Characterization of cytoskeletal components in epithelial and mesenchymal liver tumors by electron and immunofluorescence microscopy

Ultrastructural hepatic alterations in hamsters and jirds after experimental infection with the liver fluke Opisthorchis viverrini

Changes in the hepatocytes of male hamsters (Mesocricetus auratus) and jirds (Meriones unguiculatus) at 220 days after experimental infection with the liver fluke Opisthorchis viverrini were studied by light and electron microscopy. The hepatocytes of the control group were characterized by an intracellular compartmentation. A globular nucleus was located centrally. The main features of the perinuclear zone were the cisternae of the rough endoplasmic reticulum (RER) and interjacent mitochondria, lysosomes, and peroxisomes. The peripheral cell region was dominated by glycogen fields and scattered lipid droplets, which were surrounded by anastomosing tubules of the smooth endoplasmic reticulum (SER). An immense proliferation of the SER was striking in the hepatocytes of animals infected with O. viverrini. Coincidentally, the intracellular compartmentation disappeared. Glycogen rosettes, RER, lysosomes, and lipid droplets were distributed irregularly all over the cell, the latter being observed more frequently than in control animals. The nuclei showed lobe-like protrusions and were enlarged. The mitochondria were often dumbbell-shaped and showed pathologic degenerations up to lysis. Our results resemble those of numerous investigations concerning hepatocellular alterations caused by N-nitroso compounds. Therefore, these observations suggest a synergistic effect for trematode infection and N-nitroso compounds in the pathogenesis of opisthorchiasis. The cellular alterations observed in the hepatocytes of Opisthorchis-infected animals together with the accumulation of intermediate filaments seen in the adjacent bile-duct epithelia and in the epithelium of the gall-bladder seem to indicate a disturbance of the cell metabolism and might be related to a neoplastic transformation.

What's new in the ultrastructure of tumor invasion in vivo?

An important point emerging from the literature on tumor invasion in vivo is the great variability of nearly all aspects studied. It seems that there is neither one particular morphologic change which renders a cell invasive, nor one particular mechanism by which a cell crosses the boundaries of its original tissue compartment to occupy another. Nevertheless, some general trends are demonstrable. The majority of invasive tumor cells appear to be characterized by prominent surface protrusions, decreased junctional contacts and, in the case of epithelium-derived tumor cells, an incomplete basement membrane. The fact that some tumors can invade foreign tissues without loosing their basement membrane is emphasized. Invasive cells frequently form organized associations with preexistent non-neoplastic cells without damaging them. Apparently, the eventual disappearance of the preexistent cells in most invaded tissues is not necessarily due to a direct action on the part of the tumor cells. It rather seems a secondary phenomenon caused by, e.g., the insertion of invasive tumor cells between the preexistent cells and their original stroma. Very often, this seems to be due to the affinity of malignant cells for basement membranes. In addition, the adhesion of tumor cells to basement membranes frequently seems to determine their pattern of spread through a tissue. A process which may turn out to be a key factor in tumor invasion is desmoplasia, the series of host reactions which creates a new environment for the tumor cells which may favor their survival, proliferation, and locomotion. With the rapid development of new techniques, electron microscopy will probably contribute to the elucidation of the exact nature, the degree of similarity to granulation tissue, and the influence on invasion of desmoplastic tumor stroma.

Stewart-Treves syndrome: an histogenetic (ultrastructural and immunohistological) study

One case of the so-called "Stewart-Treves syndrome" (STS), appearing on a lymphoedematous arm complicating radical mastectomy for breast cancer, was characterized electronmicroscopically and immunohistologically, in order to elucidate its disputed (epithelial vs endothelial) histogenesis. Epithelial and endothelial differentiation markers used comprised: antibodies against keratin, vimentin, factor VIII-related antigen (F VIII-RA), HLA-DR antigens and the lectin Ulex europeaus agglutinin I (UEA I). At the ultrastructural level, neoplastic cells were found to contain typical Weibel-Palade bodies, whereas by immunohistological techniques they proved to be keratin-negative/vimentin+, F VIII-RA+, UEAI+, HLA-DR+. These results rule out a possible epithelial differentiation and strongly favour an endothelial one for STS.

