title: Phospholamban degradation is induced by phosphorylation-mediated ubiquitination and inhibited by interaction with cardiac type Sarco(endo)plasmic reticulum Ca(2+)-ATPase.
abstract: Phospholamban (PLN) regulates cardiac type sarco (endo)plasmic reticulum Ca(2+)-ATPase (SERCA2a) via Ser(16)-phosphorylation. During heart failure, PLN expression is downregulated with SERCA2a; however, the mechanism of its regulation is not fully understood. Phosphorylation triggers protein degradation and because PLN phosphorylation is upregulated in failing hearts, we examined whether PLN is degraded by Ser(16)-phosphorylation. Cells overexpressing PLN exhibited its degradation post isoproterenol (Iso), forskolin, or 3-isobutyl-1-methylxanthine (IBMX) addition. Moreover, this degradation was inhibited by a cAMP-dependent protein kinase (PKA) inhibitor--H89. Co-immunoprecipitation revealed that Lys(3) of PLN was oligo-ubiquitinated when ubiquitin was overexpressed, and was degraded by Iso treatment. However, when co-expressed with SERCA2a, oligo-ubiquitinated PLN at Lys(3) was not degraded by Iso treatment. In failing hearts from 16 week-old TgPLN(R9C) mice, oligo-ubiquitinated PLN levels increased and PLN expression was downregulated. Furthermore, SERCA2a mRNA levels in TgPLN(R9C) mice hearts were lower than that in wild type mice; however, PLN mRNA levels showed no changes. In another heart failure model, MG132 treatment reversed PLN degradation. These data suggest that PLN is, at least partially, oligo-ubiquitinated at Lys(3) and degraded through Ser(16)-phosphorylation-mediated poly-ubiquitination during heart failure.
authors.affiliation: Department of Pharmacology, Faculty of Medicine, Osaka Medical College, Osaka, Japan.
authors.forename: Takatoshi
authors.initials: T
authors.lastname: Nakagawa
authors.affiliation: Department of Pharmacology, Faculty of Medicine, Osaka Medical College, Osaka, Japan.
authors.forename: Shunichi
authors.initials: S
authors.lastname: Yokoe
authors.affiliation: Department of Pharmacology, Faculty of Medicine, Osaka Medical College, Osaka, Japan. Electronic address: masahi@osaka-med.ac.jp.
authors.forename: Michio
authors.initials: M
authors.lastname: Asahi
mesh_terms: D000818:Animals; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D008297:Male; D051379:Mice; D032383:Myocytes, Cardiac / Q000378:metabolism*; D010766:Phosphorylation / Q000502:physiology; D059748:Proteolysis; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism*; D054875:Ubiquitination / Q000502:physiology*; D000099211:Phospholamban
chemical_list: D002135:Calcium-Binding Proteins; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000099211:Phospholamban
keywords: Heart failure; Phophorylation; Phospholamban; Protein degradation; Sarco(endo)plasmic reticulum Ca(2+)-ATPase; Ubiquitination