Polarity of prostate specific membrane antigen, prostate stem cell antigen, and prostate specific antigen in prostate tissue and in a cultured epithelial cell line

Application of Porcine Kidney-Derived Extracellular Matrix as Coating, Hydrogel, and Scaffold Material for Renal Proximal Tubular Epithelial Cell

Background

Human renal proximal tubular epithelial (RPTE) cell is a very useful tool for kidney-related experiments in vitro/ex vivo. However, only a few primary RPTE cells can be obtained through kidney biopsy, the proliferation rate of primary cell is very low, and the cultured cell properties are easily altered in artificial conditions. Thus, RPTE cell usage is very tricky; we applied porcine kidney-derived extracellular matrix (renal ECM) as coating, hydrogel, and scaffold material to increase cell proliferation and maintain cellular properties providing three-dimensional (3D) niche, which can be a valuable cell delivery vehicle.

Methods

Porcine renal ECM was prepared by decellularization using 1% Triton X-100, solubilized with 0.5 M acetic acid. The final protein concentration was adjusted to 10 μg/μL (pH 7.0). The efficacies as coating, hydrogel, and scaffold materials were analyzed through cell morphology, proliferation rate, renal-associated gene expressions, chemical composition, and microstructure evaluation. The efficacies as a coating material were compared with Matrigel, collagen type 1 (col1), gelatin, fibrinogen, and thrombin. After confirmation of coating effects, the effective concentration range was decided. The efficacies as hydrogel and scaffold materials were compared with hyaluronic acid (HA) and col1, respectively.

Results

As the coating material, renal ECM showed a higher cell proliferation rate compared to other materials, except for Matrigel. Renal-associated gene expressions were significantly enhanced in the renal ECM than other materials. Coating effect on cell proliferation was dependent on the renal ECM concentration, and the effective concentration ranged from 30 to 100 μg. As the hydrogel material, renal ECM showed a distinct inner cell network morphology and significantly increased renal-associated gene expressions, compared to HA hydrogel. As the scaffold material, renal ECM showed specific amide peaks, enhanced internal porosity, cell proliferation rate, and renal-associated gene expression compared to the col1 scaffold.

Conclusions

We concluded that renal ECM can be a suitable material for RPTE cell culture and usage. More practically, the coated renal ECM stimulates RPTE cell proliferation, and the hydrogel and scaffold of renal ECM provide useful 3D culture niche and cell delivery vehicles maintaining renal cell properties.

Evaluation of a Pretargeting Strategy for Molecular Imaging of the Prostate Stem Cell Antigen with a Single Chain Antibody

In pretargeted radio-immunotherapy, the gradual administration of a non-radioactive tumor antigen-addressing antibody-construct and the subsequent application of a radioactive labeled, low molecular weight substance enable a highly effective and selective targeting of tumor tissue. We evaluated this concept in prostate stem cell antigen (PSCA)-positive cancers using the antigen-specific, biotinylated single chain antibody scFv(AM1)-P-BAP conjugated with tetrameric neutravidin. To visualize the systemic biodistribution, a radiolabeled biotin was injected to interact with scFv(AM1)-P-BAP/neutravidin conjugate. Biotin derivatives conjugated with different chelators for complexation of radioactive metal ions and a polyethylene glycol linker (n = 45) were successfully synthesized and evaluated in vitro and in a mouse xenograft model. In vivo, the scFv(AM1)-P-BAP showed highly PSCA-specific tumor retention with a PSCA⁺ tumor/PSCA^- tumor accumulation ratio of ten. PEGylation of radiolabeled biotin resulted in lower liver uptake improving the tumor to background ratio.

Rapid and Short-term Extracellular Matrix-mediated In Vitro Culturing of Tumor and Nontumor Human Primary Prostate Cells From Fresh Radical Prostatectomy Tissue

OBJECTIVE

To culture prostate cells from fresh biopsy core samples from radical prostatectomy (RP) tissue. Further, given the genetic heterogeneity of prostate cells, the ability to culture single cells from primary prostate tissue may be of importance toward enabling single-cell characterization of primary prostate tissue via molecular and cellular phenotypic biomarkers.

