Cellular junctions in a spectrum of human malignant tumors

Molecular competition for NKG2D: H60 and RAE1 compete unequally for NKG2D with dominance of H60

NKG2D is a potent activating receptor on natural killer cells, T cells, and macrophages. Mouse NKG2D interacts with two cell surface ligands related to class I MHC molecules: RAE1 and H60. We used soluble versions of NKG2D, RAE1, and H60 to characterize their interactions. RAE1 and H60 each bind NKG2D with nanomolar affinities, indicating tighter binding than most cell surface immune interactions, but NKG2D binds to H60 with approximately 25-fold higher affinity than to RAE1. RAE1 and H60 compete directly for occupancy of NKG2D, and, thus, NKG2D can be occupied by only one ligand at a time. The NKG2D-H60 interaction is more temperature dependent and makes greater use of electrostatic interactions than the NKG2D-RAE1 interaction. The distinct thermodynamic profiles provide insights into the different molecular mechanisms of the binding interactions.

Perturbation of the tight junction permeability barrier by occludin loop peptides activates beta-catenin/TCF/LEF-mediated transcription

Here we show that interference with the integrity of the transepithelial permeability barrier of mouse mammary epithelial cells by treatment with synthetic peptides, homologous to the second extracellular domain of occludin, decreased the amount of occludin protein present at tight junctions and led to the formation of multilayered, unpolarized cell clusters. In addition, transcription of the adherens junction protein beta-catenin was induced. Following accumulation of soluble beta-catenin protein, transcription by beta-catenin/TCF/LEF was increased, as revealed by transcriptional assays following transient transfection of the reporter construct. Furthermore, treatment with occludin-II peptides up-regulated RNA levels of the known beta-catenin/TCF/LEF downstream target gene c-myc. The data presented imply a functional cross-talk between tight and adherens junctions that possibly contributes to the stepwise transformation during oncogenesis.

The roles of claudin superfamily proteins in paracellular transport

The claudin superfamily consists of at least 18 homologous proteins in humans. These proteins are important structural and functional components of tight junctions in paracellular transport. Complexed with two other integral transmembrane proteins, occludin and junctional adhesion molecule, claudins are located in both epithelial and endothelial cells in all tight junction-bearing tissues. Claudins interact directly with tight junction-specific, membrane-associated guanylate kinase homologues, ZO-1, ZO-2, and ZO-3, and indirectly with AF-6 and the myosin-binding molecule cingulin. These protein-protein interactions promote scaffolding of the tight junction transmembrane proteins and provide a link to the actin cytoskeleton for transducing regulatory signals to and from tight junctions. The distinct permeability properties observed in different epithelia and endothelia seemingly result from the restricted tissue expression, variability of the homopolymer and heteropolymer assembly, regulated transcription and translation, and the subcellular localization of claudin family proteins. Defects in claudins are causatively associated with a variety of human diseases, demonstrating that claudins play important roles in human physiology. In conditions where the cell adhesion function contributed by tight junctions is essential, such as in altered paracellular transport, in proliferative diseases, and during morphogenesis, the claudin superfamily of homologous proteins provides the molecular basis for the uniqueness of tight junctions and emerges as a new target for intervention.

Oncogenic Raf-1 disrupts epithelial tight junctions via downregulation of occludin

Occludin is an integral membrane protein of the epithelial cell tight junction (TJ). Its potential role in coordinating structural and functional events of TJ formation has been suggested recently. Using a rat salivary gland epithelial cell line (Pa-4) as a model system, we have demonstrated that occludin not only is a critical component of functional TJs but also controls the phenotypic changes associated with epithelium oncogenesis. Transfection of an oncogenic Raf-1 into Pa-4 cells resulted in a complete loss of TJ function and the acquisition of a stratified phenotype that lacked cell-cell contact growth control. The expression of occludin and claudin-1 was downregulated, and the distribution patterns of ZO-1 and E-cadherin were altered. Introduction of the human occludin gene into Raf-1-activated Pa-4 cells resulted in reacquisition of a monolayer phenotype and the formation of functionally intact TJs. In addition, the presence of exogenous occludin protein led to a recovery in claudin-1 protein level, relocation of the zonula occludens 1 protein (ZO-1) to the TJ, and redistribution of E-cadherin to the lateral membrane. Furthermore, the expression of occludin inhibited anchorage-independent growth of Raf-1-activated Pa-4 cells in soft agarose. Thus, occludin may act as a pivotal signaling molecule in oncogenic Raf- 1-induced disruption of TJs, and regulates phenotypic changes associated with epithelial cell transformation.

