Sialyl-Tn antigen expression and O-linked GalNAc-Thr synthesis by Trypanosoma cruzi

Trypanosoma cruzi, Chagas disease and cancer: putting together the pieces of a complex puzzle

Considering the extensive and widespread impact on individuals, cancer can presently be categorized as a pandemic. In many instances, the development of tumors has been linked to endemic microbe infections. Among parasitic infections, Trypanosoma cruzi stands out as one of the most extensively discussed protozoans in the literature that explores the association between diseases of parasite origin and cancer. However, the effective association remains an unsolved paradox. Both the parasite, along with protozoan-derived molecules, and the associated antiparasitic immune response can induce alterations in various host cell pathways, leading to modifications in cell cycle, metabolism, glycosylation, DNA mutations, or changes in neuronal signaling. Furthermore, the presence of the parasite can trigger cell death or a senescent phenotype and modulate the immune system, the metastatic cascade, and the formation of new blood vessels. The interaction among the parasite (and its molecules), the host, and cancer undoubtedly encompasses various mechanisms that operate differentially depending on the context. Remarkably, contrary to expectations, the evidence tilts the balance toward inhibiting tumor growth or resisting tumor development. This effect is primarily observed in malignant cells, rather than normal cells, indicating a selective or specific component. Nevertheless, nonspecific bystander mechanisms, such as T. cruzi's adjuvancy or the presence of proinflammatory cytokines, may also play a significant role in this phenomenon. This work aims to elucidate this complex scenario by synthesizing the main findings presented in the literature and by proposing new questions and answers, thereby adding pieces to this challenging puzzle.

Role of a 49 kDa Trypanosoma cruzi Mucin-Associated Surface Protein (MASP49) during the Infection Process and Identification of a Mammalian Cell Surface Receptor

Trypanosoma cruzi is the etiologic agent of Chagas disease, a parasitic disease of great medical importance on the American continent. Trypomastigote infection's initial step in a mammalian host is vital for the parasite's life cycle. A trypomastigote's surface presents many molecules, some of which have been proposed to be involved in the infection process, including a glycoprotein family called mucin-associated surface proteins (MASPs). This work describes a 49-kDa molecule (MASP49) that belongs to this family and is expressed mainly on the surfaces of amastigotes and trypomastigotes but can be found in extracts and the membrane-enriched fractions of epimastigotes. This protein is partially GPI-anchored to the surface and has a role during the internalization process, since its blockade with specific antibodies decreases parasite entry into Vero cells by 62%. This work shows that MASP49 binds to peritoneal macrophages and rat cardiomyocytes, undergoes glycosylation via galactose N-acetylgalactosamine, and can attach to the macrophage murine C-type lectin receptor (mMGL). These results suggest that MASP49 can be considered a virulence factor in T. cruzi, and a better understanding of its role in the infection process is necessary.

Targeting Tumor Glycans for Cancer Therapy: Successes, Limitations, and Perspectives

Simple Summary

Aberrant glycosylation is a common feature of many cancers, and it plays crucial roles in tumor development and biology. Cancer progression can be regulated by several physiopathological processes controlled by glycosylation, such as cell–cell adhesion, cell–matrix interaction, epithelial-to-mesenchymal transition, tumor proliferation, invasion, and metastasis. Different mechanisms of aberrant glycosylation lead to the formation of tumor-associated carbohydrate antigens (TACAs), which are suitable for selective cancer targeting, as well as novel antitumor immunotherapy approaches. This review summarizes the strategies developed in cancer immunotherapy targeting TACAs, analyzing molecular and cellular mechanisms and state-of-the-art methods in clinical oncology.

Abstract

Aberrant glycosylation is a hallmark of cancer and can lead to changes that influence tumor behavior. Glycans can serve as a source of novel clinical biomarker developments, providing a set of specific targets for therapeutic intervention. Different mechanisms of aberrant glycosylation lead to the formation of tumor-associated carbohydrate antigens (TACAs) suitable for selective cancer-targeting therapy. The best characterized TACAs are truncated O-glycans (Tn, TF, and sialyl-Tn antigens), gangliosides (GD2, GD3, GM2, GM3, fucosyl-GM1), globo-serie glycans (Globo-H, SSEA-3, SSEA-4), Lewis antigens, and polysialic acid. In this review, we analyze strategies for cancer immunotherapy targeting TACAs, including different antibody developments, the production of vaccines, and the generation of CAR-T cells. Some approaches have been approved for clinical use, such as anti-GD2 antibodies. Moreover, in terms of the antitumor mechanisms against different TACAs, we show results of selected clinical trials, considering the horizons that have opened up as a result of recent developments in technologies used for cancer control.