METHODS

A total of 260 consecutive tissue samples from RPs were collected between October 2014 and January 2016, transported at 4°C in serum-free media to an off-site central laboratory, dissociated, and cultured. A culture protocol, including a proprietary extracellular matrix formulation (ECMf), was developed that supports rapid and short-term single-cell culture of primary human prostate cells derived from fresh RP samples.

RESULTS

A total of 251 samples, derived from RP samples, yielded primary human tumor and nontumor prostate cells. Cultured cells on ECMf exhibit (1) survival after transport from the operating room to the off-site centralized laboratory, (2) robust (>80%) adhesion and survival, and (3) expression of different cell-type-specific markers. Cells derived from samples of increasing Gleason score exhibited a greater number of focal adhesions and more focal adhesion activation as measured by phospho-focal adhesion kinase (Y397) immunofluorescence when patient-derived cells were cultured on ECMf. Increased Ki67 immunofluorescence levels were observed in cells derived from cancerous RP tissue when compared to noncancerous RP tissue.

CONCLUSION

By utilizing a unique and defined extracellular matrix protein formulation, tumor and nontumor cells derived from primary human prostate tissue can be rapidly cultured and analyzed within 72 hours after harvesting from RP tissue.

PSMA redirects cell survival signaling from the MAPK to the PI3K-AKT pathways to promote the progression of prostate cancer

Increased abundance of the prostate-specific membrane antigen (PSMA) on prostate epithelium is a hallmark of advanced metastatic prostate cancer (PCa) and correlates negatively with prognosis. However, direct evidence that PSMA functionally contributes to PCa progression remains elusive. We generated mice bearing PSMA-positive or PSMA-negative PCa by crossing PSMA-deficient mice with transgenic PCa (TRAMP) models, enabling direct assessment of PCa incidence and progression in the presence or absence of PSMA. Compared with PSMA-positive tumors, PSMA-negative tumors were smaller, lower-grade, and more apoptotic with fewer blood vessels, consistent with the recognized proangiogenic function of PSMA. Relative to PSMA-positive tumors, tumors lacking PSMA had less than half the abundance of type 1 insulin-like growth factor receptor (IGF-1R), less activity in the survival pathway mediated by PI3K-AKT signaling, and more activity in the proliferative pathway mediated by MAPK-ERK1/2 signaling. Biochemically, PSMA interacted with the scaffolding protein RACK1, disrupting signaling between the β₁ integrin and IGF-1R complex to the MAPK pathway, enabling activation of the AKT pathway instead. Manipulation of PSMA abundance in PCa cell lines recapitulated this signaling pathway switch. Analysis of published databases indicated that IGF-1R abundance, cell proliferation, and expression of transcripts for antiapoptotic markers positively correlated with PSMA abundance in patients, suggesting that this switch may be relevant to human PCa. Our findings suggest that increase in PSMA in prostate tumors contributes to progression by altering normal signal transduction pathways to drive PCa progression and that enhanced signaling through the IGF-1R/β₁ integrin axis may occur in other tumors.

Biochemical characterization of prostate-specific membrane antigen from canine prostate carcinoma cells

BACKGROUND

Prostate-specific membrane antigen (PSMA) remains an important target for diagnostic and therapeutic application for human prostate cancer. Model cell lines have been recently developed to study canine prostate cancer but their PSMA expression and enzymatic activity have not been elucidated. The present study was focused on determining PSMA expression in these model canine cell lines and the use of fluorescent small-molecule enzyme inhibitors to detect canine PSMA expression by flow cytometry.

METHODS

Western blot and RT-PCR were used to determine the transcriptional and translational expression of PSMA on the canine cell lines Leo and Ace-1. An endpoint HPLC-based assay was used to monitor the enzymatic activity of canine PSMA and the potency of enzyme inhibitors. Flow cytometry was used to detect the PSMA expressed on Leo and Ace-1 cells using a fluorescently tagged PSMA enzyme inhibitor.

