Trimeric G proteins modulate the dynamic interaction of PKAII with the Golgi complex

The Golgi complex represents a major subcellular location of protein kinase A (PKA) concentration in mammalian cells where it has been previously shown to be involved in vesicle-mediated protein transport processes. We have studied the factors that influence the interaction of PKA typeII subunits with the Golgi complex. In addition to the cytosol, both the catalytic (Cα) and regulatory (RIIα) subunits of PKAII were detected at both sides of the Golgi stack, particularly in elements of the cis- and trans-Golgi networks. PKAII subunits, in contrast, were practically absent from the middle Golgi cisternae. Cell treatment with either brefeldin A, AlF4 − or at low temperature induced PKAII dissociation from the Golgi complex and redistribution to the cytosol. This suggested the existence of a cycle of association/dissociation of PKAII holoenzyme to the Golgi. The interaction of purified RIIα with Golgi membranes was studied in vitro and found not to be affected by brefeldin A while it was sensitive to modulators of heterotrimeric G proteins such as AlF4 −, GTPγS, βγ subunits and mastoparan. RIIα binding was stimulated by recombinant, myristoylated Gαi3 subunit and inhibited by cAMP. Pretreatment of Golgi membranes with bacterial toxins known to catalyze ADP-ribosylation of selected Gα subunits also modified RIIα binding. Taken together the data support a regulatory role for Golgi-associated Gα proteins in PKAII recruitment from the cytosol