Protein tyrosine phosphatase-1C is rapidly phosphorylated in tyrosine in macrophages in response to colony stimulating factor-1

An ~64-kDa cytoplasmic protein is rapidly phosphorylated in tyrosine in the response of macrophages to colony stimulating factor-1. To identify this protein, BAC1.2F5 macrophages were incubated with or without colony stimulating factor-1, the phosphotyrosine-containing portion of their cytosolic fractions subjected to size exclusion chromatography, and the 45- 70-kDa fraction further fractionated by reverse phase high pressure liquid chromatography (RP-HPLC). Tryptic peptides of pooled RP-HPLC fractions from stimulated cells (containing the ~64-kDa protein and an ~54-kDa protein) and from unstimulated cells (containing the ~54-kDa protein alone), were sequenced directly. All seven readable sequences of 8 sequenceable peptides present uniquely in the stimulated fraction were present in the sequence of the src homology 2 domain-containing protein tyrosine phosphatase-1C (PTP- 1C). The identity of the ~64-kDa protein was confirmed by Western blotting with an antibody raised to a PTP-1C peptide. The rapid, growth factor- induced tyrosine phosphorylation of PTP-1C suggests that it may be involved in very early events in growth factor signal transduction.