Hydrolyzes the second messenger 3',5'-cyclic AMP (cAMP), which is a key regulator of many important physiological processes. Efficiently hydrolyzes cAMP. Efficiently hydrolyzes cAMP. 3',5'-cyclic AMP + H2O = AMP + H(+) 3',5'-cyclic AMP + H2O = AMP + H(+) Binds 2 divalent metal cations per subunit. Site 1 may preferentially bind zinc ions. Binds 2 divalent metal cations per subunit (By similarity). Site 2 has a preference for magnesium and/or manganese ions (By similarity). Inhibited by rolipram. Purine metabolism; 3',5'-cyclic AMP degradation; AMP from 3',5'-cyclic AMP: step 1/1. Interacts with LYN (via SH3 domain). Interacts with ARRB2. Isoform 2 is testis specific. Phosphorylated by MAPKAPK2 at Ser-147; it counteracts PKA-induced activation of PDE4A and modulates intracellular cAMP levels. Likely involved in cellular desensitization to cAMP signaling. Proteolytically cleaved by CASP3. Incomplete sequence. Belongs to the cyclic nucleotide phosphodiesterase family. PDE4 subfamily.