Cancer-associated changes in glycosylation of fibronectin

Consequences of platelet-educated cancer cells on the expression of inflammatory and metastatic glycoproteins

Cancer-associated thrombosis, a major cause of mortality in cancer patients, exhibits a 4 to 7 times higher incidence compared to the general population. Platelet activation by tumor cells contributes to this pro-thrombotic state. Cancer cell-educated platelets have also been described to be implicated in promoting metastasis. Intriguingly, our team, among others, unveils a reverse process, wherein platelets educate cancer cells by transferring lipids, RNAs, and proteins. Here, focusing on colorectal and pancreatic cancers, our study investigates genes and proteins mediating platelet education of cancer cells. We demonstrated, for the first time, that platelets can educate cancer cells by inducing changes in the transcription of genes related to glycosylation, inflammation, and metastasis in cancer cells themselves. These results indicate a direct impact of platelets on cancer cell phenotype. This novel insight suggests potential therapeutic avenues for cancer treatment, disrupting platelet-mediated alterations and influencing the course of cancer progression.

Bittersweet Sugars: How Unusual Glycan Structures May Connect Epithelial-to-Mesenchymal Transition and Multidrug Resistance in Cancer

Cancer cells are characterized by metabolic reprogramming, which enables their survival in of-ten inhospitable conditions. A very well-documented example that has gained attraction in re-cent years and is already considered a hallmark of transformed cells is the reprogramming of carbohydrate metabolism. Such a feature, in association with the differential expression of en-zymes involved in the biosynthesis of glycoconjugates, generically known as glycosyltransfer-ases, contributes to the expression of structurally atypical glycans when compared to those ex-pressed in healthy tissues. The latest studies have demonstrated that glycophenotypic alterations are capable of modulating multifactorial events essential for the development and/or progres-sion of the disease. Herein, we will address the importance of glycobiology in modern medi-cine, focusing on the ability of unusual/truncated O-linked glycans to modulate two complex and essential phenomena for cancer progression: the acquisition of the multidrug resistance (MDR) phenotype and the activation of molecular pathways associated with the epithelial-mesenchymal transition (EMT) process, an event deeply linked with cancer metastasis.

The Blessed Union of Glycobiology and Immunology: A Marriage That Worked

In this article, we discuss the main aspects regarding the recognition of cell surface glycoconjugates and the immunomodulation of responses against the progression of certain pathologies, such as cancer and infectious diseases. In the first part, we talk about different aspects of glycoconjugates and delve deeper into the importance of N-glycans in cancer immunotherapy. Then, we describe two important lectin families that have been very well studied in the last 20 years. Examples include the sialic acid-binding immunoglobulin (Ig)-like lectins (siglecs), and galectins. Finally, we discuss a topic that needs to be better addressed in the field of glycoimmunology: the impact of oncofetal antigens on the cells of the immune system. New findings in this area are of great importance for advancement, especially in the field of oncology, since it is already known that cellular interactions mediated by carbohydrate-carbohydrate and/or carbohydrate proteins are able to modulate the progression of different types of cancer in events that compromise the functionality of the immune responses.

Invasion-Associated Reorganization of Laminin 332 in Oral Squamous Cell Carcinomas: The Role of the Laminin γ2 Chain in Tumor Biology, Diagnosis, and Therapy

Invasion of the connective tissue by carcinoma cells is accompanied by disintegration and reorganization of the hemidesmosomes, which connect the basement membrane to the basal epithelial cells. In terms of mediating the basement membrane, i.e., basal cell interactions, the heterotrimeric laminin 332 is the most important bridging molecule. Due to this distinct function, laminin 332, especially its gamma 2 chain, came into the focus of cancer research. Specific de novo synthesis and deposition patterns of laminin 332 are evident upon development and progression of oral squamous cell carcinomas (OSCCs). Loss from the basement membrane, cytoplasmic accumulation, and extracellular deposition are associated with crucial processes such as stromal activation and immune response, epithelial to mesenchymal transition, and tumor cell budding. In networks with components of the tumor microenvironment, altered expression of laminin 332 chains, proteolytic processing, and interaction with integrin receptors seem to promote cancer cell migration. Indeed, reorganization patterns are shown to have a high diagnostic and prognostic value. Here, we summarize the current knowledge on laminin 332 reorganization in OSCCs with special focus on its gamma 2 chain and provide, based on the current literature, evidence on its promising role as a grading and monitoring parameter and as a potential therapeutic target.

