Isolation and expression of novel human glutamate carboxypeptidases with N-acetylated alpha-linked acidic dipeptidase and dipeptidyl peptidase IV activity

Theranostics Nuclear Medicine in Prostate Cancer

Theranostic Nuclear Medicine is based on the idea of combining the same molecule (or drug) with different radioisotopes for both diagnosis and treatment, a concept that emerged in the early 1940s with the use of radioactive iodine for thyroid diseases. Theranostic Nuclear Medicine has since expanded to diseases of higher incidence, such as prostate cancer, with several imaging methods used to assess the extent of the disease and the corresponding radiopharmaceuticals used for treatment. For example, by detecting osteoblastic metastases by bone scintigraphy, corresponding radiopharmaceuticals with therapeutic properties can be administered to eliminate or reduce pain associated with metastases and/or determine overall survival gain. The purpose of this review is to discuss the role of Theranostic Nuclear Medicine in prostate cancer, addressing the main diagnostic imaging studies with their corresponding treatments in the Theranostic model.

Discovery of Glutamate Carboxypeptidase III Ligands to Compete the Uptake of [177Lu]Lu-PSMA-617 in Healthy Organs

Prostate-specific membrane antigen (PSMA)-targeted radio ligand therapeutics (RLTs), such as [177Lu]Lu-PSMA-617 (Pluvicto), have been shown to accumulate in salivary glands and kidneys, potentially leading to undesired side effects. As unwanted accumulation in normal organs may derive from the cross-reactivity of PSMA ligands to glutamate carboxypeptidase III (GCPIII), it may be convenient to block this interaction with GCPIII-selective ligands. Parallel screening of a DNA-encoded chemical library (DEL) against GCPIII and PSMA allowed the identification of GCPIII binders. Structure-activity relationship (SAR) studies resulted in the identification of nanomolar GCPIII ligands with up to 1000-fold selectivity over PSMA. We studied the ability of GCPIII ligands to counteract the binding of [177Lu]Lu-PSMA-617 to human salivary glands by autoradiography and could demonstrate a partial radioprotection.

Parallel Metabolomics and Lipidomics of a PSMA/GCPII Deficient Mouse Model Reveal Alteration of NAAG Levels and Brain Lipid Composition

Glutamate carboxypeptidase II (GCPII, also known as PSMA or FOLH1) is responsible for the cleavage of N-acetyl-aspartyl-glutamate (NAAG) to N-acetyl-aspartate and glutamate in the central nervous system and facilitates the intestinal absorption of folate by processing dietary folyl-poly-γ-glutamate in the small intestine. The physiological function of GCPII in other organs like kidneys is still not known. GCPII inhibitors are neuroprotective in various conditions (e.g., ischemic brain injury) in vivo; however, their utilization as potential drug candidates has not been investigated in regard to not yet known GCPII activities. To explore the GCPII role and possible side effects of GCPII inhibitors, we performed parallel metabolomic and lipidomic analysis of the cerebrospinal fluid (CSF), urine, plasma, and brain tissue of mice with varying degrees of GCPII deficiency (fully deficient in Folh1, -/-; one allele deficient in Folh1, +/-; and wild type, +/+). Multivariate analysis of metabolites showed no significant differences between wild-type and GCPII-deficient mice (except for NAAG), although changes were observed between the sex and age. NAAG levels were statistically significantly increased in the CSF, urine, and plasma of GCPII-deficient mice. However, no difference in NAAG concentrations was found in the whole brain lysate likely because GCPII, as an extracellular enzyme, can affect only extracellular and not intracellular NAAG concentrations. Regarding the lipidome, the most pronounced genotype-linked changes were found in the brain tissue. In brains of GCPII-deficient mice, we observed statistically significant enrichment in phosphatidylcholine-based lipids and reduction of sphingolipids and phosphatidylethanolamine plasmalogens. We hypothesize that the alteration of the NAA-NAAG axis by absent GCPII activity affected myelin composition. In summary, the absence of GCPII and thus similarly its inhibition do not have detrimental effects on metabolism, with just minor changes in the brain lipidome.

The genetic landscape of autism spectrum disorder in the Middle Eastern population

Introduction: Autism spectrum disorder (ASD) is characterized by aberrations in social interaction and communication associated with repetitive behaviors and interests, with strong clinical heterogeneity. Genetic factors play an important role in ASD, but about 75% of ASD cases have an undetermined genetic risk. Methods: We extensively investigated an ASD cohort made of 102 families from the Middle Eastern population of Qatar. First, we investigated the copy number variations (CNV) contribution using genome-wide SNP arrays. Next, we employed Next Generation Sequencing (NGS) to identify de novo or inherited variants contributing to the ASD etiology and its associated comorbid conditions in families with complete trios (affected child and the parents). Results: Our analysis revealed 16 CNV regions located in genomic regions implicated in ASD. The analysis of the 88 ASD cases identified 41 genes in 39 ASD subjects with de novo (n = 24) or inherited variants (n = 22). We identified three novel de novo variants in new candidate genes for ASD (DTX4, ARMC6, and B3GNT3). Also, we have identified 15 de novo variants in genes that were previously implicated in ASD or related neurodevelopmental disorders (PHF21A, WASF1, TCF20, DEAF1, MED13, CREBBP, KDM6B, SMURF1, ADNP, CACNA1G, MYT1L, KIF13B, GRIA2, CHM, and KCNK9). Additionally, we defined eight novel recessive variants (RYR2, DNAH3, TSPYL2, UPF3B KDM5C, LYST, and WNK3), four of which were X-linked. Conclusion: Despite the ASD multifactorial etiology that hinders ASD genetic risk discovery, the number of identified novel or known putative ASD genetic variants was appreciable. Nevertheless, this study represents the first comprehensive characterization of ASD genetic risk in Qatar's Middle Eastern population.

Uncovering the essential roles of glutamate carboxypeptidase 2 orthologs in Caenorhabditis elegans

Human glutamate carboxypeptidase 2 (GCP2) from the M28B metalloprotease group is an important target for therapy in neurological disorders and an established tumor marker. However, its physiological functions remain unclear. To better understand general roles, we used the model organism Caenorhabditis elegans to genetically manipulate its three existing orthologous genes and evaluate the impact on worm physiology. The results of gene knockout studies showed that C. elegans GCP2 orthologs affect the pharyngeal physiology, reproduction, and structural integrity of the organism. Promoter-driven GFP expression revealed distinct localization for each of the three gene paralogs, with gcp-2.1 being most abundant in muscles, intestine, and pharyngeal interneurons, gcp-2.2 restricted to the phasmid neurons, and gcp-2.3 located in the excretory cell. The present study provides new insight into the unique phenotypic effects of GCP2 gene knockouts in C. elegans, and the specific tissue localizations. We believe that elucidation of particular roles in a non-mammalian organism can help to explain important questions linked to physiology of this protease group and in extension to human GCP2 involvement in pathophysiological processes.

Deletion of glutamate carboxypeptidase II (GCPII), but not GCPIII, provided long-term benefits in mice with traumatic brain injury

MAIN PROBLEM

N-acetylaspartylglutamate (NAAG) has neuroprotective effects in traumatic brain injury (TBI) by activating metabotropic glutamate receptor 3 (mGluR3) and reducing glutamate release. Glutamate carboxypeptidase II (GCPII) is the primary enzyme responsible for the hydrolysis of NAAG. It remains unclear whether glutamate carboxypeptidase III (GCPIII), a homolog of GCPII, can partially compensate for GCPII's function.

