Glycomic characterization of prostate-specific antigen and prostatic acid phosphatase in prostate cancer and benign disease seminal plasma fluids

In-Depth Glycoproteomic Assay of Urinary Prostatic Acid Phosphatase

Prostate-specific antigen (PSA) is a well-known clinical biomarker in prostate cancer (PCa) diagnosis, but a better test is still needed, as the serum-level-based PSA quantification exhibits limited specificity and comes with poor predictive value. Prior to PSA, prostatic acid phosphatase (PAP) was used, but it was replaced by PSA because PSA improved the early detection of PCa. Upon revisiting PAP and its glycosylation specifically, it appears to be a promising new biomarker candidate. Namely, previous studies have indicated that PAP glycoforms differ between PCa and non-PCa individuals. However, an in-depth characterization of PAP glycosylation is still lacking. In this study, we established an in-depth glycoproteomic assay for urinary PAP by characterizing both the micro- and macroheterogeneity of the PAP glycoprofile. For this purpose, PAP samples were analyzed by capillary electrophoresis coupled to mass spectrometry after affinity purification from urine and proteolytic digestion. The developed urinary PAP assay was applied on a pooled DRE (digital rectal examination) urine sample from nine individuals. Three glycosylation sites were characterized, namely N94, N220, and N333, via N-glycopeptide analysis. Taking sialic acid linkage isomers into account, a total of 63, 27, and 4 N-glycan structures were identified, respectively. The presented PAP glycoproteomic assay will enable the determination of potential glycomic biomarkers for the early detection and prognosis of PCa in cohort studies.

Aberrant Mannosylated and Highly Fucosylated Glycoepitopes of Prostatic Acid Phosphatase as Potential Ligands for Dendritic-Cell Specific ICAM-Grabbing Nonintegrin (DC-SIGN) in Human Seminal Plasma-A Step towards Explaining Idiopathic Infertility

Semen prostatic acid phosphatase (PAP) has been proposed as an endogenous ligand for dendritic cell-specific ICAM-3-grabbing nonintegrin (DC-SIGN), which plays a critical immuno-modulating role in maintaining homeostasis in the female reproductive tracts. In the current study, we assumed that semen PAP bears a set of fucosylated and mannosylated glycans, which may mediate the efficient binding of PAP to DC-SIGN. To investigate this hypothesis, we developed ELISA assays using Galanthus nivalis and Lotus tetragonolobus lectins capable of binding mannose-containing glycans or LewisX and LewisY motifs, respectively. In our assay with Galanthus nivalis, we detected that the relative reactivity of PAP mannose-presenting glycans in the normozoospermic idiopathic group was significantly higher than in the asthenozoospermic, oligozoospermic and oligoasthenozoospermic groups. Simultaneously, we observed slight differences in the relative reactivities of PAP glycans with Lotus tetragonolobus lectin among groups of patients with abnormal semen parameters. Subsequently, we examined whether DC-SIGN interacts with seminal plasma PAP glycans, and we detected a significantly higher relative reactivity in the normozoospermic group compared to the oligozoospermic group. Finally, we concluded that the significantly aberrant abundance of mannosylated functional groups of PAP among patients with semen disorders can suggest that PAP may thereby be engaged in modulating the immune response and promoting a tolerogenic response to male antigens in the female reproductive system.

Site-Specific Intact N-Linked Glycopeptide Characterization of Prostate-Specific Membrane Antigen from Metastatic Prostate Cancer Cells

The composition of N-linked glycans that are conjugated to the prostate-specific membrane antigen (PSMA) and their functional significance in prostate cancer progression have not been fully characterized. PSMA was isolated from two metastatic prostate cancer cell lines, LNCaP and MDAPCa2b, which have different tissue tropism and localization. Isolated PSMA was trypsin-digested, and intact glycopeptides were subjected to LC-HCD-EThcD-MS/MS analysis on a Tribrid Orbitrap Fusion Lumos mass spectrometer. Differential qualitative and quantitative analysis of site-specific N-glycopeptides was performed using Byonic and Byologic software. Comparative quantitative analysis demonstrates that multiple glycopeptides at asparagine residues 51, 76, 121, 195, 336, 459, 476, and 638 were in significantly different abundance in the two cell lines (p < 0.05). Biochemical analysis using endoglycosidase treatment and lectin capture confirm the MS and site occupancy data. The data demonstrate the effectiveness of the strategy for comprehensive analysis of PSMA glycopeptides. This approach will form the basis of ongoing experiments to identify site-specific glycan changes in PSMA isolated from disease-stratified clinical samples to uncover targets that may be associated with disease progression and metastatic phenotypes.

Seminal Plasma Glycoproteins as Potential Ligands of Lectins Engaged in Immunity Regulation

Environmental pollution, chronic stress, and unhealthy lifestyle are factors that negatively affect reproductive potential. Currently, 15-20% of couples in industrialized countries face the problem of infertility. This growing health and social problem prompts researchers to explore the regulatory mechanisms that may be important for successful fertilization. In recent years, more attention has been paid to male infertility factors, including the impact of seminal plasma components on regulation of the female immune response to allogenic sperm, embryo and fetal antigens. Directing this response to the tolerogenic pathway is crucial to achieve a healthy pregnancy. According to the fetoembryonic defense hypothesis, the regulatory mechanism may be associated with the interaction of lectins and immunomodulatory glycoepitopes. Such interactions may involve lectins of dendritic cells and macrophages, recruited to the cervical region immediately after intercourse. Carbohydrate binding receptors include C type lectins, such as DC-SIGN and MGL, as well as galectins and siglecs among others. In this article we discuss the expression of the possible lectin ligands, highly fucosylated and high mannose structures, which may be recognized by DC-SIGN, glycans of varying degrees of sialylation, which may differ in their interaction with siglecs, as well as T and Tn antigens in O-glycans.

Glycosylation Changes in Prostate Cancer Progression

Prostate Cancer (PCa) is the most commonly diagnosed malignancy and second leading cause of cancer-related mortality in men. With the use of next generation sequencing and proteomic platforms, new biomarkers are constantly being developed to both improve diagnostic sensitivity and specificity and help stratify patients into different risk groups for optimal management. In recent years, it has become well accepted that altered glycosylation is a hallmark of cancer progression and that the glycan structures resulting from these mechanisms show tremendous promise as both diagnostic and prognostic biomarkers. In PCa, a wide range of structural alterations to glycans have been reported such as variations in sialylation and fucosylation, changes in branching, altered levels of Lewis and sialyl Lewis antigens, as well as the emergence of high mannose “cryptic” structures, which may be immunogenic and therapeutically relevant. Furthermore, aberrant expression of galectins, glycolipids, and proteoglycans have also been reported and associated with PCa cell survival and metastasis. In this review, we discuss the findings from various studies that have explored altered N- and O-linked glycosylation in PCa tissue and body fluids. We further discuss changes in O-GlcNAcylation as well as altered expression of galectins and glycoconjugates and their effects on PCa progression. Finally, we emphasize the clinical utility and potential impact of exploiting glycans as both biomarkers and therapeutic targets to improve our ability to diagnose clinically relevant tumors as well as expand treatment options for patients with advanced disease.