Sequential cellular changes during chemical carcinogenesis

Phenotypically altered, preneoplastic cell populations were detected by micromorphological and cytochemical methods in a number of tissues treated with various chemical carcinogens. Further cellular analysis of carcinogenesis has shown that different cellular phenotypes follow each other during tumor development. Thus, stages of the neoplastic transformation leading from preneoplastic to early and advanced neoplastic cells can be observed directly. The cellular changes preceding the various tumor types suggest that cytologically different neoplasms have also a different cytogenesis. The identification of putative preneoplastic and early neoplastic cell populations by morphological and cytochemical methods allows for the first time the dissection and subsequent detailed investigation of target cells of chemical carcinogens that are at high risk of becoming cancer cells. Recent results of the cytochemical and biochemical microanalysis of preneoplastic hepatocytes support the concept that the well-known aberration of carbohydrate metabolism in tumor cells might occur in response to a carcinogen-induced metabolic derangement, which frequently appears to be associated with an excessive storage of polysaccharides or lipids persisting for weeks and months until fast-growing tumors develop. The increasing reports on the appearance of hepatic tumors in humans suffering from inborn hepatic glycogenosis agree with this hypothesis. Whereas the cause of the persisting storage phenomena is most probably fixed at the genetic level, epigenetic changes, namely an adaptation of cellular enzymes gradually activating alternative metabolic pathways, might be responsible for the ultimate neoplastic transformation of the cell.

Adenomatoid tumor: immunohistological features suggesting a mesothelial origin

Four adenomatoid tumors of the epididymis were evaluated immunohistologically for the expression of intermediate filaments and endothelial cell markers, factor VIII-related antigen and binding of Ulex europaeus I-lectin (UEA I). Immunofluorescence microscopy showed a strong reaction with antikeratin but not with anti-vimentin antibodies, indicating that adenomatoid tumor cells contain epithelial but not mesenchymal type of intermediate filaments. No staining of tumor cells was seen with anti-FVIII-related antigen antibodies or with fluorochrome-coupled UEA I. The results support the mesothelial, non-endothelial origin of adenomatoid tumors.

Antibodies to intermediate filament proteins in the immunohistochemical identification of human tumours: an overview

Intermediate-sized filament proteins (IFP) are tissue specific in that antibodies to keratin, vimentin, desmin, glial fibrillary acidic protein (GFAP) and the neurofilament proteins can distinguish between cells of epithelial and mesenchymal origin as well as of myogenic and neural origin respectively. Malignant cells retain their tissue-specific IFP, which makes it possible to use these antibodies in tumour diagnosis. Carcinomas are exclusively detected by antibodies to keratin. Monoclonal antibodies to keratin have allowed the differentiation between subgroups of epithelial tumours until now between adenocarcinomas and squamous cell carcinomas. Lymphomas, melanomas and several soft tissue tumours are distinctly recognized by antibodies to vimentin. On the other hand, rhabdomyosarcomas and leiomyosarcomas are positive for desmin, while astrocytomas give a strong reaction with GFAP antibodies. Thus, antibodies to IFP are useful tools for differential diagnosis in surgical pathology.

Mediastinal tumors: ultrastructural and immunohistochemical evaluation of intermediate filaments as diagnostic aids

The histogenesis of six mediastinal tumors was investigated ultrastructurally and immunohistochemically using monospecific antibodies against intermediate filament proteins. Four of the tumors, showing different appearances by light microscopy, displayed desmosomes and cytoplasmic tonofilaments, by electron microscopy, compatible with an epithelial thymoma. These cases also showed keratin positivity by immunofluorescence microscopy. One spindle cell tumor showed zonula adherens-type junctions, prominent collections of intermediate filaments, and abundant cytoplasmic neurosecretory granules consistent with a neuroendocrine tumor. In this tumor, neurofilaments could be demonstrated by immunofluorescence microscopy, a feature also consistent with a neuroendocrine tumor. One malignant tumor, lacking tonofilaments and desmosomes but showing a few primitive junctions, did not contain keratin but showed vimentin positivity. This suggests a mesenchymal origin and a diagnosis of primitive sarcoma. These cases illustrate the diagnostic usefulness of electron microscopy and immunohistochemical evaluation of intermediate filaments.

Neuroendocrine carcinoma of the skin (Merkel cell carcinoma): ultrastructural and immunohistochemical demonstration of neurofilaments

In this study we characterized a skin tumor that grew in the temporal region of a 69-year-old woman. On the basis of tumor morphology, a metastasis from a small cell carcinoma of the lung was initially suggested, but X-ray and bronchoscopic studies were negative. The tumor recurred twice within a year, yet no tumors were found elsewhere in the body. Ultrastructurally, cytoplasmic organelles compatible with neuroendocrine storage granules and perinuclear aggregates of intermediate-sized (8-10 nm) filaments were found in many tumor cells. Indirect immunofluorescence microscopy revealed neurofilament-type intermediate filaments in the tumor cells but no keratin- or vimentin-type filaments. Our results further demonstrate neural properties of this tumor type, which is generally considered to have its origin from Merkel cells, the cutaneous neuroendocrine cells.