METHODS

GCPII-/- , GCPIII-/- , and GCPII/III-/- mice were generated using CRISPR/Cas9 technology. Mice brain injury model was established through moderate controlled cortical impact (CCI). The relationship between GCPII and GCPIII was explored by analyzing injury response signals in the hippocampus and cortex of mice with different genotypes at the acute (1 day) and subacute (7 day) phase after TBI.

RESULTS

In this study, we found that deletion of GCPII reduced glutamate production, excitotoxicity, and neuronal damage and improved cognitive function, but GCPIII deletion had no significant neuroprotective effect. Additionally, there was no significant difference in the neuroprotective effect between the combination of GCPII and GCPIII deletion and GCPII deletion alone.

CONCLUSION

These results suggest that GCPII inhibition may be a therapeutic option for TBI, and that GCPIII may not act as a complementary enzyme to GCPII in this context.

Transcriptomic Changes Following Induced De-Masculinisation of Australian Red Claw Crayfish Cherax quadricarinatus

The Australian red claw crayfish Cherax quadricarinatus, an emerging species within the freshwater aquaculture trade, is not only an ideal species for commercial production due to its high fecundity, fast growth, and physiological robustness but also notoriously invasive. Investigating the reproductive axis of this species has been of great interest to farmers, geneticists, and conservationists alike for many decades; however, aside from the characterisation of the key masculinising insulin-like androgenic gland hormone (IAG) produced by the male-specific androgenic gland (AG), little remains known about this system and the downstream signalling cascade involved. This investigation used RNA interference to silence IAG in adult intersex C. quadricarinatus (Cq-IAG), known to be functionally male but genotypically female, successfully inducing sexual redifferentiation in all individuals. To investigate the downstream effects of Cq-IAG knockdown, a comprehensive transcriptomic library was constructed, comprised of three tissues within the male reproductive axis. Several factors known to be involved in the IAG signal transduction pathway, including a receptor, binding factor, and additional insulin-like peptide, were found to not be differentially expressed in response to Cq-IAG silencing, suggesting that the phenotypic changes observed may have occurred through post-transcriptional modifications. Many downstream factors displayed differential expression on a transcriptomic level, most notably related to stress, cell repair, apoptosis, and cell proliferation. These results suggest that IAG is required for sperm maturation, with necrosis of arrested tissue occurring in its absence. These results and the construction of a transcriptomic library for this species will inform future research involving reproductive pathways as well as biotechnological developments in this commercially and ecologically significant species.

The "Ins and Outs" of Prostate Specific Membrane Antigen (PSMA) as Specific Target in Prostate Cancer Therapy

Prostate-specific membrane antigen (PSMA) is expressed in epithelial cells of the prostate gland and is strongly upregulated in prostatic adenocarcinoma, with elevated expression correlating with metastasis, progression, and androgen independence. Because of its specificity, PSMA is a major target of prostate cancer therapy; however, detectable levels of PSMA are also found in other tissues, especially in salivary glands and kidney, generating bystander damage of these tissues. Antibody target therapy has been used with relative success in reducing tumor growth and prostate specific antigen (PSA) levels. However, since antibodies are highly stable in plasma, they have prolonged time in circulation and accumulate in organs with an affinity for antibodies such as bone marrow. For that reason, a second generation of PSMA targeted therapeutic agents has been developed. Small molecules and minibodies have had promising clinical trial results, but concerns about their specificity had arisen with side effects due to accumulation in salivary glands and kidneys. Herein we study the specificity of small molecules and minibodies that are currently being clinically tested. We observed a high affinity of these molecules for PSMA in prostate, kidney and salivary gland, suggesting that their effect is not prostate specific. The search for specific prostate target agents must continue so as to optimally treat patients with prostate cancer, while minimizing deleterious effects in other PSMA expressing tissues.

Identification of alternative protein targets of glutamate-ureido-lysine associated with PSMA tracer uptake in prostate cancer cells

Glutamate-ureido-lysine (GUL) probes are specific for prostate-specific membrane antigen (PSMA), overexpressed by most prostate cancers. This antigen can be lost as the cancer progresses. Recent reports have indicated that GUL probes can still identify these PSMA-negative tumors, indicating that the expression of alternative PSMA-like proteins may change during disease progression. In this study we identified two such candidate protein targets, NAALADaseL and mGluR8, by using a combined computational chemistry, data mining, molecular biology, radiochemistry, and synthetic chemistry approach. This work consequently prepares the groundwork for developing specific probes that can identify this progression, indicates directions for neuroendocrine prostate cancer research, and highlights the utility of a multidisciplinary approach for the rapid identification of unidentified proteins interacting with diagnostic probes.

Prostate-specific membrane antigen (PSMA) is highly overexpressed in most prostate cancers and is clinically visualized using PSMA-specific probes incorporating glutamate-ureido-lysine (GUL). PSMA is effectively absent from certain high-mortality, treatment-resistant subsets of prostate cancers, such as neuroendocrine prostate cancer (NEPC); however, GUL-based PSMA tracers are still reported to have the potential to identify NEPC metastatic tumors. These probes may bind unknown proteins associated with PSMA-suppressed cancers. We have identified the up-regulation of PSMA-like aminopeptidase NAALADaseL and the metabotropic glutamate receptors (mGluRs) in PSMA-suppressed prostate cancers and find that their expression levels inversely correlate with PSMA expression and are associated with GUL-based radiotracer uptake. Furthermore, we identify that NAALADaseL and mGluR expression correlates with a unique cell cycle signature. This provides an opportunity for the future study of the biology of NEPC and potential therapeutic directions. Computationally predicting that GUL-based probes bind well to these targets, we designed and synthesized a fluorescent PSMA tracer to investigate these proteins in vitro, where it shows excellent affinity for PSMA, NAALADaseL, and specific mGluRs associated with poor prognosis.

Therapeutic Efficacy of a Bivalent Inhibitor of Prostate-Specific Membrane Antigen Labeled with 67Cu

Radionuclide therapy targeting prostate-specific membrane antigen (PSMA) is promising for prostate cancer. We previously reported a ligand, ⁶⁴Cu-CuSarbisPSMA, featuring 2 lysine-ureido-glutamate groups. Here, we report the therapeutic potential of ⁶⁷Cu-CuSarbisPSMA. Methods: Growth of PSMA-positive xenografts was evaluated after treatment with ⁶⁷Cu-CuSarbisPSMA or ¹⁷⁷Lu-LuPSMA imaging and therapy (I&T). Results: At 13 d after injection, tumor growth was similarly inhibited by the 2 tracers in a dose-dependent manner. Survival was comparable after single (30 MBq) or fractionated (2 × 15 MBq, 2 wk apart) administrations. Conclusion: ⁶⁷Cu-CuSarbisPSMA is efficacious in a PSMA-expressing model of prostate cancer.

Highly pleiotropic functions of CYP78As and AMP1 are regulated in non-cell-autonomous/organ-specific manners

The cytochrome P450 CYP78A5/KLUH in Arabidopsis thaliana is predicted to be involved in the synthesis of a mobile signal molecule that has a pleiotropic function that is distinct from classical phytohormones. CYP78A5 has five close relatives in Arabidopsis. We first investigated their functions, focusing on the plastochron, leaf size, and leaf senescence. Our analyses revealed that CYP78A5 and CYP78A7 are involved in the plastochron and leaf size, and CYP78A6 and CYP78A9 are involved in leaf senescence. Complementation analyses using heterologous promoters and expression analyses suggested that CYP78A isoforms have a common biochemical function and are functionally differentiated via organ-specific expression. The altered meristem program1 (amp1) carboxypeptidase mutant shows a phenotype very similar to that of the cyp78a5 mutant. Complementation analyses using boundary and organizing center-specific promoters suggested that both CYP78A5 and AMP1 act in a non-cell-autonomous manner. Analyses of multiple cyp78a mutants and crosses between cyp78a and amp1 mutants revealed that AMP1/LIKE AMP1 (LAMP1) and CYP78A isoforms regulate plastochron length and leaf senescence in the same genetic pathway, whereas leaf size is independently regulated. Furthermore, we detected feedback regulation between CYP78A6/CYP78A9 and AMP1 at the gene expression level. These observations raise the possibility that AMP1 and CYP78A isoforms are involved in the synthesis of the same mobile signal molecule, and suggest that AMP1 and CYP78A signaling pathways have a very close, albeit complex, functional relationship.