Direct N-Glycosylation Profiling of Urine and Prostatic Fluid Glycoproteins and Extracellular Vesicles

Expressed prostatic secretions (EPS), also called post digital rectal exam urines, are proximal fluids of the prostate that are widely used for diagnostic and prognostic assays for prostate cancer. These fluids contain an abundant number of glycoproteins and extracellular vesicles secreted by the prostate gland, and the ability to detect changes in their N-glycans composition as a reflection of disease state represents potential new biomarker candidates. Methods to characterize these N-glycan constituents directly from clinical samples in a timely manner and with minimal sample processing requirements are not currently available. In this report, an approach is described to directly profile the N-glycan constituents of EPS urine samples, prostatic fluids and urine using imaging mass spectrometry for detection. An amine reactive slide is used to immobilize glycoproteins from a few microliters of spotted samples, followed by peptide N-glycosidase digestion. Over 100 N-glycan compositions can be detected with this method, and it works with urine, urine EPS, prostatic fluids, and urine EPS-derived extracellular vesicles. A comparison of the N-glycans detected from the fluids with tissue N-glycans from prostate cancer tissues was done, indicating a subset of N-glycans present in fluids derived from the gland lumens. The developed N-glycan profiling is amenable to analysis of larger clinical cohorts and adaptable to other biofluids.

Glycosylation: Rising Potential for Prostate Cancer Evaluation

Simple Summary

Aberrant protein glycosylation is a well-known hallmark of cancer and is associated with differential expression of enzymes such as glycosyltransferases and glycosidases. The altered expression of the enzymes triggers cancer cells to produce glycoproteins with specific cancer-related aberrations in glycan structures. Increasing number of data indicate that glycosylation patterns of PSA and other prostate-originated proteins exert a potential to distinguish between benign prostate disease and cancer as well as among different stages of prostate cancer development and aggressiveness. This review summarizes the alterations in glycan sialylation, fucosylation, truncated O-glycans, and LacdiNAc groups outlining their potential applications in non-invasive diagnostic procedures of prostate diseases. Further research is desired to develop more general algorithms exploiting glycobiology data for the improvement of prostate diseases evaluation.

Abstract

Prostate cancer is the second most commonly diagnosed cancer among men. Alterations in protein glycosylation are confirmed to be a reliable hallmark of cancer. Prostate-specific antigen is the biomarker that is used most frequently for prostate cancer detection, although its lack of sensitivity and specificity results in many unnecessary biopsies. A wide range of glycosylation alterations in prostate cancer cells, including increased sialylation and fucosylation, can modify protein function and play a crucial role in many important biological processes in cancer, including cell signalling, adhesion, migration, and cellular metabolism. In this review, we summarize studies evaluating the prostate cancer associated glycosylation related alterations in sialylation, mainly α2,3-sialylation, core fucosylation, branched N-glycans, LacdiNAc group and presence of truncated O-glycans (sTn, sT antigen). Finally, we discuss the great potential to make use of glycans as diagnostic and prognostic biomarkers for prostate cancer.

TALEN-mediated generation of Nkx3.1 knockout rat model

BACKGROUND

Recent developments in gene editing, using transcriptional activator-like effector nucleases (TALENs), have greatly helped the generation of genetically engineered animal models. The NK3 homeobox 1 (NKX3.1) protein plays important roles in prostate development and protein production, and functions as a tumor suppressor. Recently, NKX3.1 was shown to be associated with breast cancer in humans.

METHODS

Our aim was to create a new rat model to elucidate the functions of NKX3.1. To that end, we generated Nkx3.1 knockout rats using TALENs and analyzed their phenotype. TALEN-mediated Nkx3.1 knockout was confirmed by T7 endonuclease I (T7E1) assay and DNA sequencing. Prostate weight and fertility were evaluated in the knockout rats, besides determining the proportion of epithelial cells and messenger RNA (mRNA) expression of genes associated with carcinogenesis. Breast tumors were examined by histopathology.

RESULTS

Results suggested Nkx3.1 knockout rats have reduced fertility, decreased prostate weights, and increased epithelial cell layers. The mRNA expression of genes related to prostate carcinogenesis, namely Ar, Akt, and Pi3k, also increased. Moreover, the Nkx3.1 knockout rats often developed malignant breast tumors.

CONCLUSIONS

We, therefore, successfully created the first Nkx3.1 knockout rat model, using TALEN-mediated gene targeting, and used it to identify defects associated with Nkx3.1 deficiency, not previously observed in mice. Loss of Nkx3.1 in rats led to lower reproductive capacity, and decreased prostate weights, apart from the risk of developing breast cancer. We, thus, proposed Nkx3.1 knockout rats as reliable models for studying the role of NKX3.1 in decreased prostate weights, fertility, and breast cancer, as well as in prostate cancer.

The Complexity and Dynamics of the Tissue Glycoproteome Associated With Prostate Cancer Progression

The complexity and dynamics of the immensely heterogeneous glycoproteome of the prostate cancer (PCa) tumor microenvironment remain incompletely mapped, a knowledge gap that impedes our molecular-level understanding of the disease. To this end, we have used sensitive glycomics and glycoproteomics to map the protein-, cell-, and tumor grade-specific N- and O-glycosylation in surgically removed PCa tissues spanning five histological grades (n = 10/grade) and tissues from patients with benign prostatic hyperplasia (n = 5). Quantitative glycomics revealed PCa grade-specific alterations of the oligomannosidic-, paucimannosidic-, and branched sialylated complex-type N-glycans, and dynamic remodeling of the sialylated core 1- and core 2-type O-glycome. Deep quantitative glycoproteomics identified ∼7400 unique N-glycopeptides from 500 N-glycoproteins and ∼500 unique O-glycopeptides from nearly 200 O-glycoproteins. With reference to a recent Tissue and Blood Atlas, our data indicate that paucimannosidic glycans of the PCa tissues arise mainly from immune cell-derived glycoproteins. Furthermore, the grade-specific PCa glycosylation arises primarily from dynamics in the cellular makeup of the PCa tumor microenvironment across grades involving increased oligomannosylation of prostate-derived glycoproteins and decreased bisecting GlcNAcylation of N-glycans carried by the extracellular matrix proteins. Furthermore, elevated expression of several oligosaccharyltransferase subunits and enhanced N-glycoprotein site occupancy were observed associated with PCa progression. Finally, correlations between the protein-specific glycosylation and PCa progression were observed including increased site-specific core 2-type O-glycosylation of collagen VI. In conclusion, integrated glycomics and glycoproteomics have enabled new insight into the complexity and dynamics of the tissue glycoproteome associated with PCa progression generating an important resource to explore the underpinning disease mechanisms.