Glycan-directed CAR-T cells

Cancer immunotherapy is rapidly advancing in the treatment of a variety of hematopoietic cancers, including pediatric acute lymphoblastic leukemia and diffuse large B cell lymphoma, with chimeric antigen receptor (CAR)-T cells. CARs are genetically encoded artificial T cell receptors that combine the antigen specificity of an antibody with the machinery of T cell activation. However, implementation of CAR technology in the treatment of solid tumors has been progressing much slower. Solid tumors are characterized by a number of challenges that need to be overcome, including cellular heterogeneity, immunosuppressive tumor microenvironment (TME), and, in particular, few known cancer-specific targets. Post-translational modifications that differentially occur in malignant cells generate valid cell surface, cancer-specific targets for CAR-T cells. We previously demonstrated that CAR-T cells targeting an aberrant O-glycosylation of MUC1, a common cancer marker associated with changes in cell adhesion, tumor growth and poor prognosis, could control malignant growth in mouse models. Here, we discuss the field of glycan-directed CAR-T cells and review the different classes of antibodies specific for glycan-targeting, including the generation of high affinity O-glycopeptide antibodies. Finally, we discuss historic and recently investigated glycan targets for CAR-T cells and provide our perspective on how targeting the tumor glycoproteome and/or glycome will improve CAR-T immunotherapy.

When tissue antigens and antibodies get along: revisiting the technical aspects of immunohistochemistry--the red, brown, and blue technique

Once focused mainly on the characterization of neoplasms, immunohistochemistry (IHC) today is used in the investigation of a broad range of disease processes with applications in diagnosis, prognostication, therapeutic decisions to tailor treatment to an individual patient, and investigations into the pathogenesis of disease. This review addresses the technical aspects of immunohistochemistry (and, to a lesser extent, immunocytochemistry) with attention to the antigen-antibody reaction, optimal fixation techniques, tissue processing considerations, antigen retrieval methods, detection systems, selection and use of an autostainer, standardization and validation of IHC tests, preparation of proper tissue and reagent controls, tissue microarrays and other high-throughput systems, quality assurance/quality control measures, interpretation of the IHC reaction, and reporting of results. It is now more important than ever, with these sophisticated applications, to standardize the entire IHC process from tissue collection through interpretation and reporting to minimize variability among laboratories and to facilitate quantification and interlaboratory comparison of IHC results.

Cross-talk between the insulin-like growth factor (IGF) axis and membrane integrins to regulate cell physiology

The biology of cross-talk between activated growth factor receptors and cell-surface integrins is an area which has attracted much interest in recent years (Schwartz and Ginsberg, 2002). This review discusses the relationship between the insulin-like growth factor (IGF) axis and cell-surface integrin receptors in the regulation of various aspects of cell physiology. Key to these interactions are signals transmitted between integrins and the IGF-I receptor (IGF-IR) when either or both are bound to their cognate ligands and we will review the current state of knowledge in this area. The IGF axis comprises many molecular components and we will also discuss the potential role of these species in cross-talk with the integrin receptor. With respect to integrin ligands, we will mainly focus on the well-characterized interactions of the two extracellular matrix (ECM) glycoproteins fibronectin (FN) and vitronectin (VN) with cell-surface ligands, and, how this affects activity through the IGF axis. However, we will also highlight the importance of other integrin activation mechanisms and their impact on IGF activity.

IIICS de novo glycosylated fibronectin as a marker for invasiveness in urothelial carcinoma of the urinary bladder (UBC)

PURPOSE

The urothelial carcinoma is the most frequent malignancy of the urinary bladder (UBC). The transition into invasive growth is accompanied by several histological changes including an oncofoetal reorganization of the extracellular matrix. Recently, the occurrence of oncofoetal fibronectin with an O-linked glycosylation in the IIICS region (oncf Fn) was shown to be present in urine from UBC patients and was recommended as a tumour marker. Until now there are no data available regarding the source and distribution of oncf Fn in UBC and its value for the assessment of invasiveness.

