Sub-family selective actions in the ability of Erk2 MAP kinase to phosphorylate and regulate the activity of PDE4 cyclic AMP-specific phosphodiesterases

1 Expressed in intact cells and in vitro, PDE4B and PDE4C isoenzymes of cyc lic nucleotide phosphodiesterase (PDE), in common with PDE4D isoenzymes, ar e shown to provide substrates for C-terminal catalytic unit phosphorylation by the extracellular signal-regulated kinase Erk2 (p42(MAPK)). 2 In contrast, PDE4A isoenzymes do not provide substrates for C-terminal ca talytic unit phosphorylation by Erk2. 3 Mutant PDE4 enzymes were generated to show that Erk2 phosphorylation occu rs at a single, cognate serine residue located within the C-terminal portio n of the PDE4 catalytic unit. 4 PDE4 long-form isoenzymes were markedly inhibited by Erk2 phosphorylation . 5 The short-form PDE4B2 isoenzyme was activated by Erk2 phosphorylation. 6 These functional changes in PDE activity were mimicked by mutation of the target serine for Erk2 phosphorylation to the negatively charged amino aci d, aspartic acid. 7 Epidermal growth factor (EGF) challenge caused diametrically opposed chan ges in cyclic AMP levels in COS1 cells transfected to express the long PDE4 B1 isoenzyme compared to cells expressing the short PDE4B2 isoenzyme. 8 We suggest that PDE4 enzymes may provide a pivotal point for integrating cyclic AMP and Erk signal transduction in cells with 4 genes encoding enzym es that are either insensitive to Erk2 action or may either be activated or inhibited. This indicates that PDE4 isoenzymes have distinct Functional ro les, giving credence to the notion that distinct therapeutic benefits may a ccrue using either PDE4 subfamily or isoenzyme-selective inhibitors.