Cyclic AMP-specific PDE4 Phosphodiesterases as Critical Components of Cyclic AMP Signaling

In the five decades that have elapsed since the identification of the second messenger cAMP, most of the components involved in this signaling pathway have been identified, and many of their functions are understood at the molecular and atomic levels. Yet an unexpected and often disconcerting outcome of this progress is the realization that apparently identical cAMP signals induce divergent physiological responses. Countless reports indicate that G protein-coupled receptors (GPCRs)1 that activate the cAMP pathway have distinct and often opposing effects on cell replication/differentiation.