Termination and activation of store‐operated cyclic AMP production

Diverse pathophysiological processes (e.g. obesity, lifespan determination, addiction and male fertility) have been linked to the expression of specific isoforms of the adenylyl cyclases (AC1‐AC10), the enzymes that generate cyclic AMP (cAMP). Our laboratory recently discovered a new mode of cAMP production, prominent in certain cell types, that is stimulated by any manoeuvre causing reduction of free Ca²⁺] within the lumen of the endoplasmic reticulum (ER) calcium store. Activation of this ‘store‐operated’ pathway requires the ER Ca²⁺ sensor, STIM1, but the identity of the enzymes responsible for cAMP production and how this process is regulated is unknown. Here, we used sensitive FRET‐based sensors for cAMP in single cells combined with silencing and overexpression approaches to show that store‐operated cAMP production occurred preferentially via the isoform AC3 in NCM460 colonic epithelial cells. Ca²⁺ entry via the plasma membrane Ca²⁺ channel, Orai1, suppressed cAMP production, independent of store refilling. These findings are an important first step towards defining the functional significance and to identify the protein composition of this novel Ca²⁺/cAMP crosstalk system.