact on costs. Further studies in large, multicenter, prospective trials are required to confirm these encouraging results on the clinical utility of these new biomarkers.

Prostate cancer relevant antigens and enzymes for targeted drug delivery

Chemotherapy is one of the most widely used approaches in combating advanced prostate cancer, but its therapeutic efficacy is usually insufficient due to poor specificity and associated toxicity. Lack of targeted delivery to prostate cancer cells is also the primary obstacles in achieving feasible therapeutic effect of other promising agents including peptide, protein, and nucleic acid. Consequently, there remains a critical need for strategies to increase the selectivity of anti-prostate cancer agents. This review will focus on various prostate cancer-relevant antigens and enzymes that could be exploited for prostate cancer targeted drug delivery. Among various targeting strategies, active targeting is the most advanced approach to specifically deliver drugs to their designated cancer cells. In this approach, drug carriers are modified with targeting ligands that can specifically bind to prostate cancer-specific antigens. Moreover, there are several specific enzymes in the tumor microenvironment of prostate cancer that can be exploited for stimulus-responsive drug delivery systems. These systems can specifically release the active drug in the tumor microenvironment of prostate cancer, leading to enhanced tumor penetration efficiency.

Prostate-specific antigen and other serum and urine markers in prostate cancer

Prostate-specific antigen (PSA) is one of the most widely used tumor markers, and strongly correlates with the risk of harboring from prostate cancer (PCa). This risk is visible already several years in advance but PSA has severe limitations for PCa detection with its low specificity and low negative predictive value. There is an urgent need for new biomarkers especially to detect clinically significant and aggressive PCa. From all PSA-based markers, the FDA-approved Prostate Health Index (phi) shows improved specificity over percent free and total PSA. Other serum kallikreins or sarcosine in serum or urine show more diverging data. In urine, the FDA-approved prostate cancer gene 3 (PCA3) has also proven its utility in the detection and management of early PCa. However, some aspects on its correlation with aggressiveness and the low sensitivity at very high values have to be re-examined. The detection of a fusion of the androgen regulated TMPRSS2 gene with the ERG oncogene (from the ETS family), which acts as transcription factor gene, in tissue of ~50% of all PCa patients was one milestone in PCa research. When combining the urinary assays for TMPRSS2:ERG and PCA3, an improved accuracy for PCa detection is visible. PCA3 and phi as the best available PCa biomarkers show an equal performance in direct comparisons.

Genetic variation in KLK2 and KLK3 is associated with concentrations of hK2 and PSA in serum and seminal plasma in young men

BACKGROUND

Genetic variants in KLK2 and KLK3 have been associated with increased serum concentrations of their encoded proteins, human kallikrein-related peptidase 2 (hK2) and prostate-specific antigen (PSA), and with prostate cancer in older men. Low PSA concentrations in seminal plasma (SP) have been associated with low sperm motility. To evaluate whether KLK2 and KLK3 genetic variants affect physiological prostatic secretion, we studied the association of SNPs with hK2 and PSA concentrations in SP and serum of young, healthy men.

METHODS

Leukocyte DNA was extracted from 303 male military conscripts (median age 18.1 years). Nine SNPs across KLK2-KLK3 were genotyped. We measured PSA and hK2 in SP and serum using immunofluorometric assays. The association of genotype frequencies with hK2 and PSA concentrations was tested with the Kruskal-Wallis test.

RESULTS

Four KLK2 SNPs (rs198972, rs198977, rs198978, and rs80050017) were strongly associated with hK2 concentrations in SP and serum, with individuals homozygous for the major alleles having 3- to 7-fold higher concentrations than the intermediate concentrations found in other homozygotes and heterozygotes (all P < 0.001). Three of these SNPs were significantly associated with percentage of free PSA (%fPSA) in serum (all P < 0.007). Three KLK3 SNPs showed associations with PSA in SP, and the rs1058205 SNP was associated with total PSA in serum (P = 0.001) and %fPSA (P = 0.015).

CONCLUSIONS

Associations observed in young, healthy men between the SP and serum concentrations of hK2 and PSA and several genetic variants in KLK2 and KLK3 could be useful to refine models of PSA cutoff values in prostate cancer testing.

Genome-wide association study identifies loci at ATF7IP and KLK2 associated with percentage of circulating free PSA

BACKGROUND

Percentage of free-to-total prostate-specific antigen (%fPSA) is an independent predictor of risk for prostate cancer among men with modestly elevated level of total PSA (tPSA) in blood. Physiological and pathological factors have been shown to influence the %fPSA value and diagnostic accuracy.