Taenia solium proteins: a beautiful kaleidoscope of pro and anti-inflammatory antigens

Background: Neurocysticercosis (NCC) is an acquired infection of central nervous system associated with epileptic seizures. The parasite 'Taenia solium' causes this disease and has a complex life cycle and molts into various stages that influence the host-parasite interaction. The disease has a long asymptomatic phase with viable cyst and degeneration of cyst and leaking cyst fluid has been associated with symptomatic phase. The parasite proteome holds the answers and clues to this complex clinical presentation and hence unraveling of proteome of parasite antigens is needed for better understanding of host-parasite interactions. Objective: To understand the proteome make-up of T. solium cyst vesicular fluid (VF) and excretory secretory proteins (ESPs). Methodology: The VF and ESPs for the study were prepared from cyst harvested from naturally infected swine. The samples were prepared for nano LC-MS by in-tube digestion of proteins. The spectra obtained were annotated and enrichment analysis was performed and in silico analysis was done. Results: T. solium VF and ESPs have 206 and 247 proteins of varied make-up including pro-inflammatory and anti-inflammatory nature. Conclusions: Due to varied make-up of VF and ESPs it can generate complex humoral and cellular immune response.

Predicted iron metabolism genes in hard ticks and their response to iron reduction in Dermacentor andersoni cells

For most organisms, iron is an essential nutrient due to its role in fundamental cellular processes. Insufficient iron causes sub-optimal metabolism with potential effects on viability, while high levels of iron are toxic due to the formation of oxidative radicals, which damage cellular components. Many molecules and processes employed in iron uptake, storage, transport and metabolism are conserved, however significant knowledge gaps remain regarding these processes in ticks due to their unique physiology. In this study, we first identified and sequenced 13 genes likely to be involved in iron metabolism in Dermacentor andersoni cells. We then developed a method to reduce iron levels in D. andersoni cells using the iron chelator 2,2'-bipyridyl and measured the transcriptional response of these genes to iron reduction. The genes include a putative transferrin receptor, divalent metal transporter 1, duodenal cytochrome b, zinc/iron transporters zip7, zip13, zip14, mitoferrin, ferrochelatase, iron regulatory protein 1, ferritin1, ferritin2, transferrin and poly r(C)-binding protein. Overall, the transcriptional response of the target genes to iron reduction was modest. The most marked changes were a decrease in ferritin2, which transports iron through the tick hemolymph, the mitochondrial iron transporter mitoferrin, and the mitochondrial enzyme ferrochelatase. Iron regulatory protein1 was the only gene with an overall increase in transcript in response to reduced iron levels. This work lays the foundation for an improved understanding of iron metabolism in ticks which may provide molecular targets for the development of novel tick control methods and aid in the understanding of tick-pathogen interactions.

Bivalent Inhibitors of Prostate-Specific Membrane Antigen Conjugated to Desferrioxamine B Squaramide Labeled with Zirconium-89 or Gallium-68 for Diagnostic Imaging of Prostate Cancer

Prostate-specific membrane antigen (PSMA) is a carboxypeptidase that is overexpressed in prostate cancer and is an excellent candidate for targeted diagnostic imaging and therapy. Lysine-ureido-glutamate inhibitors of PSMA radiolabeled with positron-emitting radionuclides can be used for diagnostic imaging with positron emission tomography (PET). A squaramide ester derivative of desferrioxamine B (H₃DFOSq) was used to prepare four new agents with either one or two lysine-ureido-glutamate pharmacophores. The H₃DFOSq ligand can be used to form stable complexes with either of the positron-emitting radionuclides gallium-68 (t_1/2 = 68 min) or zirconium-89 (t_1/2 = 3.3 days). The complexes were evaluated in PSMA-positive xenograft mouse models. Bivalent inhibitors, where two pharmacophores are tethered to a single DFOSq ligand, have better tumor uptake than their monovalent analogues. The ligands presented here, which can be labeled with either gallium-68 or zirconium-89, have the potential to increase the number of clinical sites that can perform diagnostic PET imaging.

Prostate-specific membrane antigen for the surgical oncologist: interpreting expression beyond the prostate

The use of prostate-specific membrane antigen (PSMA) radiotracer in positron emission tomography (PET) has been successfully incorporated into the clinical management of prostate cancer. However, PSMA tracer uptake is not limited to prostate cancer tissue. We reviewed studies exploring PSMA expression beyond the prostate gland using techniques of ⁶⁸ Ga-PSMA PET imaging and immunohistochemistry. PSMA expression has been associated with a variety of solid tumours, and the vasculature associated with neoplastic disease, suggesting that this trans-membrane glycoprotein may be involved in the neovascularisation process in malignancy. These studies demonstrate the need for more research into the potential utility for ⁶⁸ Ga-PSMA PET imaging in patients with non-prostatic cancers.

A novel PSMA/GCPII-deficient mouse model shows enlarged seminal vesicles upon aging

BACKGROUND

Prostate-specific membrane antigen (PSMA), also known as glutamate carboxypeptidase II (GCPII), is an important diagnostic and therapeutic target in prostate cancer. PSMA/GCPII is also expressed in many healthy tissues, but its function has only been established in the brain and small intestine. Several research groups have attempted to produce PSMA/GCPII-deficient mice to study the physiological role of PSMA/GCPII in detail. The outcomes of these studies differ dramatically, ranging from embryonic lethality to production of viable PSMA/GCPII-deficient mice without any obvious phenotype.

METHODS

We produced PSMA/GCPII-deficient mice (hereafter also referred as Folh1^-/- mice) by TALEN-mediated mutagenesis on a C57BL/6NCrl background. Using Western blot and an enzyme activity assay, we confirmed the absence of PSMA/GCPII in our Folh1^-/- mice. We performed anatomical and histopathological examination of selected tissues with a focus on urogenital system. We also examined the PSMA/GCPII expression profile within the mouse urogenital system using an enzyme activity assay and confirmed the presence of PSMA/GCPII in selected tissues by immunohistochemistry.

RESULTS

Our Folh1^-/- mice are viable, breed normally, and do not show any obvious phenotype. Nevertheless, aged Folh1^-/- mice of 69-72 weeks exhibit seminal vesicle dilation, which is caused by accumulation of luminal fluid. This phenotype was also observed in Folh1^+/- mice; the overall difference between our three cohorts (Folh1^-/- , Folh1^+/- , and Folh1^+/+ ) was highly significant (P < 0.002). Of all studied tissues of the mouse urogenital system, only the epididymis appeared to have a physiologically relevant level of PSMA/GCPII expression. Additional experiments demonstrated that PSMA/GCPII is also present in the human epididymis.

CONCLUSIONS

In this study, we provide the first evidence characterizing the reproductive tissue phenotype of PSMA/GCPII-deficient mice. These findings will help lay the groundwork for future studies to reveal PSMA/GCPII function in human reproduction.

