Molecular characterization and expression of dipeptidase 3, a testis-specific membrane-bound dipeptidase: complex formation with TEX101, a germ-cell-specific antigen in the mouse testis

Dipeptidase‑2 is a prognostic marker in lung adenocarcinoma that is correlated with its sensitivity to cisplatin

Lung cancer accounts for the highest percentage of cancer morbidity and mortality worldwide, and lung adenocarcinoma (LUAD) is the most prevalent subtype. Although numerous therapies have been developed for lung cancer, patient prognosis is limited by tumor metastasis and more effective treatment targets are urgently required. In the present study, gene expression profiles were extracted from the Gene Expression Omnibus database and mRNA expression data were downloaded from The Cancer Genome Atlas database. In addition, TIMER 2.0 database was used to analyze the expression of genes in normal and multiple tumor tissues. Protein expression was confirmed using the Human Protein Atlas database and LUAD cell lines, sphere formation assay, western blotting, and a xenograft mouse model were used to confirm the bioinformatics analysis. Dipeptidase‑2 (DPEP2) expression was significantly decreased in LUAD and was negatively associated with prognosis. DPEP2 overexpression substantially inhibited epithelial‑mesenchymal transition (EMT) as well as LUAD cell metastasis, and limited the expression of the cancer stem cell transformation markers, CD44 and CD133. In addition, DPEP2 improved LUAD sensitivity to cisplatin by inhibiting EMT; this was verified in vitro and in vivo. These data indicated that DPEP2 upregulates E‑cadherin, thereby regulating cell migration, cancer stem cell transformation, and cisplatin resistance, ultimately affecting the survival of patients with LUAD. Overall, the findings of the present suggest that DPEP2 is important in the development of LUAD and can be used both as a prognostic marker and a target for future therapeutic research.

Non-Invasive Diagnostics of Male Spermatogenesis from Seminal Plasma: Seminal Proteins

The compounds of seminal plasma have great potential as biomarkers of male fertility and can be used as a diagnostic tool for types of azoospermia. Azoospermia occurs in approximately 1% of the male population, and for an effective therapy of this form of male infertility, it is important to distinguish between obstructive and non-obstructive azoospermia. Proteins in seminal plasma can serve as biomarkers for diagnosing azoospermia. Considering the various types of obstructions, a combination of multiple proteins is advisable for diagnostic purposes. In this context, testicular and epididymal proteins are particularly significant, as they are specific to these tissues and typically absent in ejaculate during most obstructions. A combination of multiple biomarkers is more effective than the analysis of a single protein. This group of markers contains TEX101 and ECM1 proteins, combined detections of these two bring a diagnostic output with a high sensitivity and specificity. Similar results were observed for combined detection of TEX101 and SPAG1. The effective using of specific biomarkers from seminal plasma can significantly improve the existing approaches to diagnosis of the causes of male infertility.

Comparative proteomics analysis of human FFPE testicular tissues reveals new candidate biomarkers for distinction among azoospermia types and subtypes

Understanding molecular mechanisms that underpin azoospermia and discovery of biomarkers that could enable reliable, non-invasive diagnosis is highly needed. Using label-free data-independent LC-MS/MS acquisition coupled with ion mobility, we compared the FFPE testicular proteome of patients with obstructive (OA) and non-obstructive azoospermia (NOA) subtypes hypospermatogenesis (Hyp) and Sertoli cell-only syndrome (SCO). Out of 2044 proteins identified based on ≥2 peptides, 61 proteins had the power to quantitatively discriminate OA from NOA and 30 to quantitatively discriminate SCO from Hyp and OA. Among these, H1-6, RANBP1 and TKTL2 showed superior potential for quantitative discrimination among OA, Hyp and SCO. Integrin signaling pathway, adherens junction, planar cell polarity/convergent extension pathway and Dectin-1 mediated noncanonical NF-kB signaling were significantly associated with the proteins that could discriminate OA from NOA. Comparison with 2 transcriptome datasets revealed 278 and 55 co-differentially expressed proteins/genes with statistically significant positive correlation. Gene expression analysis by qPCR of 6 genes (H1-6, RANBP1, TKTL2, TKTL1, H2BC1, and ACTL7B) with the highest discriminatory power on protein level and the same regulation trend with transcriptomic datasets, confirmed proteomics results. In summary, our results suggest some underlying pathways in azoospermia and broaden the range of potential novel candidates for diagnosis. SIGNIFICANCE: Using a comparative proteomics approach on testicular tissue we have identified several pathways associated with azoospermia and a number of testis-specific and germ cell-specific proteins that have the potential to pinpoint the type of spermatogenesis failure. Furthermore, comparison with transcriptomics datasets based on genome-wide gene expression analyses of human testis specimens from azoospermia patients identified proteins that could discriminate between obstructive and non-obstructive azoospermia subtypes on both protein and mRNA levels. Up to our knowledge, this is the first integrated comparative analysis of proteomics and transcriptomics data from testicular tissues. We believe that the data from our study contributes significantly to increase the knowledge of molecular mechanisms of azoospermia and pave the way for new investigations in regards to non-invasive diagnosis.

