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. Author manuscript; available in PMC: 2016 Jan 26.
Published in final edited form as: Curr Opin Pharmacol. 2011 Oct 31;11(6):689–697. doi: 10.1016/j.coph.2011.10.003

Figure 1.

Figure 1

Summary of cyclic nucleotide signaling pathways: cyclic nucleotides are generated by adenylyl-cyclase and guanylyl-cyclase; the former, activated by G-protein-coupled receptors, and the latter, by molecules such as natriuretic peptide or nitric oxide. In turn, cAMP activates PKA and EPAC. EPAC is involved in the regulation of several cellular processes, including integrin-mediated cell adhesion and cell–cell junction formation [74], exocytosis [75,76,77], and insulin secretion, while PKA is involved in metabolic processes, cell growth, differentiation, and proliferation. cGMP activates PKG which in turn mediates the phosphorylation of proteins involved in apoptosis, inflammation, and other physiologic processes, including smooth muscle contractility [78], the visual transduction cascade, and platelet aggregation. By catalyzing hydrolysis of cAMP and cGMP, PDEs regulate their intracellular concentrations and, consequently, their myriad biological effects.