UDP-N-acetyl-α-D-galactosamine:polypeptide N-acetylgalactosaminyltransferase from the snail Biomphalaria glabrata - structural reflections

UDP-GalNAc:polypeptide GalNAc transferase (ppGalNAcT; EC 2.4.1.41) is the initiating enzyme for mucin-type O-glycosylation in animals. Members of this highly conserved glycosyltransferase family catalyse a single glycosidic linkage. They transfer an N-acetylgalactosamine (GalNAc) residue from an activated donor (UDP-GalNAc) to a serine or threonine of an acceptor polypeptide chain. A ppGalNAcT from the freshwater snail Biomphalaria glabrata is the only characterised member of this enzyme family from mollusc origin. In this work, we interpret previously published experimental characterization of this enzyme in the context of in silico models of the enzyme and its acceptor substrates. A homology model of the mollusc ppGalNAcT is created and various substrate peptides are modelled into the active site. We hypothesize about possible molecular interpretations of the available experimental data and offer potential explanations for observed substrate and cofactor specificity. Here, we review and synthesise the current knowledge of Bge-ppGalNAcT, supported by a molecular interpretation of the available data.

Infectious Agents in Childhood Leukemia

Acute leukemia is the most common pediatric cancer, representing one-third of all cancers that occurs in under 15 year olds, with a varied incidence worldwide. Although a number of advances have increased the knowledge of leukemia pathophysiology, its etiology remains less well understood. The role of infectious agents, such as viruses, bacteria, or parasites, in the pathogenesis of leukemia has been discussed. To date, several cellular mechanisms involving infectious agents have been proposed to cause leukemia following infections. However, although leukemia can be triggered by contact with such agents, they can also be beneficial in developing immune stimulation and protection despite the risk of leukemic clones. In this review, we analyze the proposed hypotheses concerning how infectious agents may play a role in the origin and development of leukemia, as well as in a possible mechanism of protection following infections. We review reported clinical observations associated with vaccination or breastfeeding, that support hypotheses such as early life exposure and the resulting early immune stimulation that lead to protection.

Trypanosoma cruzi extracts elicit protective immune response against chemically induced colon and mammary cancers

Trypanosoma cruzi, the protozoan parasite that causes Chagas' disease, has anticancer effects mediated, at least in part, by parasite-derived products which inhibit growth of tumor cells. We investigated whether immunity to T. cruzi antigens could induce antitumor activity, using two rat models which reproduce human carcinogenesis: colon cancer induced by 1,2-dimethylhydrazine (DMH), and mammary cancer induced by N-nitroso-N-methylurea (NMU). We found that vaccination with T. cruzi epimastigote lysates strongly inhibits tumor development in both animal models. Rats immunized with T. cruzi antigens induce activation of both CD4(+) and CD8(+) T cells and splenocytes from these animals showed higher cytotoxic responses against tumors as compared to rats receiving adjuvant alone. Tumor-associated immune responses included increasing number of CD11b/c(+) His48(-) MHC II(+) cells corresponding to macrophages and/or dendritic cells, which exhibited augmented NADPH-oxidase activity. We also found that T. cruzi lysate vaccination developed antibodies specific for colon and mammary rat cancer cells, which were capable of mediating antibody-dependent cellular cytotoxicity (ADCC) in vitro. Anti-T. cruzi antibodies cross-reacted with human colon and breast cancer cell lines and recognized 41/60 (68%) colon cancer and 38/63 (60%) breast cancer samples in a series of 123 human tumors. Our results suggest that T. cruzi antigens can evoke an integrated antitumor response involving both the cellular and humoral components of the immune response and provide novel insights into the understanding of the intricate relationship between parasite infection and tumor growth.