A Role of the TEX101 Interactome in the Common Aetiology Behind Male Subfertility and Testicular Germ Cell Tumor

Patients who develop testicular germ cell tumours (TGCT) are at higher risk to be subfertile than the general population. The conditions are believed to originate during foetal life, however, the mechanisms behind a common aetiology of TGCT and male subfertility remains unknown. Testis-expressed 101 (TEX101) is a glycoprotein that is related to male fertility, and downregulation of the TEX101 gene was shown in pre-diagnostic TGCT patients. In this review, we summarize the current knowledge of TEX101 and its interactome related to fertility and TGCT development. We searched literature and compilation of data from curated databases. There are studies from both human and animals showing that disruption of TEX101 result in abnormal semen parameters and sperm function. Members of the TEX101 interactome, like SPATA19, Ly6k, PICK1, and ODF genes are important for normal sperm function. We found only two studies of TEX101 related to TGCT, however, several genes in its interactome may be associated with TGCT development, such as PLAUR, PRSS21, CD109, and ALP1. Some of the interactome members are related to both fertility and cancer. Of special interest is the presence of the glycosylphosphatidylinositol anchored proteins TEX101 and PRSS21 in basophils that may be coupled to the immune response preventing further development of TGCT precursor cells. The findings of this review indicate that members of the TEX101 interactome could be a part of the link between TGCT and male subfertility.

Role of the Glycosylphosphatidylinositol-Anchored Protein TEX101 and Its Related Molecules in Spermatogenesis

Glycosylphosphatidylinositol (GPI)-anchored proteins (APs) on the plasma membrane are involved in several cellular processes, including sperm functions. Thus far, several GPI-APs have been identified in the testicular germ cells, and there is increasing evidence of their biological significance during fertilization. Among GPI-APs identified in the testis, this review focuses on TEX101, a germ cell-specific GPI-AP that belongs to the lymphocyte antigen 6/urokinase-type plasminogen activator receptor superfamily. This molecule was originally identified as a glycoprotein that contained the antigen epitope for a specific monoclonal antibody; it was produced by immunizing female mice with an allogenic testicular homogenate. This review mainly describes the current understanding of the biochemical, morphological, and physiological characteristics of TEX101. Furthermore, future avenues for the investigation of testicular GPI-Aps, including their potential role as regulators of ion channels, are discussed.

Tamrintamab pamozirine (SC-003) in patients with platinum-resistant/refractory ovarian cancer: Findings of a phase 1 study

OBJECTIVE

Epithelial ovarian carcinoma (EOC) is diagnosed at advanced stage in the majority of women and, despite being initially chemosensitive, eventually recurs and develops resistance to known therapies. SC-003 is a pyrrolobenzodiazepine-based antibody-drug conjugate targeting dipeptidase 3 (DPEP3), a membrane-bound dipeptidase associated with tumor-initiating cells in patient-derived EOC xenograft models. This first-in-human phase 1a/1b study evaluated the safety/tolerability, pharmacokinetics, and preliminary antitumor activity of SC-003 alone or in combination with budigalimab (formerly ABBV-181), an antibody targeting PD-1, in patients with platinum-resistant/refractory EOC (NCT02539719).