Separation based characterization methods for the N-glycosylation analysis of prostate-specific antigen

Prostate cancer has the highest malignancy rate diagnosed in men worldwide. Albeit, the gold standard serum prostate-specific antigen (PSA) assays reduced the mortality rate of the disease, the number of false positive diagnoses steeply increased. Therefore, there is an urgent need for complementary biomarkers to enhance the specificity and selectivity of current diagnostic methods. Information about PSA glycosylation can help to fulfill this gap as alterations of its carbohydrate moieties due to cancerous transformation may represent additional markers to distinguish malignant from benign tumors. However, development of suitable methods and instrumentations to investigate the N-glycosylation profile of PSA represents a challenge. In this paper, we critically review the current bioanalytical trends and strategies in the field of PSA glycobiomarker research focusing on separation based characterization methods.

Novel endo-β-N-acetylglucosaminidases from Tannerella species hydrolyze multibranched complex-type N-glycans with different specificities

Endo-β-N-acetylglucosaminidases are enzymes that hydrolyze the N,N'-diacetylchitobiose unit of N-glycans. Many endo-β-N-acetylglucosaminidases also exhibit transglycosylation activity, which corresponds to the reverse of the hydrolysis reaction. Because of these activities, some of these enzymes have recently been used as powerful tools for glycan remodeling of glycoproteins. Although many endo-β-N-acetylglucosaminidases have been identified and characterized to date, there are few enzymes that exhibit hydrolysis activity toward multibranched (tetra-antennary or more) complex-type N-glycans on glycoproteins. Therefore, we searched for novel endo-β-N-acetylglucosaminidases that exhibit hydrolysis activity toward multibranched complex-type N-glycans in this study. From database searches, we selected three candidate enzymes from Tannerella species-Endo-Tsp1006, Endo-Tsp1263 and Endo-Tsp1457-and prepared them as recombinant proteins. We analyzed the hydrolysis activity of these enzymes toward N-glycans on glycoproteins and found that Endo-Tsp1006 and Endo-Tsp1263 exhibited hydrolysis activity toward complex-type N-glycans, including multibranched N-glycans, preferentially, whereas Endo-Tsp1457 exhibited hydrolysis activity toward high-mannose-type N-glycans exclusively. We further analyzed substrate specificities of Endo-Tsp1006 and Endo-Tsp1263 using 18 defined glycopeptides as substrates, each having a different N-glycan structure. We found that Endo-Tsp1006 preferred N-glycans with galactose or α2,6-linked sialic acid residues in their nonreducing ends as substrates, whereas Endo-Tsp1263 preferred N-glycans with N-acetylglucosamine residues in their nonreducing ends as substrates.

High-throughput glycopeptide profiling of prostate-specific antigen from seminal plasma by MALDI-MS

An altered total seminal plasma glycosylation has been associated with male infertility, and the highly abundant seminal plasma glycoprotein prostate-specific antigen (PSA) plays an important role in fertilization. However, the exact role of PSA glycosylation in male fertility is not clear. To understand the involvement of PSA glycosylation in the fertilization process, analytical methods are required to study the glycosylation of PSA from seminal plasma with a high glycoform resolution and in a protein-specific manner. In this study, we developed a novel, high-throughput PSA glycopeptide workflow, based on matrix-assisted laser desorption/ionization-mass spectrometry, allowing the discrimination of sialic acid linkage isomers via the derivatization of glycopeptides. The method was successfully applied on a cohort consisting of seminal plasma from infertile and fertile men (N = 102). Forty-four glycopeptides were quantified in all samples, showing mainly complex-type glycans with high levels of fucosylation and sialylation. In addition, N,N-diacetyllactosamine (LacdiNAc) motives were found as well as hybrid-type and high mannose-type structures. Our method showed a high intra- and interday repeatability and revealed no difference in PSA glycosylation between fertile and infertile men. Next to seminal plasma, the method is also expected to be of use for studying PSA glycopeptides derived from other biofluids and/or in other disease contexts.

An in-depth Comparison of the Pediatric and Adult Urinary N-glycomes

We performed an in-depth characterization and comparison of the pediatric and adult urinary glycomes using a nanoLC-MS/MS based glycomics method, which included normal healthy pediatric (1-10 years, n = 21) and adult (21-50 years, n = 22) individuals. A total of 116 N-glycan compositions were identified, and 46 of them could be reproducibly quantified. We performed quantitative comparisons of the 46 glycan compositions between different age and sex groups. The results showed significant quantitative changes between the pediatric and adult cohorts. The pediatric urinary N-glycome was found to contain a higher level of high-mannose (HM), asialylated/afucosylated glycans (excluding HM), neutral fucosylated and agalactosylated glycans, and a lower level of trisialylated glycans compared with the adult. We further analyzed gender-associated glycan changes in the pediatric and adult group, respectively. In the pediatric group, there was almost no difference of glycan levels between males and females. In adult, the majority of glycans were more abundant in males than females, except the high-mannose and tetrasialylated glycans. These findings highlight the importance to consider age-matching and adult sex-matching for urinary glycan studies. The identified normal pediatric and adult urinary glycomes can serve as a baseline reference for comparisons to other disease states affected by glycosylation.

Biomarkers for the Early Detection of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a leading cause of cancer-related death worldwide, and the cancer with the fastest increase in mortality in the United States, with more than 39,000 cases and 29,000 deaths in 2018. As with many cancers, survival is significantly improved by early detection. The median survival of patients with early HCC is >60 months but <15 months when detected at an advanced stage. Surveillance of at-risk patients improves outcome, but fewer than 20% of those at risk for HCC receive surveillance, and current surveillance strategies have limited sensitivity and specificity. Ideally, blood-based biomarkers with adequate sensitivity or specificity would be available for early detection of HCC; however, the most commonly used biomarker for HCC, alpha-fetoprotein, has inadequate performance characteristics. There are several candidate serum proteomic, glycomic, and genetic markers that have gone through early stages of biomarker validation and have shown promise for the early detection of HCC, but these markers require validation in well-curated cohorts. Ongoing prospective cohort studies will permit retrospective longitudinal (phase III biomarker study) validation of biomarkers. In this review, we highlight promising candidate biomarkers and biomarker panels that have completed phase II evaluation but require further validation prior to clinical use.See all articles in this CEBP Focus section, "NCI Early Detection Research Network: Making Cancer Detection Possible."

Glycosylation products in prostate diseases

Although prostate cancer is notable for its high incidence and mortality in men worldwide, its identification remains a challenge. Biomarkers have been useful tools for the specific detection of prostate cancer. Unfortunately, benign prostate diseases cause similar alterations in screening assays thus reducing the potential for early and specific diagnosis. Changes in glycan and glycoprotein expression have often been associated with the onset and progression of cancer. Abnormal glycans and glycoproteins have been reported as new biomarkers of prostate metabolism that can distinguish benign prostate disease and cancer in non-aggressive and aggressive stages. Carbohydrate-binding proteins known as lectins have been valuable tools to detect these changes, investigate potential biomarkers and improve our understanding aberrant glycosylation in cancer. Here we review progress in elucidating prostate disease and discuss the roles of glycans in the differential detection of benign and cancerous prostate disease. We also summarize the lectin-based tools for detecting glycosylation changes.

