AKAP6

AKAP6 Full Name

A kinase (PRKA) anchor protein 6

AKAP6 Introduction

AKAP6, also known as A-kinase anchoring protein 6 or mAKAP, is a scaffold protein that anchors protein kinase A and other signaling enzymes to the nuclear envelope of cardiac and skeletal muscle cells, where it regulates gene expression, calcium handling, and hypertrophic responses. The human AKAP6 gene is located on chromosome 14q12, spans a large genomic region, and encodes a large protein with a molecular weight exceeding two hundred kilodaltons. AKAP6 is a member of the AKAP family, characterized by an amphipathic helix that binds the regulatory subunits of protein kinase A, thereby tethering the kinase to specific subcellular compartments. Unlike many AKAPs that are widely expressed, AKAP6 expression is highly enriched in striated muscle, particularly in the heart and in slow-twitch skeletal muscle fibers, with lower expression detected in the brain and other tissues. Within the cell, AKAP6 localizes to the perinuclear space and the nuclear envelope, where it associates with the inner nuclear membrane protein emerin and with nesprins, which are components of the linker of nucleoskeleton and cytoskeleton complex. Through its ability to bind multiple signaling enzymes simultaneously, including protein kinase A, protein kinase C, calmodulin, the protein phosphatase PP2A, and the phosphodiesterase PDE4D3, AKAP6 functions as a signal transduction hub that integrates inputs from the 尾-adrenergic receptor pathway, calcium signaling, and the extracellular matrix, ultimately controlling the phosphorylation state of transcription factors and other nuclear targets. Dysregulation of AKAP6 has been implicated in cardiac hypertrophy, heart failure, muscular dystrophy, and arrhythmogenic cardiomyopathy, making it a key regulator of muscle physiology and disease.

Figure 1. Schematic structure of AKAP6.

Molecular Structure and Scaffolding Function
AKAP6 is a large scaffolding protein that contains multiple protein interaction domains, allowing it to bind a diverse array of signaling enzymes simultaneously. At its core is an amphipathic helix that binds the dimerization and docking domain of the regulatory subunits of protein kinase A, particularly the RI and RII isoforms. This interaction tethers protein kinase A to the nuclear envelope, positioning the kinase to phosphorylate nuclear substrates upon activation by cyclic AMP. In addition to the protein kinase A binding site, AKAP6 contains a leucine zipper motif that binds to calmodulin in a calcium-dependent manner, linking calcium signaling to the scaffold. AKAP6 also binds to protein kinase C epsilon through a region distinct from the protein kinase A binding site, allowing cross-talk between the cyclic AMP and diacylglycerol signaling pathways. The scaffold further interacts with the catalytic subunit of protein phosphatase 2A, which dephosphorylates protein kinase A substrates, providing a mechanism for signal termination and dynamic regulation. Finally, AKAP6 binds to the cyclic AMP-specific phosphodiesterase PDE4D3, which hydrolyzes cyclic AMP and creates a local gradient of cyclic AMP concentration around the scaffold.

Regulation of AKAP6 Expression and Activity
AKAP6 expression is dynamically regulated in response to physiological and pathological stimuli. In the heart, AKAP6 expression is induced by pressure overload and by β-adrenergic agonists, acting through the cyclic AMP response element-binding protein transcription factor. This induction is part of the hypertrophic response, as increased AKAP6 expression enhances the sensitivity of the nucleus to cyclic AMP signals and promotes further hypertrophy. In contrast, in end-stage heart failure, AKAP6 expression is reduced, possibly due to degradation by the ubiquitin-proteasome system or to transcriptional repression by inflammatory cytokines. The activity of AKAP6 is also regulated by post-translational modifications, including phosphorylation, ubiquitination, and sumoylation. Protein kinase A itself can phosphorylate AKAP6, which may affect its stability or its ability to bind other partners. The scaffolding function of AKAP6 can also be modulated by competition from other AKAPs that bind the same partners, or by signaling-induced dissociation of the complex. For example, activation of the mitogen-activated protein kinase pathway leads to the dissociation of protein phosphatase 2A from AKAP6, shifting the balance toward increased phosphorylation of MEF2 and enhanced hypertrophy.

Alternate Names for AKAP6

AKAP6; A kinase (PRKA) anchor protein 6; A-kinase anchor protein 6; ADAP6; AKAP100; KIAA0311; mAKAP; PRKA6; protein kinase A anchoring protein 6; AKAP-6; AKAP 100; A-kinase anchor protein 100 kDa; protein kinase A-anchoring protein 6; ADAP100; MGC165020;