RESULTS

Canine PSMA expression on the Leo cell line was confirmed by Western blot and RT-PCR, the enzyme activity, and flow cytometry. Kinetic parameters Km and Vmax of PSMA enzymatic activity for the synthetic substrate (PABGγG) were determined to be 393 nM and 220 pmol min(-1)  mg protein(-1) , respectively. The inhibitor core 1 and fluorescent inhibitor 2 were found to be potent reversible inhibitors (IC50  = 13.2 and 1.6 nM, respectively) of PSMA expressed on the Leo cell line. Fluorescent labeling of Leo cells demonstrated that the fluorescent PSMA inhibitor 2 can be used for the detection of PSMA-positive canine prostate tumor cells. Expression of PSMA on Ace-1 was low and not detectable by flow cytometry.

CONCLUSIONS

The results described herein have demonstrated that PSMA is expressed on canine prostate tumor cells and exhibits similar enzymatic characteristics as human PSMA. The findings show that the small molecule enzyme inhibitors currently being studied for use in diagnosis and therapy of human prostate cancer can also be extended to include canine prostate cancer. Importantly, the findings demonstrate that the potential of the inhibitors for use in diagnosis and therapy can be evaluated in an immunocompetent animal model that naturally develops prostate cancer before use in humans.

Prostate-specific membrane antigen associates with anaphase-promoting complex and induces chromosomal instability

Prostate-specific membrane antigen (PSMA) is a transmembrane protein highly expressed in advanced and metastatic prostate cancers. The pathologic consequence of elevated PSMA expression in not known. Here, we report that PSMA is localized to a membrane compartment in the vicinity of mitotic spindle poles and associates with the anaphase-promoting complex (APC). PSMA-expressing cells prematurely degrade cyclin B and exit mitosis due to increased APC activity and incomplete inactivation of APC by the spindle assembly checkpoint. Further, expression of PSMA in a karyotypically stable cell line induces aneuploidy. Thus, these findings provide the first evidence that PSMA has a causal role in the induction of aneuploidy and might play an etiologic role in the progression of prostate cancer.

Bioadhesive hydrogel microenvironments to modulate epithelial morphogenesis

Epithelial cells polarize and differentiate into organotypic cell aggregates in response to cell-cell and cell-matrix interactions. For example, Madin-Darby Canine Kidney (MDCK) cells form spherical cell aggregates (cysts) with distinct apical and basolateral polarity when cultured three dimensionally (embedded) in type I collagen gels. To investigate the effects of individual extracellular factors on epithelial morphogenesis, we engineered fast degrading protease-responsive polyethylene glycol (PEG) hydrogels functionalized with controlled densities of various bioligands (RGD peptide, laminin-1 (LN)) to allow 3D culturing of MDCK cells, cyst expansion, and morphogenesis/polarization. Cysts formed after 15 days of culture in these hydrogels were analyzed with multiphoton fluorescence microscopy for markers of apical and basolateral membrane domains. Epithelial cysts formed in bioadhesive ligand-functionalized PEG gels exhibited a higher frequency of central lumen and interior apical pole formation as well as basolateral polarization compared to those of unmodified PEG hydrogels. These results demonstrate that incorporation of specific bioadhesive motifs into synthetic hydrogels provides 3D culture environments that support epithelial morphogenesis. These microenvironments provide a flexible and controlled system for systematic investigations into normal and pathologic morphogenic behaviours as well as synthetic environments for promoting tissue morphogenesis for regenerative medicine applications.

Putative tissue markers in prostate cancer

A variety of putative prostate cancer markers have been described in human serum, urine, seminal fluid, and histological specimens. These markers exhibit varying capacities to detect prostate cancer and to predict disease course. In order to be considered markers for diagnosis or prognosis of disease course, and to be brought forward for large-scale clinical evaluation, they should fulfill several criteria. Firstly, there should be a biological or therapeutic rationale for choosing the marker, or at least a consistent association with disease presence, disease characteristics such as stage, or disease aggressiveness. Secondly, there should be an assessment of the strength of marker association with disease outcome. Thirdly, the marker should be assessed as an independent predictor in a multivariate analysis.

