Structure of a hepatoblastoma of pure epithelial type

Chapter 6: cubic membranes the missing dimension of cell membrane organization

Biological membranes are among the most fascinating assemblies of biomolecules: a bilayer less than 10 nm thick, composed of rather small lipid molecules that are held together simply by noncovalent forces, defines the cell and discriminates between “inside” and “outside”, survival, and death. Intracellular compartmentalization—governed by biomembranes as well—is a characteristic feature of eukaryotic cells, which allows them to fulfill multiple and highly specialized anabolic and catabolic functions in strictly controlled environments. Although cellular membranes are generally visualized as flat sheets or closely folded isolated objects, multiple observations also demonstrate that membranes may fold into “unusual”, highly organized structures with 2D or 3D periodicity. The obvious correlation of highly convoluted membrane organizations with pathological cellular states, for example, as a consequence of viral infection, deserves close consideration. However, knowledge about formation and function of these highly organized 3D periodic membrane structures is scarce, primarily due to the lack of appropriate techniques for their analysis in vivo. Currently, the only direct way to characterize cellular membrane architecture is by transmission electron microscopy (TEM). However, deciphering the spatial architecture solely based on two-dimensionally projected TEM images is a challenging task and prone to artifacts. In this review, we will provide an update on the current progress in identifying and analyzing 3D membrane architectures in biological systems, with a special focus on membranes with cubic symmetry, and their potential role in physiological and pathophysiological conditions. Proteomics and lipidomics approaches in defined experimental cell systems may prove instrumental to understand formation and function of 3D membrane morphologies.

Expression of transforming growth factor-alpha in hepatoblastoma

BACKGROUND

Transforming growth factor-alpha (TGF-alpha) is a potent stimulator of cell proliferation in the liver and in liver tumors; however, its significance and association with hepatocyte proliferation remains unclear.

METHODS

Expression of TGF-alpha and proliferation markers, such as proliferating cell nuclear antigen (PCNA) and cyclin A, were studied and correlated with each other in samples of tumor and surrounding liver tissue taken from nine patients with hepatoblastoma. An avidin-biotin-peroxidase immunohistochemical method was used for detection of TGF-alpha, PCNA, and cyclin A, and in situ hybridization was used to detect TGF-alpha mRNA.

RESULTS

Two types of tumor cells of epithelial origin were distinguished based on the expression of TGF-alpha protein and RNA. The more differentiated "fetal" phenotype had a high expression of TGF-alpha and correlated with a low expression of proliferation markers. The less differentiated "embryonal" phenotype had low TGF-alpha expression and high proliferation activity.

CONCLUSIONS

The expression of TGF-alpha is associated with a certain morphologic phenotype of tumor cells in hepatoblastoma; higher expression can be detected in more differentiated tumor cells. The negative correlation between the expression of TGF-alpha and proliferation markers suggests that the less differentiated embryonal cells do not depend on growth stimulation provided by TGF-alpha.

Hepatoblastomas: an ultrastructural and immunohistochemical study

Seven hepatoblastomas were studied by electron microscopy, and four of these were studied by immunohistochemistry. Five tumors were purely epithelial, and two were mixed epithelial-mesenchymal. They showed a spectrum of cellular differentiation ranging from primitive epithelial cells to differentiated cells resembling adult hepatocytes. Glycogen, lipid, basal lamina, and canaliculi were present in all cases. Mitochondria with large, membrane-bound, amorphous inclusions were present in one tumor, and large, complex, basal cell processes were present in two tumors. Ultrastructural features most characteristic of hepatocytes were most common in fetal type hepatoblastomas. Immunoreactive chromogranin cells were present in two tumors, one of which also contained immunoreactive somatostatin cells. The somatostatin-positive tumor had cells with granules resembling those seen in somatostatin-containing cells of normal pancreas and somatostatin-containing neuroendocrine carcinomas. Other immunoreactive substances were present, including alpha 1-antitrypsin (four cases), vimentin (embryonal cells in four cases; fetal cells in three cases), low-molecular weight cytokeratin (embryonal cells in three cases; fetal cells in four cases), and high-molecular weight cytokeratin (embryonal cells in one case; fetal cells in two cases). Osteoidlike material was positive for epithelial membrane antigen, vimentin, and S-100 protein.

