PARTIAL CHARACTERIZATION OF PROTEIN TYROSINE KINASE-ACTIVITY IN NORMAL AND LEUKEMIC HUMAN MYELOID CELLS

We have examined the expression of the protein tyrosine kinase (PTK) encoding oncogenes fes and abl in normal and malignant human myeloid cells in immunoblotting experiments. fes was markedly present in all cytosolic and most membrane fractions of normal and malignant cells. abl was only visible in normal cells, and occurred mostly in the cytosolic fractions. Molecular weights of identified proteins were different from the known products of fes and abl, possibly by alternative splicing at the mRNA level or by proteolysis. PTKs in myeloid cells were further purified by fast liquid protein chromatography (FPLC). PTK-activities of column fractions were assayed using a solid-phase non-radioactive dot-blot assay. Cytosolic and membrane fractions showed a FPLC pattern with a constant as well as a variable part in both normal and malignant cells, possibly indicative for PTKs with specialized functions in normal cell growth and transformation. Partial characterization of PTKs from different eluted peaks of AML-M4 blast cells demonstrated that PTKs from these peaks are kinetically distinct from each other.