Feline sarcoma virus-specific transformation-related proteins and protein kinase activity in tumor cells

Infection with feline leukemia virus associated with induction of humoral response to a normal cell protein

Selected populations of cats that were naturally exposed to the feline leukemia virus (FeLV) were found to have humoral antibodies to a normal cell protein designated NCP105. Earlier studies revealed that cats exposed to FeLV often had serum antibodies to the feline oncornavirus-associated cell membrane (FOCMA) as well as to a feline sarcoma virus (FeSV) -specific transforming protein designated gag-fes. Cats with no history of exposure to FeLV or FeSV lacked antibodies to all three antigens: NCP105, FOCMA, and gag-fes. Following exposure to FeLV, cats develop antibodies to either NCP105 or to gag-fes and FOCMA, but not to both groups of antigens. NCP105 is present in both normal and transformed cells from a wide variety of species. It lacks peptide homology with gag-fes and it is not a phosphoprotein. The presence of antibodies to NCP105 in cats exposed to FeLV but not in unexposed cats suggests that FeLV may activate the NCP105 gene or increase the relative immunogenicity of this protein in vivo.

Antibodies to cell membrane antigens associated with human T-cell leukemia virus in patients with AIDS

The acquired immune deficiency syndrome (AIDS), which has recently occurred at increasing rates in homosexual men, intravenous drug users, and others, is characterized by the development of Kaposi's sarcoma and several opportunistic infections including pneumonia caused by Pneumocystis carinii. Serum samples from patients with AIDS and from matched and unmatched control subjects were examined for the presence of antibodies to cell membrane antigens associated with human T-cell leukemia virus. Nineteen of 75 of the AIDS patients had antibodies directed to surface antigens of Hut 102, a reference T lymphoid cell line infected with leukemia virus, as did two of the 336 control subjects.

Detection and localization of a phosphotyrosine-containing onc gene product in feline tumor cells

Protein phosphorylation by a tyrosine-specific kinase is now recognized as a common event in retrovirus-transformed cells. We report in this communication that the feline sarcoma virus (FeSV) encoded transformation-specific proteins (gag-fes fusion proteins) and their associated protein kinases are also found in the FeSV in vivo induced tumor preparations, either in the form of fresh tumor homogenate or in the form of cultured cells. With the combined use of subcellular fractionation and detergent extraction we found that the protein kinase activity was present in both the membrane fraction (P100) and the cytosol (S100). The gag-fes proteins of two different strains of FeSV were found to associate with the cell framework to different degrees, suggesting that the specific conformational presentation of these proteins may be dictated by the unique portion of each polyprotein. The same gag-fes transformation related proteins could be immunoprecipitated with antiserum to phosphotyrosine.