Specialized junctional complexes in human meningioma

Facets of Communication: Gap Junction Ultrastructure and Function in Cancer Stem Cells and Tumor Cells

Gap junction proteins are expressed in cancer stem cells and non-stem cancer cells of many tumors. As the morphology and assembly of gap junction channels are crucial for their function in intercellular communication, one focus of our review is to outline the data on gap junction plaque morphology available for cancer cells. Electron microscopic studies and freeze-fracture analyses on gap junction ultrastructure in cancer are summarized. As the presence of gap junctions is relevant in solid tumors, we exemplarily outline their role in glioblastomas and in breast cancer. These were also shown to contain cancer stem cells, which are an essential cause of tumor onset and of tumor transmission into metastases. For these processes, gap junctional communication was shown to be important and thus we summarize, how the expression of gap junction proteins and the resulting communication between cancer stem cells and their surrounding cells contributes to the dissemination of cancer stem cells via blood or lymphatic vessels. Based on their importance for tumors and metastases, future cancer-specific therapies are expected to address gap junction proteins. In turn, gap junctions also seem to contribute to the unattainability of cancer stem cells by certain treatments and might thus contribute to therapeutic resistance.

Immunohistochemical and ultrastructural study of gap junction proteins connexin26 and 43 in human arachnoid villi and meningeal tumors

Human arachnoid villi and meningiomas are known to have gap junctions formed by connexin (Cx) proteins. We examined the expression and localization of Cxs in normal human arachnoid villi and meningeal tumors (meningiomas and hemangiopericytomas) by immunohistochemistry and Western blots. In arachnoid villi, strong immunopositivity for connexin26 (Cx26) and connexin43 (Cx43) was detected in the cap cell layer, cap cell cluster, and central core. They were weakly expressed in the fibrous capsule. In meningiomas they were strongly expressed in the meningotheliomatous area and weakly positive in the fibrous area. None of them were expressed in hemangiopericytomas. By immunoelectron microscopy, Cx26 and Cx43 were distributed on the cell membranes in arachnoid villi and meningiomas. In the Western blots in arachnoid villi and meningiomas, Cx26 and Cx43 were shown at bands with molecular weights of 26 kD and 42-47 kD, respectively. The degree of positivity for Cxs was different between subtypes of meningiomas. These findings suggest that expression of Cx26 and Cx43 might be related to the differentiation of the arachnoid villi and meningiomas, and exhibit the different origin of various subtypes of meningiomas. We proposed that Cx expression is one of the useful markers for the differentiation of meningioma and hemangiopericytoma.

Extracranial meningioma in the parapharyngeal space

A case of extracranial meningioma in the parapharyngeal space is reported. A 24 year old woman presented with swelling and tenderness of the parapharyngeal region. A tumor was palpable in this region, and the tumor was surgically removed. Macroscopically the tumor occurred from the portion between the axis and atlas. Histologically the tumor cells, which had oval nuclei and a slightly eosinophilic cytoplasm, proliferated in fibrous connective tissues to form small nests. As the cell borders were not clear, the tumor structure appeared to be syncytium-like. Immunohistochemically the tumor cells were positive for anti-vimentin antibodies, anti-S-100 protein antibodies and anti-epithelial membrane antigen (EMA) antibodies in part. Electron microscopically the tumor cells had complex interdigitations of their adjacent plasma membranes. These were studded with many desmosomes. Bundles of intermediate filaments were visible in the cytoplasm. On the basis of the clinical, histological, immunohistochemical and electron microscopical features, the tumor was diagnosed as extracranial meningotheliomatous meningioma. The parapharyngeal space is an extremely rare location for extracranial meningioma, and our case is the first in Japan as far as we know.

Immunocytochemistry of intracranial meningiomas

Fifty meningiomas of four major histological types have been examined by immunocytochemical methods applied to formalin fixed paraffin embedded material and using readily available commercial antisera. The expression of GFAP, S100, NSE, vimentin, cytokeratin, fibronectin and desmoplakin was investigated. The majority of tumours contained NSE (86%) and S100 (78%), and all irrespective of histological type, contained vimentin and fibronectin. The epithelial marker cytokeratin was found in 56% of cases, but showed only focal expression. The relevance of these findings to histogenesis and metabolism is discussed and it is suggested that intermediate filament typing provides valuable information on meningiomas structure and function. The possible role of NSE and S100 in meningeal neoplasm is discussed.

