Unique antigen of cultured Hodgkin's cells. A putative sialyltransferase

Differential expression of terminal transferase (TdT) in acute lymphocytic leukaemia expressing myeloid antigens and TdT positive acute myeloid leukaemia as compared to myeloid antigen negative acute lymphocytic leukaemia

We examined whether the allegedly aberrant expression of the lymphoid lineage associated DNA polymerase, terminal deoxynucleotidyl transferase (TdT), in acute myeloid leukaemia (AML) is associated with alterations of the enzyme at the cellular, biochemical or transcriptional level when compared to lymphoid leukaemia (ALL), either lacking or expressing myeloid antigens. By flowcytometric analysis, the intensity of TdT staining with monoclonal anti-TdT antibody was considerably weaker in TdT+ AML and myeloid+ ALL (M+ ALL) than in myeloid- ALL (M- ALL). TdT enzyme activity in TdT+ AML was on an average 10%, and in M+ ALL 25% of that measured in M- ALL. Anti-TdT antibodies precipitated a major specific protein of identical relative molecular mass (58 kD) from metabolically labelled TdT+ myeloblasts and lymphoblasts. By Northern blot analysis and ribonuclease protection assay, TdT transcript levels were significantly lower in TdT+ myeloblasts and M+ lymphoblasts than in M- ALL (P < 0.0001). The level of TdT transcription in AML was independent of the simultaneous expression of lymphoid-specific antigens, such as CD2 and CD19. Our data demonstrate that TdT expression is downregulated in association with myeloid features, not only in AML but also in ALL. This observation may provide the molecular basis for the differential therapeutic responsiveness, particularly to glucocorticoids, in these various leukaemia subtypes.

Recent results on the biology of Hodgkin and Reed-Sternberg cells. II. Continuous cell lines

The relative scarcity of Hodgkin (H) and Reed-Sternberg (RS) cells within biopsies from cases with Hodgkin's disease (HD) is an impediment to the analysis of the nature and function of these cells. Continuous cell lines as uniform and permanently available sources of cells provide a valid alternative. Development of HD cell lines has proven to be rather difficult when compared with the results on leukemia and Non-Hodgkin lymphoma cells. Only a few cell lines containing cells that resemble in-vivo H-RS cells have been established. Because the in-vitro culture conditions favor the self-propagation of residual normal cells, e.g. Epstein-Barr virus transformed B-lymphoblastoid cells or monocyte/macrophage monolayers, early attempts at culturing HD tissue resulted mainly in the generation of such cell lines. Even for the bona fide HD cell lines it is difficult to prove that the immortalized cells originated from an H-RS cell. These 13 HD cell lines have been extensively characterized in a large variety of aspects. These data have resulted in widely varying conclusions about the nature of the cell lines. It is apparent that all HD cell lines are unique among hematopoietic cell lines and are also different from one another. No conclusive evidence towards the origin of the cells has been obtained for some cell lines, while others could be operationally, albeit not always unequivocally, assigned to the T- or B-cell or monocyte-macrophage lineages. The overall phenotypes are often not concordant with those of normal hematopoietic cells; some cell lines show clearly mixed lineage attributes. The artifactual expansion of non-HRS cells in culture and the acquisition or loss of certain properties during the adaptation to culture systems cannot be excluded. There was also a bias for the establishment of cell lines from cases with advanced clinical stages, nodular sclerosing subtype and pleural effusions. The extensive analysis of a few cell lines has provided a wealth of information useful for the understanding of the biology of H-RS cells. The striking heterogeneity could be reflective of a biologically heterogeneous disease.

Expression of CD15 in tumours of the nervous system

The expression of the CD15 epitope was investigated by immunohistochemistry, western blotting and immuno-thin-layer chromatography on a large series of human nervous system tumours and ethylnitrosourea-induced rat gliomas. Our results show that CD15 is expressed as a glycoprotein- or glycolipid-associated epitope in normal human and rat brain. In contrast, immunoreactivity for CD15 was absent in tumour cells of experimental rat gliomas. In human tumours we found a more complex expression pattern. While intra- and perivascular granulocytes as well as macrophages in necrotic areas of anaplastic tumours were always strongly CD15-positive, immunoreactive tumour cells were detectable only in a fraction of low-grade gliomas. Anaplastic gliomas and glioblastomas consistently did not express the epitope on their tumour cells. In addition to individual low-grade gliomas, we found CD15-positive cases among metastatic carcinomas, craniopharyngeomas, meningiomas, germinomas and malignant melanomas. Our results suggest that immunohistochemistry for CD15 is potentially useful in diagnostic neuropathology as a marker for granulocytes in paraffin sections, as a supplementary tool for the histopathological grading of gliomas, and as an aid for differentiation between anaplastic glioma cells and non-neoplastic glia. Furthermore, it can be speculated that the lack of CD15 expression on anaplastic glioma cells may potentially be responsible for some of their characteristics--such as altered cellular interaction and loss of contact inhibition.