Antibodies against mucin-based glycopeptides affect Trypanosoma cruzi cell invasion and tumor cell viability

This study describes the synthesis of glycopeptides NHAc[βGal]-(Thr)2 -[αGalNAc]-(Thr)2 -[αGlcNAc]-(Thr)2 Gly-OVA (1-OVA) and NHAc[βGal-αGalNAc]-(Thr)3 -[αLacNAc]-(Thr)3 -Gly-OVA (2-OVA) as mimetics of both T. cruzi and tumor mucin glycoproteins. These glycopeptides were obtained by solid-phase synthesis, which involved the prior preparation of the protected glycosyl amino acids αGlcNAc-ThrOH (3), αGalNAc-ThrOH (4), βGal-ThrOH (5), αLacNAc-ThrOH (6), and βGal-αGalNAc-ThrOH (7) through glycosylation reactions. Immunizations of mice with glycopeptides 1-OVA and 2-OVA induced high antibody titers (1:16 000), as verified by ELISA tests, whereas flow cytometry assays showed the capacity of the obtained anti-glycopeptides 1-OVA and 2-OVA antibodies to recognize both T. cruzi and MCF-7 tumor cells. In addition, antisera induced by glycopeptides 1-OVA and 2-OVA were also able to inhibit T. cruzi fibroblast cell invasion (70 %) and to induce antibody-mediated cellular cytotoxicity (ADCC) against MCF-7 cells, with 50 % reduction of cell viability.

Expression and characterization of the first snail-derived UDP-N-acetyl-α-D-galactosamine:polypeptide N-acetylgalactosaminyltransferase

UDP-GalNAc:polypeptide GalNAc transferase (ppGalNAcT; EC 2.4.1.41) catalyzes the first step in mucin-type O-glycosylation. To date, several members of this large enzyme family have been analyzed in detail. In this study we present cloning, expression and characterization of the first representative of this type of glycosyltransferase from mollusk origin, namely from Biomphalaria glabrata. The full length sequence of the respective gene was obtained by screening of a cDNA library using homology-based PCR. The entire gene codes for a protein consisting of 600 amino acids comprising the features of a typical type II membrane protein containing a cytoplasmic tail at the N-terminus, a transmembrane and a catalytic domain as well as a ricin-like motif at the C-terminus. Sequence comparison with ppGalNAcTs from various species revealed high similarities in terms of structural architecture. The enzyme is O-glycosylated but does not have any putative N-glycosylation sites. All four tested acceptor peptides were functional substrates, with Muc2 being the best one. Further biochemical parameters tested, confirmed a close relationship to the family of yet known ppGalNAcTs.

Module based antibody engineering: a novel synthetic REDantibody

We describe the facile generation of a stable recombinant antibody with intrinsic red fluorescent properties for qualitative and potentially quantitative immunofluorescence analysis. The REDantibody based on the X-ray crystallographic structures of the anti-sialyl-Tn antibody B72.3 and 3D model of the monomeric red fluorescent protein was designed to retain optimal spatial geometry between the C- and N-termini of the V(H) and V(L) chains respectively to mimic the domains interface pairing in antibody Fab fragments and to incorporate the red fluorescent protein as a bridging scaffold. The model was further validated by assembling a REDantibody based on CA19.9 the anti-sialylated Lewis (Le)(a) blood group antigen and 4D5-8 the anti-p185(HER2) antibodies. The chimeric heavy and light chains containing red fluorescent protein as a bridge were correctly processed and secreted into Escherichia coli periplasm for assembly and disulphide bond formation, further analysis revealed the molecules to be exclusively monomers. Purified anti-glycan proteins were used for an immunofluorescent analysis of Trypanosoma cruzi epimastigotes, and the anti-p185(HER2) used to determine the binding properties. The REDantibody platform facilitates rapid generation of scFv chimeras that could be used for screening antibodies against cell surface markers. Furthermore, such modular assembly should permit the interchange of binding sites and of fluorophores to create robust panels of coloured antibodies.

Glycopeptide-preferring polypeptide GalNAc transferase 10 (ppGalNAc T10), involved in mucin-type O-glycosylation, has a unique GalNAc-O-Ser/Thr-binding site in its catalytic domain not found in ppGalNAc T1 or T2

Mucin-type O-gly co sy la tion is initiated by a large family of UDP-GalNAc:polypeptide alpha-N-acetylgalactosaminyltransferases (ppGalNAc Ts) that transfer GalNAc from UDP-GalNAc to the Ser and Thr residues of polypeptide acceptors. Some members of the family prefer previously gly co sylated peptides (ppGalNAc T7 and T10), whereas others are inhibited by neighboring gly co sy la tion (ppGalNAc T1 and T2). Characterizing their peptide and glycopeptide substrate specificity is critical for understanding the biological role and significance of each isoform. Utilizing a series of random peptide and glycopeptide substrates, we have obtained the peptide and glycopeptide specificities of ppGalNAc T10 for comparison with ppGalNAc T1 and T2. For the glycopeptide substrates, ppGalNAc T10 exhibited a single large preference for Ser/Thr-O-GalNAc at the +1 (C-terminal) position relative to the Ser or Thr acceptor site. ppGalNAc T1 and T2 revealed no significant enhancements suggesting Ser/Thr-O-GalNAc was inhibitory at most positions for these isoforms. Against random peptide substrates, ppGalNAc T10 revealed no significant hydrophobic or hydrophilic residue enhancements, in contrast to what has been reported previously for ppGalNAc T1 and T2. Our results reveal that these transferases have unique peptide and glycopeptide preferences demonstrating their substrate diversity and their likely roles ranging from initiating transferases to filling-in transferases.

