Zinc dependent activation of cAMP-specific phosphodiesterase (PDE4A)

Cyclic nucleotide phosphodiesterases (PDE), including PDE4A, contain two consensus sequences (HX3HX24-26E) which have been associated with Zn2+-binding and activation with other proteins. This study shows that Zn2+ activates purified recombinant human PDE4A with an EC50 of <1 mu M. The EC50 for Mg2+, the generally accepted activating metal ion, is approximate to 100 mu M. Zn2+ concentrations higher than 5 mu M are inhibitory. Mn2+, Co2+ and Ni2+ also activate PDE4A with EC50 values of approximately 2, 3 and 10 mu M, respectively. PDE4A binds Zn-65(2+) with a K-d of 0.4 mu M and approximate to 1:1 stoichiometry. Titrations of PDE4A inhibition with Mg2+ and Zn2+ as activating metal ions showed that the competitive inhibitors R-Rolipram, CDP-840, RS-14203 and KF18280 are shifted at least 10-fold to lower potency in the presence of Zn2+. The effect is likely at the site of inhibitor binding as the K-m for cAMP in the presence of Mg2+ and Zn2+ is similar (1-3 mu M). The K-d of [H-3]-R-Rolipram for PDE4A was increased at least 30-fold from 3 nM (with Mg2+) by the presence of Zn2+. The high affinity of Zn2+ for PDE4A indicates that this metal may play a role in the regulation of PDE4A activity. (C) 1997 Academic Press.