MATERIALS/METHODS

To evaluate genetic determinants of %fPSA, we conducted a genome-wide association study of serum %fPSA by genotyping 642,584 single nucleotide polymorphisms (SNPs) in 3192 men of European ancestry, each with a tPSA level of 2.5 to 10 ng/ml, that were recruited in the REduction by DUtasteride of Prostate Cancer Events study. Single nucleotide polymorphisms (SNPs) with P < 10(-5) were further evaluated among the controls of a population-based case-control study in Sweden (2899 prostate cancer cases and 1722 male controls), including 464 controls having tPSA levels of 2.5 to 10 ng/ml.

RESULTS

We identified two loci that were associated with %fPSA at a genome-wide significance level (P <5 x 10(-8)). The first associated SNP was rs3213764 (P = 6.45 x 10(-10)), a nonsynonymous variant (K530R) in the ATF7IP gene at 12p13. This variant was also nominally associated with tPSA (P = .015). The second locus was rs1354774 (P = 1.25 x 10(-12)), near KLK2 at 19q13, which was not associated with tPSA levels, and is separate from the rs17632542 locus at KLK3 that was previously associated with tPSA levels and prostate cancer risk. Neither rs3213764 nor rs1354774 was associated with prostate cancer risk or aggressiveness.

CONCLUSIONS

These findings demonstrate that genetic variants at ATF7IP and KLK2 contribute to the variance of %fPSA.

Quantification of human kallikrein-2 in clinical samples by selected reaction monitoring

Recently, the number of mass spectrometry-based quantification assays has been increased, partially due to the global efforts of chromosome-centric human proteome project (C-HPP). Our goal at the Chromosome 19 Consortium is to provide novel selected reaction monitoring (SRM) assays of proteins coded on chromosome 19. We have selected the two most useful signature peptides (NSQVWLGR and HNLFEPEDTGQR) of human kallikrein-2 (hK2 - NX_P20151) and developed an SRM assay. Details of the analytical parameters, including multiple transitions by peptides, are presented. The endogenous levels of hK2 were determined in clinical samples (n = 35). The limit of quantification was also estimated by spiking heavy isotope-labeled peptides into seminal plasma samples at various concentrations (LOQ ≈ 29 ng/mL).

Prostate-specific kallikrein-related peptidases and their relation to prostate cancer biology and detection. Established relevance and emerging roles

Kallikreins are a family of serine proteases with a range of tissue-specific and essential proteolytic functions. Among the best studied are the prostate tissue-specific KLK2 and KLK3 genes and their secreted protease products, human kallikrein 2, hk2, and prostate-specific antigen (PSA). Members of the so-called classic kallikreins, these highly active trypsin-like serine proteases play established roles in human reproduction. Both hK2 and PSA expression is regulated by the androgen receptor which has a fundamental role in prostate tissue development and progression of disease. This feature, combined with the ability to sensitively detect different forms of these proteins in blood and biopsies, result in a crucially important biomarker for the presence and recurrence of cancer. Emerging evidence has begun to suggest a role for these kallikreins in critical vascular events. This review discusses the established and developing biological roles of hK2 and PSA, as well as the historical and advanced use of their detection to accurately and non-invasively detect and guide treatment of prostatic disease.

Porous silicon antibody microarrays for quantitative analysis: measurement of free and total PSA in clinical plasma samples

The antibody microarrays have become widespread, but their use for quantitative analyses in clinical samples has not yet been established. We investigated an immunoassay based on nanoporous silicon antibody microarrays for quantification of total prostate-specific-antigen (PSA) in 80 clinical plasma samples, and provide quantitative data from a duplex microarray assay that simultaneously quantifies free and total PSA in plasma. To further develop the assay the porous silicon chips was placed into a standard 96-well microtiter plate for higher throughput analysis. The samples analyzed by this quantitative microarray were 80 plasma samples obtained from men undergoing clinical PSA testing (dynamic range: 0.14-44 ng/ml, LOD: 0.14 ng/ml). The second dataset, measuring free PSA (dynamic range: 0.40-74.9 ng/ml, LOD: 0.47 ng/ml) and total PSA (dynamic range: 0.87-295 ng/ml, LOD: 0.76 ng/ml), was also obtained from the clinical routine. The reference for the quantification was a commercially available assay, the ProStatus PSA Free/Total DELFIA. In an analysis of 80 plasma samples the microarray platform performs well across the range of total PSA levels. This assay might have the potential to substitute for the large-scale microtiter plate format in diagnostic applications. The duplex assay paves the way for a future quantitative multiplex assay, which analyzes several prostate cancer biomarkers simultaneously.

Trypsin-like proteolytic contamination of commercially available psa purified from human seminal fluid

BACKGROUND

Prostate-Specific Antigen (PSA) is a serine protease whose expression is maintained in all stages of prostate cancer. A role for PSA in the pathobiology for prostate cancer has not been firmly established. Experimental studies to date support a role for PSA through mechanisms such as release or processing of growth factors and degradation of the extracellular matrix. Exposure of prostate cancer cells to exogenous PSA also results in gene expression changes. These in vitro and biochemical assays rely on the use of commercially available PSA. Contamination of these commercial preparations can significantly impact the results of these in vitro studies.