METHODS

oncf Fn was analysed in noninvasive and invasive UBC using immunohistochemistry and western blot. Additionally, the mRNA expression of the IIICS splicing region was evaluated by quantitative real time RT-PCR.

RESULTS

Immunohistochemical results reveal a highly significant correlation of oncf Fn to invasiveness. Papillary tumours regularly show no positivity. In western blot, invasive UBC show a strongly increased amount of the 250 kDa oncf Fn. Additionally, several smaller bands could be shown suggesting a proteolytic processing of Fn. The mRNA of the IIICS region shows a 21.5-fold increase in invasive UBC compared with noninvasive carcinomas.

CONCLUSIONS

In summary, immunohistochemistry of oncf Fn is a valuable histological marker for invasiveness of urothelial carcinoma of the urinary bladder. The restricted and invasion-associated tissue distribution of immunoreactivity enables to monitor the recurrence of invasive UBC by a quantitative evaluation of IIICS O-linked glycosylated Fn in urine.

Technical aspects of immunohistochemistry

Immunohistochemistry is an integral technique in many veterinary laboratories for diagnostic and research purposes. In the last decade, the ability to detect antigens (Ags) in tissue sections has improved dramatically, mainly by countering the deleterious effects of formaldehyde with antigen retrieval (AR) and increasing sensitivity of the detection systems. In this review, I address these topics and provide an overview of technical aspects of immunohistochemistry, including those related to antibodies (Abs) and Ags, fixation, AR, detection methods, background, and troubleshooting. Microarray technology and the use of rabbit monoclonal Abs in immunohistochemistry are also discussed.

Distribution of laminin and fibronectin isoforms in oral mucosa and oral squamous cell carcinoma

The expression of laminin and fibronectin isoforms varies with cellular maturation and differentiation and these differences may well influence cellular processes such as adhesion and motility. The basement membrane (BM) of fetal oral squamous epithelium contains the laminin chains, alpha2, alpha3, alpha5, beta1, beta2, beta3, gamma1 and gamma2. The BM of adult normal oral squamous epithelium comprises the laminin chains, alpha3, alpha5, beta1, beta3, gamma1 and gamma2. A re-expression of the laminin alpha2 and beta2 chains could be shown in adult hyperproliferative, dysplastic and carcinomatous lesions. In dysplasia and oral squamous cell carcinoma (OSCC), multifocal breaks of the BM are present as indicated by laminin chain antibodies. These breaks correlate to malignancy grade in their extent. Moreover, in the invasion front the alpha3 and gamma2 chain of laminin-5 can immunohistochemically be found outside the BM within the cytoplasm of budding carcinoma cells and in the adjacent stroma. The correlation between the morphological pattern of invasive tumour clusters and a laminin-5 immunostaining in the adjacent stroma may suggest, first, that a laminin-5 deposition outside the BM is an immunohistochemical marker for invasion and second, that OSCC invasion is guided by the laminin-5 matrix. Expression of oncofetal fibronectins (IIICS de novo glycosylated fibronectin and ED-B fibronectin) could be demonstrated throughout the stromal compartment. However, the ED-B fibronectin synthesizing cells (RNA/RNA in situ hybridization) are confined to small stroma areas and to single stroma and inflammatory cells in the invasion front. A correlation of the number of ED-B fibronectin synthesizing cells to malignancy grade could not be seen. ED-B fibronectin mRNA-positive cells seem to be concentrated in areas of fibrous stroma recruitment with a linear alignment of stromal fibro-/myofibroblasts (desmoplasia). Double staining experiments (ED-B fibronectin in situ hybridization and alpha-smooth muscle actin immunohistochemistry) indicated that the stroma myofibroblasts are a preferential source of ED-B fibronectin. In conclusion, in OSCC, a fetal extracellular matrix conversion is demonstrable. Tumour cells (laminin alpha2 and beta2 chain) and recruited stromal myofibroblasts (oncofetal ED-B fibronectin) contribute to the fetal extracellular matrix milieu.