Molecular analysis of a UDP-GlcNAc:polypeptide alpha-N-acetylglucosaminyltransferase implicated in the initiation of mucin-type O-glycosylation in Trypanosoma cruzi

Trypanosoma cruzi, the causative agent of Chagas disease, is surrounded by a mucin coat that plays important functions in parasite survival/invasion and is extensively O-glycosylated by Golgi and cell surface glycosyltransferases. The addition of the first sugar, alpha-N-acetylglucosamine (GlcNAc) linked to Threonine (Thr), is catalyzed by a polypeptide alpha-GlcNAc-transferase (pp-alphaGlcNAcT) which is unstable to purification. Here, a comparison of the genomes of T. cruzi and Dictyostelium discoideum, an amoebazoan which also forms this linkage, identified two T. cruzi genes (TcOGNT1 and TcOGNT2) that might encode this activity. Though neither was able to complement the Dictyostelium gene, expression in the trypanosomatid Leishmania tarentolae resulted in elevated levels of UDP-[(3)H]GlcNAc:Thr-peptide GlcNAc-transferase activity and UDP-[(3)H]GlcNAc breakdown activity. The ectodomain of TcOGNT2 was expressed and the secreted protein was found to retain both activities after extensive purification away from other proteins and the endogenous activity. Product analysis showed that (3)H was transferred as GlcNAc to a hydroxyamino acid, and breakdown was due to hydrolysis. Both activities were specific for UDP-GlcNAc relative to UDP-GalNAc and were abolished by active site point mutations that inactivate a related Dictyostelium enzyme and distantly related animal pp-alphaGalNAcTs. The peptide preference and the alkaline pH optimum were indistinguishable from those of the native activity in T. cruzi microsomes. The results suggest that mucin-type O-glycosylation in T. cruzi is initiated by conserved members of CAZy family GT60, which is homologous to the GT27 family of animal pp-alphaGalNAcTs that initiate mucin-type O-glycosylation in animals.

Conservation of peptide acceptor preferences between Drosophila and mammalian polypeptide-GalNAc transferase ortholog pairs

UDP-GalNAc:polypeptide alpha-N-acetylgalactosaminyltrans- ferases (ppGalNAc Ts) comprise a large family of glycosyltransferases that initiate mucin-type protein O-glycosylation, transferring alpha-GalNAc to Thr and Ser residues of polypeptide acceptors. Families of ppGalNAc Ts are found across diverse eukaryotes with orthologs identifiable from mammals to single-cell organisms. The peptide substrate specificity and specific protein targets of the individual ppGalNAc T family members remain poorly understood. Previously, we reported a series of oriented random peptide substrate libraries for quantitatively determining the peptide substrate specificities of the mammalian ppGalNAc T1 and T2 (Gerken TA, Raman J, Fritz TA, Jamison O. 2006. Identification of common and unique peptide substrate preferences for the UDP-GalNAc:polypeptide alpha-N-acetylgalactosaminyltransferases T1 & T2 (ppGalNAc T1 & T2) derived from oriented random peptide substrates. J Biol Chem. 281:32403-32416). With these substrates, previously unknown features of the transferases were revealed. Utilizing these and a new lengthened set of random peptides, studies have now been performed on PGANT5 and PGANT2, the Drosophila orthologs of T1 and T2. The results from these studies suggest that the major peptide substrate determinants for these transferases are contained within 2 to 3 residues flanking the site of glycosylation. It is further found that the mammalian and fly T1 orthologs display very similar peptide substrate preferences, while the T2 orthologs are nearly indistinguishable, suggesting similar peptide preferences amongst orthologous pairs have been maintained across evolution. This conclusion is further supported by sequence homology comparisons of each of the transferase orthologs, showing that the peptide substrate and UDP binding site residues are more highly conserved between species relative to their remaining catalytic and lectin domain residues.