Existence of junction-like structures in large B-cell non-Hodgkin's lymphomas. An ultrastructural study

The purpose of this work is to study the presence of cell junction-like structures in large B-cell lymphomas. The ultrastructural study, based on 20 cases of this entity proved by immunohistochemistry and flow cytometry, demonstrated four types of junction-like devices easily found between tumor cells. Several explanations are offered about the possible nature of such structures, including the possibility of them being the result of adhesion phenomena. It should also be emphasized that they can potentially complicate the differential diagnosis of those neoplasms. We should, therefore, be careful in rejecting an ultrastructural diagnosis of large B-cell lymphoma based only on the presence of junction-like structures.

The tight junction protein ZO-1 is homologous to the Drosophila discs-large tumor suppressor protein of septate junctions

Tight junctions form an intercellular barrier between epithelial cells, serve to separate tissue compartments, and maintain cellular polarity. Paracellular sealing properties vary among cell types and are regulated by undefined mechanisms. Sequence of the full-length cDNA for human ZO-1, the first identified tight junction component, predicts a protein of 1736 aa. The N-terminal 793 aa are homologous to the product of the lethal(1)discs-large-1 (dlg) tumor suppressor gene of Drosophila, located in septate junctions, and to a 95-kDa protein located in the postsynaptic densities of rat brain, PSD-95. All three proteins contain both a src homology region 3 (SH3 domain), previously identified in membrane proteins involved in signal transduction, and a region homologous to guanylate kinase. ZO-1 contains an additional 943-aa C-terminal domain that is proline-rich (14.1%) and contains an alternatively spliced domain, whose expression was previously shown to correlate with variable properties of tight junctions. dlg mutations result in loss of apical-basolateral epithelial cell polarity and in neoplastic growth. These results suggest a protein family specialized for signal transduction on the cytoplasmic surface of intercellular junctions. These results also provide biochemical evidence for similarity between invertebrate septate and vertebrate tight junctions. The C-terminal domain of ZO-1, and its alternatively spliced region, appears to confer variable properties unique to tight junctions.

The ultrastructural spectrum of synovial sarcomas: a study of the epithelial type differentiation of primary tumors, recurrences, and metastases

Synovial sarcomas (SS) are malignant soft tissue tumors of unknown origin. Their classification as carcinomas (monophasic synovial sarcomas, MSS) or carcinosarcomas (biphasic synovial sarcomas, BSS) still raises controversy. In an attempt to settle this controversy, an ultrastructural study was undertaken of 25 primary SS (12 BSS and 13 MSS), 5 recurrences (3 BSS and 2 MSS), and 2 metastases (2 BSS) based upon precise selection of different aspects of BSS and MSS on numerous semithin sections from each case. Ultrastructural markers of epithelial type differentiation of neoplastic cells were found in every type of cellular component of SS regardless of the tumoral pattern (biphasic or not). No major differences were found between MSS and the nonglandular areas of BSS (not even regarding the presence of abortive glandular lumina). Cytoarchitectural transitions were frequently observed; these included spindle to epithelioid cell types and fascicular to solid (MSS and BSS) or fascicular to glandular (BSS) patterns. These findings support the assumption that spindle cells of SS are neoplastic and may evolve to glandular cells in SS. Based on the cytogenetic data pointing to a common pathogenesis of both phenotypes (BSS and MSS), SS may represent true carcinomas of soft tissues with a biphasic and/or monophasic pattern depending on the degree of differentiation.

Osteogenic sarcoma with epithelial differentiation

This case report details an osteogenic sarcoma arising in a vertebra in which cytokeratin intermediate filaments were detected immunohistochemically with three different antibodies. This feature was present not only in the primary neoplasm but also in two local recurrences and a metastasis to the iliac bone. What is unique about this primary bone tumor, however, is the structural evidence for epithelial differentiation. Ultrastructurally, well-formed desmosomes and tonofilaments were present in all four surgically resected specimens. This tumor expands the list of soft tissue and bone tumors in which anomalous expression of intermediate filaments can occur but, more important, illustrates that changes in genetic expression of neoplasia of mesenchymal origin can result in paradoxic epithelial differentiation.