Glu-Ureido-Based Inhibitors of Prostate-Specific Membrane Antigen: Lessons Learned During the Development of a Novel Class of Low-Molecular-Weight Theranostic Radiotracers

In recent years, several radioligands targeting prostate-specific membrane antigen (PSMA) have been clinically introduced as a new class of theranostic radiopharmaceuticals for the treatment of prostate cancer (PC). In the second decade of the 21^st century, a new era in nuclear medicine was initiated by the clinical introduction of small-molecule PSMA inhibitor radioligands, 40 y after the clinical introduction of ¹⁸F-FDG. Because of the high incidence and mortality of PC, the new PSMA radioligands have already had a remarkable impact on the clinical management of PC. For the continuing clinical development and long-term success of theranostic agents, designing modern prospective clinical trials in theranostic nuclear medicine is essential. First-in-human studies with PSMA radioligands derived from small-molecule PSMA inhibitors showed highly sensitive imaging of PSMA-positive PC by means of PET and SPECT as well as a dramatic response of metastatic castration-resistant PC after PSMA radioligand therapy. This tremendous success logically led to the initiation of prospective clinical trials with several PSMA radioligands. Meanwhile, MIP-1404, PSMA-11, 2-(3-{1-carboxy-5-[(6-fluoro-pyridine-3-carbonyl)-amino]-pentyl}-ureido)-pentanedioic acid (DCFPyL), PSMA-617, PSMA-1007, and others have entered or will enter prospective clinical trials soon in several countries. The significance becomes apparent by, for example, the considerable increase in the number of publications about PSMA-targeted PET imaging from 2013 to 2016 (e.g., a search of the Web of Science for "PSMA" AND "PET" found only 19 publications in 2013 but 218 in 2016). Closer examination of the initial success of PC treatment with PSMA inhibitor radiotracers leads to several questions from the basic research perspective as well as from the perspective of clinical demands: What lessons have been learned regarding the design of PSMA radioligands that have already been developed? Has an acceptable compromise between optimal PSMA radioligand design and a broad range of clinical demands been reached? Can the lessons learned from multiple successes within the PSMA experience be transferred to further theranostic approaches?

The therapeutic and diagnostic potential of the prostate specific membrane antigen/glutamate carboxypeptidase II (PSMA/GCPII) in cancer and neurological disease

Prostate specific membrane antigen (PSMA) otherwise known as glutamate carboxypeptidase II (GCPII) is a membrane bound protein that is highly expressed in prostate cancer and in the neovasculature of a wide variety of tumours including glioblastomas, breast and bladder cancers. This protein is also involved in a variety of neurological diseases including schizophrenia and ALS. In recent years, there has been a surge in the development of both diagnostics and therapeutics that take advantage of the expression and activity of PSMA/GCPII. These include gene therapy, immunotherapy, chemotherapy and radiotherapy. In this review, we discuss the biological roles that PSMA/GCPII plays, both in normal and diseased tissues, and the current therapies exploiting its activity that are at the preclinical stage. We conclude by giving an expert opinion on the future direction of PSMA/GCPII based therapies and diagnostics and hurdles that need to be overcome to make them effective and viable.

Dpp4 inhibition as a therapeutic strategy in cardiometabolic disease: Incretin-dependent and -independent function

Cardiometabolic disorders including obesity, diabetes and cardiovascular disease are among the most severe health problems worldwide. DPP4 enzymatic inhibitors were first developed as anti-diabetic reagents which preserve incretin hormones and promote post-prandial insulin secretion. It's been shown in animal studies that incretin-based therapy has a beneficial effect on cardiovascular disease. Recent studies demonstrated novel non-catalytic functions of DPP4 that may play a role in cardiometabolic disease. Although the role of DPP4 inhibition-mediated incretin effects has been well-reviewed, little information of its incretin-independent actions was introduced in cardiometabolic disease. In the current review, we will summarize the catalytic dependent and independent effects of DPP4 inhibition on cardiometabolic disease.

•

Discuss the findings from recent large scale clinical trials (EXAMINE and SAVOR-TIMI 53)

•

Summarize the catalytic dependent and independent effects of DPP4 inhibition on cardiometabolic disease

•

Focus on recent evidence linking DPP4 inhibition therapy with cardiovascular disease

•

Provide mechanistic insights into the cardiovascular effect of DPP4

Design of highly potent urea-based, exosite-binding inhibitors selective for glutamate carboxypeptidase II

We present here a structure-aided design of inhibitors targeting the active site as well as exosites of glutamate carboxypeptidase II (GCPII), a prostate cancer marker, preparing potent and selective inhibitors that are more than 1000-fold more active toward GCPII than its closest human homologue, glutamate carboxypeptidase III (GCPIII). Additionally, we demonstrate that the prepared inhibitor conjugate can be used for sensitive and selective imaging of GCPII in mammalian cells.

Structural and biochemical characterization of a novel aminopeptidase from human intestine

N-acetylated α-linked acidic dipeptidase-like protein (NAALADase L), encoded by the NAALADL1 gene, is a close homolog of glutamate carboxypeptidase II, a metallopeptidase that has been intensively studied as a target for imaging and therapy of solid malignancies and neuropathologies. However, neither the physiological functions nor structural features of NAALADase L are known at present. Here, we report a thorough characterization of the protein product of the human NAALADL1 gene, including heterologous overexpression and purification, structural and biochemical characterization, and analysis of its expression profile. By solving the NAALADase L x-ray structure, we provide the first experimental evidence that it is a zinc-dependent metallopeptidase with a catalytic mechanism similar to that of glutamate carboxypeptidase II yet distinct substrate specificity. A proteome-based assay revealed that the NAALADL1 gene product possesses previously unrecognized aminopeptidase activity but no carboxy- or endopeptidase activity. These findings were corroborated by site-directed mutagenesis and identification of bestatin as a potent inhibitor of the enzyme. Analysis of NAALADL1 gene expression at both the mRNA and protein levels revealed the small intestine as the major site of protein expression and points toward extensive alternative splicing of the NAALADL1 gene transcript. Taken together, our data imply that the NAALADL1 gene product's primary physiological function is associated with the final stages of protein/peptide digestion and absorption in the human digestive system. Based on these results, we suggest a new name for this enzyme: human ileal aminopeptidase (HILAP).

PSA-responsive and PSMA-mediated multifunctional liposomes for targeted therapy of prostate cancer

In the hormone-refractory stage of prostate cancer (PC), the expression of prostate-specific antigen (PSA) and prostate-specific membrane antigen (PSMA) often remains highly active. Accumulating studies have demonstrated that these two proteins are attractive targets for specific delivery of functional molecules to advanced PC, not merely as potential sensitive markers for PC detection. In this study, we constructed a dual-modified liposome that incorporated PSA-responsive and PSMA-mediated liposomes and potentially offers double selectivity for PC. The folate moiety binds quickly to PSMA-positive tumors, and the PSA-responsive moiety is cleaved by PSA that was enriched in tumor tissues. The activated liposomes (folate and cell-penetrating peptides dual-modifications) are subsequently taken up by the tumor cells via polyarginine's penetrating effects and receptor-mediated endocytosis. To corroborate these assumptions, a series of experiments were conducted, including PSA-responsive peptide hydrolysis kinetics, cellular uptake, internalization mechanism and escape from endosomes in PC-3 and/or 22Rv1 cells, biodistribution and antitumor activity of siRNA-loaded liposomes after systemic administration, gene silencing and cell apoptosis in vitro and in vivo. The results reveal that multivalent interactions play a key role in enhancing PC cell recognition and uptake while reducing nonspecific uptake. The dual-modified liposomes carrying small interfering RNA (siRNA) have significant advantages over the control liposomes, including single-modified (folate, CPP, PSA-responsive only) and non-modified liposomes. The dual-modified liposomes elevated cellular uptake, downregulated expression of polo-like kinase 1 (PLK-1) and augmented cell apoptosis in prostate tumor cells. The entry of the dual-modified liposomes into 22Rv1 cells occurred via multiple endocytic pathways, including clathrin-mediated endocytosis and macropinocytosis, followed by an effective endosomal escape of the entrapped siRNA into the cytoplasm. In vivo studies conducted on a 22Rv1 xenograft murine model demonstrated that the dual-modified liposomes demonstrated the maximized accumulation, retention and knockdown of PLK-1 in tumor cells, as well as the strongest inhibition of tumor growth and induction of tumor cell apoptosis. In terms of targeting capacity and therapeutic potency, the combination of a PSA-responsive and PSMA-mediated liposome presents a promising platform for therapy and diagnosis of PSMA/PSA-positive PC.