Attachment of vimentin filaments to desmosomal plaques in human meningiomal cells and arachnoidal tissue

Desmosomal proteins are co-expressed with intermediate-sized filaments (IF) of the cytokeratin type in epithelial cells, and these IF are firmly attached to the desmosomal plaque. In meningiomal and certain arachnoidal cells, however, vimentin IF are attached to desmosomal plaques. Meningiomas obtained after surgery, arachnoid "membranes", and arachnoid granulations at autopsy, as well as meningiomal cells grown in short-term culture have been examined by single and double immunofluorescence and immunoelectron microscopy using antibodies to desmoplakins, vimentin, cytokeratins, glial filament protein, neurofilament protein, and procollagen. In addition, two-dimensional gel electrophoresis of the cytoskeletal proteins has been performed. Using all of these techniques, vimentin was the only IF protein that was detected in significant amounts. The junctions morphologically resembling desmosomes of epithelial cells have been identified as true desmosomes by antibodies specific for desmoplakins and they provided the membrane attachment sites for the vimentin IF. These findings show that anchorage of IF to the cell surface at desmosomal plaques is not restricted to cytokeratin IF as in epithelial cells and desmin IF as in cardiac myocytes, suggesting that binding to desmosomes and hemidesmosomes is a more common feature of IF organization. The co-expression of desmosomal proteins and IF of the vimentin type only defines a new class of cell ("desmofibrocyte") and may also provide an important histodiagnostic criterion.

Exocytosis of neurosecretory granules in small cell undifferentiated carcinoma

The tumor cells in the pleural effusions of a case of small cell undifferentiated carcinoma have been studied by light microscopy and by thin section and freeze-fracture electron microscopy. Evidence of exocytosis of neurosecretory granules from the tumor cells is presented. The tumor cells form clumps, with the cells joined by focal tight junctions and small desmosomes. These findings are discussed with reference to the neuroendocrine origin of these tumors and the role of the junctional complexes in the formation of tumor cell aggregates.

Granulofilamentous inclusions in a meningioma

We have studied the histology, immunocytochemistry, and ultrastructure of a syncytial meningioma which contained the unusual feature of large eosinophilic intracytoplasmic inclusions. Electron microscopic examination revealed that these bodies were granular, osmiophilic masses, closely associated with cytoplasmic filaments of intermediate size. Desmosomal junctions with a somewhat abnormal morphology were also observed, and the possible relationship between the inclusions and the dense components of desmosomes is discussed. This tumor is also compared to other tumors of the central nervous system with hyaline and granulofilamentous inclusions.

Alterations of intercellular junctions in acinic cell carcinoma of the canine pancreas

Intercellular junctions in spontaneous canine pancreatic acinic cell adenocarcinomas were compared to those in control canine pancreas. The neoplastic cells displayed proliferation and fragmentation of tight junctions and reduction in size and number of gap junctions. Marked decrease in desmosomal density was observed only in the poorly differentiated carcinoma. In the well differentiated carcinomas a few of the desmosomes were characteristic of those found in squamous cells. No quantatitive or qualitative differences in cell junctions were noted between primary and metastatic tumor.

Extraneuraxial canine meningioma. A light and electron microscopic study

A tumor mass removed from the subcutaneous tissue of the shoulder of a dog had the light and electron microscopic features of extraneuraxial meningioma. The neoplasm probably arose from arachnoid cap cells displaced during embryogenesis.

Hemidesmosome-like intercellular specializations in human meningiomas

Desmosomes, gap junctions and tight junctions are intercellular specializations which have been described in human meningiomas. We report, in five of five meningiomas, including a pulmonary metastasis from a malignant intracranial meningioma, a fourth type of intercellular specialization which is similar to but not identical with the hemidesmosome of the epidermis. Idential intercellular specializations have been described between arachnoidal cells, but not between dural fibroblasts. The presence of the junction in human meningeal neoplasms of diverse histologic pattern supports the origin of the meningioma from arachnoidal epithelium. The consistent occurrence of these structures in a pulmonary metastasis as well as benign intracranial tumors suggests that they may be a useful morphologic marker in the differential diagnosis of putative extracranial metastatic meningiomas.

Gap junctions between human meningioma cells maintained in organ culture

Intercellular junctions were commonly observed in a human syncitial meningioma maintained in organ culture for up to 44 days in vitro (DIV) using gelatin sponge foam matrices. The junctions were identified as one of three types: desmosomes; tight junctions; or gap junctions. Of the three types, gap junctions were frequently encountered and showed preservation of their characteristic ladder-like substructure. The results suggest that organ culture provides an environment that may facilitate correlation of the structure and function of gap junctions between coupled human meningioma cells.

Plasma membrane structures of medulloblastoma and cerebellar sarcoma

Three medulloblastomas and 1 cerebellar sarcoma were studied on their plasma membrane structures. The average number of membrane particles per mum2 plasma membrane was 710 on face A and 70 on face B of medulloblastoma and 1280 on face A and 160 on face B of cerebellar sarcoma. The membrane particles were often aggregated in medulloblastoma and diffusely scattered in cerebellar sarcoma. Small gap junctions were occasionally found in cerebellar sarcoma and not evident in medulloblastoma. Round membrane protrusions, about 0.5-0.6 mu in diameter and provided with several small depressions on their foot, were often observed in region of narrow perinuclear cytoplasm of cerebellar sarcoma and different in structure from cytoplasmic processes. The present series is too limited in number to allow a definite conclusion, but indicates that the plasma membrane structures are different in medulloblastoma and cerebellar sarcoma.