Comparative characterization of the canine normal prostate in intact and castrated animals

BACKGROUND

Prostate diseases in the dog are generally regarded as representative for their human counterparts. We characterized the normal canine prostate in comparison to the normal human prostate.

METHODS

Prostates of dogs were examined histomorphologically and by immunohistochemical detection of the markers CK14, HMWCK, CK5, CK18, CK7, UPIII, PSA, and PSMA.

RESULTS

Histomorphologically, the canine prostate lacks the human zonal differentiation, has much more prominent acini, while comprising less stromal tissue. In general, the canine prostate epithelium displayed a highly differentiated character, with no cells expressing CK14, minimal amounts of cells expressing HMWCK/CK5 and the vast majority of cells expressing CK18 and PSA. After castration, the prostate epithelium regressed, and the remaining tubules were largely populated by cells showing a ductal phenotype (HMWCK+/CK5+/CK18+/CK7+).

CONCLUSIONS

The human and canine prostate are histologically differently organized. The general scheme of cellular differentiation of the prostate epithelium may however be applicable to both species.

Different glycoforms of prostate-specific membrane antigen are intracellularly transported through their association with distinct detergent-resistant membranes

Hormone-refractory prostate carcinomas as well as the neovasculature of different tumours express high levels of PSMA (prostate-specific membrane antigen). PSMA is a type II-transmembrane glycoprotein and a potential tumour marker for both diagnosis and passive immunotherapy. Here, we report on the association of PSMA with DRMs (detergent-resistant membranes) at different stages of the protein maturation pathway in human prostate carcinoma LNCaP cells. At least three PSMA glycoforms were biochemically identified based on their extractability behaviour in different non-ionic detergents. In particular, one precursor glycoform of PSMA is associated with Tween 20-insoluble DRMs, whereas the complex glycosylated protein segregates into membrane structures that are insoluble in Lubrol WX and display a different lipid composition. Association of PSMA with these membranes occurs in the Golgi compartment together with the acquisition of a native conformation. PSMA homodimers reach the plasma membrane of LNCaP cells in Lubrol WX-insoluble lipid/protein complexes. At the steady state, the majority of PSMA remains within these membrane microdomains at the cell surface. We conclude that the intracellular transport of PSMA occurs through populations of DRMs distinct for each biosynthetic form and cellular compartment.

Differing effects of microtubule depolymerizing and stabilizing chemotherapeutic agents on t-SNARE–mediated apical targeting of prostate-specific membrane antigen

Prostate-specific membrane antigen (PSMA) is a protein up-regulated in the vast majority of prostate cancers. Antibodies to PSMA have proved highly specific for prostate cancer cells, and the therapeutic potential of such antibodies is currently being assessed in clinical trials. We have previously shown that PSMA at the cell surface of polarized epithelial cells is predominantly expressed at the apical plasma membrane and that microtubule depolymerization abolishes apical PSMA targeting. In the current report, we implicate a functional role for a target membrane soluble N-ethylmaleimide-sensitive factor adaptor protein receptor, syntaxin 3, in the microtubule-dependent apical targeting of PSMA. PSMA and syntaxin 3 are similarly localized to the apical plasma membrane of the prostatic epithelium and Madin-Darby canine kidney cells. Introduction of a point mutation into syntaxin 3 abolishes its polarized distribution and causes PSMA to be targeted in a nonpolarized fashion. Additionally, treatment of polarized Madin-Darby canine kidney cells with vinblastine, a microtubule depolymerizing chemotherapeutic agent, causes both syntaxin 3 and PSMA to redistribute in a nonpolarized fashion. However, following treatment with the microtubule stabilizing chemotherapeutic agent Taxotere, both syntaxin 3 and PSMA continue to localize in a polarized manner at the apical plasma membrane. Thus, microtubule depolymerizing and stabilizing chemotherapeutic drugs might exact similar cytotoxic effects but have disparate effects on protein targeting. This phenomenon might have important clinical implication, especially related to antibody-mediated immunotherapy, and could potentially be exploited for therapeutic benefit.

