Specific CD3 epsilon association of a phosphodiesterase 4B isoform determines its selective tyrosine phosphorylation after CD3 ligation

cAMP-specific phosphodiesterases (PDE) comprise an extensive family of enzy mes that control intracellular levels of cAMP and thus regulate T cell resp onses. It is not known how the function of these enzymes is altered by TCR engagement, We have examined this issue by studying one of the PDE isozymes (PDE4B), PDE4B RNA and protein were detected in resting PBLs, and the leve ls of PDE4B protein increased with cell cycling. In peripheral blood T cell s, two previously reported PDE4B isoforms could be detected: one was 75-80 kDa (PDE4B1) and the other was 65-67 kDa (PDE4B2), These two isoforms diffe red in their N-terminal sequence, with the presence of four potential myris tylation sites in the PDE4B2 that are absent in PDE4B1. Consequently, only PDE4B2 was found in association with the CD3 epsilon chain of the TCR, In a ddition, although both isoforms were phosphorylated in tyrosines in pervana date-stimulated T cells, only the TCR-associated PDE4B2 was tyrosine-phosph orylated following CD3 ligation, The kinetics of phosphorylation of TCR-ass ociated PDE4B2 correlated with changes in cAMP levels, suggesting that tyro sine phosphorylation of the TCR-associated PDE4B isoform upon engagement of this receptor may be an important regulatory step in PDE4B function. Our r esults reveal that selectivity of PDE4B activation can be achieved by diffe rential receptor association and phosphorylation of the alternatively splic ed forms of this PDE.