Prostate-specific antigen glycoprofiling as diagnostic and prognostic biomarker of prostate cancer

The initial part of this review details the controversy behind the use of a serological level of prostate-specific antigen (PSA) for the diagnostics of prostate cancer (PCa). Novel biomarkers are in demand for PCa diagnostics, outperforming traditional PSA tests. The review provides a detailed and comprehensive summary that PSA glycoprofiling can effectively solve this problem, thereby considerably reducing the number of unnecessary biopsies. In addition, PSA glycoprofiling can serve as a prognostic PCa biomarker to identify PCa patients with an aggressive form of PCa, avoiding unnecessary further treatments which are significantly life altering (incontinence or impotence).

Investigation on core-fucosylated prostate-specific antigen as a refined biomarker for differentiation of benign prostate hyperplasia and prostate cancer of different aggressiveness

Prostate cancer represents a major cause of cancer death in men worldwide. Novel non-invasive methods are still required for differentiation of non-aggressive from aggressive tumors. Recently, changes in prostate-specific antigen glycosylation pattern, such as core-fucosylation, have been described in prostate cancer. The objective of this study was to evaluate whether the core-fucosylation determinant of serum prostate-specific antigen may serve as refined marker for differentiation between benign prostate hyperplasia and prostate cancer or identification of aggressive prostate cancer. A previously developed liquid chromatography-mass spectrometry/mass spectrometry-based strategy was used for multiplex analysis of core-fucosylated prostate-specific antigen (fuc-PSA) and total prostate-specific antigen levels in sera from 50 benign prostate hyperplasia and 100 prostate cancer patients of different aggressiveness (Gleason scores, 5-10) covering the critical gray area (2-10 ng/mL). For identification of aggressive prostate cancer, the ratio of fuc-PSA to total prostate-specific antigen (%-fuc-PSA) yielded a 5%-8% increase in the area under the curve (0.60) compared to the currently used total prostate-specific antigen (area under the curve = 0.52) and %-free prostate-specific antigen (area under the curve = 0.55) tests. However, our data showed that aggressive prostate cancer (Gleason score > 6) and non-aggressive prostate cancer (Gleason score ≤ 6) could not significantly (p-value = 0.08) be differentiated by usage of %-fuc-PSA. In addition, both non-standardized fuc-PSA and standardized %-fuc-PSA had no diagnostic value for differentiation of benign prostate hyperplasia from prostate cancer. The %-fuc-PSA serum levels could not improve the differentiation of non-aggressive and aggressive prostate cancer compared to conventional diagnostic prostate cancer markers. Still, it is unclear whether these limitations come from the biomarker, the used patient cohort, or the imprecision of the applied method itself. Therefore, %-fuc-PSA should be further investigated, especially by more precise methods whether it could be clinically used in prostate cancer diagnosis.

Human Serum Low Molecular Mass Prostate-specific Antigen As Biomarker

Background

Prostate-specific antigen (PSA) is a glycoprotein tumor marker known to exist as numerous glycospecies. Investigations on its glycobiochemical properties aimed at their use in the preparation of adjuncts in determining PSA concentration for clinical purposes have accumulated a lot of data on its structural properties. In this study, we reconsidered unexplored ubiquitously present low molecular mass species of PSA regarding to molecular mass, origin and pathophysiological source specificity in order to evaluate them as biomarkers.

Methods

Data on low molecular mass PSA-immunoreactive species from sera of subjects with prostate cancer (PCa), benign prostatic hyperplasia (BPH), breast cancer (BCa), and urine of healthy males obtained by on-chip immunoaffinity chromatography combined with mass spectrometry were analyzed.

Results

The results obtained indicated PSA species common to BCa, PCa, and BPH at 12-13 kDa, 17-19 kDa and 21-24 kDa. The striking difference in predominant frequencies made the profile characteristic in each examined pathophysiological condition. On the other hand, paired groups of prostatic and extraprostatic PSA contained rare species with small differences among groups concerning individual species. Low molecular mass PSA also included rare species unique for each group of samples.

Conclusion

The results obtained revealed that uniformity of low molecular mass PSA-immunoreactive species in sera prevails over diversity related to cancer and non-cancer conditions, but at the same time some of them are molecules with biomarker potential for BPH detection.

Effects of Glycosylation on the Enzymatic Activity and Mechanisms of Proteases

Posttranslational modifications are an important feature of most proteases in higher organisms, such as the conversion of inactive zymogens into active proteases. To date, little information is available on the role of glycosylation and functional implications for secreted proteases. Besides a stabilizing effect and protection against proteolysis, several proteases show a significant influence of glycosylation on the catalytic activity. Glycans can alter the substrate recognition, the specificity and binding affinity, as well as the turnover rates. However, there is currently no known general pattern, since glycosylation can have both stimulating and inhibiting effects on activity. Thus, a comparative analysis of individual cases with sufficient enzyme kinetic and structural data is a first approach to describe mechanistic principles that govern the effects of glycosylation on the function of proteases. The understanding of glycan functions becomes highly significant in proteomic and glycomic studies, which demonstrated that cancer-associated proteases, such as kallikrein-related peptidase 3, exhibit strongly altered glycosylation patterns in pathological cases. Such findings can contribute to a variety of future biomedical applications.

Improvement of Prostate Cancer Diagnosis by Detecting PSA Glycosylation-Specific Changes

New markers based on PSA isoforms have recently been developed to improve prostate cancer (PCa) diagnosis. However, novel approaches are still required to differentiate aggressive from non-aggressive PCa to improve decision making for patients.

PSA glycoforms have been shown to be differentially expressed in PCa. In particular, changes in the extent of core fucosylation and sialylation of PSA N-glycans in PCa patients compared to healthy controls or BPH patients have been reported. The objective of this study was to determine these specific glycan structures in serum PSA to analyze their potential value as markers for discriminating between BPH and PCa of different aggressiveness.

In the present work, we have established two methodologies to analyze the core fucosylation and the sialic acid linkage of PSA N-glycans in serum samples from BPH (29) and PCa (44) patients with different degrees of aggressiveness. We detected a significant decrease in the core fucose and an increase in the α2,3-sialic acid percentage of PSA in high-risk PCa that differentiated BPH and low-risk PCa from high-risk PCa patients. In particular, a cut-off value of 0.86 of the PSA core fucose ratio, could distinguish high-risk PCa patients from BPH with 90% sensitivity and 95% specificity, with an AUC of 0.94. In the case of the α2,3-sialic acid percentage of PSA, the cut-off value of 30% discriminated between high-risk PCa and the group of BPH, low-, and intermediate-risk PCa with a sensitivity and specificity of 85.7% and 95.5%, respectively, with an AUC of 0.97. The latter marker exhibited high performance in differentiating between aggressive and non-aggressive PCa and has the potential for translational application in the clinic.

