Abstract
The CaV1.1 and CaV1.2 voltage-gated calcium channels initiate excitation-contraction coupling in skeletal and cardiac myocytes, excitation-transcription coupling in neurons, and many other cellular processes. Up-regulation of their activity by the β-adrenergic-PKA signaling pathway increases these physiological responses. PKA up-regulation of CaV1.2 activity can be reconstituted in a transfected cell system expressing CaV1.2Δ1800 truncated at the in vivo proteolytic processing site, the distal C-terminal domain (DCT; CaV1.2[1801-2122]), the auxiliary α2δ and β subunits of CaV1.2 channels, and A-kinase anchoring protein-15 (AKAP15), which binds to a site in the DCT. AKAP79/150 binds to the same site in the DCT as AKAP15. Here we report that AKAP79 is ineffective in supporting up-regulation of CaV1.2 channel activity by PKA, even though it binds to the same site in the DCT and inhibits the up-regulation of CaV1.2 channel activity supported by AKAP15. Mutation of the calcineurin-binding site in AKAP79 (AKAP79ΔPIX) allows it to support PKA-dependent up-regulation of CaV1.2 channel activity, suggesting that calcineurin bound to AKAP79 rapidly dephosphorylates CaV1.2 channels, thereby preventing their regulation by PKA. Both AKAP15 and AKAP79ΔPIX exert their regulatory effects on CaV1.2 channels in transfected cells by interaction with the modified leucine zipper motif in the DCT. Our results introduce an unexpected mode of differential regulation by AKAPs, in which binding of different AKAPs at a single site can competitively confer differential regulatory effects on the target protein by their association with different signaling proteins.