Tyrosine-kinase-dependent signaling pathways

Protein tyrosine kinases are important transducers of a variety of extracellular signals that regulate proliferation, differentiation, and specific functions of differentiated cells. Most of the known protein tyrosine kinases are associated with cell surface receptors. Ligand binding to the receptor activates one or more protein tyrosine kinases to initiate a network of signaling pathways that regulate metabolism and gene expression. Recently, a focal adhesion tyrosine kinase (FAK) has been shown to respond to the assembly of adhesion junctions, indicating a role for tyrosine kinase in the transduction of cell adhesion signal. The discovery of a DNA-binding tyrosine kinase, c-Abl, and the identification of RNA polymerase II as a substrate of nuclear tyrosine kinases demonstrate that protein tyrosine kinases may also directly regulate transcription. Highlights of these recent developments in tyrosine-kinase-dependent signaling pathways are summarized here.