The role of glycans in the development and progression of prostate cancer

Prostate cancer is a unique and heterogeneous disease. Currently, a major unmet clinical need exists to develop biomarkers that enable indolent disease to be distinguished from aggressive disease. The prostate is an abundant secretor of glycoproteins of all types, and alterations in glycans are, therefore, attractive as potential biomarkers and therapeutic targets. Despite progress over the past decade in profiling the genome and proteome, the prostate cancer glycoproteome remains relatively understudied. A wide range of alterations in the glycoproteins on prostate cancer cells can occur, including increased sialylation and fucosylation, increased O-β-N-acetylglucosamine (GlcNAc) conjugation, the emergence of cryptic and high-mannose N-glycans and alterations to proteoglycans. Glycosylation can alter protein function and has a key role in many important biological processes in cancer including cell adhesion, migration, interactions with the cell matrix, immune surveillance, cell signalling and cellular metabolism; altered glycosylation in prostate cancer might modify some, or all of these processes. In the past three years, powerful tools such as glycosylation-specific antibodies and glycosylation gene signatures have been developed, which enable detailed analyses of changes in glycosylation. Thus, emerging data on these often overlooked modifications have the potential to improve risk stratification and therapeutic strategies in patients with prostate cancer.

A case for protein-level and site-level specificity in glycoproteomic studies of disease

Abnormal glycosylation of proteins is known to be either resultant or causative of a variety of diseases. This makes glycoproteins appealing targets as potential biomarkers and focal points of molecular studies on the development and progression of human ailment. To date, a majority of efforts in disease glycoproteomics have tended to center on either determining the concentration of a given glycoprotein, or on profiling the total population of glycans released from a mixture of glycoproteins. While these approaches have demonstrated some diagnostic potential, they are inherently insensitive to the fine molecular detail which distinguishes unique and possibly disease relevant glycoforms of specific proteins. As a consequence, such analyses can be of limited sensitivity, specificity, and accuracy because they do not comprehensively consider the glycosylation status of any particular glycoprotein, or of any particular glycosylation site. Therefore, significant opportunities exist to improve glycoproteomic inquiry into disease by engaging in these studies at the level of individual glycoproteins and their exact loci of glycosylation. In this concise review, the rationale for glycoprotein and glycosylation site specificity is developed in the context of human disease glycoproteomics with an emphasis on N-glycosylation. Recent examples highlighting disease-related perturbations in glycosylation will be presented, including those involving alterations in the overall glycosylation of a specific protein, alterations in the occupancy of a given glycosylation site, and alterations in the compositional heterogeneity of glycans occurring at a given glycosylation site. Each will be discussed with particular emphasis on how protein-specific and site-specific approaches can contribute to improved discrimination between glycoproteomes and glycoproteins associated with healthy and unhealthy states.

Analysis of Urinary Prostate-Specific Antigen Glycoforms in Samples of Prostate Cancer and Benign Prostate Hyperplasia

Glycans of prostate-specific antigen (PSA) in prostate cancer were found to be different from that in benign disease. It is difficult to analyze heterogeneous PSA glycoforms in each individual specimen because of low protein abundance and the limitation of detection sensitivity. We developed a method for prostate cancer diagnosis based on PSA glycoforms. Specific glycoforms were screened in each clinical sample based on liquid chromatography-tandem mass spectrometry with ion accumulation. To look for potential biomarkers, normalized abundance of each glycoform in benign prostate hyperplasia (BPH) and in prostate cancer was evaluated. The PSA glycoform, Hex5HexNAc4NeuAc1dHex1, and monosialylated, sialylated, and unfucosylated glycoforms differed significantly between the prostate cancer and BPH samples. The detection sensitivity (87.5%) and specificity (60%) for prostate cancer identification are higher than those of the serum PSA marker. As low as 100 amol PSA could be detected with the ion accumulation method which has not been reported before. The improved detection specificity can help reduce unnecessary examinations.

N-Glycoproteomics of Human Seminal Plasma Glycoproteins

Seminal plasma aids sperm by inhibiting premature capacitation, helping in the intracervical transport and formation of an oviductal sperm reservoir, all of which appear to be important in the fertilization process. Epitopes such as Lewis x and y are known to be present on seminal plasma glycoproteins, which can modulate the maternal immune response. It is suggested by multiple studies that seminal plasma glycoproteins play, largely undiscovered, important roles in the process of fertilization. We have devised a strategy to analyze glycopeptides from a complex, unknown mixture of protease-digested proteins. This analysis provides identification of the glycoproteins, glycosylation sites, glycan compositions, and proposed structures from the original sample. This strategy has been applied to human seminal plasma total glycoproteins. We have elucidated glycan compositions and proposed structures for 243 glycopeptides belonging to 73 N-glycosylation sites on 50 glycoproteins. The majority of the proposed glycan structures were complex type (83%) followed by high-mannose (10%) and then hybrid (7%). Most of the glycoproteins were either sialylated, fucosylated, or both. Many Lewis x/a and y/b epitopes bearing glycans were found, suggesting immune-modulating epitopes on multiple seminal plasma glycoproteins. The study also shows that large scale N-glycosylation mapping is achievable with current techniques and the depth of the analysis is roughly proportional to the prefractionation and complexity of the sample.

The use of matrix coating assisted by an electric field (MCAEF) to enhance mass spectrometric imaging of human prostate cancer biomarkers

In this work, we combined a newly developed matrix coating technique - matrix coating assisted by an electric field (MCAEF) and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) to enhance the imaging of peptides and proteins in tissue specimens of human prostate cancer. MCAEF increased the signal-to-noise ratios of the detected proteins by a factor of 2 to 5, and 232 signals were detected within the m/z 3500-37500 mass range on a time-of-flight mass spectrometer and with the sinapinic acid MALDI matrix. Among these species, three proteins (S100-A9, S100-A10, and S100-A12) were only observed in the cancerous cell region and 14 proteins, including a fragment of mitogen-activated protein kinase/extracellular signal-regulated kinase kinase kinase 2, a fragment of cAMP-regulated phosphoprotein 19, 3 apolipoproteins (C-I, A-I, and A-II), 2 S100 proteins (A6 and A8), β-microseminoprotein, tumor protein D52, α-1-acid glycoprotein 1, heat shock protein β-1, prostate-specific antigen, and 2 unidentified large peptides at m/z 5002.2 and 6704.2, showed significantly differential distributions at the p < 0.05 (t-test) level between the cancerous and the noncancerous regions of the tissue. Among these 17 species, the distributions of apolipoprotein C-I, S100-A6, and S100-A8 were verified by immunohistological staining. In summary, this study resulted in the imaging of the largest group of proteins in prostate cancer tissues by MALDI-MS reported thus far, and is the first to show a correlation between S100 proteins and prostate cancer in a MS imaging study. The successful imaging of the three proteins only found in the cancerous tissues, as well as those showing differential expressions demonstrated the potential of MCAEF-MALDI/MS for the in situ detection of potential cancer biomarkers. Copyright © 2015 John Wiley & Sons, Ltd.

