Activity of Adenylyl Cyclase Type 6 Is Suppressed by Direct Binding of the Cytoskeletal Protein 4.1G

The G protein-coupled receptor (GPCR) signaling pathways mediated by trimeric G proteins have been extensively elucidated, but their associated regulatory mechanisms remain unclear. Parathyroid hormone (PTH)/PTH-related protein receptor (PTHR) is a GPCR coupled with G_s and G_q G_s activates adenylyl cyclases (ACs), which produces cAMP to regulate various cell fates. We previously showed that cell surface expression of PTHR was increased by its direct interaction with a subcortical cytoskeletal protein, 4.1G, whereas PTHR-mediated G_s/AC/cAMP signaling was suppressed by 4.1G through an unknown mechanism in human embryonic kidney (HEK)293 cells. In the present study, we found that AC type 6 (AC6), one of the major ACs activated downstream of PTHR, interacts with 4.1G in HEK293 cells, and the N-terminus of AC6 (AC6-N) directly and selectively binds to the 4.1/ezrin/radixin/moesin (FERM) domain of 4.1G (4.1G-FERM) in vitro. AC6-N was distributed at the plasma membrane, which was disturbed by knockdown of 4.1G. An AC6-N mutant, AC6-N-3A, in which three consecutive arginine residues are mutated to alanine residues, altered both binding to 4.1G-FERM and its plasma membrane distribution in vivo. Further, we overexpressed AC6-N to competitively inhibit the interaction of endogenous AC6 and 4.1G in cells. cAMP production induced by forskolin, an adenylyl cyclase activator, and PTH-(1-34) was enhanced by AC6-N expression and 4.1G-knockdown. In contrast, AC6-N-3A had no impact on forskolin- and PTH-(1-34)-induced cAMP productions. These data provide a novel regulatory mechanism that AC6 activity is suppressed by the direct binding of 4.1G to AC6-N, resulting in attenuation of PTHR-mediated G_s/AC6/cAMP signaling.