Characterization of the carcinoma-associated Tk antigen in helminth parasites

Expression of Tk antigen, a truncated carbohydrate antigen, was examined in helmith parasites. Using the monoclonal antibody LM389, this antigen was detected in extracts from Taenia hydatigena, Mesocestoides vogae (syn corti), and Taenia crassiceps. No reactivity was observed in Thysanosoma spp., Dipylidium caninum, Fasciola hepatica, and Nyppostrongylus brasiliensis. On the basis of their electrophoretic mobility, different patterns of Tk-bearing glycoproteins were observed among T. hydatigena, M. corti and T. crassiceps by immunoblotting, with certain components resolved as broad bands typical of mucin-like glycoproteins. Most Tk-reactive material remained in the 0.6 N perchloric acid-soluble fraction, confirming that Tk epitopes are carried by mucin-type glycoproteins. Immunohistochemical analysis revealed that in T. hydatigena, Tk antigen is mainly expressed in the tegument, whereas in M. corti the reactivity was principally observed in the subtegumental parenchyma. The presence of a novel tumor-associated carbohydrate antigen in invertebrates, contributes to strengthen the notion that truncated mucin-type O-glycosylation is a normal phenomenon in parasitic worms and may help identify new biological characteristics of helminth parasites.

Identification of common and unique peptide substrate preferences for the UDP-GalNAc:polypeptide alpha-N-acetylgalactosaminyltransferases T1 and T2 derived from oriented random peptide substrates

A large family of UDP-GalNAc:polypeptide alpha-N-acetylgalactosaminyltransferases (ppGalNAc Ts) catalyzes the first step of mucin-type protein O-glycosylation by transferring GalNAc to serine and threonine residues of acceptor polypeptides. The acceptor peptide substrate specificity and specific protein targets of the individual ppGalNAc T family members remain poorly characterized and poorly understood, despite the fact that mutations in two individual isoforms are deleterious to man and the fly. In this work a series of oriented random peptide substrate libraries, based on the GAGAXXXTXXXAGAGK sequence motif (where X = randomized positions), have been used to obtain the first comprehensive determination of the peptide substrate specificities of the mammalian ppGalNAc T1 and T2 isoforms. ppGalNAc T-glycosylated random peptides were isolated by lectin affinity chromatography, and transferase amino acid preferences were determined by Edman amino acid sequencing. The results reveal common and unique position-sensitive features for both transferases, consistent with previous reports of the preferences of ppGalNAc T1 and T2. The random peptide substrates also reveal additional specific features that have never been described before that are consistent with the x-ray crystal structures of the two transferases and furthermore are reflected in a data base analysis of in vivo O-glycosylation sites. By using the transferase-specific preferences, optimum and selective acceptor peptide substrates have been generated for each transferase. This approach represents a relatively complete, facile, and reproducible method for obtaining ppGalNAc T peptide substrate specificity. Such information will be invaluable for identifying isoform-specific peptide acceptors, creating isoform-specific substrates, and predicting O-glycosylation sites.

Tumor-derived MUC1 mucins interact with differentiating monocytes and induce IL-10highIL-12low regulatory dendritic cell

Dendritic cells (DC) initiate immunity by the activation of naive T cells and control immunity through their ability to induce unresponsiveness of lymphocytes by mechanisms that include deletion and induction of regulatory cells. An inadequate presentation to T cells by tumor-induced "regulatory" DC, among several mechanisms, can explain tolerance to tumor-associated Ags. In this study, we show that tumor-derived mucin profoundly affects the cytokine repertoire of monocyte-derived DC and switch them into IL-10(high)IL-12(low) regulatory APCs with a limited capacity to trigger protective Th1 responses. In fact, DC cocultured with pancreatic tumor cell lines in a Transwell system did not reach full maturation, had low immunostimulatory functions, did not produce IL-12, and released high levels of IL-10. The involvement of known tumor-derived immune-suppressive factors (e.g., vascular endothelial growth factor, TGF-beta, IL-6, and IL-10) was considered and excluded. We provide evidence that tumor-derived MUC1 mucins are responsible for the impaired DC maturation and function. DC obtained in the presence of tumor microenvironment preferentially polarized IL-4(+) response. Moreover, T cells primed by these regulatory DC became anergic and behaved as suppressor/regulatory cells. These findings identify mucin secretion as a novel mechanism of tumor escape from immune surveillance and provide the basis for the generation of potentially tolerogenic DC.