METHODS

Patients received SC-003 at 1 of 6 dose levels (0.025-0.4 mg/kg) every 3 weeks (Q3W), utilizing a standard 3 + 3 design (dose-limiting toxicity [DLT] period: 21 days). Patients with DPEP3-positive tumors were enrolled in the dose-expansion phase of the study and treated with SC-003 monotherapy or in combination with budigalimab.

RESULTS

Seventy-four patients (n = 29, dose escalation; n = 45, dose expansion; n = 3 budigalimab combination) were enrolled and received ≥1 dose of study drug. One DLT occurred (grade 3 ileus) but was considered unrelated to study drug. The MTD for the Q3W schedule was 0.3 mg/kg and the SC-003 doses selected for the dose-expansion phase of the study were 0.3 mg/kg and 0.2 mg/kg. The most common treatment-emergent adverse events were fatigue, nausea, decreased appetite, pleural effusion, abdominal pain, and peripheral edema. The overall response rate was low (4%), and responses were not durable. Post-hoc examination of antitumor activity suggested a higher response rate in patients with higher DPEP3 expression.

CONCLUSIONS

SC-003 lacked the requisite safety profile and antitumor activity to warrant further development.

The mercapturic acid pathway

The mercapturic acid pathway is a major route for the biotransformation of xenobiotic and endobiotic electrophilic compounds and their metabolites. Mercapturic acids (N-acetyl-l-cysteine S-conjugates) are formed by the sequential action of the glutathione transferases, γ-glutamyltransferases, dipeptidases, and cysteine S-conjugate N-acetyltransferase to yield glutathione S-conjugates, l-cysteinylglycine S-conjugates, l-cysteine S-conjugates, and mercapturic acids; these metabolites constitute a "mercapturomic" profile. Aminoacylases catalyze the hydrolysis of mercapturic acids to form cysteine S-conjugates. Several renal transport systems facilitate the urinary elimination of mercapturic acids; urinary mercapturic acids may serve as biomarkers for exposure to chemicals. Although mercapturic acid formation and elimination is a detoxication reaction, l-cysteine S-conjugates may undergo bioactivation by cysteine S-conjugate β-lyase. Moreover, some l-cysteine S-conjugates, particularly l-cysteinyl-leukotrienes, exert significant pathophysiological effects. Finally, some enzymes of the mercapturic acid pathway are described as the so-called "moonlighting proteins," catalytic proteins that exert multiple biochemical or biophysical functions apart from catalysis.

Dark side of the epididymis: tails of sperm maturation

BACKGROUND

The Hermes body (HB) previously called the cytoplasmic droplet is a focal distension of the flagellar cytoplasm of epididymal spermatozoa consisting mainly of isolated flattened Golgi cisternae.

OBJECTIVE

To define a functional role for the HB of epididymal spermatozoa.

METHODS

Isolated fractions of HBs of epididymal spermatozoa were prepared and by quantitative tandem mass spectrometry revealed 1511 proteins.

RESULTS

The glucose transporter GLUT-3 was the most abundant protein followed by hexokinase 1, which along with the presence of all glycolytic enzymes suggested a role for the HB in glycolysis. Several TMED/p24 Golgi trafficking proteins were abundant with TMED7/p27 and TMED2/p24 defining the identity of the flattened cisternae within the HB as Golgi, along with the known Golgi proteins, GBF1, GOLPH3, Man2α1, and ManIIX. The Golgi trafficking protein TMED7/p27 via small 50-nm vesicles emanating from the Golgi cisternae was proposed to transport GLUT-3 to the plasma membrane for ATP production related to sperm motility. The internal membranes revealed abundant proteins not only of Golgi cisternae, but also of endoplasmic reticulum and endosomes. COPI and COPII coats, clathrin, SNAREs, annexins, atlastins, and GTPases were identified for vesicular trafficking and membrane fusion, in addition to ribosomes, stress proteins for protection, proteasome proteins involved in degradation, and cytoskeletal elements for migration of the HB along the flagellum. The biogenesis of the HB occurring at step 19 spermatids of the testis just prior to their release was uncovered as a key step in germ cell differentiation, where several proteins were expressed, some for the first time.

