GM-CSF signals for protein tyrosine phosphorylation in LNCaP cells. (A) Protein tyrosine phosphorylation. Cells were incubated in the absence (−) or in the presence (+) of 1 nmol/L GM-CSF from 2 seconds to 20 minutes at 37°C (upper panel), or with 0.01 nmol/L to 1 μmol/L GM-CSF for 2 minutes at 37°C (bottom panel). Tyrosine phosphoproteins were identified by immunoblotting with antiphosphotyrosine antibodies. Black and white arrowheads indicate proteins phosphorylated and dephosphorylated in response to GM-CSF, respectively. (B) Phosphorylation of MAP kinase. Cells were incubated with 10 pmol/L to 0.3 μmol/L GM-CSF for 1 minute at 37°C, or were incubated in the absence (−) or in the presence (+) of 100 nmol/L GM-CSF from 2 seconds to 20 minutes at 37°C. Phosphorylation of MAP kinase was assessed by immunoblotting with an antiphospho MAP kinase antibody. MAP kinase was identified with an anti-MAP kinase antibody. The arrowheads indicate the positions of the p42 and p44 MAP kinases.