Hydrolyzes the second messenger cAMP, which is a key regulator of many important physiological processes. May be involved in maintaining basal levels of the cyclic nucleotide and/or in the cAMP regulation of germ cell development. Binding to RAF1 reduces RAF1 'Ser-259' inhibitory-phosphorylation and stimulates RAF1-dependent EGF-activated ERK-signaling. Protects against cell death induced by hydrogen peroxide and staurosporine. 3',5'-cyclic AMP + H2O = AMP + H(+) Binds 2 divalent metal cations per subunit. Site 1 may preferentially bind zinc ions, while site 2 has a preference for magnesium and/or manganese ions. Inhibited by dipyridimole. Insensitive to selective PDE inhibitor rolipram and to the non-selective inhibitor, IBMX. Purine metabolism; 3',5'-cyclic AMP degradation; AMP from 3',5'-cyclic AMP: step 1/1. Interacts with RAF1. The interaction promotes RAF1 activity. Expressed in multiple tissues, with highest levels in testis, followed by liver, heart, skeletal muscle, and kidney. In the testis, expressed specifically in the seminiferous tubules, in postmitotic pachytene spermatocytes (PubMed:9671792). Low expression, if any, in lung, smooth muscle, pancreas, thyroid, thymus, submaxillary gland, spleen, prostate, epididymus, uterus (PubMed:9671792). Expressed in embryos at 7 dpc. Not detected at later stages, including 11, 15 and 17 dpc (PubMed:9671792). In the testis, expression restricted to middle and late pachytene spermatocytes (PubMed:9671792). Composed of a C-terminal catalytic domain containing two putative divalent metal sites and an N-terminal regulatory domain. Phosphorylated at Ser-355 by PKA under elevated cAMP conditions, this enhances catalytic activity. Reduced phosphorylation of Mapk1/Erk2 and Mapk3/Erk1, both basal levels and those induced by EGF treatment. Belongs to the cyclic nucleotide phosphodiesterase family. PDE8 subfamily.