Association of prostate-specific membrane antigen with caveolin-1 and its caveolae-dependent internalization in microvascular endothelial cells: Implications for targeting to tumor vasculature

Prostate-specific membrane antigen (PSMA) is a transmembrane protein with a highly restricted profile of expression. Expression is primarily limited to secretory cells of the prostatic epithelium, with elevated levels observed in prostate cancer. As an integral membrane protein correlated with prostate cancer, PSMA offers a potentially valuable target for immunotherapy. PSMA is also detected in the neovasculature of a variety of solid tumors but not in the endothelial cells of preexisting blood vessels. Although the significance of PSMA expression in these cells remains elusive, this pattern of expression implies that PSMA may perform a functional role in angiogenesis and may offer a therapeutic target for the treatment of a broad spectrum of solid tumors. In this study, we have expressed PSMA in human microvascular endothelial cells and demonstrate that PSMA binds to caveolin-1 and undergoes internalization via a caveolae-dependent mechanism. The association between PSMA and caveolae in endothelial cells may provide important insight into PSMA function and ways to best exploit this protein for therapeutic benefit.

Apical Transport and Folding of Prostate-specific Membrane Antigen Occurs Independent of Glycan Processing

Prostate-specific membrane antigen (PSMA) is an integral cell-surface membrane glycoprotein that is overexpressed in prostate carcinomas rendering it an appropriate target for antibody-based therapeutic strategies. The biosynthesis of PSMA in transfected COS-1 cells reveals a slow conversion of mannose-rich to complex glycosylated PSMA compatible with slow transport kinetics from the endoplasmic reticulum to the Golgi. Importantly, mannose-rich PSMA persists as a trypsin-sensitive protein throughout its entire life cycle, and only Golgi-located PSMA glycoforms acquire trypsin resistance. This resistance, used here as a tool to examine correct folding, does not depend on the type of glycosylation, because different PSMA glycoforms generated in the presence of inhibitors of carbohydrate processing in the Golgi are also trypsin resistant. The conformational transition of PSMA to a correctly folded molecule is likely to occur in the Golgi and does not implicate ER molecular chaperones, such as BiP. We show here that PSMA is not only heavily N-but also O-glycosylated. The question arising is whether glycans, which do not play a role in folding of PSMA, are implicated in its transport to the cell surface. Neither the cell-surface expression of PSMA nor its efficient apical sorting in polarized Madin-Darby canine kidney cells are influenced by modulators of N- and O-glycosylation. The acquisition of folding determinants in the Golgi, therefore, is an essential prerequisite for protein trafficking and sorting of PSMA and suggests that altered or aberrant glycosylation often occurring during tumorigenesis has no regulatory effect on the cell-surface expression of PSMA.

N-glycosylation and microtubule integrity are involved in apical targeting of prostate-specific membrane antigen: implications for immunotherapy

Prostate-specific membrane antigen (PSMA) is an important biomarker expressed in prostate cancer cells with levels proportional to tumor grade. The membrane association and correlation with disease stage portend a promising role for PSMA as an antigenic target for antibody-based therapies. Successful application of such modalities necessitates a detailed knowledge of the subcellular localization and trafficking of target antigen. In this study, we show that PSMA is expressed predominantly in the apical plasma membrane in epithelial cells of the prostate gland and in well-differentiated Madin-Darby canine kidney cells. We show that PSMA is targeted directly to the apical surface and that sorting into appropriate post-Golgi vesicles is dependent upon N-glycosylation of the protein. Integrity of the microtubule cytoskeleton is also essential for delivery and retention of PSMA at the apical plasma membrane domain, as destabilization of microtubules with nocodazole or commonly used chemotherapeutic Vinca alkaloids resulted in the basolateral expression of PSMA and increased the uptake of anti-PSMA antibody from the basolateral domain. These results may have important relevance to PSMA-based immunotherapy and imaging strategies, as prostate cancer cells can maintain a well-differentiated morphology even after metastasis to distal sites. In contrast to antigens on the basolateral surface, apical antigens are separated from the circulation by tight junctions that restrict transport of molecules across the epithelium. Thus, antigens expressed on the apical plasma membrane are not exposed to intravenously administered agents. The ability to reverse the polarity of PSMA from apical to basolateral could have significant implications for the use of PSMA as a therapeutic target.