Effect of chelators on the pharmacokinetics of (99m)Tc-labeled imaging agents for the prostate-specific membrane antigen (PSMA)

Technetium-99m, the most commonly used radionuclide in nuclear medicine, can be attached to biologically important molecules through a variety of chelating agents, the choice of which depends upon the imaging application. The prostate-specific membrane antigen (PSMA) is increasingly recognized as an important target for imaging and therapy of prostate cancer (PCa). Three different (99m)Tc-labeling methods were employed to investigate the effect of the chelator on the biodistribution and PCa tumor uptake profiles of 12 new urea-based PSMA-targeted radiotracers. This series includes hydrophilic ligands for radiolabeling with the [(99m)Tc(CO)3](+) core (L8-L10), traditional NxSy-based chelating agents with varying charge and polarity for the (99m)Tc-oxo core (L11-L18), and a (99m)Tc-organohydrazine-labeled radioligand (L19). (99m)Tc(I)-Tricarbonyl-labeled [(99m)Tc]L8 produced the highest PSMA+ PC3 PIP to PSMA- PC3 flu tumor ratios and demonstrated the lowest retention in normal tissues including kidney after 2 h. These results suggest that choice of chelator is an important pharmacokinetic consideration in the development of (99m)Tc-labeled radiopharmaceuticals targeting PSMA.

Glutamate carboxypeptidase II in diagnosis and treatment of neurologic disorders and prostate cancer

Glutamate carboxypeptidase II (GCPII) is a membrane-bound binuclear zinc metallopeptidase with the highest expression levels found in the nervous and prostatic tissue. Throughout the nervous system, glia-bound GCPII is intimately involved in the neuron-neuron and neuron-glia signaling via the hydrolysis of N-acetylaspartylglutamate (NAAG), the most abundant mammalian peptidic neurotransmitter. The inhibition of the GCPII-controlled NAAG catabolism has been shown to attenuate neurotoxicity associated with enhanced glutamate transmission and GCPII-specific inhibitors demonstrate efficacy in multiple preclinical models including traumatic brain injury, stroke, neuropathic and inflammatory pain, amyotrophic lateral sclerosis, and schizophrenia. The second major area of pharmacological interventions targeting GCPII focuses on prostate carcinoma; GCPII expression levels are highly increased in androgen-independent and metastatic disease. Consequently, the enzyme serves as a potential target for imaging and therapy. This review offers a summary of GCPII structure, physiological functions in healthy tissues, and its association with various pathologies. The review also outlines the development of GCPII-specific small-molecule compounds and their use in preclinical and clinical settings.

Molecular identification of β-citrylglutamate hydrolase as glutamate carboxypeptidase 3

β-Citrylglutamate (BCG), a compound present in adult testis and in the CNS during the pre- and perinatal periods is synthesized by an intracellular enzyme encoded by the RIMKLB gene and hydrolyzed by an as yet unidentified ectoenzyme. To identify β-citrylglutamate hydrolase, this enzyme was partially purified from mouse testis and characterized. Interestingly, in the presence of Ca(2+), the purified enzyme specifically hydrolyzed β-citrylglutamate and did not act on N-acetyl-aspartylglutamate (NAAG). However, both compounds were hydrolyzed in the presence of Mn(2+). This behavior and the fact that the enzyme was glycosylated and membrane-bound suggested that β-citrylglutamate hydrolase belonged to the same family of protein as glutamate carboxypeptidase 2 (GCP2), the enzyme that catalyzes the hydrolysis of N-acetyl-aspartylglutamate. The mouse tissue distribution of β-citrylglutamate hydrolase was strikingly similar to that of the glutamate carboxypeptidase 3 (GCP3) mRNA, but not that of the GCP2 mRNA. Furthermore, similarly to β-citrylglutamate hydrolase purified from testis, recombinant GCP3 specifically hydrolyzed β-citrylglutamate in the presence of Ca(2+), and acted on both N-acetyl-aspartylglutamate and β-citrylglutamate in the presence of Mn(2+), whereas recombinant GCP2 only hydrolyzed N-acetyl-aspartylglutamate and this, in a metal-independent manner. A comparison of the structures of the catalytic sites of GCP2 and GCP3, as well as mutagenesis experiments revealed that a single amino acid substitution (Asn-519 in GCP2, Ser-509 in GCP3) is largely responsible for GCP3 being able to hydrolyze β-citrylglutamate. Based on the crystal structure of GCP3 and kinetic analysis, we propose that GCP3 forms a labile catalytic Zn-Ca cluster that is critical for its β-citrylglutamate hydrolase activity.

Identification of metabolites in the normal ovary and their transformation in primary and metastatic ovarian cancer

In this study, we characterized the metabolome of the human ovary and identified metabolic alternations that coincide with primary epithelial ovarian cancer (EOC) and metastatic tumors resulting from primary ovarian cancer (MOC) using three analytical platforms: gas chromatography mass spectrometry (GC/MS) and liquid chromatography tandem mass spectrometry (LC/MS/MS) using buffer systems and instrument settings to catalog positive or negative ions. The human ovarian metabolome was found to contain 364 biochemicals and upon transformation of the ovary caused changes in energy utilization, altering metabolites associated with glycolysis and β-oxidation of fatty acids--such as carnitine (1.79 fold in EOC, p<0.001; 1.88 fold in MOC, p<0.001), acetylcarnitine (1.75 fold in EOC, p<0.001; 2.39 fold in MOC, p<0.001), and butyrylcarnitine (3.62 fold, p<0.0094 in EOC; 7.88 fold, p<0.001 in MOC). There were also significant changes in phenylalanine catabolism marked by increases in phenylpyruvate (4.21 fold; p = 0.0098) and phenyllactate (195.45 fold; p<0.0023) in EOC. Ovarian cancer also displayed an enhanced oxidative stress response as indicated by increases in 2-aminobutyrate in EOC (1.46 fold, p = 0.0316) and in MOC (2.25 fold, p<0.001) and several isoforms of tocopherols. We have also identified novel metabolites in the ovary, specifically N-acetylasparate and N-acetyl-aspartyl-glutamate, whose role in ovarian physiology has yet to be determined. These data enhance our understanding of the diverse biochemistry of the human ovary and demonstrate metabolic alterations upon transformation. Furthermore, metabolites with significant changes between groups provide insight into biochemical consequences of transformation and are candidate biomarkers of ovarian oncogenesis. Validation studies are warranted to determine whether these compounds have clinical utility in the diagnosis or clinical management of ovarian cancer patients.

Computational tools for the interactive exploration of proteomic and structural data

Linking proteomics and structural data is critical to our understanding of cellular processes, and interactive exploration of these complementary data sets can be extremely valuable for developing or confirming hypotheses in silico. However, few computational tools facilitate linking these types of data interactively. In addition, the tools that do exist are neither well understood nor widely used by the proteomics or structural biology communities. We briefly describe several relevant tools, and then, using three scenarios, we present in depth two tools for the integrated exploration of proteomics and structural data.

