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

Cathrine R. Carlson, Jan Magnus Aronsen, Anna Bergan-Dahl, Marie Christine Moutty, Marianne Lunde, Per Kristian Lunde, Hilde Jarstadmarken, Pimthanya Wanichawan, Laetitia Pereira, Terje R.S. Kolstad, Bjørn Dalhus, Hariharan Subramanian, Susanne Hille, Geir Christensen, Oliver J. Müller, Viacheslav Nikolaev, Donald M. Bers, Ivar Sjaastad, Xin Shen, William E. LouchEnno Klussmann, Ole M. Sejersted

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

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 CaMKIId anchoring to SERCA2-PLN and RYR and its regulation by local Ca2+ signals remain elusive. The objective of this study was to investigate CaMKIId anchoring and regulation at SERCA2-PLN and RYR. METHODS: A role for AKAP18δ (A-kinase anchoring protein 18δ) in CaMKIId 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 CaMKIId activity at SERCA2-PLN and RYR, via 2 distinct AKAP18δ regions. An N-terminal region (AKAP18δ-N) inhibited CaMKIId 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 CaMKIIa activator peptide (N2B-s), activated CaMKIId 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 CaMKIId 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.

Original languageEnglish (US)
Pages (from-to)27-44
Number of pages18
JournalCirculation research
Volume130
Issue number1
DOIs
StatePublished - Jan 7 2022
Externally publishedYes

Keywords

  • Calcium-calmodulin-dependent protein kinase type 2
  • Calmodulin
  • Myocytes, cardiac
  • Phospholamban
  • Ryanodine receptor
  • Sarcoplasmic reticulum calcium-transporting ATPases

ASJC Scopus subject areas

  • Physiology
  • Cardiology and Cardiovascular Medicine

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