Electron-microscopic examination of primary diffuse tracheobronchial amyloidosis. Role of fibroblasts in amyloid formation

The author reports on the electron-microscopic examination of the diffuse tracheobronchial amyloidosis of a 51-year-old patient. The amyloid deposits were located in the lamina propria of the tracheal and bronchial mucosa. At the edge of the nodular deposits, condensation and radial arrangement of amyloid fibrils could be seen. Closely connected with the amyloid, active fibroblasts were present and their cytoplasm contained amyloid fibrils. The cell membrane of the fibroblasts was missing in part. Intracellular amyloid fibrils mingled with extracellular deposits. It can be assumed that active fibroblasts play an important role in local amyloid formation.

Endomyocardial fibrosis in rats treated with N-nitrosomorpholine

Endomyocardial fibrosis was observed after long lag periods in male Sprague-Dawley rats treated for 1-14 weeks with the carcinogen N-nitrosomorpholine. The fibrosis developed predominantly in the left ventricle. It occurred during 29-78 weeks after withdrawal of the carcinogen in 5% and 79-108 weeks after withdrawal in 20% of the experimental animals, but was never observed in controls of the same age. We suggest that endomyocardial fibrosis was induced by a direct effect of the carcinogen on the fibroblasts of the endomyocardium.

The cytoskeleton in tumor cells

During the past few years several laboratories investigated the occurrence of cytoskeletal components in epithelial and mesenchymal cells by electron microscopy and/or immunocytochemical methods in a number of tumor types growing in vitro or in the body. Since it is well established that antibodies to different intermediate-sized filament proteins can distinguish cells and tissues of epithelial, mesenchymal, muscle, astrocytic and neural origin special attention has been paid to the behaviour of these filaments in neoplastic cells recently. While the organisation of the cytoskeleton in tumor cells growing in vitro is very variable, regularities relevant for the diagnosis and the determination of the histogenetic origin of tumors have been observed in tumor cells growing in the body. In general, ultrastructural and immunological features of intermediate filaments are maintained during neoplastic transformation in the body. Thus immunofluorescence microscopy with antibodies to cytoskeletal proteins is a powerful tool for the classification and differential diagnosis of tumors, especially for the distinction between epithelial and mesenchymal tumors, including metastases. The concept that presence of an excess of contractile proteins such as actin is an important prerequisite for the metastatic spread of malignant cells has not been unequivocally supported by more recent results. However, an accumulation of various types of intermediate filaments (e.g. prekeratin, vimentin, acidic glial fibrillar protein) has been shown in different tumor types. The further elucidation of this alteration could contribute to a better understanding of the molecular mechanisms of neoplastic cell transformation.

Intermediate-sized filaments in cells of normal human colon mucosa, adenomas and carcinomas

The distribution of intermediate - sized filaments in human colon mucosa as well as in adenomas and carcinomas of the colon was studied by means of both immunohistology and electron microscopy. The epithelial cells of the colonic mucosa are definitely labelled with antibodies against prekeratin (cytokeratin). Interwoven filaments of the prekeratin type are present in the basal compartments of the epithelial cells; they surround the nuclei and mucus droplets and form an apical skeletal disc. Pericryptal connective tissue is prekeratin negative and vimentin positive. Benign hyperplastic polyps have a high content of prekeratin. The potential precursors of colonic carcinoma, i.e., the tubular and villous adenomas, also show an increase in intermediate-sized filaments of the prekeratin type. Correspondingly, electron microscopy reveals elongated bundles of intermediate-sized filaments arising from the desmosomes of the lateral and basal cell membranes. The prekeratin content is particularly high in adenocarcinomas and highest in mucinous carcinomas. As expected, the stroma of all neoplasms studied is prekeratin-negative, but distinctly vimentin-positive. In one moderately differentiated adenocarcinoma there was evidence of "vimentin-positive" tumor cells. These changes may be caused by binding of cytokeratins with an unknown substance in vimentin antisera, as observed similarly by Moll et al. (1982) in a transitional cloacogenic carcinoma.

Expression of intermediate filaments in soft-tissue sarcomas

Monospecific antibodies and indirect immunofluorescence microscopy were used to investigate the presence of cytoskeletal intermediate filaments of the keratin, vimentin and desmin types in 43 soft-tissue sarcomas. The results showed that vimentin was present in the neoplastic cells of all types of soft-tissue sarcomas studied, whereas keratin was absent, the only exception being the epithelial-like cells in biphasic synovial sarcoma. The presence of desmin was confined to leiomyosarcomas and rhabdomyosarcomas, which usually showed desminpositivity. In addition, malignant fibrous histiocytomas occasionally displayed some desmin-positive cells. Thus, determination of intermediate filaments is of aid in the histogenetical diagnosis of tumors, because keratin-positivity largely excludes the possibility of a sarcoma, and desmin-positivity aids in recognizing leiomyosarcomas and rhabdomyosarcomas.