Cloning and characterization of a close homologue of human UDP-N-acetyl-alpha-D-galactosamine:Polypeptide N-acetylgalactosaminyltransferase-T3, designated GalNAc-T6. Evidence for genetic but not functional redundancy

The UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase, designated GalNAc-T3, exhibits unique functions. Specific acceptor substrates are used by GalNAc-T3 and not by other GalNAc-transferases. The expression pattern of GalNAc-T3 is restricted, and loss of expression is a characteristic feature of poorly differentiated pancreatic tumors. In the present study, a sixth human UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase, designated GalNAc-T6, with high similarity to GalNAc-T3, was characterized. GalNAc-T6 exhibited high sequence similarity to GalNAc-T3 throughout the coding region, in contrast to the limited similarity that exists between homologous glycosyltransferase genes, which is usually restricted to the putative catalytic domain. The genomic organizations of GALNT3 and GALNT6 are identical with the coding regions placed in 10 exons, but the genes are localized differently at 2q31 and 12q13, respectively. Acceptor substrate specificities of GalNAc-T3 and -T6 were similar and different from other GalNAc-transferases. Northern analysis revealed distinct expression patterns, which were confirmed by immunocytology using monoclonal antibodies. In contrast to GalNAc-T3, GalNAc-T6 was expressed in WI38 fibroblast cells, indicating that GalNAc-T6 represents a candidate for synthesis of oncofetal fibronectin. The results demonstrate the existence of genetic redundancy of a polypeptide GalNAc-transferase that does not provide full functional redundancy.

An overview of the complexities and subtleties of immunohistochemistry

Immunohistochemistry has the potential to be a powerful research tool. However, immunohistochemical studies are frequently undertaken without regard to the complexities and subtleties of these useful techniques. This review aims to address the problems and limitations that are often encountered, and the procedures that should be considered in both the planning and interpretation of immunohistochemical studies. Particular reference is made to the generation of functionally different protein isoforms from a single gene by alternative splicing and post-translational modifications, primary antibody selection, the effects of tissue manipulation such as fixation and antigen retrieval, the need for appropriate controls and interpretation of staining patterns.

Identification of oncofetal fibronectin in patients with advanced epithelial ovarian cancer: detection in ascitic fluid and localization to primary sites and metastatic implants

BACKGROUND

The mechanisms by which metastatic ovarian cancer adheres to peritoneal surfaces are not well understood. A role for tumor-derived extracellular matrix adhesive molecules such as fibronectin (FN) has been proposed. Because oncofetal fibronectin (onfFN) isoforms function in the adhesion of trophoblasts and have been identified in association with several malignancies, we sought to study onfFN in patients with advanced epithelial ovarian cancer.

METHODS

Total FN was identified with the nonspecific anti-FN monoclonal antibody CAF. OnfFN was identified using the specific monoclonal antibodies FDC-6 and X18A4. These antibodies were applied to: 1) ascitic fluid from advanced epithelial ovarian cancer patients and peritoneal fluid from patients without pathologic conditions and 2) tissue sections of primary lesions and metastatic ovarian cancer implants. Comparative histologic specimens included normal ovarian tissue and small bowel implants of endometriosis.

RESULTS

When measured by sandwich enzyme-linked immunoadsorbent assay, all peritoneal fluids (32 malignant and 32 benign) contained marked quantities of total (CAF reactive) FN, although malignant ascites had higher concentrations than benign samples (173.2 +/- 36.8 microg/mL vs. 76.4 +/- 31.8 microg/mL; P = 0.001). Malignant ascites also had significantly higher levels of onfFN than benign peritoneal fluid (FDC-6: 3.4 +/- 0.6 vs. 0.9 +/- 0.2 microg/mL; and X18A4: 5.1 +/- 1.3 vs. 1.1 +/- 0.4 microg/mL; P = 0.0001). Immunohistochemical staining of malignant lesions revealed prominent localization of both CAF reactive FN and onfFN to the stroma surrounding epithelial tumor nests. More delicate fibrillar staining within tumor nests also was evident. In contrast, implants of endometriosis revealed strong stromal staining for CAF reactive FN but not for onfFN.

CONCLUSIONS

These results demonstrate the presence of onfFN in advanced ovarian malignancies. We speculate that onfFN may participate in tumor-associated peritoneal adhesive interactions.

