pp75: A Novel Tyrosine Phosphorylated Protein that Heralds Differentiation of HL-60 Cells
The promyelocytic (HL-60) leukemia cells are an excellent model system to study cellular differentiation since they undergo morphological changes in response to various differentiation agents which result in a phenotype with the characteristics of a monocyte/macrophage or a granulocyte (Collins, 1987). Alterations in protein tyrosine phosphorylation were implicated as playing an important role in the induction and maintenance of the differentiated phenotype of HL-60 cells (Frank and Sartorelli, 1988) as several specific oncogene products which possess protein tyrosine kinase (PTK) activity are expressed during early stages of myeloid differentiation (Sariban et al. 1985; Gee et al. 1986; Yu and Glazer, 1987). Hence, Potential substrates for these PTKs could play an important role in regulating the differentiation process. To observe changes in phosphotyrosine metabolism at the substrates level, HL-60 cells were treated with a combination of H2O2 and vanadate to inhibit the intracellular protein tyrosine phosphatase (PTPase) activity (Heffetz et al. 1990). Such treatment enabled us to enhance markedly protein tyrosine phosphorylation and detect a novel 75 kDa protein that undergoes enhanced tyrosine phosphorylation during early stages of differentiation of these cells.
KeywordsH2O2 Tyrosine Leukemia Superoxide Vanadate
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