Human Golgi beta-galactoside alpha-2,6-sialyltransferase generates a group of sialylated B lymphocyte differentiation antigens

The role of the human beta-galactoside alpha-2,6-sialyltransferase (hu alpha-2,6-ST) in the generation of B cell surface antigens was investigated by selecting subclones of COS cells (monkey kidney epithelial cells) constitutively expressing a transfected cDNA which encodes the hu alpha-2,6-ST (COS alpha-2,6-ST cells). Expression of hu alpha-2,6-ST in COS cells was sufficient to generate sialylated cell surface epitopes on different glycosylated antigens recognized by monoclonal antibodies to CDw75, CD76, and the unclustered monoclonal antibodies HB-4 and EBU-65. These epitopes were sensitive to sialidase treatment and are likely to contain terminal alpha-2,6-linked sialic acid residues. A novel antiserum raised against bacterially expressed hu alpha-2,6-ST fusion protein was used to localize the sialyltransferase in two cell lines with high expression of either endogenous (B cell line JOK-1) or recombinant (COS alpha-2,6-ST cells) hu alpha-2,6-ST. In both cell lines, the enzyme was detected only intracellularly in the juxtanuclear region and not on the cell surface. In contrast, CDw75, formerly proposed to be identical with an alpha-2,6-ectosialyltransferase, was strongly expressed on the cell surface. The different expression patterns show that neither the CDw75 antigen nor any of the other sialylated antigens analyzed is identical with the hu alpha-2,6-ST. Furthermore, the presence of a surface-expressed alpha-2,6-ST appears unlikely in these cell lines. We propose that CDw75, CD76, HB-4, and EBU-65 represent a unique group of B cell differentiation antigens the production of which requires the enzymatic activity of alpha-2,6-ST.

Cell adhesion molecules in Hodgkin's disease

The fact that Hodgkin's cells are capable of binding lymphocytes has been observed both in vivo and in vitro. It is not unexpected, therefore, that cultured Hodgkin's cells have been found to express a high number of adhesive sites, including representative molecules from various adhesion molecule families.

Cellular protein profiles of the Hodgkin's disease cell lines L428, KM-H2 and HDLM-2: a comparative study

The origin of the malignant mononuclear Hodgkin's cell and the classic Reed-Sternberg cell in Hodgkin's disease (HD) remains controversial despite extensive immunohistological and lymphoid gene analysis. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) in combination with protein staining and radioactive labelling has not been fully exploited in analysing the HD-derived cell lines available. The NP40 solubilised cellular proteins from the three HD cell lines, L428, KM-H2 and HDLM-2 were analysed using these techniques and compared with other haemopoietic cell lines and leucocytes of myeloid and lymphoid origin. The electrophoretic patterns of the three HD cell lines, although clearly different from one another, had many features in common. No major differences between the cell types were detected by Coomassie brilliant blue staining. The HD cell lines were more readily distinguished from the myeloid and to a lesser extent the lymphoid cell lines by silver staining, but HD cell line specific proteins (13, 19, 36, 60, 150 kD) were detected only on one line, L428. Iodination of cell membrane molecules, SDS-PAGE and subsequent autoradiography revealed three molecules (118, 22, 12 kD) which were restricted to the HD cell lines and the B-cell line Mann, and one molecule (144 kD) restricted to the HD cell lines and U937. Molecules unique to HDLM-2 (211 kD) and L428 (46 kD) were also detected by this method. Cell surface labelling with NaB3H4 identified a glycoprotein of 102 kD limited to HDLM-2 and L428, as well as a glycoprotein of 97 kD present on KM-H2 alone and one of 63 kD on L428 alone. Overall the HD cell line protein profiles displayed little similarity to the patterns of the other cell types studied and provide further evidence to support functional and phenotypic studies which identify Hodgkin's cells as a unique cell type. The molecules identified as HD cell line restricted may have potential as markers for this cell type.

Differences in the abundance of variably spliced transcripts for the second asialoglycoprotein receptor polypeptide, H2, in normal and transformed human liver

The human hepatic asialoglycoprotein receptor comprises two homologous polypeptides designated H1 and H2. Two distinct complementary DNA clones encoding these receptor subunits have been previously isolated from the human hepatoblastoma cell line HepG2. We discovered that multiple variants of H2 transcripts exist both in HepG2 cells and in the normal human liver that, at least in part, appear to be the result of alternative splicing events. We have found that (a) the complementary DNA clone for H2 previously isolated from HepG2 cells, characterized by a 57-nucleotide insertion within the 5' end of the complementary DNA that is absent from H1, represented only one third of H2-related sequences in an unamplified normal human liver complementary DNA library and less than 10% of H2 clones in HepG2 cells; (b) the predominant message for H2 expressed in the liver and HepG2 cells, designated L-H2, appeared to represent the fully processed product of the gene encoding both L-H2 and H2; and (c) a variant H2 transcript existed in HepG2 cells, designated H2', that contained a novel, 5' 88-bp nucleotide insertion. Poly(A+) RNA analysis of the normal liver and HepG2 cells by complementary RNA hybridization and ribonuclease protection corroborated the observations made during the screening of complementary DNA libraries regarding the abundance of the various messages. A striking incongruity was found between the levels of messenger RNA containing the H2-specific 57-nucleotide sequence and the levels of polypeptide expressed in the liver and HepG2 cells as recognized by antiserum specifically raised against this sequence.