CONCLUSION

As epididymal spermatozoa undergo remodeling of their protein makeup through selective degradation of sperm proteins during epididymal transit, then remodeling as a consequence of new protein synthesis is not excluded by our observations.

Identification of TEX101-associated Proteins Through Proteomic Measurement of Human Spermatozoa Homozygous for the Missense Variant rs35033974

TEX101 is a germ-cell-specific protein and a validated biomarker of male infertility. Mouse TEX101 was found essential for male fertility and was suggested to function as a cell surface chaperone involved in maturation of proteins required for sperm migration and sperm-oocyte interaction. However, the precise functional role of human TEX101 is not known and cannot be studied in vitro due to the lack of human germ cell lines. Here, we genotyped 386 men for a common missense variant rs35033974 of TEX101 and identified 52 heterozygous and 4 homozygous men. We then discovered by targeted proteomics that the variant allele rs35033974 was associated with the near-complete degradation (>97%) of the corresponding G99V TEX101 form and suggested that spermatozoa of homozygous men could serve as a knockdown model to study TEX101 function in humans. Differential proteomic profiling with label-free quantification measured 8,046 proteins in spermatozoa of eight men and identified eight cell-surface and nine secreted testis-specific proteins significantly down-regulated in four patients homozygous for rs35033974. Substantially reduced levels of testis-specific cell-surface proteins potentially involved in sperm migration and sperm-oocyte interaction (including LY6K and ADAM29) were confirmed by targeted proteomics and Western blotting assays. Because recent population-scale genomic data revealed homozygous fathers with biological children, rs35033974 is not a monogenic factor of male infertility in humans. However, median TEX101 levels in seminal plasma were found fivefold lower (p = 0.0005) in heterozygous than in wild-type men of European ancestry. We conclude that spermatozoa of rs35033974 homozygous men have substantially reduced levels of TEX101 and could be used as a model to elucidate the precise TEX101 function, which will advance biology of human reproduction.

Alterations in oxidative responses and post-translational modification caused by p,p´-DDE in Mus spretus testes reveal Cys oxidation status in proteins related to cell-redox homeostasis and male fertility

The major derivate of DDT, 1,1-dichloro-2,2-bis (p-chlorophenyl) ethylene (p,p´-DDE), is a persistent pollutant previously associated with oxidative stress. Additionally, p,p´-DDE has been linked to several metabolic alterations related to sexual function in rodents. In this study, we analysed the effects of a non-lethal p,p´-DDE dose to Mus spretus mice in testes, focusing on oxidative damage to biomolecules, defence mechanisms against oxidative stress and post-translational protein modifications. No increase in lipid or DNA oxidation was observed, although antioxidative enzymatic defences and redox status of glutathione were altered in several ways. Global protein carbonylation and phosphorylation were significantly reduced in testes from p,p´-DDE-exposed mice; however, the total redox state of Cys thiols did not exhibit a defined pattern. We analysed the reversible redox state of specific Cys residues in detail with differential isotopic labelling and a shotgun labelling-based MS/MS proteomic approach for identification and quantification of altered peptides. Our results show that Cys residues are significantly affected by p,p´-DDE in several proteins related to oxidative stress and/or male fertility, particularly those participating in fertilization, sperm capacitation and blood coagulation. These molecular changes could explain the sexual abnormalities previously described in p,p´-DDE exposed organisms.

Discovery of a Human Testis-specific Protein Complex TEX101-DPEP3 and Selection of Its Disrupting Antibodies

TEX101 is a testis-specific protein expressed exclusively in male germ cells and is a validated biomarker of male infertility. Studies in mice suggest that TEX101 is a cell-surface chaperone which regulates, through protein-protein interactions, the maturation of proteins involved in spermatozoa transit and oocyte binding. Male TEX101-null mice are sterile. Here, we identified by co-immunoprecipitation-mass spectrometry the interactome of human TEX101 in testicular tissues and spermatozoa. The testis-specific cell-surface dipeptidase 3 (DPEP3) emerged as the top hit. We further validated the TEX101-DPEP3 complex by using hybrid immunoassays. Combinations of antibodies recognizing different epitopes of TEX101 and DPEP3 facilitated development of a simple immunoassay to screen for disruptors of TEX101-DPEP3 complex. As a proof-of-a-concept, we demonstrated that anti-TEX101 antibody T4 disrupted the native TEX101-DPEP3 complex. Disrupting antibodies may be used to study the human TEX101-DPEP3 complex, and to develop modulators for male fertility.