PLASTOCHRON3/GOLIATH encodes a glutamate carboxypeptidase required for proper development in rice

Most aerial parts of the plant body are products of the continuous activity of the shoot apical meristem (SAM). Leaves are the major component of the aerial plant body, and their temporal and spatial distribution mainly determines shoot architecture. Here we report the identification of the rice gene PLASTOCHRON3 (PLA3)/GOLIATH (GO) that regulates various developmental processes including the rate of leaf initiation (the plastochron). PLA3/GO encodes a glutamate carboxypeptidase, which is thought to catabolize small acidic peptides and produce small signaling molecules. pla3 exhibits similar phenotypes to pla1 and pla2- a shortened plastochron, precocious leaf maturation and rachis branch-to-shoot conversion in the reproductive phase. However, in contrast to pla1 and pla2, pla3 showed pleiotropic phenotypes including enlarged embryo, seed vivipary, defects in SAM maintenance and aberrant leaf morphology. Consistent with these pleiotropic phenotypes, PLA3 is expressed in the whole plant body, and is involved in plant hormone homeostasis. Double mutant analysis revealed that PLA1, PLA2 and PLA3 are regulated independently but function redundantly. Our results suggest that PLA3 modulates various signaling pathways associated with a number of developmental processes.

Structural basis of interactions between human glutamate carboxypeptidase II and its substrate analogs

Human glutamate carboxypeptidase II (GCPII) is involved in neuronal signal transduction and intestinal folate absorption by means of the hydrolysis of its two natural substrates, N-acetyl-aspartyl-glutamate and folyl-poly-gamma-glutamates, respectively. During the past years, tremendous efforts have been made toward the structural analysis of GCPII. Crystal structures of GCPII in complex with various ligands have provided insight into the binding of these ligands, particularly to the S1' site of the enzyme. In this article, we have extended structural characterization of GCPII to its S1 site by using dipeptide-based inhibitors that interact with both S1 and S1' sites of the enzyme. To this end, we have determined crystal structures of human GCPII in complex with phosphapeptide analogs of folyl-gamma-glutamate, aspartyl-glutamate, and gamma-glutamyl-glutamate, refined at 1.50, 1.60, and 1.67 A resolution, respectively. The S1 pocket of GCPII could be accurately defined and analyzed for the first time, and the data indicate the importance of Asn519, Arg463, Arg534, and Arg536 for recognition of the penultimate (i.e., P1) substrate residues. Direct interactions between the positively charged guanidinium groups of Arg534 and Arg536 and a P1 moiety of a substrate/inhibitor provide mechanistic explanation of GCPII preference for acidic dipeptides. Additionally, observed conformational flexibility of the Arg463 and Arg536 side chains likely regulates GCPII affinity toward different inhibitors and modulates GCPII substrate specificity. The biochemical experiments assessing the hydrolysis of several GCPII substrate derivatives modified at the P1 position, also included in this report, further complement and extend conclusions derived from the structural analysis. The data described here form an a solid foundation for the structurally aided design of novel low-molecular-weight GCPII inhibitors and imaging agents.

The Maize Viviparous8 locus, encoding a putative ALTERED MERISTEM PROGRAM1-like peptidase, regulates abscisic acid accumulation and coordinates embryo and endosperm development

We describe a mutant of Zea mays isolated from a W22 inbred transposon population, widow's peak mutant1 (wpk1), with an altered pattern of anthocyanin synthesis and aleurone cell differentiation in endosperm. In addition, a failure of the developing mutant embryo to form leaf initials is associated with decreased expression of a subset of meristem regulatory genes that includes Abphyl1 and Td1. We show that the viviparous8 (vp8) mutant has a similar pleiotropic phenotype in the W22 inbred background in contrast to the viviparous embryo phenotype exhibited in the standard genetic background, and we confirmed that wpk1 is allelic to vp8. Further genetic analysis revealed that the standard vp8 stock contains an unlinked, partially dominant suppressor of the vp8 mutation that is not present in W22. Consistent with the early-onset viviparous phenotype of vp8, expression of several embryonic regulators, including LEC1/B3 domain transcription factors, was reduced in the mutant embryo. Moreover, reduced abscisic acid (ABA) content of vp8/wpk1 embryos was correlated with altered regulation of ABA biosynthesis, as well as ABA catabolic pathways. The ABA biosynthetic gene Vp14 was down-regulated in the nonsuppressed background, whereas the ZmABA8'oxA1a ABA 8'-hydroxylase gene was strongly up-regulated in both genetic backgrounds. Molecular analysis revealed that Vp8 encodes a putative peptidase closely related to Arabidopsis thaliana ALTERED MERISTEM PROGRAM1. Because the Vp8 regulates meristem development as well as seed maturation processes, including ABA accumulation, we propose that VP8 is required for synthesis of an unidentified signal that integrates meristem and embryo formation in seeds.

Tissue expression and enzymologic characterization of human prostate specific membrane antigen and its rat and pig orthologs

BACKGROUND

Prostate specific membrane antigen (PSMA), also called glutamate carboxypeptidase II (GCPII), is a target enzyme for diagnosis and treatment of prostate cancer. Moreover, it is upregulated in the vasculature of most solid tumors and is therefore a potential target for the generation of novel antineoplastics. In this context, we analyze the possibility of using rat and pig as animal models for enzymologic and in vivo studies.

METHODS

We prepared the recombinant extracellular part of human, rat, and pig GCPII in S2 cell media and characterized the activity and inhibition profiles of the three orthologs by radioenzymatic assay. We performed Western blot analysis of GCPII expression in human, rat, and pig tissues using the monoclonal antibody GCP-04 and confirmed these findings by activity measurements and immunohistochemistry.

RESULTS

The three recombinant proteins show similar specific enzymatic activities and inhibition profiles. Tissue expression analysis revealed that most of the pig and human tissues show at least some GCPII-positivity, while the expression pattern in rat is more restricted. Moreover, tissues such as prostate and testes exhibit different GCPII expression levels among the species studied.

CONCLUSIONS

The rat and pig orthologs of GCPII seem to be suitable to approximate human GCPII in enzymologic studies. However, the diffuse expression pattern of GCPII in animal and human tissues could be a caveat for the potential utilization of GCPII-targeted anticancer drugs. Furthermore, variations in GCPII tissue distribution among the species studied should be considered when using rat or pig as models for antineoplastic drug discovery.

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.

Effects of CpG-B ODN on the protein expression profile of swine PBMC

The CpG motif within bacterial DNA is a potent immuno-stimulatory moiety. Here, using a 2-D electrophoretic approach, we investigated the effect of synthetic oligodeoxynucleotide containing a B type CpG motif (CpG-B ODN) on the protein expression profile of swine peripheral blood mononuclear cells (PBMC). We found that several proteins including spondin 1, N-acetolactate alpha linked acidic dipeptidase; V kappa light chain, T cell receptor variable alpha chain, heat shock protein (Hsp) 60, Hsp70, KIAA0857 protein, and PNAS-146 were up-regulated in PBMC by CpG-B ODN stimulation. Further studies showed that CpG-B ODN-mediated Hsp60, Hsp70 and Hsp90 expressions were closely associated with the TLR9 signalling pathway. Pretreatment with inhibitors of Hsp70, Hsp90 and TLR9 all blocked the CpG-B ODN-mediated anti-apoptotic effect in swine PBMC. These results suggest that CpG-B ODN treatment of swine PBMC may enhance the expression of biologically active proteins, notably spondin 1, V kappa light chain, T cell receptor variable alpha chain and Hsps, which may play an important role in CpG-B ODN-mediated activation of immune responses and enhancement of swine PBMC survival.