Biological and NMR markers for cancer

The search for a universal tumor marker continues. Present markers range from tumor products (polyamines, glycoproteins, peptides, hormones or carbohydrate-linked markers) to reaction products produced by the host tissues during tumor invasion. Techniques used to identify them include the classical methods of histology and cytochemistry as well as the more recent radioimmunoassay and metabolic probes. The in vivo techniques of increasing use for patient monitoring are MRS (magnetic resonance spectroscopy) and MRI (magnetic resonance imaging). The efficiency of some markers and statistical methods used in analyzing data are discussed, as are the ethical problems surrounding the use of new testing methods. Recent developments in MRI and MRS, marker elucidation, and evidence for a new autocrine differentiation-inhibiting factor (ADIF) are reviewed. Future needs and approaches focus on greater utilization of indicators of the preneoplastic state and of risk to cancer, as well as more careful attention to statistical analysis.

The rat hepatocyte plasma membrane organic anion binding protein is immunologically related to the mitochondrial F1 adenosine triphosphatase beta-subunit

A 55-kD organic anion binding protein (OABP) was identified previously in liver cell plasma membrane sinusoidal subfractions. Although this protein was localized to the surface of hepatocytes by immunofluorescence, immunoblot analysis revealed reactivity toward both plasma membrane and mitochondrial fractions. To clarify these findings, an immunoreactive clone from a rat liver cDNA expression library was isolated, the 1,500-base pair cDNA insert was sequenced, and the corresponding beta-galactosidase fusion protein was expressed and purified. The resulting sequence corresponded to that of the rat mitochondrial F1-adenosine triphosphatase (F1-ATPase) beta-subunit. This protein and OABP are of similar size and are mutually immunologically cross-reactive. That the antigen was present on the cell surface as well as in mitochondria was suggested from studies of immunoprecipitation after cell-surface iodination, and light- and electron-microscopic immunocytochemistry. Photoaffinity labeling of bovine F1-ATPase with high-specific-activity [35S]sulfobromophthalein revealed binding only to the beta-subunit. Hepatocyte uptake of bilirubin and sulfobromophthalein requires cellular ATP and mitochondria also transport these organic anions, which at high doses inhibit respiration. The presence of an organic anion binding site on the F1-ATPase beta-subunit suggests that it may play a role in these processes.

A marker and putative pathoantigen of Hodgkin's cells

A galactose-specific lectin, recently described by our laboratory, is immunologically demonstrable on the surface of neoplastic cells derived from patients with Hodgkin's disease. This Hodgkin's lectin is shown to be functionally and antigenically related to the galactose-N-acetylgalactosamine-specific lectin of the hepatocyte (HBP). Poly- and monoclonal antibodies against either the cytoplasmic tail or the cell-surface binding site of HBP recognize the Hodgkin's lectin as a 55 Kd protein. Expression of the 55 Kd antigen appears to be restricted to Hodgkin's disease involved tissues and cells of the monocyte/macrophage lineage. The putative identification of the Hodgkin's lectin as an ectosialyltransferase unique to Hodgkin's cells is supported by inhibition of enzymatic activity by anti-HBP antibodies. Cultured Hodgkin's cells, in analogy to purified HBP, agglutinate T-lymphocytes mediated by the Hodgkin's lectin. This cell-to-cell interaction results in the incorporation of sialic acid into lymphocyte surface asialoglycans as well as in the stimulation of lymphocyte proliferation. The function of the Hodgkin's lectin as lymphocyte agglutinant in vitro suggests its role as an immunomodulator contributing to the immunodeficiencies associated with Hodgkin's disease.

Effect of monensin on receptor recycling during continuous endocytosis of asialoorosomucoid

The binding of asialoglycoproteins to their liver cell receptor results in internalization of the ligand-receptor complex. These complexes rapidly appear in intracellular compartments termed endosomes whose acidification results in ligand-receptor dissociation. Ligand and receptor subsequently segregate: ligand is transported to lysosomes and is degraded while receptor recycles to the cell surface. The proton ionophore monensin prevents acidification of endosomes and reversibly inhibits this acid-dependent dissociation of ligand from receptor. The present study determined the effect of monensin treatment of short-term cultured rat hepatocytes on cell-surface-receptor content, determined both by their binding activity and immunologically, following continuous endocytosis of asialoorosomucoid. Inclusion of 5 microM monensin in the incubation medium reduced the number of immunologically detectable cell-surface receptors by 20% in the absence of ligand. During continuous endocytosis of asialoorosomucoid, inclusion of monensin resulted in a 30-40% reduction of cell-surface receptor detectable either by ligand binding or immunologically. These results suggest that the reduced liver-cell-surface content of receptor in monensin is due to intracellular trapping of ligand-receptor complexes. The reduction of surface receptor during monensin incubation in the absence of ligand suggests that "constitutive recycling" of plasma membrane components also requires intracellular acidification.