METHODS

We characterized PSA and trypsin-like activity of PSA preparations obtained from three commercial sources: Calbiochem, Fitzgerald, and AbD Serotec. Silver stained gels were used to compare the purity of each preparation and mass spectrometry was performed to characterize contaminating proteases.

RESULTS

PSA activity varied between PSA preparations with AbD Serotec PSA having highest degree of activity. Significant trypsin-like activity, which was inhibited by aprotinin, was observed in PSA preparations from Calbiochem and Fitzgerald, but not AbD Serotec. These former two PSA preparations also contained the greatest degree of non-PSA contaminants by silver stain and mass spectrometry.

CONCLUSIONS

Commercially available preparations of PSA contain contaminating proteins, including trypsin-like protease activity, that could potentially complicate the interpretation of results obtained from in vitro studies assessing PSA proteolysis of potential protein substrates and effects of PSA on gene expression.

From prostate-specific antigen (PSA) to precursor PSA (proPSA) isoforms: a review of the emerging role of proPSAs in the detection and management of early prostate cancer

Despite the popularity of PSA blood testing for prostate cancer, there are a number of important limitations of this popular serum marker including the limited ability to accurately distinguish patients with and without prostate cancer and those who harbour an aggressive form of the disease. This is especially true when the total PSA is <10 ng/mL. Thus, significant efforts have been placed to find new serum markers that can help overcome these limitations. In this review article, we discuss the emerging role of the various precursor forms of PSA (proPSAs), with a special emphasis on [-2]proPSA in the detecion and management of early prostate cancer. The clinical utility of Prostate Health Index (phi) is also discussed. Despite the overall success of prostate-specific antigen (PSA) blood test, its use as a serum marker for prostate cancer has been limited due to the lack of specificity, especially in men presenting with a total PSA (tPSA) level of <10 ng/mL. PSA testing has also resulted in an increase in the number of patients being diagnosed with low-grade, potentially clinically insignificant prostate cancer. There is therefore an urgent need for new markers that can accurately detect as well as differentiate patients with aggressive vs unaggressive prostate cancer. In this review, we discuss the emerging role of precursor forms of PSA (proPSAs) and the Prostate Health Index (phi) measurement in the detection and management of early stage prostate cancer. A literature search was conducted using PubMed® to identify key studies. Studies to date suggest that [-2]proPSA, a truncated form of proPSA is the most cancer-specific form of all, being preferentially expressed in cancerous prostatic epithelium and being significantly elevated in serum of men with prostate cancer. There is evidence to suggest that %[-2]proPSA measurement ([-2]proPSA/free PSA [fPSA] × 100) improves the specificity of both tPSA and fPSA in detecting prostate cancer. phi incorporating [-2]proPSA, fPSA and tPSA measurements has also yielded promising results and appears superior to tPSA and fPSA in predicting those patients with prostate cancer. Increased phi levels also seem to preferentially detect patients harbouring more aggressive disease. Further studies in the form of large, multicentre, prospective trials with detailed health economic analyses are required to evaluate the true clinical applicability of these novel markers.

Glycosylation of prostate specific antigen and its potential diagnostic applications

Prostate specific antigen (PSA) assays are widely used for early detection of prostate cancer. However, those analyses are associated with considerable sensitivity and specificity problems. Several approaches have been developed to tackle this issue. PSA is a glycoprotein, which is primarily produced by the prostatic epithelial cells. Aberrant glycosylation modification of proteins is a fundamental characteristic of tumorigenesis. Study of PSA glycoforms offers interesting diagnostic perspectives. Modern technology allows us to analyze PSA glycoforms in a variety of clinical samples (serum or plasma, urine, seminal fluid, tissue). A number of novel techniques, such as lectin-based detection methods, mass spectrometry, 2-dimensional electrophoresis and capillary electrophoresis have been developed to analyze PSA glycosylation. This article reviews the technical and diagnostic aspects of PSA glycoforms.

PSA regulates androgen receptor expression in prostate cancer cells

BACKGROUND

Prostate-specific antigen (PSA) is a pivotal downstream target gene of the androgen receptor (AR), and a serum biomarker to monitor prostate cancer (PrCa) progression. It has been reported that PSA transactivates AR, but the mechanistic requirements of this response have not been investigated.

METHODS

We studied the localization of PSA, AR, and Src in intracellular compartments of synthetic androgen (R1881)-stimulated LNCaP and C4-2B PrCa cells, using immunofluorescence and subcellular fractionation approaches. We also investigated the effect of downregulation of PSA on AR expression by immunoblotting and real-time PCR using short hairpin RNA (shRNA) and small interfering RNA (siRNA). Src activity was analyzed by immunoblotting.