Substrate specificities of three members of the human UDP-N-acetyl-alpha-D-galactosamine:Polypeptide N-acetylgalactosaminyltransferase family, GalNAc-T1, -T2, and -T3

Mucin-type O-glycosylation is initiated by UDP-N-acetylgalactosamine:polypeptide N-acetylgalactosaminyltransferases (GalNAc-transferases). The role each GalNAc-transferase plays in O-glycosylation is unclear. In this report we characterized the specificity and kinetic properties of three purified recombinant GalNAc-transferases. GalNAc-T1, -T2, and -T3 were expressed as soluble proteins in insect cells and purified to near homogeneity. The enzymes have distinct but partly overlapping specificities with short peptide acceptor substrates. Peptides specifically utilized by GalNAc-T2 or -T3, or preferentially by GalNAc-T1 were identified. GalNAc-T1 and -T3 showed strict donor substrate specificities for UDP-GalNAc, whereas GalNAc-T2 also utilized UDP-Gal with one peptide acceptor substrate. Glycosylation of peptides based on MUC1 tandem repeat showed that three of five potential sites in the tandem repeat were glycosylated by all three enzymes when one or five repeat peptides were analyzed. However, analysis of enzyme kinetics by capillary electrophoresis and mass spectrometry demonstrated that the three enzymes react at different rates with individual sites in the MUC1 repeat. The results demonstrate that individual GalNAc-transferases have distinct activities and the initiation of O-glycosylation in a cell is regulated by a repertoire of GalNAc-transferases.

Cell surface carbohydrates as prognostic markers in human carcinomas

Tumour development is usually associated with changes in cell surface carbohydrates. These are often divided into changes related to terminal carbohydrate structures, which include incomplete synthesis and modification of normally existing carbohydrates, and changes in the carbohydrate core structure. The latter includes chain elongation of both glycolipids and proteins, increased branching of carbohydrates in N-linked glycoproteins, and blocked synthesis of carbohydrates in O-linked mucin-like glycoproteins. In mature organisms, expression of distinct carbohydrates is restricted to specific cell types; within a given tissue, variation in expression may be related to cell maturation. Tumour-associated carbohydrate structures often reflect a certain stage of cellular development; most of these moieties are structures normally found in other adult or embryonic tissues. There is no unique tumour carbohydrate structure, since certain structures which are tumour-related in one organ may be normal constituents of other tissues. Tumour-associated carbohydrate changes have been used in the diagnosis of human cancers. Recently, however, it has been demonstrated that the expression of some carbohydrate structures is associated with prognosis. Tn, sialyl-Tn, and T are cell membrane-bound mucin-like carbohydrate structures that may be expressed in tumours due to blocked synthesis of the core carbohydrate chain of mucin-like structures. Their expression is strongly associated with prognosis in certain tumours, but the biological relationship between their expression and tumour progression is at present unknown. The blood group-related carbohydrate structures Le(x), sialyl-Le(x), ABH, and Le(y) are examples of terminal carbohydrate structures which are related to tumour prognosis. These structures are of increasing interest since they may function as adhesion molecules; adhesion of tumour cells to endothelial cells of blood vessels may be mediated by an interaction between sialosyl-Le(x) and E-selectin and studies indicate that Le(y) is related to cell motility. These findings are now the basis for tumour therapeutic experiments.

Subpopulations of fetal-like gingival fibroblasts: characterisation and potential significance for wound healing and the progression of periodontal disease

Wound healing in the adult is commonly compromised by excessive scar formation. In contrast, fetal wound healing is a regenerative process characterised by the conspicuous absence of scarring. Available evidence suggests that phenotypic differences between fetal and adult fibroblasts are important determinants of these distinct modes of tissue repair. In this context, a number of groups (including our own) have documented differences between fetal and adult fibroblasts with respect to such potentially relevant characteristics as migratory activity, motogenic response to cytokines and the synthesis of motility factors, cytokines and matrix macromolecules. The oral mucosa appears to be a privileged site in the adult in that it continues to display a fetal-like mode of wound healing. Data are presented in this review indicating that a subpopulation of gingival fibroblasts expresses several 'fetal-like' phenotypic characteristics. These observations are discussed in terms of both the continued expression of a fetal-like mode of wound healing in the oral mucosa and the possible differential involvement of distinct fibroblast subpopulations in the progression of periodontal disease.

Matrix remodelling in dilated cardiomyopathy entails the occurrence of oncofetal fibronectin molecular variants

OBJECTIVES

To investigate whether disturbance of the cellular homoeostasis and integrity of cardiomyocytes in dilated cardiomyopathy (DCM) is accompanied by alterations in cell-matrix relations as indicated by changes in the deposition of fibronectin (FN) isoforms.

