Abstract
Intracellular fluctuations of the second messenger cyclic AMP (cAMP) are regulated with spatial and temporal precision. This regulation is supported by the sophisticated arrangement of cyclases, phosphodiesterases, anchoring proteins, and receptors for cAMP. Discovery of these nuances to cAMP signaling has been facilitated by the development of genetically encodable tools for monitoring and manipulating cAMP and the proteins that support cAMP signaling. In this review, we discuss the state-of-the-art in development of different genetically encoded tools for sensing cAMP and the activity of its primary intracellular receptor protein kinase A (PKA). We introduce sequences for encoding adenylyl cyclases that enable cAMP levels to be artificially elevated within cells. We chart the evolution of sequences for selectively modifying protein–protein interactions that support cAMP signaling, and for driving cAMP sensors and manipulators to different subcellular locations. Importantly, these different genetically encoded tools can be applied synergistically, and we highlight notable instances that take advantage of this property. Finally, we consider prospects for extending the utility of the tool set to support further insights into the role of cAMP in health and disease.
Highlights
The discovery that some hormones elevate the second messenger cyclic AMP without triggering canonical effects such as increased phosphorylase activity (Keely, 1979; Hayes et al, 1980) indicated that cAMP may be compartmentalized in cells (Edwards et al, 2012)
We introduce genetically encoded sensors of cAMP and protein kinase A (PKA) activity, before discussing tools based upon ACs
We describe sequences that are available for targeting such tool proteins to specific sub-cellular locations and for modifying protein interactions involving cAMP signaling proteins
Summary
The discovery that some hormones elevate the second messenger cyclic AMP (cAMP) without triggering canonical effects such as increased phosphorylase activity (Keely, 1979; Hayes et al, 1980) indicated that cAMP may be compartmentalized in cells (Edwards et al, 2012). They have illuminated how PKA interacts spatiotemporally with phosphodiesterase (PDE) enzymes that degrade cAMP (Willoughby et al, 2006), with the exchange-protein activated by cyclic AMP (Epac; Dodge-Kafka et al, 2005), and with Ca2+ signals (Cooper and Tabbasum, 2014) This genetically encoded tool set has been applied to establish a role for localized cAMP signaling in diseases (Gold et al, 2013b) such as heart failure (Nikolaev et al, 2010), muscular dystrophy (Roder et al, 2009), diabetes (Zhang et al, 2005), breast cancer (Hansen et al, 2009), and adrenal Cushing’s syndrome (Beuschlein et al, 2014). We consider how the tool set might be extended and combined in novel ways to enable further advances in the understanding of cAMP signaling
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