RESULTS

R1881 stimulation induced nuclear localization of both PSA and AR in LNCaP and C4-2B PrCa cells as well as increased phosphorylation of Src. Stable shRNA or transient siRNA knockdown of PSA resulted in reduced AR protein levels as well as AR mRNA levels in C4-2B cells. Similar to C4-2B cells, ablation of AR levels upon silencing of PSA was also confirmed in VCaP cells, another androgen-independent cell line. Silencing of PSA did not cause significant changes in Src activation; besides, Src regulation by integrins did not appear to affect AR transcriptional activity.

CONCLUSIONS

PSA localizes to nuclei of androgen-stimulated PrCa cells, and controls AR mRNA and protein levels. This regulatory loop is specific for PSA, does not involve known AR activators such as Src and AKT, and may contribute to AR signaling under conditions of increasing PSA levels in patients.

Molecular microheterogeneity of prostate specific antigen in seminal fluid by mass spectrometry

OBJECTIVES

Prostate specific antigen (PSA) is a widely used and clinically valuable marker for prostate disease. In order to enable the development of new PSA assays and progress the understanding of the biology of PSA we have analyzed PSA in seminal plasma.

DESIGN AND METHODS

PSA in seminal plasma from men attending a fertility clinic and healthy controls was analyzed using SDS-PAGE, Western blotting and mass spectrometry.

RESULTS

Using mass spectrometry, different forms of PSA could be identified in 1-9 bands seen on SDS-PAGE analysis of the respective sample. However, a majority of these molecular forms of PSA were not observed on Western blots. Enzymatic activity of PSA isoforms was demonstrated by sequencing data in zymogram gels. Multivariate analysis of clinical data revealed well-separated patient groups.

CONCLUSIONS

We demonstrated that PSA in seminal plasma occurs in several isoforms, yet not all were detectable using an antibody based clinical routine method. The heterogeneity of PSA expression might be of clinical significance, by an improved patient phenotyping.

Enzymatically active prostate-specific antigen promotes growth of human prostate cancers

BACKGROUND

Prostate specific antigen (PSA) is the best-known member of the kallikrein-related peptidase family, with an established role as a prostatic disease biomarker. Although it is produced at high levels by all stages of prostate cancer, it is uncertain if PSA plays a role in prostate cancer initiation and progression. We decided to investigate the impact of PSA and its enzymatic activity on tumor cell growth rates.

METHODS

A gene-specific shRNA lentiviral construct reduced endogenous PSA expression in the LNCaP human prostate cancer cell line. Resulting changes in growth rates in vitro and in vivo were determined. Using a mass spectroscopy-based approach, alterations to the LNCaP proteome due to reduced PSA were measured. Finally, to evaluate the importance of PSA's proteolytic activity, the PSA-null Du145 human prostate cancer cell line was engineered to express either enzymatically inactive pro-PSA (WT) or a furin-activated variant (FR) with high enzymatic activity. The resulting clones were evaluated for PSA-induced changes in growth rates in vivo and in vitro.

RESULTS

Lowered PSA levels dramatically reduced LNCaP growth rates. Expressing active PSA (FR), but not the inactive WT variant, conferred a growth advantage on Du145 cells. Proteomics analysis revealed global changes to the LNCaP proteome as a result of reduced PSA expression.

CONCLUSIONS

These studies demonstrate the importance of PSA to prostate cancer cell growth. We also show that the enzymatic activity of PSA confers an enhanced growth rate to human prostate cancer cells, suggesting a causal role in prostate cancer progression.

PSA affects prostate cancer cell invasion in vitro and induces an osteoblastic phenotype in bone in vivo

BACKGROUND

Patients with advanced prostate cancer frequently have a poor prognosis as a result of metastasis and present with high serum PSA levels. There is evidence suggesting that the serine protease activity of PSA could be involved in the invasion and metastasis of prostate cancer. In this study, we determined the effects of PSA and its precursor, pro-PSA, on invasion and the type of bone metastasis.

METHODS

We stably transfected prostate adenocarcinoma cells, human DU-145 and rat MatLyLu, with either the full-length prepro-PSA sequence or pre-PSA DNA, to generate subclones of cells that secrete pro-PSA or free PSA, respectively. Secretion of PSA was measured by western blot analysis and enzyme-linked immunosorbent assay (ELISA). The invasive and migratory properties of the cells were determined using a basement membrane extract and were compared with corresponding empty vector control cells. Twelve days after injection of PSA-secreting MatLyLu cells into the femora of nude mice, bone tumor burden and histomorphometry were determined using a stereological technique.

