Association of specific tyrosine phosphorylation with stages of B-cell differentiation in human lymphoid leukemias

Differentiation of Burkitt lymphoma cells by hexamethylenbisacetamide

Hexamethylenbisacetamide (HMBA) can induce the Burkitt lymphoma Raji cells to enter the differentiation process as evidenced by the decrease of HLA-DR antigens. This event is preceded by a decrease of c-myc expression and of the phosphorylation of cellular proteins, due to either a decrease of tyrosine protein kinase activity or an increase of tyrosine phosphatase activity. These three events form a sequence and are part of the genetic program for differentiation and growth though they may not be causally related.

Cell lines and peripheral blood leukocytes derived from individuals with chronic myelogenous leukemia display virtually identical proteins phosphorylated on tyrosine residues

An aberrant p210BCR-ABL protein that possesses constitutive protein-tyrosine kinase activity is presumed to be involved in the development of the neoplastic phenotype in chronic myelogenous leukemia (CML). Using a highly specific antibody against phosphotyrosine, we have isolated the tyrosine-phosphorylated p210BCR-ABL and several other proteins containing phosphotyrosine from a variety of CML cell lines. p210BCR-ABL isolated by the monoclonal anti-phosphotyrosine antibody possessed protein-tyrosine kinase activity in vitro comparable to that of the p210BCR-ABL isolated by antibody to a specific peptide sequence in the ABL protein-tyrosine kinase. Other prominent proteins containing phosphorylated tyrosine residues were observed at 185, 150, 120, 105, 63, 56, 36, and 32 kDa, and less prominent proteins were observed at 195, 155, 94, 53, 40, and less than 29 kDa. Staphylococcal V8 peptide mapping indicated that proteins of similar molecular weights were highly homologous to each other across cell lines, despite the diverse hematopoietic lineages of these cells and the genetic heterogeneity of the patients from whom the CML cell lines were derived. Phosphopeptide mapping also revealed that these proteins were distinct from each other as well as from p210BCR-ABL. Because virtually identical phosphotyrosine-containing proteins were found in peripheral blood leukocytes taken directly from CML patients, these proteins are not an artifact of long-term tissue culture but appear to be an integral part of the CML phenotype.