Compartmentalization of membrane trafficking, glucose transport, glycolysis, actin, tubulin and the proteasome in the cytoplasmic droplet/Hermes body of epididymal sperm

Discovered in 1909 by Retzius and described mainly by morphology, the cytoplasmic droplet of sperm (renamed here the Hermes body) is conserved among all mammalian species but largely undefined at the molecular level. Tandem mass spectrometry of the isolated Hermes body from rat epididymal sperm characterized 1511 proteins, 43 of which were localized to the structure in situ by light microscopy and two by quantitative electron microscopy localization. Glucose transporter 3 (GLUT-3) glycolytic enzymes, selected membrane traffic and cytoskeletal proteins were highly abundant and concentrated in the Hermes body. By electron microscope gold antibody labelling, the Golgi trafficking protein TMED7/p27 localized to unstacked flattened cisternae of the Hermes body, as did GLUT-3, the most abundant protein. Its biogenesis was deduced through the mapping of protein expression for all 43 proteins during male germ cell differentiation in the testis. It is at the terminal step 19 of spermiogenesis that the 43 characteristic proteins accumulated in the nascent Hermes body.

Transcriptome analysis of highly purified mouse spermatogenic cell populations: gene expression signatures switch from meiotic-to postmeiotic-related processes at pachytene stage

Background

Spermatogenesis is a complex differentiation process that involves the successive and simultaneous execution of three different gene expression programs: mitotic proliferation of spermatogonia, meiosis, and spermiogenesis. Testicular cell heterogeneity has hindered its molecular analyses. Moreover, the characterization of short, poorly represented cell stages such as initial meiotic prophase ones (leptotene and zygotene) has remained elusive, despite their crucial importance for understanding the fundamentals of meiosis.

Results

We have developed a flow cytometry-based approach for obtaining highly pure stage-specific spermatogenic cell populations, including early meiotic prophase. Here we combined this methodology with next generation sequencing, which enabled the analysis of meiotic and postmeiotic gene expression signatures in mouse with unprecedented reliability. Interestingly, we found that a considerable number of genes involved in early as well as late meiotic processes are already on at early meiotic prophase, with a high proportion of them being expressed only for the short time lapse of lepto-zygotene stages. Besides, we observed a massive change in gene expression patterns during medium meiotic prophase (pachytene) when mostly genes related to spermiogenesis and sperm function are already turned on. This indicates that the transcriptional switch from meiosis to post-meiosis takes place very early, during meiotic prophase, thus disclosing a higher incidence of post-transcriptional regulation in spermatogenesis than previously reported. Moreover, we found that a good proportion of the differential gene expression in spermiogenesis corresponds to up-regulation of genes whose expression starts earlier, at pachytene stage; this includes transition protein-and protamine-coding genes, which have long been claimed to switch on during spermiogenesis. In addition, our results afford new insights concerning X chromosome meiotic inactivation and reactivation.

Conclusions

This work provides for the first time an overview of the time course for the massive onset and turning off of the meiotic and spermiogenic genetic programs. Importantly, our data represent a highly reliable information set about gene expression in pure testicular cell populations including early meiotic prophase, for further data mining towards the elucidation of the molecular bases of male reproduction in mammals.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2618-1) contains supplementary material, which is available to authorized users.

