title: Molecular basis for PP2A regulatory subunit B56alpha targeting in cardiomyocytes.
abstract: Protein phosphatase 2A (PP2A) is a multifunctional protein phosphatase with critical roles in excitable cell signaling. In the heart, PP2A function is linked with modulation of beta-adrenergic signaling and has been suggested to regulate key ion channels and transporters including Na/Ca exchanger, ryanodine receptor, inositol 1,4,5-trisphosphate receptor, and Na/K ATPase. Although many of the functional roles and molecular targets for PP2A in heart are known, little is established regarding the cellular pathways that localize specific PP2A isoform activities to subcellular sites. We report that the PP2A regulatory subunit B56alpha is an in vivo binding partner for ankyrin-B, an adapter protein required for normal subcellular localization of the Na/Ca exchanger, Na/K ATPase, and inositol 1,4,5-trisphosphate receptor. Ankyrin-B and B56alpha are colocalized and coimmunoprecipitate in primary cardiomyocytes. Using multiple strategies, we identified the structural requirements on B56alpha for ankyrin-B association as a 13 residue motif in the B56alpha COOH terminus not present in other B56 family polypeptides. Finally, we report that reduced ankyrin-B expression in primary ankyrin-B(+/-) cardiomyocytes results in disorganized distribution of B56alpha that can be rescued by exogenous expression of ankyrin-B. These new data implicate ankyrin-B as a critical targeting component for PP2A in heart and identify a new class of signaling proteins targeted by ankyrin polypeptides.
authors.affiliation: Department of Internal Medicine, Division of Cardiology, University of Iowa Carver College of Medicine, 285 Newton Road, Iowa City, IA 52242, USA. naina-bhasin@uiowa.edu
authors.forename: Naina
authors.initials: N
authors.lastname: Bhasin
authors.forename: Shane R
authors.initials: SR
authors.lastname: Cunha
authors.forename: Malkanthi
authors.initials: M
authors.lastname: Mudannayake
authors.forename: Marisa S
authors.initials: MS
authors.lastname: Gigena
authors.forename: Terry B
authors.initials: TB
authors.lastname: Rogers
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Mohler
mesh_terms: D000818:Animals; D017487:Ankyrins / Q000378:metabolism*; D001665:Binding Sites; D002478:Cells, Cultured; D016503:Drug Delivery Systems / Q000379:methods*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D032383:Myocytes, Cardiac / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010744:Phosphoric Monoester Hydrolases / Q000737:chemistry*; D011485:Protein Binding; D054648:Protein Phosphatase 2; D051381:Rats; D017207:Rats, Sprague-Dawley; D013347:Subcellular Fractions / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D017487:Ankyrins; C513662:B56alpha protein, rat; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D010744:Phosphoric Monoester Hydrolases