Background

The second messenger 3′,5′-cyclic adenosine monophosphate (cAMP) is involved in multiple physiological functions. In response to a variety of different hormones and other extracellular cues that operate via activation of G protein-coupled receptors (GPCRs), cAMP affects cellular processes that range from modulation of metabolic enzymes to regulation of transcription, from the control of cell survival to cross-talk with multiple other signalling pathways. In eukaryotic cells, cAMP activates three ubiquitously expressed intracellular cAMP effector proteins, the cAMP-dependent protein kinase A (PKA), the cyclic nucleotide gated ion channels, and the exchange protein activated by cAMP (Epac) . The presence of these three cAMP effector families contributes to convey a precise and integrated functional outcome to the cAMP signals. A fourth family of proteins, the Popeye domain containing proteins bind cAMP, although their specific function remains unclear.