TEX101, a glycoprotein essential for sperm fertility, is required for stable expression of Ly6k on testicular germ cells

TEX101, a germ cell-specific glycosyl-phosphatidylinositol (GPI)-anchored glycoprotein, is associated with Ly6k during spermatogenesis in testis. Although both Tex101^−/− and Ly6k^−/− mice can produce morphologically intact spermatozoa, both knockout mice show an infertile phenotype due to a disorder of spermatozoa to migrate into the oviduct. Since Ly6k specifically interacts with TEX101, complex formation of TEX101/Ly6k appears to be potentially important for functional sperm production. This study evaluated the fate of Ly6k in the presence or absence of TEX101 to explore the molecular interaction of both GPI-anchored proteins in seminiferous tubules. The present study showed that: 1) Although Ly6k mRNA was detected, the protein was present at very low levels in mature testes of Tex101^−/− mice, 2) Ly6k mRNA level was within the normal range in Tex101^−/− mice, 3) Ly6k mRNA was translated into a polypeptide in the testes of Tex101^+/+ and Tex101^−/− mice, and 4) TEX101, as well as Ly6k, are co-factors that affect to molecular expression. These results indicate that both TEX101 and Ly6k contribute to the post-translational counterpart protein expression at the cell membrane. This mechanism may be important in maintaining the production of fertile spermatozoa during spermatogenesis.

Chemical Characterization of N-Linked Oligosaccharide As the Antigen Epitope Recognized by an Anti-Sperm Auto-Monoclonal Antibody, Ts4

Ts4, an anti-sperm auto-monoclonal antibody, possesses immunoreactivity to the acrosomal region of mouse epididymal spermatozoa. In addition, the mAb shows specific immunoreactivity to reproduction-related regions such as testicular germ cells and early embryo. Our qualitative study previously showed that the antigen epitope for Ts4 contained a N-linked common oligosaccharide (OS) chain on testicular glycoproteins as determined by Western blotting for testicular glycoproteins after treatment with several glycohydrolases. Since the distribution of the Ts4-epitope is unique, the OS chain in Ts4-epitope may have role(s) in the reproductive process. The aim of this study was to clarify the molecular structure of the Ts4-epitope, particularly its OS moiety. Using Ts4 immunoprecipitation combined with liquid chromatography and multiple-stage mass spectrometry, the candidate carbohydrate structure in the Ts4-epitope is proposed to be N-linked fucosylated agalacto-biantennary with bisecting N-acetylglucosamine (GlcNAc) or with N-acetylgalactosamine-GlcNAc motif. Further binding analyses using various lectins against the mouse testicular Ts4-immunoprecipitants revealed that Phaseolus vulgaris erythroagglutinin and Pisum sativum agglutinin showed positive staining of the bands corresponding to Ts4 reactive proteins. Moreover, the immunoreactivity of Ts4 against the testicular extract was completely abrogated after digestion with β-N-acetylglucosaminidase. These results show that the Ts4-epitope contains agalacto-biantennary N-glycan with bisecting GlcNAc carrying fucose residues.

Identification and Characterization of TEX101 in Bovine Epididymal Spermatozoa

Several studies exhibit the presence of Ricinus Communis Agglutinin I (RCA) binding glycocalyx in mammalian spermatozoa. However, the molecular characterization of RCA binding glycocalyx in sperm membranes and its mechanism of action are poorly understood. The objective of the study was to identify and to characterize RCA binding glycoprotein of the bovine sperm plasma membranes (PM). Lectin blots of caput and cauda sperm PM revealed a 38 kDa polypeptide exhibiting the highest affinity to RCA among the several major RCA binding polypeptides. The 38 kDa RCA binding polypeptide of cauda sperm PM was purified and exhibited a charge train of three distinct spots with isoelectric points (pH 5.3 and 5.8). Proteomic identification yielded ten peptides that matched the sequence of Testis Expressed 101 protein (TEX101). Western blots data revealed that bovine sperm TEX101 is present in both testicular and epididymal sperm PM fractions. The native TEX101 polypeptide contains ~17 kDa N-linked oligosaccharides and the polypeptide is anchored to sperm membrane via a glycosylphosphatidylinositol lipid linkage. Immunofluorescence staining of sperm with anti-TEX101 demonstrated that the polypeptide is localized at the head of cauda sperm. Our biochemical results provide evidence on the presence of TEX101 in bovine epididymal sperm plasma membranes and may have a potential role in sperm-egg interaction.