TYROSINE KINASE JAK1 IS ASSOCIATED WITH THE GRANULOCYTE-COLONY-STIMULATING FACTOR-RECEPTOR AND BOTH BECOME TYROSINE-PHOSPHORYLATED AFTER RECEPTOR ACTIVATION

Granulocyte-colony-stimulating factor (G-CSF) stimulates the prolifera tion and differentiation of cells of the neutrophil lineage by interac tion with a specific receptor. Early signal transduction events follow ing G-CSF receptor activation were studied. We detected tyrosine phosp horylation of both the G-CSF receptor and the protein tyrosine kinase JAK1 following G-CSF binding to the human G-CSF receptor. In vitro, th e kinase activity of JAK1 was increased by G-CSF stimulation. Coimmuno precipitation of JAK1 with the G-CSF receptor suggested a physical ass ociation which existed prior to G-CSF stimulation.