Glycoprotein fucosylation is increased in seminal plasma of subfertile men

Fucose, the monosaccharide frequent in N- and O-glycans, is a part of Lewis-type antigens that are known to mediate direct sperm binding to the zona pellucida. Such interaction was found to be inhibited in vitro by fucose-containing oligo- and polysaccharides, as well as neoglycoproteins. The objective of this study was to screen seminal plasma proteins of infertile/subfertile men for the content and density of fucosylated glycoepitopes, and compare them to samples of fertile normozoospermic subjects. Seminal proteins were separated in polyacrylamide gel electrophoresis and blotted onto nitrocellulose membrane and probed with fucose-specific Aleuria aurantia lectin (AAL). Twelve electrophoretic bands were selected for quantitative densitometric analysis. It was found that the content, and especially the density of fucosylated glycans, were higher in glycoproteins present in seminal plasma of subfertile men. No profound differences in fucosylation density were found among the groups of normozoospermic, oligozoospermic, asthenozoospermic, and oligoasthenozoospermic subfertile men. According to the antibody probing, AAL-reactive bands can be attributed to male reproductive tract glycoproteins, including prostate-specific antigen, prostatic acid phosphatase, glycodelin and chorionic gonadotropin. Fibronectin, α₁-acid glycoprotein, α₁-antitrypsin, immunoglobulin G and antithrombin III may also contribute to this high fucosylation. It is suggested that the abundant fucosylated glycans in the sperm environment could interfere with the sperm surface and disturb the normal course of the fertilization cascade.

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.

Use of Aleuria alantia Lectin Affinity Chromatography to Enrich Candidate Biomarkers from the Urine of Patients with Bladder Cancer

Developing a urine test to detect bladder tumours with high sensitivity and specificity is a key goal in bladder cancer research. We hypothesised that bladder cancer-specific glycoproteins might fulfill this role. Lectin-ELISAs were used to study the binding of 25 lectins to 10 bladder cell lines and serum and urine from bladder cancer patients and non-cancer controls. Selected lectins were then used to enrich glycoproteins from the urine of bladder cancer patients and control subjects for analysis by shotgun proteomics. None of the lectins showed a strong preference for bladder cancer cell lines over normal urothlelial cell lines or for urinary glycans from bladder cancer patients over those from non-cancer controls. However, several lectins showed a strong preference for bladder cell line glycans over serum glycans and are potentially useful for enriching glycoproteins originating from the urothelium in urine. Aleuria alantia lectin affinity chromatography and shotgun proteomics identified mucin-1 and golgi apparatus protein 1 as proteins warranting further investigation as urinary biomarkers for low-grade bladder cancer. Glycosylation changes in bladder cancer are not reliably detected by measuring lectin binding to unfractionated proteomes, but it is possible that more specific reagents and/or a focus on individual proteins may produce clinically useful biomarkers.

Terminal Mannose Residues in Seminal Plasma Glycoproteins of Infertile Men Compared to Fertile Donors

The impact of seminal plasma components on the fertilization outcomes in humans is still under question. The increasing number of couples facing problems with conception raises the need for predictive biomarkers. Detailed understanding of the molecular mechanisms accompanying fertilization remains another challenge. Carbohydrate–protein recognition may be of key importance in this complex field. In this study, we analyzed the unique glycosylation pattern of seminal plasma proteins, the display of high-mannose and hybrid-type oligosaccharides, by means of their reactivity with mannose-specific Galanthus nivalis lectin. Normozoospermic infertile subjects presented decreased amounts of lectin-reactive glycoepitopes compared to fertile donors and infertile patients with abnormal semen parameters. Glycoproteins containing unveiled mannose were isolated in affinity chromatography, and 17 glycoproteins were identified in liquid chromatography-tandem mass spectrometry with electrospray ionization. The N-glycome of the isolated glycoproteins was examined in matrix-assisted laser desorption ionization mass spectrometry. Eleven out of 27 identified oligosaccharides expressed terminal mannose residues, responsible for lectin binding. We suggest that lowered content of high-mannose and hybrid type glycans in normozoospermic infertile patients may be associated with impaired sperm protection from preterm capacitation and should be considered in the search for new infertility markers.

Clusterin glycopeptide variant characterization reveals significant site-specific glycan changes in the plasma of clear cell renal cell carcinoma

Cancer-related alterations in protein glycosylation may serve as diagnostic or prognostic biomarkers or may be used for monitoring disease progression. Clusterin is a medium abundance, yet heavily glycosylated, glycoprotein that is upregulated in clear cell renal cell carcinoma (ccRCC) tumors. We recently reported that the N-glycan profile of clusterin is altered in the plasma of ccRCC patients. Here, we characterized the occupancy and the degree of heterogeneity of individual N-glycosylation sites of clusterin in the plasma of patients diagnosed with localized ccRCC, before and after curative nephrectomy (n = 40). To this end, we used tandem mass spectrometry of immunoaffinity-enriched plasma samples to analyze the individual glycosylation sites in clusterin. We determined the levels of targeted clusterin glycoforms containing either a biantennary digalactosylated disialylated (A2G2S2) glycan or a core fucosylated biantennary digalactosylated disialylated (FA2G2S2) glycan at N-glycosite N374. We showed that the presence of these two clusterin glycoforms differed significantly in the plasma of patients prior to and after curative nephrectomy for localized ccRCC. Removal of ccRCC led to a significant increase in the levels of both FA2G2S2 and A2G2S2 glycans in plasma clusterin. These changes were further confirmed by lectin blotting of plasma clusterin. It is envisioned that these identified glycan alterations may provide an additional level of therapeutic or biomarker sensitivity than levels currently achievable by monitoring expression differences alone.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update for 2009-2010

This review is the sixth update of the original article published in 1999 on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2010. General aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, arrays and fragmentation are covered in the first part of the review and applications to various structural typed constitutes the remainder. The main groups of compound that are discussed in this section are oligo and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals. Many of these applications are presented in tabular form. Also discussed are medical and industrial applications of the technique, studies of enzyme reactions and applications to chemical synthesis.

The analysis of sialylation, N-glycan branching, and expression of O-glycans in seminal plasma of infertile men

Carbohydrates are known to mediate some events involved in successful fertilization. Although some studies on the glycosylation of seminal plasma proteins are available, the total glycan profile was rarely analyzed as a feature influencing fertilization potential. In this work we aimed to compare some glycosylation traits in seminal plasma glycoproteins of fertile and infertile men. The following findings emerge from our studies: (1) in human seminal plasma the presence and alterations of O-linked glycans were observed; (2) the expression of SNA-reactive sialic acid significantly differs between asthenozoospermia and both normozoospermic (fertile and infertile) groups; (3) the expression of PHA-L-reactive highly branched N-glycans was significantly lower in oligozoospermic patients than in both normozoospermic groups. Indication of the appropriate lectins that would enable the possibly precise determination of the glycan profile seems to be a good supplement to mass spectrum analysis. Extension of the lectin panel is useful for the further research.

