Biochemical characterization of tumor-specific cell surface antigens on avian oncornavirus transformed cells

Reflections on the pathogenesis of diseases caused by the acute avian leukosis/sarcoma viruses with special reference to avian erythroblastosis

The various diseases that follow experimental infection with the acute and non-acute avian oncoviruses are discussed with special reference to the pathogenesis of avian erythroblastosis. One view, based on in vitro studies, sees erythroblastosis as the product of a failure in the differentiation of virus-infected stem cells to mature erythrocytes, as a result of cell 'transformation'. The results of some in vivo studies, however, point to a resemblance of the disease to a haemolytic anaemia, where cellular death is an important component. It seems probable that the disease is the result of transformation of cells of the erythroblastic series followed by the death of many of these cells due to influences that have not yet been determined. Determination of the causes of this cellular death may prove to be as important for our understanding of the problem of leukaemia as the work that has already been accomplished in explaining the causes of cell transformation. It is also suggested that the tendency of gs amino acid sequences of the avian leukosis viruses and mouse leukaemia viruses to form fusion proteins with a variety of proto-oncogenes may be part of a wider phenomenon, and that these sequences may fuse with other proteins, altering their properties. More work is required on the possibility that there is an undiscovered immunological component in the progression of the L/S diseases.

Release of an Mr 140,000 glycoprotein in the culture media of certain human sarcoma and melanoma cell lines

A 140 K glycoprotein was detected in the culture media of human sarcoma and melanoma cell lines by labeling with several radioactive amino acid and sugar precursors, followed by sodium dodecylsulfate-polyacrylamide gel electrophoresis and fluorography. In contrast to this, in the culture media of metabolically labeled embryonic and skin fibroblasts this glycoprotein was not found. Likewise, a protein with an identical molecular weight of 140 K was also found in culture media after cell surface labeling of the neoplastic cells but not in the culture media from control cells. The [35S]methionine-labeled 140 K was not split by collagenase and did not appear to be a fragment of fibronectin. We discuss the possibility that secretion of the 140 K glycoprotein is a transformation-related phenomenon.

Cell-surface antigens induced by RNA tumour viruses

Host animals show an immune response to the surface of cells infected with RNA tumour viruses. An element of this response is due to expression of viral structural antigens, but the major part is due to virus-induced cell-surface antigens (CSAs). This article compares the properties of CSAs of the avian, murine and feline retrovirus systems.

Immunologic identification of fetal calf serum-derived proteins on the surfaces of cultured transformed and untransformed rat cells

The antigens of rat embryo fibroblasts (REF) and of rat Rous sarcoma cells (derived by in vivo passage of oncogenically transformed REF) were studied using the technique of non-ionic detergent solubilization of radiolabelled cells. Solubilized antigens were complexed with rat immune IgG, and precipitation of the complexes was accomplished with rabbit anti-rat IgG. The precipitated radiolabelled antigens were then dissolved in sodium dodecyl sulfate and separated by polyacrylamide gel electrophoresis. This investigation disclosed the existence of cell surface antigenic proteins which are derived from the fetal calf serum (FCS) used in the cell-culture medium. These FCS-dependent antigens include at least three molecular species of approximate molecular weights 95,000, 80,000 and 98,000 daltons. They are probably derived from simple adsorption of FCS proteins to the cell surface, although more complex interactions are possible. One of these proteins (95,000 daltons) is of particular interest. It tenaciously adheres to the cell surface so that a trace amount remains even after subculture in the absence of FCS. Rat Rous sarcomas which are morphologically highly transformed appear to bind very little or none of this protein to their surfaces, whereas untransformed rat embryo fibroblasts bind large quantities. A rat Rous sarcoma line which is intermediate in morphological transformation binds an intermediate amount of this antigen. These findings invite speculation that the interaction of certain serum components with the cell surface may be related to plasma membrane properties which distinguish untransformed and transformed cells.

[Model studies on virus-induced tumors and their immunological treatment (author's transl)]

After a review of the general biological properties of C-type oncorna viruses, results are presented on the structure of an exogenous murine leukemia virus (FLV) and on the serobiological properties of its structural proteins. Our findings suggested a major role of the viral surface glycoprotein gp71 in immunological defense mechanisms. This was confirmed by vaccination experiments with isolated gp71 in mice. The induced immunity was highly specific and not operative against endogenous murine C-viruses belonging to other serotypes. Surprisingly the latter were found to be activated by the vaccination with gp71 of FLV. In heterologous animal species isolated FLV-gp71 induced the formation of broadly reacting antibodies. They were found to be effective in the therapy of infections with FLV in mice as well as with feline leukaemia virus in cats. Most impressive results were obtained with an antiserum prepared against feline leukaemia virus in a goat. This serum completely suppressed sarcomas induced by infection with feline sarcoma virus.

Separation of the Moloney leukemia virus-determined cell surface antigen (MCSA) from known virion proteins associated with the cell membrane

Cell membranes of Moloney lymphoma cells (YAC, of strain A origin) were solubilized by NP40. The antigenicity of the solubilized protein fraction was assayed by inhibition of the corresponding cytotoxic reaction against YAC target cells. The Moloney leukemia virus (MLV)-determined cell surface antigen (MCSA) was detected with mouse antisera, produced by the repeated inoculation of heavily irradiated YAC cells into syngeneic mice. Virion proteins gp71, p30, p15, p12 and p10 were identified with goat or rabbit antisera against purified Rauscher and Friend leukemia virus proteins. MCSA was found to bind to Con-A--Sepharose and was eluted by mannoside together with H-2A AND GP71. In contrast, p30, p12, p10 and part of p15 and p15(E), were not retained on the column and could be separated from MCSA. Passage of the glycoprotein fraction through Sephadex G-200 led to the separation of MCSA activity from gp71 and H-2A. MCSA eluted between the immunoglobulin (IgG) and the bovine serum albumin (BSA) size markers. MCSA could be also separated from the known viral proteins and from H-2 by velocity centrifugation in sucrose gradients. It sedimented with approximately 6.6 S ahead of gp71 (4.4 S) and H-2 (3.2 S). It is suggested that MCSA may be a glycoprotein with an approximate molecular weight of 110,000 and distinct from the known viral proteins gp71, p30, p15(E), p12, p10 and from H-2.

The effect of transformation-defective avian oncornavirus mutants on tumor antigen expression

The recent isolation of conditional (temperature sensitive) and nonconditional transformation-defective mutants of avian sarcoma virus strains has facilitated the investigation of the effect of virus transformation on the cell's phenotype, e.g., with respect to morphology, growth pattern, or cell surface antigenicity. Special emphasis was laid on elucidating the correlation between transformed phenotype and tumor antigen expression. All of the tested nontransforming deletion mutants and the majority of the temperature-sensitive mutants were unable to induce tumor antigens in phenotypically untransformed cells. However, 3 temperature-sensitive mutants were found which were able to support the expression of tumor specific surface antigens even at restrictive temperature, when cells otherwise exhibited a normal phenotype. The theoretical and practical implications of this association between normal phenotype and tumor antigen expression are discussed.