REGULATION OF ZAP-70 INTRACELLULAR-LOCALIZATION - VISUALIZATION WITH THE GREEN FLUORESCENT PROTEIN

To investigate the cellular dynamics of ZAP-70, we have studied the di stribution and regulation of its intracellular location using a ZAP-70 green fluorescent protein chimera. Initial experiments in epithelial cells indicated that ZAP-70 is diffusely located throughout the quiesc ent cell, and accumulates at the: plasma membrane upon cellular activa tion, a phenotype enhanced hy the coexpression of Lck and the initiati on of: ZAP-70 kinase activity. Subsequent studies in T cells confirmed this phenotype. Intriguingly, a large amount of ZAP-70, both chimeric and endogenous, resides in the nucleus of quiescent and activated cel ls. Nuclear ZAP-70 becomes tyrosine phosphorylated upon stimulation vi a the T cell receptor, indicating that it may have an important biolog ic function.