Glycosylation and liver cancer

Liver cancer is the fifth most common cancer, but the second leading cause of cancer death, in the world, with more than 700,000 fatalities annually. The major etiology of liver cancer is infection with an hepatotropic virus such as hepatitis B virus or hepatitis C virus infection. While chronic viral infection remains the main cause of liver disease and risk of hepatocellular carcinoma (HCC), rates of nonviral-associated HCC are occurring at an alarmingly increasing rate. Like many cancers, survival rates are closely associated with time of detection. If HCC is caught early, survival rates can be as high as 50%. Regrettably, most cases of HCC are caught late where survival rates can be as low as 2-7%. Thus, there has been great interest in discovering serum biomarkers that could be used to identify those with HCC. To this end, many groups have examined the N-linked glycans to identify changes that occur with HCC. As the liver secretes the vast majority of proteins into the serum, this has often been a starting point for study. In serum, alterations in core fucosylation, outer-arm fucosylation, increased sialylation, and glycan branching have been observed in patients with HCC. Similar findings have been found directly in HCC tissue suggesting that these glycan changes may play a role in tumor formation and development.

Altered glycosylation in prostate cancer

Prostate cancer is annually the most common newly diagnosed cancer in men. The prostate functions as a major secretory gland for the production of glycoproteins critical to sperm activation and reproduction. Prostate-specific antigen (PSA), produced by the prostate, is one of the most commonly assayed glycoproteins in blood, serving as a biomarker for early detection and progression of prostate cancer. The single site of N-glycosylation on PSA has been the target of multiple glycan characterization studies. In this review, the extensive number of studies that have characterized the changes in O-linked and N-linked glycosylations associated with prostate cancer development and progression will be summarized. This includes analysis of the glycosylation of PSA, and other prostate glycoproteins, in tissues, clinical biofluids, and cell line models. Other studies are summarized in the context of understanding the complexities of these glycan changes in order to address the many confounding questions associated with prostate cancer, as well as efforts to improve prostate cancer biomarker assays using targeted glycomic-based strategies.

Can glycoprofiling be helpful in detecting prostate cancer?

Glycans are chains of carbohydrates attached to proteins (glycoproteins and proteoglycans) or lipids (glycolipids). Glycosylation is a posttranslational modification and glycans have a wide range of functions in a human body including involvement in oncological diseases. Change in a glycan structure cannot only indicate presence of a pathological process, but more importantly in some cases also its stage. Thus, a glycan analysis has a potential to be an effective and reliable tool in cancer diagnostics. Lectins are proteins responsible for natural biorecognition of glycans, even carbohydrate moieties still attached to proteins or whole cells can be recognized by lectins, what makes them an ideal candidate for designing label-free biosensors for glycan analysis. In this review we would like to summarize evidence that glycoprofiling of biomarkers by lectin-based biosensors can be really helpful in detecting prostate cancer.

Lectin approaches for glycoproteomics in FDA-approved cancer biomarkers

The nine FDA-approved protein biomarkers for the diagnosis and management of cancer are approaching maturity, but their different glycosylation compositions relevant to early diagnosis still remain practically unexplored at the sub-glycoproteome scale. Lectins generally exhibit strong binding to specific sub-glycoproteome components and this property has been quite poorly addressed as the basis for the early diagnosis methods. Here, we discuss some glycoproteome issues that make tackling the glycoproteome particularly challenging in the cancer biomarkers field and include a brief view for next generation technologies.

Recent Advances in Metabolic Profiling And Imaging of Prostate Cancer

Cancer is a metabolic disease. Cancer cells, being highly proliferative, show significant alterations in metabolic pathways such as glycolysis, respiration, the tricarboxylic acid (TCA) cycle, oxidative phosphorylation, lipid metabolism, and amino acid metabolism. Metabolites like peptides, nucleotides, products of glycolysis, the TCA cycle, fatty acids, and steroids can be an important read out of disease when characterized in biological samples such as tissues and body fluids like urine, serum, etc. The cancer metabolome has been studied since the 1960s by analytical techniques such as mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy. Current research is focused on the identification and validation of biomarkers in the cancer metabolome that can stratify high-risk patients and distinguish between benign and advanced metastatic forms of the disease. In this review, we discuss the current state of prostate cancer metabolomics, the biomarkers that show promise in distinguishing indolent from aggressive forms of the disease, the strengths and limitations of the analytical techniques being employed, and future applications of metabolomics in diagnostic imaging and personalized medicine of prostate cancer.

Role of RUNX3 in suppressing metastasis and angiogenesis of human prostate cancer

RUNX3 (runt-related transcription factor-3) has been reported to suppress tumor tumorigenesis and metastasis in different human cancers. In this study, we used tissue microarray (TMA) to determine the significance of RUNX3 in prostate cancer progession. Our results showed ectopic expression of RUNX3 in prostate cancer tissues when compared with tumor adjacent normal prostate tissues, and reduced RUNX3 staining was significantly correlated with TNM stage. Moreover, we demonstrated that RUNX3 overexpression inhibited prostate cancer cell migration and invasion resulting from the elevated upregulation of tissue inhibitor of matrix metalloproteinase-2 (TIMP-2), which subsequently inhibited metalloproteinase-2 (MMP-2) expression and activity in vitro. Knock down of RUNX3 expression broke up the balance of TIMP-2/MMP-2, whereas silence of TIMP-2 resulted in the inhibition of MMP-2 expression in prostate cells. We also showed that restoration of RUNX3 decreased vascular endothelial growth factor (VEGF) secretion and suppressed endothelial cell growth and tube formation. Strikingly, RUNX3 was demonstrated to inhibit tumor metastasis and angiogenesis in vivo. Altogether, our results support the tumor suppressive role of RUNX3 in human prostate cancer, and provide insights into development of targeted therapy for this disease.

Evaluation of molecular species of prostate-specific antigen complexed with immunoglobulin M in prostate cancer and benign prostatic hyperplasia

This study was aimed at defining molecular species of prostate-specific antigen (PSA) in immune complexes with immunoglobulin M (IgM). Having in mind the oligoreactivity of IgM and its preference for carbohydrate antigens, there is the possibility that it can selectively recognize known PSA glycoisoforms. PSA-IgM complexes and free PSA fractions were separated from the sera of subjects with prostate cancer (PCa) and benign prostatic hyperplasia (BPH) by gel filtration and subjected to on-chip immunoaffinity and ion-exchange chromatography. PSA-immunoreactive species were detected using surface-enhanced laser desorption/ionization time of flight mass spectrometry. The obtained spectra were analyzed for protein and glycan composition. The general pattern of the molecular species of PCa PSA and BPH PSA found in complexes with IgM was similar. It comprised major peaks at 17 kDa and minor peaks at 28 kDa, corresponding to the entire mature glycosylated PSA. The main difference was the presence of incompletely glycosylated 26.8 kDa species, having putative paucimannosidic structures, observed in PCa PSA-IgM, but not in BPH PSA-IgM. Characteristic PCa PSA-IgM glycoforms pose the question of the possible role of glycosylation as a framework for immune surveillance and may be of interest in light of recent data indicating mannose-containing glycans as cancer biomarker.