Mapping of the active site of glutamate carboxypeptidase II by site-directed mutagenesis

Human glutamate carboxypeptidase II [GCPII (EC 3.4.17.21)] is recognized as a promising pharmacological target for the treatment and imaging of various pathologies, including neurological disorders and prostate cancer. Recently reported crystal structures of GCPII provide structural insight into the organization of the substrate binding cavity and highlight residues implicated in substrate/inhibitor binding in the S1' site of the enzyme. To complement and extend the structural studies, we constructed a model of GCPII in complex with its substrate, N-acetyl-l-aspartyl-l-glutamate, which enabled us to predict additional amino acid residues interacting with the bound substrate, and used site-directed mutagenesis to assess the contribution of individual residues for substrate/inhibitor binding and enzymatic activity of GCPII. We prepared and characterized 12 GCPII mutants targeting the amino acids in the vicinity of substrate/inhibitor binding pockets. The experimental results, together with the molecular modeling, suggest that the amino acid residues delineating the S1' pocket of the enzyme (namely Arg210) contribute primarily to the high affinity binding of GCPII substrates/inhibitors, whereas the residues forming the S1 pocket might be more important for the 'fine-tuning' of GCPII substrate specificity.

Catalytic mechanism of SGAP, a double-zinc aminopeptidase from Streptomyces griseus

The catalytic mechanism underlying the aminopeptidase from Streptomyces griseus (SGAP) was investigated. pH-dependent activity profiles revealed the enthalpy of ionization for the hydrolysis of leucine-para-nitroanilide by SGAP. The value obtained (30 +/- 5 kJ.mol(-1)) is typical of a zinc-bound water molecule, suggesting that the zinc-bound water/hydroxide molecule acts as the reaction nucleophile. Fluoride was found to act as a pure noncompetitive inhibitor of SGAP at pH values of 5.9-8 with a K(i) of 11.4 mM at pH 8.0, indicating that the fluoride ion interacts equally with the free enzyme as with the enzyme-substrate complex. pH-dependent pK(i) experiments resulted in a pK(a) value of 7.0, suggesting a single deprotonation step of the catalytic water molecule to an hydroxide ion. The number of proton transfers during the catalytic pathway was determined by monitoring the solvent isotope effect on SGAP and its general acid-base mutant SGAP(E131D) at different pHs. The results indicate that a single proton transfer is involved in catalysis at pH 8.0, whereas two proton transfers are implicated at pH 6.5. The role of Glu131 in binding and catalysis was assessed by determining the catalytic constants (K(m), k(cat)) over a temperature range of 293-329 degrees K for both SGAP and the E131D mutant. For the binding step, the measured and calculated thermodynamic parameters for the reaction (free energy, enthalpy and entropy) for both SGAP and the E131D mutant were similar. By contrast, the E131D point mutation resulted in a four orders of magnitude decrease in k(cat), corresponding to an increase of 9 kJ.mol(-1) in the activation energy for the E131D mutant, emphasizing the crucial role of Glu131 in catalysis.

Neuropeptide Y (NPY) cleaving enzymes: structural and functional homologues of dipeptidyl peptidase 4

N-terminal truncation of NPY has important physiological consequences, because the truncated peptides lose their capability to activate the Y1-receptor. The sources of N-terminally truncated NPY and related peptides are unknown and several proline specific peptidases may be involved. First, we therefore provide an overview on the peptidases, belonging to structural and functional homologues of dipeptidyl peptidase 4 (DP4) as well as aminopeptidase P (APP) and thus, represent potential candidates of NPY cleavage in vivo. Second, applying selective inhibitors against DP4, DP8/9 and DP2, respectively, the enzymatic distribution was analyzed in brain extracts from wild type and DP4 deficient F344 rat substrains and human plasma samples in activity studies as well as by matrix assisted laser desorption/ionisation-time of flight (MALDI-TOF)-mass spectrometry. Third, co-transfection of Cos-1 cells with Dpp4 and Npy followed by confocal lasermicroscopy illustrated that hNPY-dsRed1-N1 was transported in large dense core vesicles towards the membrane while rDP4-GFP-C1 was transported primarily in different vesicles thereby providing no clear evidence for co-localization of NPY and DP4. Nevertheless, the review and experimental results of activity and mass spectrometry studies support the notion that at least five peptidases (DP4, DP8, DP9, XPNPEP1, XPNPEP2) are potentially involved in NPY cleavage while the serine protease DP4 (CD26) could be the principal peptidase involved in the N-terminal truncation of NPY. However, DP8 and DP9 are also capable of cleaving NPY, whereas no cleavage could be demonstrated for DP2.

Biochemical characterization of human glutamate carboxypeptidase III

Human glutamate carboxypeptidase II (GCPII) is a transmembrane metallopeptidase found mainly in the brain, small intestine, and prostate. In the brain, it cleaves N-acetyl-L-aspartyl-glutamate, liberating free glutamate. Inhibition of GCPII has been shown to be neuroprotective in models of stroke and other neurodegenerations. In prostate, it is known as prostate-specific membrane antigen, a cancer marker. Recently, human glutamate carboxypeptidase III (GCPIII), a GCPII homolog with 67% amino acid identity, was cloned. While GCPII is recognized as an important pharmaceutical target, no biochemical study of human GCPIII is available at present. Here, we report the cloning, expression, and characterization of recombinant human GCPIII. We show that GCPIII lacks dipeptidylpeptidase IV-like activity, its activity is dependent on N-glycosylation, and it is effectively inhibited by several known inhibitors of GCPII. In comparison to GCPII, GCPIII has lower N-acetyl-L-aspartyl-glutamate-hydrolyzing activity, different pH and salt concentration dependence, and distinct substrate specificity, indicating that these homologs might play different biological roles. Based on a molecular model, we provide interpretation of the distinct substrate specificity of both enzymes, and examine the amino acid residues responsible for the differences by site-directed mutagenesis. These results may help to design potent and selective inhibitors of both enzymes.

Molecular Evolution of the Transferrin Receptor/Glutamate Carboxypeptidase II Family

The transferrin receptor family is represented by at least seven different homologous proteins in primates. Transferrin receptor (TfR1) is a type II membrane glycoprotein that, as a cell surface homodimer, binds iron-loaded transferrin as part of the process of iron transfer and uptake. Other family members include transferrin receptor 2 (TfR2), glutamate carboxypeptidase II (GCP2 or PSMA), N-acetylated alpha-linked acidic dipeptidase-like protein (NLDL), N-acetylated alpha-linked acidic dipeptidase 2 (NAALAD2), and prostate-specific membrane antigen-like protein (PMSAL/GCPIII). We compared 86 different sequences from 24 different species, from mammals to fungi. Through this comparison, we have identified several highly conserved residues specific to each family not previously associated with clinical mutations. The evolutionary history of the TfR/GCP2 family shows repeated episodes of duplications consistent with recent theories that nondispensable, slowly evolving genes are more likely to form multiple gene families.

