Tracking functions of cGMP-dependent protein kinases (cGK).

The options available for distinguishing the effects of cGMP mediated by cGK versus those mediated by other cGMP targets are discussed and evaluated. These include the unnecessary but often sole reliance on synthetic, small-molecule activators and inhibitors of cGK which are increasingly recognized as deficient in specificity. Other important adjunct options include cGK overexpression using adenoviral vectors and transgenic animals, or use of cGK-deficient systems, i.e. cells which have spontaneously lost cGK during repetitive passaging in cell culture, cells treated with siRNA, or genetically-engineered cGK-deficient mice. Finally, cGK-dependent phosphorylation of substrates such as vasodilator stimulated phosphoprotein (VASP) and phosphodiesterase 5 (PDE 5) is described as a useful monitor of cGK presence and activity associated with physiological functions or dysfunctions of signaling pathways.