AKAP18δ Anchors and Regulates CaMKII Activity at Phospholamban-SERCA2 and RYR

Circ Res. 2022 Jan 7;130(1):27-44. doi: 10.1161/CIRCRESAHA.120.317976. Epub 2021 Nov 24.


Background: The sarcoplasmic reticulum (SR) Ca2+-ATPase 2 (SERCA2) mediates Ca2+ reuptake into SR and thereby promotes cardiomyocyte relaxation, whereas the ryanodine receptor (RYR) mediates Ca2+ release from SR and triggers contraction. Ca2+/CaMKII (CaM [calmodulin]-dependent protein kinase II) regulates activities of SERCA2 through phosphorylation of PLN (phospholamban) and RYR through direct phosphorylation. However, the mechanisms for CaMKIIδ anchoring to SERCA2-PLN and RYR and its regulation by local Ca2+ signals remain elusive. The objective of this study was to investigate CaMKIIδ anchoring and regulation at SERCA2-PLN and RYR.

Methods: A role for AKAP18δ (A-kinase anchoring protein 18δ) in CaMKIIδ anchoring and regulation was analyzed by bioinformatics, peptide arrays, cell-permeant peptide technology, immunoprecipitations, pull downs, transfections, immunoblotting, proximity ligation, FRET-based CaMKII activity and ELISA-based assays, whole cell and SR vesicle fluorescence imaging, high-resolution microscopy, adenovirus transduction, adenoassociated virus injection, structural modeling, surface plasmon resonance, and alpha screen technology.

Results: Our results show that AKAP18δ anchors and directly regulates CaMKIIδ activity at SERCA2-PLN and RYR, via 2 distinct AKAP18δ regions. An N-terminal region (AKAP18δ-N) inhibited CaMKIIδ through binding of a region homologous to the natural CaMKII inhibitor peptide and the Thr17-PLN region. AKAP18δ-N also bound CaM, introducing a second level of control. Conversely, AKAP18δ-C, which shares homology to neuronal CaMKIIα activator peptide (N2B-s), activated CaMKIIδ by lowering the apparent Ca2+ threshold for kinase activation and inducing CaM trapping. While AKAP18δ-C facilitated faster Ca2+ reuptake by SERCA2 and Ca2+ release through RYR, AKAP18δ-N had opposite effects. We propose a model where the 2 unique AKAP18δ regions fine-tune Ca2+-frequency-dependent activation of CaMKIIδ at SERCA2-PLN and RYR.

Conclusions: AKAP18δ anchors and functionally regulates CaMKII activity at PLN-SERCA2 and RYR, indicating a crucial role of AKAP18δ in regulation of the heartbeat. To our knowledge, this is the first protein shown to enhance CaMKII activity in heart and also the first AKAP (A-kinase anchoring protein) reported to anchor a CaMKII isoform, defining AKAP18δ also as a CaM-KAP.

Keywords: calcium-calmodulin-dependent protein kinase type 2; calmodulin; myocytes, cardiac; phospholamban; ryanodine receptor; sarcoplasmic reticulum calcium-transporting ATPases.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing / chemistry
  • Adaptor Proteins, Signal Transducing / metabolism*
  • Animals
  • Binding Sites
  • Calcium Signaling
  • Calcium-Binding Proteins / metabolism*
  • Calcium-Calmodulin-Dependent Protein Kinase Type 2 / chemistry
  • Calcium-Calmodulin-Dependent Protein Kinase Type 2 / metabolism*
  • Cells, Cultured
  • HEK293 Cells
  • Humans
  • Myocytes, Cardiac / metabolism
  • Protein Binding
  • Rats
  • Rats, Wistar
  • Ryanodine Receptor Calcium Release Channel / metabolism*
  • Sarcoplasmic Reticulum Calcium-Transporting ATPases / metabolism*


  • Adaptor Proteins, Signal Transducing
  • Akap7 protein, rat
  • Atp2a2 protein, rat
  • Calcium-Binding Proteins
  • Ryanodine Receptor Calcium Release Channel
  • phospholamban
  • Calcium-Calmodulin-Dependent Protein Kinase Type 2
  • Sarcoplasmic Reticulum Calcium-Transporting ATPases