RESULTS

The transfected cells secreted 0.15-2.23 ng PSA/10(6) cells/day. Pro-PSA-secreting subclones increased invasion and migration by 24-263%. Conversely, the PSA-secreting subclones significantly reduced both invasion and migration by 59-70%. The divergent effects on invasion and migration observed in pro-PSA- and PSA-secreting subclones indicate that different forms of PSA may have different functions. Intrafemoral injections with PSA-secreting MatLyLu cells resulted in an increase in osteoblastic parameters when compared with non-PSA-secreting subclones as measured by bone histomorphometry. Concomitantly, a decrease in osteoclasts and eroded surface was observed.

CONCLUSIONS

Our in vitro data suggest that PSA, dependent on the predominant form secreted, may decrease or increase invasive properties of prostate cancer cells. The in vivo results indicate that PSA in the bone microenvironment may contribute to the osteoblastic phenotype of bone metastasis frequently observed in prostate cancer.

Immunoassay for the discrimination of free prostate-specific antigen (fPSA) forms with internal cleavages at Lys(₁₄₅) or Lys(₁₄₆) from fPSA without internal cleavages at Lys(₁₄₅) or Lys(₁₄₆)

Total levels of circulating prostate-specific antigen (tPSA) are strongly associated with prostate cancer (PCa) risk and outcome but benign prostate disease is the most frequent cause of a moderately elevated PSA level. Free PSA (fPSA) forms are independently associated with PCa risk and contribute modest diagnostic enhancements above and beyond tPSA alone. We developed an immunoassay for fPSA subfractions containing internal cleavages at Lys(145) or Lys(146) (fPSA-N). The assay was based on blocking intact single-chain fPSA (fPSA-I) with antibody 4D4 which does not detect PSA containing internal cleavages at Lys(145) or Lys(146). We also measured fPSA-N in blood from healthy volunteers and in anti-coagulated plasma from 76 men with or without evidence of PCa at biopsy. The analytical and functional detection limits of this assay were 0.016 ng/mL and 0.10 ng/mL, respectively. The median recovery of male fPSA-N from female plasma was 95.0%. All 12 female samples (average age 28 years) had fPSA-N concentrations at or below the analytical detection limit. The median fPSA-N concentration (0.050 ng/mL) in 9 healthy male volunteers (age<40 years) was below the functional detection limit, 0.420 ng/mL in 27 patients with benign prostate conditions and 0.239 ng/mL in 49 patients with PCa. Deming regression analysis of the patient samples showed that the measured fPSA-N concentrations were generally 23% lower than the previously calculated (fPSA minus fPSA-I) concentrations, likely due to differences in the antibody combinations used. In conclusion, we have developed a sensitive, specific and direct immunoassay for fPSA-N which can be used to study the clinical relevance of this PSA isoform.

Exploratory study of a KLK2 polymorphism as a prognostic marker in prostate cancer

OBJECTIVES

An association of a single nucleotide polymorphism (SNP) of the KLK2 gene (rs198977; c.748C>T; R250W) with risk for developing prostate cancer has been observed. We evaluated the role of R250W SNP for prognosis in prostate cancer.

METHODS

The c.748C>T SNP was genotyped from blood DNA of 182 patients after completing initial cancer treatments. For evaluating prognosis of genotype groups, associations were performed with Gleason score (GS) and biochemical recurrence free survival (bRFS) in patients demonstrating PSA-recurrence after initial cancer therapy.

RESULTS

Overall distribution of the CC, CT and TT genotypes for the SNP was 48%, 44% and 8%, respectively. The distribution of high (8-10), moderate (5-7) and low (2-4) GS among the genotype groups was 17%, 74% and 9% for CC group compared to 25%, 74% and 1% for the CT/TT (P=0.04). Median bRFS time for CT/TT group was 36.5 months compared to 44.5 months for the CC group (P=0.16), while genotype groups combined with morphology revealed significantly different bRFS (P=0.004).

CONCLUSIONS

This exploratory analysis in prostate cancer patients revealed the W allele of the KLK2 R250W SNP to be less likely associated with low GS morphology. Further studies will be needed to confirm this observation in larger cohorts.

Genetic association study of a single nucleotide polymorphism of kallikrein-related peptidase 2 with male infertility

Objective

To investigate a kallikrein-related peptidase 2 (KLK2) single nucleotide polymorphism (SNP) in relation to male infertility because of its role in semen processing. We investigated the genetic association of the KLK2+255G>A genotype with male infertility.

Methods

We genotyped the SNP site located in intron 1 (+255G>A, rs2664155) of KLK2 from 218 men with male infertility (cases) and 220 fertile males (controls). Pyrosequencing analysis was performed for the genotyping.