Interlaboratory study on differential analysis of protein glycosylation by mass spectrometry: the ABRF glycoprotein research multi-institutional study 2012

One of the principal goals of glycoprotein research is to correlate glycan structure and function. Such correlation is necessary in order for one to understand the mechanisms whereby glycoprotein structure elaborates the functions of myriad proteins. The accurate comparison of glycoforms and quantification of glycosites are essential steps in this direction. Mass spectrometry has emerged as a powerful analytical technique in the field of glycoprotein characterization. Its sensitivity, high dynamic range, and mass accuracy provide both quantitative and sequence/structural information. As part of the 2012 ABRF Glycoprotein Research Group study, we explored the use of mass spectrometry and ancillary methodologies to characterize the glycoforms of two sources of human prostate specific antigen (PSA). PSA is used as a tumor marker for prostate cancer, with increasing blood levels used to distinguish between normal and cancer states. The glycans on PSA are believed to be biantennary N-linked, and it has been observed that prostate cancer tissues and cell lines contain more antennae than their benign counterparts. Thus, the ability to quantify differences in glycosylation associated with cancer has the potential to positively impact the use of PSA as a biomarker. We studied standard peptide-based proteomics/glycomics methodologies, including LC-MS/MS for peptide/glycopeptide sequencing and label-free approaches for differential quantification. We performed an interlaboratory study to determine the ability of different laboratories to correctly characterize the differences between glycoforms from two different sources using mass spectrometry methods. We used clustering analysis and ancillary statistical data treatment on the data sets submitted by participating laboratories to obtain a consensus of the glycoforms and abundances. The results demonstrate the relative strengths and weaknesses of top-down glycoproteomics, bottom-up glycoproteomics, and glycomics methods.

Increased bisecting N-acetylglucosamine and decreased branched chain glycans of N-linked glycoproteins in expressed prostatic secretions associated with prostate cancer progression

PURPOSE

Using prostatic fluids rich in glycoproteins like prostate-specific antigen and prostatic acid phosphatase (PAP), the goal of this study was to identify the structural types and relative abundance of glycans associated with prostate cancer status for subsequent use in emerging MS-based glycopeptide analysis platforms.

EXPERIMENTAL DESIGN

A series of pooled samples of expressed prostatic secretions (EPS) and exosomes reflecting different stages of prostate cancer disease were used for N-linked glycan profiling by three complementary methods, MALDI-TOF profiling, normal-phase HPLC separation, and triple quadropole MS analysis of PAP glycopeptides.

RESULTS

Glycan profiling of N-linked glycans from different EPS fluids indicated a global decrease in larger branched tri- and tetra-antennary glycans. Differential exoglycosidase treatments indicated a substantial increase in bisecting N-acetylglucosamines correlated with disease severity. A triple quadrupole MS analysis of the N-linked glycopeptides sites from PAP in aggressive prostate cancer pools was done to cross-reference with the glycan profiling data.

CONCLUSION AND CLINICAL RELEVANCE

Changes in glycosylation as detected in EPS fluids reflect the clinical status of prostate cancer. Defining these molecular signatures at the glycopeptide level in individual samples could improve current approaches of diagnosis and prognosis.

Comparing the Immunoexpression of FUT3 and FUT6 between Prostatic Adenocarcinoma and Benign Prostatic Hyperplasia

Prostatic Adenocarcinoma (PA) and Benign Prostatic Hyperplasia (BPH) have their etiology not fully understood mainly in glycidic aspects. Glycan changes are associated with cell alterations where glycosylation is carried out by glycosyltransferases, such as fucosyltransferases (FUTs). These enzymes catalyze the insertion of L-fucose residues in a variety of glycan structures often in the final stage of glycosylation. The present study aimed to investigate the expression of FUT3 and FUT6 in PA and BPH as well as to correlate immunostaining of these transferases with PA clinic-histopathologic data. The FUT3 and FUT6 expressions were evaluated by immunohistochemistry in formalin-fixed, paraffin-embedded biopsies of PA (n=40) and BPH (n=40). FUT3 and FUT6 showed a high expression in both prostatic diseases, especially FUT6. FUT6 was more immunoexpressed in PA cases than the FUT3 (p<0.0001) as well as in BPH cases but in a not significant way (p=0.0661). Besides, FUT3 was more expressed in BHP lesion than in PA cases (p<0.0001). Our study presented a new data about FUT3 and FUT6 expression in PA and BPH, revealing high FUT6 expression in both lesions and FUT3 overexpression in BHP in relation to PA, proposing that this enzyme could be a promising biomarker for benign prostate alterations.

Polyacrylamide brush layer for hydrophilic interaction liquid chromatography of intact glycoproteins

A chromatographic column of nonporous silica particles with a bonded phase of linear polyacrylamide chains is evaluated for hydrophilic interaction liquid chromatography (HILIC) of intact glycoproteins. The column is shown to retain glycoproteins significantly more strongly than non-glycoproteins. A particle diameter of 700nm gives two-fold higher resolution than does a 1.4μm particle diameter, and the column efficiency is found to be mostly limited by packing heterogeneity. LCMS is able to resolve the five glycoforms of ribonuclease B and give high quality mass spectra, but there is loss of resolution of the isomers of glycoforms due to the lower amount of TFA. Compared to two leading commercial HILIC columns operated at 60°C, the polyacrylamide column operated at 30°C provided at least two-fold higher resolution for intact ribonuclease B, and showed peaks for glycoforms of prostate specific antigen, although not resolved.

Human prostatic acid phosphatase: structure, function and regulation

Human prostatic acid phosphatase (PAcP) is a 100 kDa glycoprotein composed of two subunits. Recent advances demonstrate that cellular PAcP (cPAcP) functions as a protein tyrosine phosphatase by dephosphorylating ErbB-2/Neu/HER-2 at the phosphotyrosine residues in prostate cancer (PCa) cells, which results in reduced tumorigenicity. Further, the interaction of cPAcP and ErbB-2 regulates androgen sensitivity of PCa cells. Knockdown of cPAcP expression allows androgen-sensitive PCa cells to develop the castration-resistant phenotype, where cells proliferate under an androgen-reduced condition. Thus, cPAcP has a significant influence on PCa cell growth. Interestingly, promoter analysis suggests that PAcP expression can be regulated by NF-κB, via a novel binding sequence in an androgen-independent manner. Further understanding of PAcP function and regulation of expression will have a significant impact on understanding PCa progression and therapy.