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.
KeywordsTyrosine Phosphorylation Insulin Receptor Kinase Activity Enhance Tyrosine Phosphorylation Intracellular Protein Tyrosine Rapid Tyrosine
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