Prostate epithelial cell differentiation and its relevance to the understanding of prostate cancer therapies

Prostate cancer is the most common malignancy in males in the western world. However, little is known about its origin and development. This review highlights the biology of the normal prostate gland and the differentiation of basal epithelial cells to a secretory phenotype. Alterations in this differentiation process leading to cancer and androgen-independent disease are discussed, as well as a full characterization of prostate epithelial cells. A full understanding of the origin and characteristics of prostate cancer epithelial cells will be important if we are to develop therapeutic strategies to combat the heterogeneous nature of this disease.

Biological impediments to monoclonal antibody–based cancer immunotherapy

The ability of antibodies to exploit antigenic differences between normal and malignant tissues and to exact a variety of antitumor responses offers significant advantages to conventional forms of therapy. Several monoclonal antibodies (mAb) have already proved to be relatively well tolerated and effective for the treatment of many different malignant diseases. However, mAbs must overcome substantial obstacles to reach antigens presented on target cells to be of therapeutic value. Intravenously administered antibodies must avoid host immune response and contend with low or heterogeneous expression of antigen on tumor cells. Antibodies must also overcome significant physical barriers en route to a solid tumor mass, including the vascular endothelium, stromal barriers, high interstitial pressure, and epithelial barriers. Here we review the application and evolution of mAbs as effective forms of treatment, with particular attention to the barriers and impediments to successful treatment and discuss strategies to overcome these barriers and improve the efficacy of mAb-based therapy.

Detection of Prostate Cancer and Predicting Progression

Carcinoma of the prostate is the second leading cause of male cancer-related death in the United States. Better indicators of prostate cancer presence and progression are needed to avoid unnecessary treatment, predict disease course, and develop more effective therapy. Numerous molecular markers have been described in human serum, urine, seminal fluid, and histological specimens that exhibit varying capacities to detect prostate cancer and predict disease course. However, to date, few of these markers have been adequately validated for clinical use. The purpose of this review is to examine the current status of these markers in prostate cancer and to assess the diagnostic potential for future markers from identified genes and molecules that display loss, mutation, or alteration in expression between tumor and normal prostate tissues. In this review we cite 91 molecular markers that display some level of correlation with prostate cancer presence, disease progression, cancer recurrence, prediction of response to therapy, and/or disease-free survival. We suggest criteria to consider when selecting a marker for further development as a clinical tool and discuss five examples of markers (chromogranin A, glutathione S-transferase pi 1, prostate stem cell antigen, prostate-specific membrane antigen, and telomerase reverse transcriptase) that fulfill some of these criteria. Finally, we discuss how to conduct evaluations of candidate prostate cancer markers and some of the issues involved in the validation process.

A novel cytoplasmic tail MXXXL motif mediates the internalization of prostate-specific membrane antigen

Prostate-specific membrane antigen (PSMA) is a transmembrane protein expressed at high levels in prostate cancer and in tumor-associated neovasculature. In this study, we report that PSMA is internalized via a clathrin-dependent endocytic mechanism and that internalization of PSMA is mediated by the five N-terminal amino acids (MWNLL) present in its cytoplasmic tail. Deletion of the cytoplasmic tail abolished PSMA internalization. Mutagenesis of N-terminal amino acid residues at position 2, 3, or 4 to alanine did not affect internalization of PSMA, whereas mutation of amino acid residues 1 or 5 to alanine strongly inhibited internalization. Using a chimeric protein composed of Tac antigen, the alpha-chain of interleukin 2-receptor, fused to the first five amino acids of PSMA (Tac-MWNLL), we found that this sequence is sufficient for PSMA internalization. In addition, inclusion of additional alanines into the MWNLL sequence either in the Tac chimera or the full-length PSMA strongly inhibited internalization. From these results, we suggest that a novel MXXXL motif in the cytoplasmic tail mediates PSMA internalization. We also show that dominant negative micro2 of the adaptor protein (AP)-2 complex strongly inhibits the internalization of PSMA, indicating that AP-2 is involved in the internalization of PSMA mediated by the MXXXL motif.