title: The anti-apoptotic protein HAX-1 interacts with SERCA2 and regulates its protein levels to promote cell survival.
abstract: Cardiac contractility is regulated through the activity of various key Ca(2+)-handling proteins. The sarco(endo)plasmic reticulum (SR) Ca(2+) transport ATPase (SERCA2a) and its inhibitor phospholamban (PLN) control the uptake of Ca(2+) by SR membranes during relaxation. Recently, the antiapoptotic HS-1-associated protein X-1 (HAX-1) was identified as a binding partner of PLN, and this interaction was postulated to regulate cell apoptosis. In the current study, we determined that HAX-1 can also bind to SERCA2. Deletion mapping analysis demonstrated that amino acid residues 575-594 of SERCA2's nucleotide binding domain are required for its interaction with the C-terminal domain of HAX-1, containing amino acids 203-245. In transiently cotransfected human embryonic kidney 293 cells, recombinant SERCA2 was specifically targeted to the ER, whereas HAX-1 selectively concentrated at mitochondria. On triple transfections with PLN, however, HAX-1 massively translocated to the ER membranes, where it codistributed with PLN and SERCA2. Overexpression of SERCA2 abrogated the protective effects of HAX-1 on cell survival, after hypoxia/reoxygenation or thapsigargin treatment. Importantly, HAX-1 overexpression was associated with down-regulation of SERCA2 expression levels, resulting in significant reduction of apparent ER Ca(2+) levels. These findings suggest that HAX-1 may promote cell survival through modulation of SERCA2 protein levels and thus ER Ca(2+) stores.
authors.affiliation: Molecular Biology Division, Biomedical Research Foundation, Academy of Athens, Greece.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Vafiadaki
authors.forename: Demetrios A
authors.initials: DA
authors.lastname: Arvanitis
authors.forename: Stamatis N
authors.initials: SN
authors.lastname: Pagakis
authors.forename: Vasiliki
authors.initials: V
authors.lastname: Papalouka
authors.forename: Despina
authors.initials: D
authors.lastname: Sanoudou
authors.forename: Aikaterini
authors.initials: A
authors.lastname: Kontrogianni-Konstantopoulos
authors.forename: Evangelia G
authors.initials: EG
authors.lastname: Kranias
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D002470:Cell Survival; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D016877:Oxidants / Q000378:metabolism; D011485:Protein Binding; D025941:Protein Interaction Mapping; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000235:genetics / Q000378:metabolism*; D019284:Thapsigargin / Q000378:metabolism; D000099211:Phospholamban
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002118:Calcium; D002135:Calcium-Binding Proteins; D004791:Enzyme Inhibitors; D006861:Hydrogen Peroxide; D016877:Oxidants; D011506:Proteins; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D019284:Thapsigargin; D000099211:Phospholamban; C104759:HAX1 protein, human; C506946:ATP2A2 protein, human