title: The human phospholamban Arg14-deletion mutant localizes to plasma membrane and interacts with the Na/K-ATPase.
abstract: Depressed Ca-handling in cardiomyocytes is frequently attributed to impaired sarcoplasmic reticulum (SR) function in human and experimental heart failure. Phospholamban (PLN) is a key regulator of SR and cardiac function, and PLN mutations in humans have been associated with dilated cardiomyopathy (DCM). We previously reported the deletion of the highly conserved amino acid residue arginine 14 (nucleic acids 39, 40 and 41) in DCM patients. This basic amino acid is important in maintaining the upstream consensus sequence for PKA phosphorylation of Ser 16 in PLN. To assess the function of this mutant PLN, we introduced the PLN-R14Del in cardiac myocytes of the PLN null mouse. Transgenic lines expressing mutant PLN-R14Del at similar protein levels to wild types exhibited no inhibition of the initial rates of oxalate-facilitated SR Ca uptake compared to PLN-knockouts (PLN-KO). The contractile parameters and Ca-kinetics also remained highly stimulated in PLN-R14Del cardiomyocytes, similar to PLN-KO, and isoproterenol did not further stimulate these hyper-contractile basal parameters. Consistent with the lack of inhibition on SR Ca-transport and contractility, confocal microscopy indicated that the PLN-R14Del failed to co-localize with SERCA2a. Moreover, PLN-R14Del did not co-immunoprecipitate with SERCA2a (as did WT-PLN), but rather co-immunoprecipitated with the sarcolemmal Na/K-ATPase (NKA) and stimulated NKA activity. In addition, studies in HEK cells indicated significant fluorescence resonance energy transfer between PLN-R14Del-YFP and NKAα1-CFP, but not with the NKA regulator phospholemman. Despite the enhanced cardiac function in PLN-R14Del hearts (as in PLN-knockouts), there was cardiac hypertrophy (unlike PLN-KO) coupled with activation of Akt and the MAPK pathways. Thus, human PLN-R14Del is misrouted to the sarcolemma, in the absence of endogenous PLN, and alters NKA activity, leading to cardiac remodeling.
authors.affiliation: Department of Pharmacology and Cell Biophysics, University of Cincinnati, College of Medicine, Cincinnati, OH 45267-0575, USA.
authors.forename: Kobra
authors.initials: K
authors.lastname: Haghighi
authors.forename: Tracy
authors.initials: T
authors.lastname: Pritchard
authors.forename: Julie
authors.initials: J
authors.lastname: Bossuyt
authors.forename: Jason R
authors.initials: JR
authors.lastname: Waggoner
authors.forename: Qunying
authors.initials: Q
authors.lastname: Yuan
authors.forename: Guo-Chang
authors.initials: GC
authors.lastname: Fan
authors.forename: Hanna
authors.initials: H
authors.lastname: Osinska
authors.forename: Ahmad
authors.initials: A
authors.lastname: Anjak
authors.forename: Jack
authors.initials: J
authors.lastname: Rubinstein
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Robbins
authors.forename: Donald M
authors.initials: DM
authors.lastname: Bers
authors.forename: Evangelia G
authors.initials: EG
authors.lastname: Kranias
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000235:genetics* / Q000378:metabolism*; D006332:Cardiomegaly / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D002462:Cell Membrane / Q000378:metabolism*; D004789:Enzyme Activation / Q000235:genetics; D006801:Humans; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000378:metabolism / Q000473:pathology; D011485:Protein Binding; D021381:Protein Transport; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D017384:Sequence Deletion; D015398:Signal Transduction; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D020257:Ventricular Remodeling / Q000235:genetics; D000099211:Phospholamban
chemical_list: D002118:Calcium; D002135:Calcium-Binding Proteins; D050505:Mutant Proteins; D000254:Sodium-Potassium-Exchanging ATPase; D000099211:Phospholamban