Two cell lines with epithelial cell-like characteristics established from malignant fibrous histiocytomas

Two malignant fibrous histiocytoma (MFH) cell lines were established: one from a storiform-pleomorph subtype and the other from a myxoid one (codes, MFH-3 and MFH-4). Light microscopic examination revealed large rounded cells, growing mostly separately, in both cell lines. Their ultrastructure was different in various aspects. The MFH-3 cells showed abundant lysosomal activity, a well-developed Golgi apparatus, and a few desmosome-like cell contacts. The MFH-4 cells had a well-developed rough endoplasmic reticulum, delicate bundles of tonofilaments, the formation of pseudoacini, and the presence of small completely developed desmosomes. Based on immunostaining and immunoblotting assays of cultured cells, both cell lines expressed immunoreactivity for vimentin; cytokeratins 7, 8, and 18; desmin; and laminin, but they lacked reactivity for cytokeratins 10 and 19, neurofilament, alpha-smooth muscle actin, S-100 protein, collagen type IV, carcinoembryonic antigen, and antigens specific for macrophages. Fibronectin and, to a variable extent, glial fibrillary acid protein and epithelial membrane antigen (EMA) were detectable in MFH-3 cells only. Furthermore, a 60-kilodalton band was present in both cell lines which was reactive for cytokeratins 8 and 18. The MFH-3 cells had the capacity to grow as xenografts with a carcinoma-like pattern. The cells retained their immunoreactivity for vimentin and cytokeratin 8 and showed the presence of desmosomes. Several of these immunophenotypic features also were noticed in established sarcoma cell lines and in short-term cultures of fibroblasts, smooth muscle cells, and endothelial cells. However, experimental data on the two MFH cell lines show that the MFH cell line may express some immunophenotypic and ultrastructural features considered to be specific for epithelial cells. The MFH cells may originate from multipotential mesenchymal cells with a capacity to differentiate to fibroblast-like cells, and less frequently, to epithelial cells, smooth muscle cells, and Schwannian cells. Such a differentiation became evident when these cells were adapted to culture conditions or grew in nude mice.

Synovial sarcoma. Inter-relationship of the biphasic and monophasic subtypes

In order to assess minimum diagnostic criteria for synovial sarcoma, particularly the monophasic variety, and the inter-relationship between the monophasic and biphasic types, 32 examples were studied histologically, immunohistochemically (26 cases), and ultrastructurally (13 cases). Of the six biphasic synovial sarcomas examined by electron microscopy, the spindle cell component did not show evidence of epithelial differentiation or resemble the epithelial phase, but did appear fibroblastic; no tumor cells transitional between the spindle and epithelial component were evident. In contrast, all of the seven monophasic lesions had ultrastructural growth patterns and some cellular features approximating the epithelial cells of the biphasic variant. In 11 biphasic synovial sarcomas, epithelial membrane antigen was detected in the glandular epithelium of all cases and cytokeratins in eight cases; in no case were these antigens detected in the spindle cell regions of biphasic lesions. Of the 15 monophasic synovial sarcomas, two were positive for cytokeratins and four for epithelial membrane antigen. Thus, the detection of epithelial markers either immunohistochemically or by electron microscopy (or both) should be the minimal diagnostic criteria for monophasic synovial sarcomas. Based on these findings, it is suggested that monophasic synovial sarcomas do not represent the spindle cell or "stromal" phase of biphasic synovial sarcomas, but are a poorly differentiated variant of the latter. As others have suggested, these tumors are, in fact, carcinosarcomas and carcinomas of the soft tissues and the designation synovial sarcoma is inappropriate for this tumor class.

Monomorphous histiocytoma in a child. Report of a case with ultrastructural features suggestive of dendritic cell differentiation

The authors describe a rapidly growing soft tissue tumor of predominantly histiocytic composition in an 8-year-old child. The tumor cells were identified as elements of the mononuclear phagocyte system by histologic, histochemical, immunologic, and electron microscopic study. Despite the presence of a minor fibroblastic component, the tumor did not conform to established criteria for a diagnosis of malignant fibrous histiocytoma. Formation of frequent desmosome-like intercellular junctions raised the possibility of dendritic reticulum cell differentiation, since the latter cells seem to be the only elements of the mononuclear phagocyte system that display such specialized cell junctions. The results of immunostaining were discrepant with those reported for normal dendritic reticulum cells, but the currently available information makes it doubtful that the entire neoplastic spectrum of dendritic cell differentiation can currently be diagnosed in surgical pathology.

