A 41-kilodalton protein is a potential substrate for the p210bcr-abl protein-tyrosine kinase in chronic myelogenous leukemia cells.
Chronic myelogenous leukemia (CML) is characterized by a translocation involving the c-abl protein-tyrosine kinase gene. A chimeric mRNA is formed containing sequences from a chromosome 22 gene (bcr) at its 5' end and all but the variable exon 1 of c-abl sequence. The product of this mRNA, p210bcr-abl, has constitutively high protein-tyrosine kinase activity. We examined K562 cells and other lines established from CML patients for the presence of phosphotyrosine (P-Tyr)-containing proteins which might be p210bcr-abl substrates. Two-dimensional gel separation of 32P-labeled proteins followed by phosphoamino acid analysis of 25 phosphoproteins, which comprised the major alkali-stable phosphoproteins, indicated that three related proteins of 41 kDa are the most prominent P-Tyr-containing proteins detected by this method. The 41-kDa phosphoproteins are found in two other CML lines that we examined but not in lines of similar lineage isolated from patients with distinct leukemic disease. A protein that comigrates with the major form of pp41 (pp41A) and contains P-Tyr is also found in murine fibroblasts and B-lymphoid cells transformed by Abelson murine leukemia virus, which encodes the v-abl protein, and in platelet-derived growth factor-treated fibroblasts, in which it has been described previously. We analyzed three pairs of Epstein-Barr virus-immortalized B-cell lines from individual CML patients and found that only the lines in which active p210bcr-abl was present contained detectable pp41. We also performed immunoblotting with anti-P-Tyr antibodies on the same CML cell lines and detected at least four other putative substrates of p210bcr-abl, which were undetected with use of the two-dimensional gel technique.
Freed
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Molecular Biology and Virology Laboratory, Salk Institute, San Diego, California 92186.
Hunter
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T
D000818:Animals; D015153:Blotting, Western; D015180:Electrophoresis, Gel, Two-Dimensional; D016044:Fusion Proteins, bcr-abl / Q000378:metabolism*; D006801:Humans; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000201:enzymology*; D010750:Phosphoproteins / Q000378:metabolism*; D013379:Substrate Specificity; D014407:Tumor Cells, Cultured
D010750:Phosphoproteins; D016044:Fusion Proteins, bcr-abl