Results

The SNP of the KLK2 gene had a statistically significant association with male infertility (p<0.05). The odds ratio for the minor allele (+255A) in the pooled sample was 0.47 (95% confidence intervals, 0.26-0.85) for rs2664155.

Conclusion

The relationship of KLK2 SNP to male infertility is statistically significant, especially within the non-azoospermia group. Further study is needed to understand the mechanisms associated with male infertility.

Evolutionary history of tissue kallikreins

The gene family of human kallikrein-related peptidases (KLKs) encodes proteins with diverse and pleiotropic functions in normal physiology as well as in disease states. Currently, the most widely known KLK is KLK3 or prostate-specific antigen (PSA) that has applications in clinical diagnosis and monitoring of prostate cancer. The KLK gene family encompasses the largest contiguous cluster of serine proteases in humans which is not interrupted by non-KLK genes. This exceptional and unique characteristic of KLKs makes them ideal for evolutionary studies aiming to infer the direction and timing of gene duplication events. Previous studies on the evolution of KLKs were restricted to mammals and the emergence of KLKs was suggested about 150 million years ago (mya). In order to elucidate the evolutionary history of KLKs, we performed comprehensive phylogenetic analyses of KLK homologous proteins in multiple genomes including those that have been completed recently. Interestingly, we were able to identify novel reptilian, avian and amphibian KLK members which allowed us to trace the emergence of KLKs 330 mya. We suggest that a series of duplication and mutation events gave rise to the KLK gene family. The prominent feature of the KLK family is that it consists of tandemly and uninterruptedly arrayed genes in all species under investigation. The chromosomal co-localization in a single cluster distinguishes KLKs from trypsin and other trypsin-like proteases which are spread in different genetic loci. All the defining features of the KLKs were further found to be conserved in the novel KLK protein sequences. The study of this unique family will further assist in selecting new model organisms for functional studies of proteolytic pathways involving KLKs.

Identification of IGFBP-3 fragments generated by KLK2 and prevention of fragmentation by KLK2-inhibiting peptides

Kallikrein-related peptidase 2 (KLK2) degrades insulin-like growth factor (IGF)-binding protein-3 (IGFBP-3) in vitro. IGFBP-3 forms complexes with IGFs, preventing them from binding to their receptors and stimulating cell proliferation and survival. IGF-independent actions have also been described for IGFBP-3. The degradation of IGFBP-3 by KLK2 or other proteases in the prostate may promote the growth of prostate cancer. We studied IGFBP-3 degradation by immunoblotting and two specific immunoassays, one recognizing only native non-fragmented IGFBP-3 and the other one recognizing both intact and proteolytically cleaved IGFBP-3. Peptides were used to inhibit the enzyme activity of KLK2 and cleavage sites in IGFBP-3 were identified by mass spectrometry. KLK2 proteolyzed IGFBP-3 into several small fragments, mostly after Arg residues, in keeping with the trypsin-like activity of KLK2. The fragmentation could be inhibited by KLK2-inhibiting peptides in a dose-dependent fashion. As degradation of IGFBP-3 could lead to a more aggressive cancer phenotype, inhibition of KLK2 activity might be useful for treatment of prostate cancer and other diseases associated with increased KLK2 activity.

Functional intersection of the kallikrein-related peptidases (KLKs) and thrombostasis axis

A large body of emerging evidence indicates a functional interaction between the kallikrein-related peptidases (KLKs) and proteases of the thrombostasis axis. These interactions appear relevant for both normal health as well as pathologies associated with inflammation, tissue injury, and remodeling. Regulatory interactions between the KLKs and thrombostasis proteases could impact several serious human diseases, including neurodegeneration and cancer. The emerging network of specific interactions between these two protease families appears to be complex, and much work remains to elucidate it. Complete understanding how this functional network resolves over time, given specific initial conditions, and how it might be controllably manipulated, will probably contribute to the emergence of novel diagnostics and therapeutic agents for major diseases.

Prostate-specific antigen (PSA) is activated by KLK2 in prostate cancer ex vivo models and in prostate-targeted PSA/KLK2 double transgenic mice

BACKGROUND

Prostate-specific antigen (PSA) is a serine protease secreted as a zymogen. Previously, cell-free biochemical studies have identified various kallikreins (KLK) as candidate activating proteases. In this study, KLK2-mediated activation of PSA in cell-based in vitro, xenograft, and transgenic models was evaluated.

METHODS

Du145-derived PSA- or KLK2-expressing clones were coincubated in vitro and in vivo to evaluate KLK2-induced PSA activity. While mice possess orthologs of KLK4-15, they do not have functional orthologs of PSA or KLK2. Therefore, transgenic animals expressing PSA or both PSA and KLK2 were generated to assess orthotopic PSA activation.