A cytokeratin-immunohistochemical study of hepatoblastoma

Six cases of hepatoblastoma (five epithelial, one mixed epithelial-mesenchymal) were studied on serially cut cryostat sections, using a panel of monoclonal antibodies directed against individual cytokeratins, vimentin, and desmin, in an indirect immunoperoxidase procedure. Embryonic and fetal-type tumor cells expressed the "hepatocellular" cytokeratins no. 8 and 18 but, surprisingly, also expressed the "bile duct type" cytokeratin no. 19. In addition, two cases had a number of tumor cells which were also positive for the "bile duct type" cytokeratin no. 7. Cells embedded in osteoid-like material were immunoreactive for vimentin but also for cytokeratins no. 7, 18, and 19. Gel electrophoresis, and Western blotting of cytoskeletal extracts, confirmed the immunohistochemical data. The implications of these findings for the histogenesis of hepatoblastoma are discussed in this report.

Ultrastructure of liver cell and bile duct carcinomas

The primary concerns of the surgical pathologist examining a biopsy specimen are whether a particular neoplasm is originating within the liver or is metastatic and, if a primary, whether differentiation is toward liver cells or bile ducts. The present study was undertaken in the hopes of providing a broader concept of the ultrastructural spectrum of liver cell carcinoma (LCC) and a more precise understanding of the changes occurring in these neoplasms with dedifferentiation. The 20 liver cell carcinomas, 13 bile duct carcinomas (BDC), and 3 hepatoblastomas were studied ultrastructurally and the findings correlated with light microscopic sections stained by hematoxylin-eosin and the periodic acid-Schiff procedure with and without prior diastase digestion. Immunocytochemical staining for alpha 1-antitrypsin was carried out on selected tumors. Ultrastructural study can be useful in the distinction of LCC from BDC in the minority of cases in which this is difficult by light microscopy. While true mixed tumors appear to be uncommon, duct formation can be simulated by LCC cells. The extent to which electron microscopy will enable the pathologist to separate metastatic neoplasms in the liver from primary liver cell tumors depends on the relative ultrastructural features. Assessment of the value of electron microscopy as an aid to light microscopy in the histologic grading of LCC and BDC will require further study.

Primary hepatic tumors of childhood

A clinicopathologic review of 73 cases of primary liver tumors at Texas Children's Hospital, Houston, and Children's Medical Center, Dallas, has documented important prognostic and therapeutic implications for the histologic classification of hepatoblastoma. The pure "fetal" pattern was associated with cure in every instance that surgical excision was achieved (six of six patients), whereas only two of 19 patients with "embryonal" or other undifferentiated patterns of growth survived five years. The relationship of hepatoblastoma and hepatocarcinoma in childhood to antecedent conditions is discussed in detail. The uncommon liver sarcomas are also reviewed in the light of experience at these two institutions.

A mixed tumor of the omentum majus in an adult with discussion related to hepatoblastoma

A mixed tumor of the omentum majus found at autopsy of a 28-year-old man with a huge liver tumor is described. The primary tumor was identified in the omentum majus by macroscopic, histologic and electron-=microscopic observations. The tumor was finally diagnosed as a mixed tumor which resembled a hepatoblastoma consisting of immature and embryonal types of epithelial component and of mesodermal tumor including hemangioma, osteoid and myxomatous tissues in the primary lesion. Widespread multiple metastases of the epithelial component mainly to the liver, and partially in the lungs, diaphragm and lymph nodes were noted. The levels of alpha-fetoprotein and carcinoembryonic antigen were within normal limits, but the epithelial component showed a resemblance to primitive hepatocytes. This tumor was discussed related to hepatoblastoma in an adult, with the features compatible with description of the same tumors reported previously in the literature.

