src-Related protein tyrosine kinases and their surface receptors

Abstract The CD4-p56 lck and CD8-p56 lck complexes have served as a paradym for an expanding number of interactions between src -family members (p56 lck , p59 fyn , p56 lyn , p55 blk ) and surface receptors. These interactions implicate src -related kinapses in the regulation of a variety of intracellular events, from lymphokine production and cytotoxicity to the expression of specific nuclear binding proteins. Different molecular mechanisms appear to have evolved to facilitate the receptor-kinase interactions, including the use of N-terminal regions, SH2 regions and kinase domains. Variations exists in stoichiometry, affinity and the nature of signals generated by these complexes in cells. The CD4-p56 lck complex differs from receptor-tyrosine kinases in a number of important ways, including mechanisms of kinase domain regulation of recruitment of substrates such as PI 3-kinase. Furthermore, they may have a special affinity for receptor-substrates such as the TcRζ, MB1/B29 or CD5 receptors, and act to recruit other SH2-carrying proteins, such as ZAP-70 to the receptor complexes. Receptor- sr kinase interactions represent the first step in a cascade of intracellular events within the protein-tyrosine kinase/phosphatase cascade.