RESULTS

PSA is activated by KLK2 when the cells are physically in contact, and through co-conditioned media. In vivo, the free (inactive PSA) to total (active + inactive PSA) ratio in the blood is decreased when PSA and KLK2-expressing cells are co-inoculated subcutaneously, suggesting increased active PSA. Additionally, double-transgenic mice expressing both genes in the prostate produce more active PSA compared to single transgenic animals. A longitudinal evaluation over a 2-year period demonstrated no morphologic changes (i.e., no PIN or prostate cancer) due to PSA or PSA/KLK2 double transgene expression relative to non-transgenic mice.

CONCLUSIONS

These data demonstrate, with biologically relevant models, that KLK2 is the protease responsible for activating PSA. While PSA is involved in the processing and release of a number of important growth factors, our results suggest that active PSA is not sufficient to induce the development of prostate cancer or prostate cancer precursors in aging PSA transgenic mice.

Pre-analytical in-vitro stability of [-2]proPSA in blood and serum

OBJECTIVES

[-2]proPSA may discriminate prostate cancer from benign biopsy results. We characterized the pre-analytical stability of [-2]proPSA.

DESIGN AND METHODS

22 volunteers, total PSA of 4.5-19.3microg/L, had blood drawn simultaneously. Baseline measurements were performed and samples were stored under various conditions prior to measurements. Freeze-thaw cycles were performed. [-2]proPSA was measured with the p2PSA automated research use only immunoassay on the Access analyzer.

RESULTS

Mean [-2]proPSA increases with clotting time, exceeding 10% change in recovery after 3h. In serum, [-2]proPSA values decline over time under investigated storage conditions. Serum samples kept frozen show less than 10% variation in recoveries over the course of 2 freeze-thaw cycles.

CONCLUSIONS

For proper measurement of [-2]proPSA, blood samples should be centrifuged within 3h of blood draw. Serum may be stored at RT or refrigerated (+4 degrees C) for a maximum of 48h and should be frozen if stored for a longer period. Two freeze-thaw cycles have no effect on [-2]proPSA stability.

Identification of prostate-specific antigen (PSA) isoforms in complex biological samples utilizing complementary platforms

Measurements of the prostate-specific antigen (PSA) levels in blood are widely used as diagnostic, predictive and prognostic marker of prostate disease. The selective detection of molecular forms of PSA can contribute clinically to meaningful enhancements of the conventional PSA-test. As it is plausible that an in-depth search for structural variants of PSA gene products may increase our ability to discriminate distinct patho-biological basis and stages of prostate diseases, we have developed a multi-step protocol comprising gel-based methods followed by mass spectrometric identification. Our current aim was to provide a comprehensive identification of PSA variants occurring in seminal fluid. We provide a proof-of-principle for this multiple step analytical approach to identify multiple PSA variants from complex biological samples that revealed distinct molecular characteristics. In addition, sequence-annotated protein bands in SDS-PAGE gels were compared to those detected by Western blots, and by monitoring the enzymatic activity in zymogram gels, using gelatin as a substrate. The high accuracy annotations were obtained by fast turnaround MALDI-Orbitrap analysis from excised and digested gel bands. Multiple PSA forms were identified utilizing a combination of MASCOT and SEQUEST search engines.

Antiangiogenic properties of prostate-specific antigen (PSA)

The prostate produces high levels of prostate-specific antigen (PSA, also known as kallikrein-related peptidase 3, KLK3), which is a potential target for tumor imaging and treatment. Although serum PSA levels are elevated in prostate cancer, PSA expression is lower in malignant than in normal prostatic epithelium and it is further reduced in poorly differentiated tumors. PSA has been shown to inhibit angiogenesis both in in vitro and in vivo models. In this review we focus on our recent studies concerning the mechanism of the antiangiogenic function of PSA. We have recently shown that the antiangiogenic activity of PSA is related to its enzymatic activity. Inactive PSA isoforms do not have antiangiogenic activity as studied by a human umbelical vein endothelial cell (HUVEC) tube formation model. Furthermore, inhibition of PSA, either by a monoclonal antibody or small molecule inhibitors abolishes the effect of PSA, while a peptide that stimulates the activity of PSA enhances the antiangiogenic effect. We have analyzed changes in gene expression associated with the PSA induced reduction of tube formation in the HUVEC model. Several small changes were observed and they were found to be opposite to those associated with tube formation. Taken together, these studies suggest that PSA exerts antiantiogenic activity related to its enzymatic activity. Thus it might be associated with the slow growth of prostate cancer.