Expression of glutamate carboxypeptidase II in human brain

Glutamate carboxypeptidase II (GCPII) is a transmembrane glycoprotein expressed in various tissues. When expressed in the brain it cleaves the neurotransmitter N-acetylaspartylglutamate (NAAG), yielding free glutamate. In jejunum it hydrolyzes folylpoly-gamma-glutamate, thus facilitating folate absorption. The prostate form of GCPII, known as prostate specific membrane antigen (PSMA), is an established cancer marker. The NAAG-hydrolyzing activity of GCPII has been implicated in a number of pathological conditions in which glutamate is neurotoxic (e.g. amyotrophic lateral sclerosis, Huntington's disease, Alzheimer's disease, epilepsy, schizophrenia, and stroke). Inhibition of GCPII was shown to be neuroprotective in tissue culture and in animal models. GCPII is therefore an interesting putative therapeutic target. However, only very limited and controversial data on the expression and localization of GCPII in human brain are available. Therefore, we set out to analyze the activity and expression of GCPII in various compartments of the human brain using a radiolabeled substrate of the enzyme and the novel monoclonal antibody GCP-04, which recognizes an epitope on the extracellular portion of the enzyme and is more sensitive to GCPII than to the homologous GCPIII. We show that this antibody is more sensitive in immunoblots than the widely used antibody 7E11. By Western blot, we show that there are approximately 50-300 ng of GCPII/mg of total protein in human brain, depending on the specific area. Immunohistochemical analysis revealed that astrocytes specifically express GCPII in all parts of the brain. GCPII is enzymatically active and the level of activity follows the expression pattern. Using pure recombinant GCPII and homologous GCPIII, we conclude that GCPII is responsible for the majority of overall NAAG-hydrolyzing activity in the human brain.

Expression of prostate-specific membrane antigen in normal and malignant human tissues

BACKGROUND

Prostate-specific membrane antigen (PSMA) is upregulated in androgen-dependent prostate carcinoma and it has been targeted for immunotherapy and diagnosis of this cancer. However, this protein is also expressed in other tissues. The objective of this study is to investigate its expression in normal and malignant human tissues.

METHODS

Using monoclonal antibodies 24.4E6 (specific for residues 638-657) and 7E11.C5 (specific for the transmembrane domain of PSMA), immunohistochemical detection of PSMA was performed in surgical specimens.

RESULTS

Prostate-specific membrane antigen was detected in the epithelium of prostate, urinary bladder, proximal tubules of kidney, liver, esophagus, stomach, small intestine, colon, breast, fallopian tubes and testicular seminiferous tubules, hippocampal neurons and astrocytes, ependyma, cortex and medulla of the adrenal gland, and ovary stroma. It was also detected in neoplasms of the prostate, kidney, urinary bladder, stomach, small intestine, colon, lung, adrenal gland, and testis. It was not detected in normal seminal vesicles or the lung.

CONCLUSIONS

These findings demonstrate that PSMA is widely distributed in normal tissues, and, depending on the tumors, its expression is up- or down-regulated, or unchanged. The broad distribution of PSMA may make it suitable for the diagnosis and therapy of a wide variety of tumors.

Array-based genomic delineation of a familial duplication 11q14.1-q22.1 associated with recurrent depression

Detection of abnormal karyotypes with associated clinical manifestations is an important tool for the identification of genes that confer susceptibility to genetic disorders. We present a family with a duplication 11q14.1-q22.1 resulting from an unbalanced familial insertion, associated with a mild dysmorphic phenotype and mood disorders, mainly major depression. This relatively large duplication of a segment from chromosome 11 is associated with a surprisingly little physical phenotypic effect in this family. The finding of mood disorders in adult members of the family who carry the insertion supports the view that the duplication may be important for the identification of contributing gene(s) to mood disorders. Major depression is considered to be a complex trait with multiple genetic alterations interacting with environmental factors. Array-based comparative genome hybridization (array CGH) analysis with a 1 Mb genomic array, defined the duplication region that extended over 16 Mb from 11q14.1 to 11q22.1. Brain-expressed genes that map within this 16 Mb region, are considered worthy of further investigation as gene(s) contributing to the etiology of major depression.

Tissue distribution and thyroid hormone regulation of Pept1 and Pept2 mRNA in rodents

Peptide transporters (Pept) have essential physiological functions and also transport various drugs. Information regarding tissue distribution and gene regulation of Pept in rodents is limited. The present study investigated the distribution of Pept1 and Pept2 mRNA in 19 tissues of male and female Sprague-Dawley rats and C57BL/6 mice, as well as thyroid hormone regulation of renal Pept expression in male rats, using the branched DNA signal amplification assay. Pept1 mRNA was not only highly expressed in small intestine, but also detectable in gonads of both species, kidney of rats, and large intestine of mice. Pept2 mRNA was the highest in kidney, followed by brain and lung. The present study offers the first evidence of considerable Pept2 mRNA expression in pituitary and reproductive organs (testis, prostate, ovary, and uterus). Interestingly, Pept2 mRNA expression in mouse prostate appeared to be much higher than that in rat prostate. Thyroidectomy increased Pept1 and Pept2 mRNA in male rat kidney; such increases were abolished by thyroid hormone replacement.

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.

Construction of prostate-specific expressed recombinant plasmids with high transcriptional activity of prostate-specific membrane antigen (PSMA) promoter/enhancer

To screen different combinations of prostate-specific membrane antigen (PSMA) promoter/enhancer with the strongest transcriptional activity in prostate-specific cells, we used PSMA regulatory elements to control specific expression of the target gene in gene therapy of prostate adenocarcinoma. PSMA promoter and enhancer DNA sequences were amplified from the LNCaP human prostate cancer cell line by polymerase chain reaction, then recombinant plasmids of the enhanced green fluorescent protein (EGFP: pEGFP-PSMA(Pro), pEGFP-PSMA(E-P), pEGFP-PSMA(E(r)-P), pEGFP-PSMA(E(d)-P), and pEGFP-PSMA(E(t)-P)) were constructed with molecular clonal techniques. At the same time, all experimental cell lines were analyzed for the expression of PSMA with the use of PSMA monoclonal antibody and the ABC immunohistochemical assay kit. After plasmids were transfected via liposome, we observed the expression of the reporter gene (EGFP) under a fluorescent microscope and compared the different levels of EGFP expression with reverse transcriptase polymerase chain reaction and flow cytometry so that we could choose the one with the highest transcriptional activity. Only the LNCaP cell line expressed PSMA positively with immunohistochemical stain. The PSMA promoter/enhancer had transcriptional activity in PSMA(+) cell lines and no activity in PSMA(-) cell lines. PSMA(E-P) achieved the strongest activity in different PSMA promoter/enhancer combinations. We confirmed the specific expression of PSMA in prostate cells again. Similarly, transcriptional activity of the PSMA promoter/enhancer was prostate specific. PSMA(E-P) achieved the strongest transcriptional activity among PSMA promoter/enhancer combinations, which could be used in advanced research for tissue-specific treatment.

Crystal structure of prostate-specific membrane antigen, a tumor marker and peptidase

Prostate-specific membrane antigen (PSMA) is highly expressed in prostate cancer cells and nonprostatic solid tumor neovasculature and is a target for anticancer imaging and therapeutic agents. PSMA acts as a glutamate carboxypeptidase (GCPII) on small molecule substrates, including folate, the anticancer drug methotrexate, and the neuropeptide N-acetyl-l-aspartyl-l-glutamate. Here we present the 3.5-A crystal structure of the PSMA ectodomain, which reveals a homodimer with structural similarity to transferrin receptor, a receptor for iron-loaded transferrin that lacks protease activity. Unlike transferrin receptor, the protease domain of PSMA contains a binuclear zinc site, catalytic residues, and a proposed substrate-binding arginine patch. Elucidation of the PSMA structure combined with docking studies and a proposed catalytic mechanism provides insight into the recognition of inhibitors and the natural substrate N-acetyl-l-aspartyl-l-glutamate. The PSMA structure will facilitate development of chemotherapeutics, cancer-imaging agents, and agents for treatment of neurological disorders.