DESIGN

Tissue from a case series of patients with DCM was investigated by immunohistochemistry with antibodies against FN (all variants, clone IST4), ED-A+ FN (clone IST9), ED-B+ FN (clone BC1), and oncofetal glycosylated FN (clone 5C10). The sites of de novo synthesis of FN were demonstrated by means of non-radioactive RNA in situ hybridisation (ISH) with biotinylated FN cDNA fragments as the probe.

SETTING

University hospital.

PATIENTS

Samples from 10 patients with clinical criteria and histological diagnosis of DCM and from 3 individuals with normal hearts.

INTERVENTIONS

Samples were obtained by right ventricular endomyocardial biopsy.

MAIN OUTCOME MEASURE

Distribution of oncofetal FN variants in DCM hearts.

RESULTS

Immunostaining of FN (IST4, all variants) showed a coarse interstitial network in normal and diseased myocardium. ED-A+ FN was deposited as fine interstitial spots in normal myocardium and in DCM samples. Immunostaining for oncofetal glycosylated FN and ED-B+ FN was not seen in normal adult myocardium, whereas myocardium from DCM patients showed focal and delicate staining in the interstitium. RNA ISH showed that these deposits resulted from local FN synthesis.

CONCLUSION

The results accord with de novo expression of oncofetal FN variants in hearts from patients with DCM. The oncofetal FN variants may serve as disease markers in myocardium affected by DCM.

Differential expression of fibronectin splice variants, oncofetal glycosylated fibronectin and laminin isoforms in nodular palmar fibromatosis

The tissue formation process in nodular palmar fibromatosis (Morbus Dupuytren) was investigated by the demonstration of fibronectin splice variants (ED-A and ED-B fibronectin), de novo glycosylated fibronectin and laminin isoforms (A, M, B1, B2, s chains) in association to the proliferative activity (Ki-67 antigen) and the occurrence of myofibroblast phenotype (alpha-smooth muscle actin, desmin). The proliferative noduli of the fibromatosis were characterized by a diffuse immunostaining for alpha-smooth muscle actin, and single cells positive for desmin and the Ki-67 antigen. In contrast to the surrounding aponeurosis as extracellular matrix, components of the whole proliferative noduli were defined: ED-A, ED-B and de novo glycosylated fibronectin, B1 and B2 laminin chain, tenascin and collagen type IV. The demonstration of the A and M laminin chain was restricted to a few cells of the proliferative noduli. S laminin could be visualized in the majority of palmar aponeurotic fibroblasts. As revealed by mRNA, in situ hybridization a de novo synthesis of fibronectin could only be detected within proliferative noduli. There is a positive correlation between the myofibroblast phenotype formation, cellular proliferation and the occurrence of ED-A and ED-B containing fibronectin, as well as de novo glycosylated fibronectin in Dupuytren's disease. The ultrastructural irregularities of myofibroblastic basal lamina and the heterogeneity of the myofibroblast phenotype are equivalent to the variability of laminin isoform immunostaining.

Monoclonal antibody X18A4 identifies an oncofetal fibronectin epitope distinct from the FDC-6 binding site

OBJECTIVE

Oncofetal fibronectin reactive with antibody FDC-6 has been associated with trophoblastic implantation and chorion structural stability. Abnormal release of this fibronectin into cervical and vaginal secretions has identified patients at risk for preterm labor and delivery. The aim of this study was to determine whether trophoblast-derived oncofetal fibronectin contains other novel epitopes distinct from the FDC-6 binding site.

STUDY DESIGN

Antitrophoblast fibronectin hybridomas were generated and screened by comparative immunoassays. One specific monoclonal antibody, X18A4, was identified and compared with antibody FDC-6 by immunocytochemical and immunoblot analyses. Both antibodies were also evaluated in "sandwich"-type double monoclonal immunosorbent assays.

