Live cell fluorescence imaging of T cell MEKK2: redistribution and activation in response to antigen stimulation of the T cell receptor.

T cell activation requires engagement of the T cell receptor (TCR) at the interface of conjugates formed with antigen-presenting cells. TCR engagement is accompanied by a redistribution of specific signaling molecules to the cytoplasmic region of the TCR complex. In this study, immunocytochemistry and live cell fluorescence imaging demonstrate that T cell MEK kinase 2 (MEKK2) is translocated to the T cell/antigen-presenting cell interface in response to antigen activation. MEKK2 translocation occurs more rapidly as the antigen concentration is increased. Biochemical activation of MEKK2 follows TCR stimulation, and expression of a dominant-negative MEKK2 inhibits TCR-mediated conjugate stabilization and ERK and p38 MAP kinase phosphorylation. Live cell fluorescence imaging thus enables characterization of signal transducers that are dynamically translocated following TCR engagement.