Hyperphosphorylation of a novel 80 kDa protein-tyrosine kinase similar to Ltk in a human Ki-1 lymphoma cell line, AMS3.

Ki-1 lymphoma is a subtype of human malignant lymphoma characterized by the expression of CD30 (Ki-1) and a peculiar morphology. It is occasionally accompanied by a unique reciprocal chromosomal translocation t(2;5)(p23;q35). A Ki-1 lymphoma cell line, AMS3, was established by maintaining biopsied tumor cells in SCID (severe combined immunodeficiency) mice. To investigate abnormalities of the signal transduction in Ki-1 lymphomas, AMS3 lysate was immunoprecipitated with anti-phosphotyrosine monoclonal antibody, 25.2G4, and the immunoprecipitates were subjected to kinase assay and immuno-blotting with 25.2G4. A unique phosphotyrosine-containing protein of MW 80,000, designated p80, was found only in AMS3 cells and not in other cell lines or mononuclear cells from healthy donors. Subsequent amino acid sequence analysis of its tryptic digests showed that p80 was a hitherto undescribed tyrosine phosphoprotein similar to Ltk (leukocyte tyrosine kinase). Furthermore, physical interaction of p80 with CD30 was suggested from immunoprecipitation experiments with AMS3 lysates.