A completed KLK activome profile: investigation of activation profiles of KLK9, 10, and 15

We previously reported the activation profiles of the human kallikrein-related peptidases (KLKs) as determined from a KLK pro-peptide fusion-protein system. That report described the activity profiles of 12 of the 15 mature KLKs versus the 15 different pro-KLK sequences. The missing profiles in the prior report, involving KLK9, 10, and 15, are now described. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis, mass spectrometry, and N-terminal sequence analyses show that KLK9 and 10 exhibit low hydrolytic activities towards all of the 15 pro-KLK sequences, while KLK15 exhibits significant activity towards both Arg- and Lys-containing KLK pro-sequences. The ability of KLK15 to activate pro-KLK8, 12, and 14 is confirmed using recombinant pro-KLK proteins, and shown to be significant for activation of pro-KLK8 and 14, but not 12. These additional data for KLK9, 10, and 15 now permit a completed KLK activome profile, using a KLK pro-peptide fusion-protein system, to be described. The results suggest that KLK15, once activated, can potentially feed back into additional pro-KLK activation pathways. Conversely, KLK9 and 10, once activated, are unlikely to participate in further pro-KLK activation pathways, although similar to KLK1 they may activate other bioactive peptides.

High-speed spinning-disk interferometry on the BioCD for human diagnostic applications

The BioCD is an optical biosensor that uses high-speed spinning-disk interferometry for direct detection of antigen binding in multiplexed immunoassay protein arrays. The high-frequency sampling suppresses the noise floor and enables a metrology-limited height resolution of 1 picometer for measuring surface-bound protein. In assay protocols there is a direct trade-off between multiplex degree and limit of detection. In this paper, we demonstrate quantitative assays and the scaling properties of direct detection on the BioCD in assays of clinical relevance for human diagnostics, including haptoglobin assays and prostate-specific antigen assays in human patient sera.

Screening for prostate cancer in 2008 II: the importance of molecular subforms of prostate-specific antigen and tissue kallikreins

CONTEXT

Over the past decades, prostate-specific antigen (PSA), its isoforms, and other members of the tissue kallikrein family have been of continuous interest with regard to early detection and screening for prostate cancer (PCa).

OBJECTIVE

This review strives to give an overview of the possible clinical utilities of these markers, focused on early diagnostics and PCa screening.

EVIDENCE ACQUISITION

Using the Medline database, a literature search was performed on the role of molecular subforms of PSA and other members of the tissue kallikrein family in PCa detection.

EVIDENCE SYNTHESIS

With respect to PSA isoforms, only the combination of the various truncated forms (pPSA) shows additional value over total PSA (tPSA) and free PSA (fPSA) in PCa detection within the range of 2-10 ng/ml tPSA. At a high sensitivity for PCa, the specificity of the ratio of pPSA to fPSA (%pPSA) is, in general, better than that of the ratio of fPSA to tPSA (%fPSA), with a gain of 5-11%. The (-2)pPSA, (-4)pPSA, (-5)pPSA, (-7)pPSA, and benign PSA (BPSA) isoforms generally show no additional value over either pPSA or the existing parameters of tPSA and fPSA. Of the other members of the tissue kallikrein family, most studies on human kallikrein 2 (hK2) show an additional value of the ratio of hK2 to fPSA (%hK2) over %fPSA alone in PCa prediction. Other tissue kallikreins cannot be recommended for diagnosing PCa, due to the lack of additional value over tPSA or fPSA or to insufficient research. Regarding a prognostic role, the value of PSA subforms as well as of other members of the tissue kallikrein family is limited with regard to existing parameters.

CONCLUSIONS

pPSA and hK2 are able to improve PCa diagnosis in the range of 4-10 ng/ml tPSA over the existing variables tPSA and fPSA.

The Tissue Kallikrein Family of Serine Proteases: Functional Roles in Human Disease and Potential as Clinical Biomarkers

Prostate specific antigen (PSA) or human kallikrein 3 (hK3) has long been an effective biomarker for prostate cancer. Now, other members of the tissue kallikrein (KLK) gene family are fast becoming of clinical interest due to their potential as prognostic biomarkers. particularly for hormone dependent cancers. The tissue kallikreins are serine proteases that are encoded by highly conserved multi-gene family clusters in rodents and humans. The rat and mouse loci contain 10 and 25 functional genes, respectively, while the human locus at 19q 13.4 contains 15 genes. The structural organization and size of these genes are similar across species; all genes have 5 coding exons that encode a prepro-enzyme. Although the physiological activators of these zymogens have not been described, in vitro biochemical studies show that some kallikreins can auto-activate and others can activate each other, suggesting that the kallikreins may participate in an enzymatic cascade similar to that of the coagulation cascade. These genes are expressed, to varying degrees, in a wide range of tissues suggesting a functional involvement in a diverse range of physiological and pathophysiological processes. These include roles in normal skin desquamation and psoriatic lesions, tooth development, neural plasticity, and Alzheimer's disease (AD). Of particular interest is the expression of many kallikreins in prostate, ovarian, and breast cancers where they are emerging as useful prognostic indicators of disease progression.