A Separate Pool of Cardiac Phospholemman That Does Not Regulate or Associate with the Sodium Pump MULTIMERS OF PHOSPHOLEMMAN IN VENTRICULAR MUSCLE

Krzysztof J. Wypijewski, Jacqueline Howie, Louise Reilly, Lindsay Tulloch, Karen L. Aughton, Linda M. McLatchie, Michael J. Shattock, Sarah C. Calaghan, William Fuller*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

19 Citations (Scopus)

Abstract

Phospholemman (PLM), the principal quantitative sarcolemmal substrate for protein kinases A and C in the heart, regulates the cardiac sodium pump. Much like phospholamban, which regulates the related ATPase SERCA, PLM is reported to oligomerize. We investigated subpopulations of PLM in adult rat ventricular myocytes based on phosphorylation status. Co-immunoprecipitation identified two pools of PLM: one not associated with the sodium pump phosphorylated at Ser(63) and one associated with the pump, both phosphorylated at Ser(68) and unphosphorylated. Phosphorylation of PLM at Ser(63) following activation of PKC did not abrogate association of PLM with the pump, so its failure to associate with the pump was not due to phosphorylation at this site. All pools ofPLMco-localized to cell surface caveolin-enriched microdomains with sodium pump alpha subunits, despite the lack of caveolin-binding motif in PLM. Mass spectrometry analysis of phosphospecific immunoprecipitation reactions revealed no unique protein interactions for Ser(63)-phosphorylated PLM, and cross-linking reagents also failed to identify any partner proteins for this pool. In lysates from hearts of heterozygous transgenic animals expressing wild type and unphosphorylatable PLM, Ser(63)-phosphorylated PLM co-immunoprecipitated unphosphorylatable PLM, confirming the existence of PLM multimers. Dephosphorylation of the PLM multimer does not change sodium pump activity. Hence like phospholamban, PLM exists as a pump-inhibiting monomer and an unassociated oligomer. The distribution of different PLM phosphorylation states to different pools may be explained by their differential proximity to protein phosphatases rather than a direct effect of phosphorylation on PLM association with the pump.

Original languageEnglish
Pages (from-to)13808-13820
Number of pages13
JournalJournal of Biological Chemistry
Volume288
Issue number19
Early online date26 Mar 2013
DOIs
Publication statusPublished - 2013

Keywords

  • PROTEIN-KINASE-C
  • NA+/K+-ATPASE
  • NA/K-ATPASE
  • SARCOPLASMIC-RETICULUM
  • CA2+ PUMP
  • FXYD PROTEINS
  • CROSS-LINKING
  • PHOSPHOLAMBAN
  • MYOCYTES
  • PHOSPHORYLATION

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