“A-kinase” regulator runs amok to provide a paradigm shift in cAMP signaling [Cell Biology] (Journal of Biological Chemistry)

The activity of the archetypal protein kinase A (PKA) is typically thought of in regards to the catalytic subunit, which is inhibited by the regulatory subunits in the absence of cAMP. However, it is now reported that one of the regulatory subunit isoforms (PKA-RI?) takes on a function of its own upon binding to cAMP, acting independently of this canonical cAMP signaling mechanism. PKA-RI? instead binds to and stimulates the catalytic activity of a guanine nucleotide exchange factor (P-REX1) that itself promotes Rac1 GTPase activation. This newly discovered function of PKA-RI? adds an additional layer of complexity to our understanding of cAMP signal transduction.