RAPID INTERFERON-GAMMA-STIMULATED TYROSINE PHOSPHORYLATION OF CYTOSOLIC AND MEMBRANAL PROTEINS IN HL-60 PROMYELOCYTIC CELLS

The involvement of tyrosine phosphorylation in the early stages of int erferon-gamma (IFNgamma)-induced monocytic differentiation of HL-60 ce lls was studied. Immunoblotting analysis demonstrated that IFNgamma in duced rapid changes in the tyrosine phosphorylation of several endogen ous cytosolic and membranal proteins. The most prominent of these poly peptides was a 84 kDa protein. In membranes, the IFNgamma-induced phos phorylation of this protein was detectable in 5 min, remained elevated for 3 h and declined thereafter, while a gradual decrease in the phos photyrosine content was observed in cytosols. In parallel, a 40% incre ase in the phosphotyrosine phosphatase activity was detected in the la ter stages of IFNgamma treatment. Rapid changes in tyrosine phosphoryl ation were detected also in a 64 kDa protein. In contrast, 2-day expos ure to IFNgamma was needed to potentiate significantly the tyrosine ph osphorylation of a 36 kDa membranal polypeptide. These data support th e involvement of tyrosine phosphorylation in the early stages of IFNga mma-induced monocytic differentiation of HL-60 cells.