Type C retroviral expression in spontaneous feline olfactory neuroblastomas

Three cases of spontaneous olfactory neuroblastoma (ONB) in domestic cats were morphologically and immunocytochemically characterized. Diagnostic light microscopic features included Flexner and Homer-Wright rosettes, while ultrastructurally the cells had neuritic processes, intracellular intermediate filaments, and intercellular junctions. Immunocytochemically, the tumors stained positively for neuron-specific enolase, cytokeratins, and S-100 protein antigens. In each case, a key finding was the identification of numerous mature type C retroviral particles within the tumors. In one case, budding of viral particles from the plasmalemma of tumor cells suggested the source of mature particles. This cat and one other were tested, and both were serologically positive for feline leukemia virus (FeLV). The virus in the tumors was identified as FeLV by polymerase chain reaction and immunocytochemistry. No other neoplasms were found in any of the cats, nor was there similar evidence of active viral infection in other non-tumor tissues, including the brain. Although the relationship between FeLV infection and ONB is uncertain, our findings indicate that FeLV should be investigated as an etiologic agent of ONB.

Cell junctions in lymphomas: study of a primary ovarian T-cell lymphoma and review of fifty-six other cases of lymphoma

A case of primary ovarian lymphoma was studied by light microscopy, immunohistochemistry, and electron microscopy. The ultrastructural study revealed the presence of cell junctions of the paired subplasmalemmal densities and tight junctions between adjacent lymphoid cells. Fifty-six cases of non-Hodgkin's lymphoma randomly selected from the files of the Electron Microscopy Facility of the Faculty of Health Sciences, McMaster University, were reviewed. Paired subplasmalemmal densities and tight junctions were identified in five of the cases (9%). This study suggests that the absence of cell junctions should not be considered an essential criterion for the ultrastructural diagnosis of lymphomas.

Epithelioid leiomyosarcoma of the left atrium: immunohistochemical and ultrastructural findings

Leiomyosarcomas of the heart are rare, with only 12 cases reported in the literature. An example of the epithelioid variant of leiomyosarcoma is described. The tumour cells expressed vimentin, desmin, muscle-specific actin and smooth muscle-specific actin. In addition, they were also labelled by monoclonal and polyclonal antibodies to cytokeratin intermediate filaments and displayed cell junctions at the ultrastructural level, features which highlight the potential pitfalls in the application of immunohistochemistry and electron microscopy in the diagnosis of poorly differentiated tumours.

Cytokeratin filaments and desmosomes in the epithelioid cells of the perineurial and arachnoidal sheaths of some vertebrate species

Using electron microscopy and immunohistochemistry with a large panel of antibodies to various cytoskeletal proteins we have noted that the single- or multi-layered sheaths of epithelioid cells ("neurothelia") surrounding peripheral nerves (perineurial cells) or structures of the central nervous system, including the optic nerve (arachnoid cells), show remarkable interspecies differences in their cytoskeletal complements. In two anuran amphibia examined (Xenopus laevis, Rana ridibunda), the cells of both forms of neurothelia, i.e., perineurial and arachnoid, are interconnected by true desmosomes and are rich intermediate-sized filaments (IFs) of the cytokeratin type. Among higher vertebrates, a similar situation is found in the bovine and chicken nervous systems, in which the arachnoid cells of the meninges contain desmosomes and IFs of both the cytokeratin (apparently with restricted epitope accessibilities in the chicken) and the vimentin type, whereas the perineurial cells of many nerves contain cytokeratin IFs, often together with vimentin, but no desmosomes. In contrast, in rat arachnoidal and perineurial cells significant reactions have been observed neither for cytokeratins nor for desmosomes. In the human nervous system, cytokeratins and desmosomes have also not been seen in the various perineuria studied whereas desmosomes are frequent in arachnoidal cell layers which are dominated by vimentin IFs and only in certain small regions of the brain contain some additional cytokeratins. The occurrence of cytokeratins in the tissues found positive by immunohistochemistry has been confirmed by gel electrophoresis of cytoskeletal proteins, followed by immunoblotting. Our results emphasize both similarities and differences between the neurothelia on the one hand and epithelia or endothelia on the other, justifying classification as a separate kind of tissue, i.e., neurothelium. The observations of interspecies differences lead to the challenging conclusion that neither desmosomes nor cytokeratins are essential for the basic functions of neurothelial sheaths nor does the specific type of IF protein expressed in these cells appear to matter in this respect. The results are also discussed in relation to the cytoskeletal characteristics of other epithelioid tissues and of human neurothelium-derived tumors.

An immunohistochemically defined non-Hodgkin's lymphoma showing intercellular junctions. A case report

A rare example of pleomorphic B cell non-Hodgkin's lymphoma is described in which tumour cells possessed simple intercellular junctions.