RESULTS

X18A4 and FDC-6 bind avidly and noncompetitively to distinct epitopes within oncofetal fibronectin. They exhibit similar immunohistochemical staining of the extracellular matrix within placental tissue, ovarian epithelial tumors, and cultured trophoblasts. However, in contrast to FDC-6, X18A4 has no detectable binding activity to human plasma fibronectin, and its binding to oncofetal fibronectin was unaffected by enzymatic deglycosylation. Immunoblot analyses of oncofetal fibronectin proteolytic digests suggest that X18A4 binds near or within the alternatively spliced type III connecting segment domain.

CONCLUSIONS

X18A4 identifies and binds with high affinity to a new epitope within oncofetal fibronectin, distinct from the FDC-6 binding site. Because X18A4 displays no detectable binding to plasma fibronectin, it could be used as an important adjunctive antibody for enhancing the specificity of clinically based oncofetal fibronectin diagnostic assays.

Simple mucin-type carbohydrate antigens (T, Tn and sialosyl-Tn) in mucoepidermoid carcinoma of the salivary glands

Thirty-two cases of mucoepidermoid carcinoma of the salivary glands were studied in order to characterize the expression of simple mucin-type carbohydrate antigens T, Tn and sialosyl-Tn and to evaluate its implication for tumour histogenesis. Monoclonal antibodies of known specificity were used on formalin-fixed, paraffin-embedded tissue, and the expression of these antigens was studied in each of the three cell types (mucous, intermediate and squamous) as well as in the secretory content of neoplastic lumina. Aberrant glycosylation of simple-mucin type antigens was found in all cell types, as compared with that of normal excretory duct cells of the salivary glands. The more 'primitive' antigens Tn and sialosyl-Tn were present in a high percentage of epidermoid and intermediate cells. Mucous cells and the intraluminal secretory content also expressed Tn in 57.7% of the cases. This contrasts with the absence of secretion of these simple mucin type carbohydrates by normal salivary gland cells. Mucin-producing cells did not express T antigen but only sialosyl-T, in contrast to 57.1% and 56.3% respectively of the epidermoid and intermediate cell types. T and sialosyl-T were also found in the secretory products of the neoplastic lumina in 11.5% and 53.6% of the cases, respectively. The distinctive glycosylation pattern between mucin-producing cells on the one hand and intermediate and squamous cells on the other does not contradict the common origin of the three cell types from the reserve cell of the salivary excretory duct, but favours the proposition that intermediate cells constitute a step in the differentiation pathway of epidermoid, but not of mucin-producing, cells.

Synthetic immunochemistry of glycohexapeptide analogues characteristic of oncofetal fibronectin. Solid-phase synthesis and antigenic activity

Monoclonal antibody FDC-6, and its second-generation antibodies FDB-1 and FDB-4, are able to distinguish between fibronectin (FN) from fetal or cancer tissue (onco-FN) vs. FN from normal adult tissue and plasma (nor-FN). The epitope structure recognized by the above antibodies is the glycohexapeptide H-Val-(GalNAc-alpha)Thr-His-Pro-Gly-Tyr-OH (P2). In order to define further the specificity of the reactive site, we synthesized various glycopeptides based on the unglycosylated hexapeptide sequence (P1) and compared their reactivities with these antibodies. In continuation of our structure-activity relationship studies the (Asn3,Ala5)-glycohexapeptide analogue (P3) was synthesized by a solid-phase procedure. The [Ala(CN)3,Ala5]-glycopeptide (P4), owing to dehydration of the asparagine side chain amide during carboxyl activation of Fmoc-Asn-OH, was also isolated. Fmoc-[GalNAc(Ac)3-alpha]Thr-OH was used for incorporating the glycosylated amino acid residue. For the sake of comparison the epitope P2 and the hexapeptide sequence P1 were also synthesized. The final products were characterized by elemental and amino acid analyses, optical rotation, analytical HPLC, proton NMR and fast-atom bombardment mass spectroscopy. Synthetic analogues were applied to inhibit onco-FN specific MAbs FDB-1, FDB-4 and FDC-6 binding to immobilized onco-FN, and their activities were compared with onco-FN and nor-FN. P2 exhibited an activity similar to that of an intact molecule of onco-FN. Deglycosylation (P1) or replacement of amino acid (P3, P4) greatly reduced activity. Data clearly showed that P2 was the minimal essential structure of the epitope in onco-FN defined by MAbs FDB-1, FDB-4 and FDC-6.(ABSTRACT TRUNCATED AT 250 WORDS)