Liver tumors distinguished by immunofluorescence microscopy with antibodies to proteins of intermediate-sized filaments

Antibodies against constitutive proteins of different types of intermediate-sized filaments were used in immunofluorescence microscopy on frozen sections of normal rat liver and various rat liver tumors induced by treatment with nitrosamines. Antibodies to tonofilament prekeratin stained bile duct epithelia and hepatocytes of normal liver and hepatocellular carcinoma cells and ductal cells of cholangiofibromas. These cells were not significantly stained by antibodies to vimentin. By contrast, antibodies to vimentin stained mesenchymal cells of normal liver and cells of early and advanced angiosarcomas and of undifferentiated spindle cell sarcoma. These mesenchymal tumor cells were not stained with antibodies to prekeratin. The presence of intermediate-sized filaments in these tumors, often in large whorl-like aggregates, was also demonstrated by electron microscopy. The results show that immunofluorescence microscopy with antibodies to cytoskeletal proteins is a powerful tool for the classification and differential diagnosis of mesenchymal and epithelial liver tumors. We propose that staining with antibodies to proteins of different types of intermediate filaments can be used to improve the identification of tumors of other organs, including metastases, as well as non-neoplastic proliferative lesions.

Ultrastructural comparison of hepatoblastoma and hepatocellular carcinoma

The ultrastructural characteristics of fetal liver, two hepatoblastomas and two hepatocellular carcinomas were compared. Tumor cells of hepatoblastoma disclosed monotonous nuclei, poorly-developed cytoplasmic membrane system, abundant free ribosomes and prominent glycogen granules. Thos of hepatocellular carcinoma revealed comparatively pleomorphic nuclei, well-developed cytoplasmic membrane system, a few free ribosomes and numerous glycogen granules. Fetal liver showed monotonous nuclei, well-developed RER abundant free ribosomes and prominent glycogen granules. Young mesenchymal cells with well-developed RER and continuous basal lamina surrounding the epithelial cells were detected in both cases of hepatoblastoma but not in those of hepatocellular carcinoma. Tumor cells of hepatoblastoma in a case showed intramitochondrial crystalloids and thick bundles of fibrils in the cytoplasm.

Intracisternal tubular inclusions in nasopharyngeal carcinoma

Biopsy specimens obtained from 20 cases of nasopharyngeal carcinoma were examined under electronmicroscope for the presence of Intracisternal Tubular Inclusions (ITI). In eight (40 per cent) of them these inclusions could be identified. Although the morphogenesis and significance of these ITI are not clearly understood, they have been found in several autoimmune and viral diseases, including infectious mononucleosis, a disease caused by EBV, and Burkitt's lymphoma, which is closely associated with EBV. Hence, the presence of ITI in NPC, another disease associated with EBV, seems to be of some significance. It is proposed that these inclusions could be the result of an immunological reaction initiated by injured cells infected with EBV, which acted as an antigen. The presence of another type of cytoplasmic inclusion, hitherto unknown, has also been reported.

Clinical, hormonal and ultrastructure studies of a virilizing hepatoblastoma

Virilizing hepatoblastoma was found to be the cause of precocious puberty in a 3 1/4-year-old boy. Both human chorionic gonadotropins and alphafetoprotein in increased amounts were detected in serum and tumor tissue. These substances disappeared from the blood after removal of the tumor. Ultrastructure studies revealed the presence of dense, membrane bound, secretory granules responsible for the hormone production.

Electron microscopic study of benign hepatoma in a patient on oral contraceptives

Electron microscopic studies of a benign hepatoma in a 31-year-old women who was on contraceptive pills are presented. The electron microscopic picture showed highly differentiated liver cells with regularly developed bile canaliculi. The mitochondrial polymorphism, the formation of paracristalloids and the appearance of giant mitochondria were striking. The main change was the occurence of the numerous capillaries of varying caliber which were highly differentiated and formed an integral part of the tumor. On the basis of these finding the tumor is regarded as a benign mixed tumor. The well developed capillary system explaines the arteriographic characteristics and the frequent bleeding complications noted in the literature.

An ultrastructural study of mixed hepatoblastoma with osteoid elements

A case of mixed hepatoblastoma with osteoid elements was studied by light and electron microscopy. The ultrastructure of the epithelial elements showed a lack of differentiation and simple cytoplasmic organelles. However, an occasional cytoplasmic crystalloid structure were seen. The ultrastructure of the osteoid foci showed fibroblast-like cells capable of collagen formation, clearly distinguishable from the epithelial elements. These cells had neoplastic characteristics of nuclear pleomorphism and high nucleo-cytoplasmic ratio. These findings support the belief that hepatoblastoma arises from a multipotential blastema capable of both epithelial and mesenchymal differentiation, with the osteoid elements being an intrinsic neoplastic component of the tumor.