The Membrane-proximal Portion of CD3 ε Associates with the Serine/Threonine Kinase GRK2

The activation of protein kinases is one of the primary mechanisms whereby T cell receptors (TCR) propagate intracellular signals. To date, the majority of kinases known to be involved in the early stages of TCR signaling are protein-tyrosine kinases such as Lck, Fyn, and ZAP-70. Here we report a constitutive association between the TCR and a serine/threonine kinase, which was mediated through the membrane-proximal portion of CD3 . Mass spectrometry analysis of CD3 -associated proteins identified G protein-coupled receptor kinase 2 (GRK2) as a candidate Ser/Thr kinase. Transient transfection assays and Western blot analysis verified the ability of GRK2 to interact with the cytoplasmic domain of CD3 within a cell. These findings are consistent with recent reports demonstrating the ability of certain G protein-coupled receptors (GPCR) and G proteins to physically associate with the / TCR. Because GRK2 is primarily involved in arresting GPCR signals, its interaction with CD3 may provide a novel means whereby the TCR can negatively regulate signals generated through GPCRs.