Journal
MOLECULAR BIOLOGY OF THE CELL
Volume 20, Issue 1, Pages 306-318Publisher
AMER SOC CELL BIOLOGY
DOI: 10.1091/mbc.E08-06-0587
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Funding
- Biomedical Research Foundation of the Academy of Athens
- John F. Kostopoulos Foundation
- Hellenic Cardiological Society
- National Institutes of Health [HL26057, HL64018, HL77101]
- Leducq Foundation Trans-Antlantic alliance
- European Union 6th Framework Program for Research and Technological Development, Life sciences, genomics and biotechnology for health, VALAPODYN [LSHG-CT-2006-037277]
- NATIONAL HEART, LUNG, AND BLOOD INSTITUTE [R01HL064018, R37HL026057, P50HL077101, R01HL026057] Funding Source: NIH RePORTER
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Cardiac contractility is regulated through the activity of various key Ca2+-handling proteins. The sarco(endo) plasmic reticulum (SR) Ca2+ transport ATPase (SERCA2a) and its inhibitor phospholamban (PLN) control the uptake of Ca2+ 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 Ca2+ levels. These findings suggest that HAX-1 may promote cell survival through modulation of SERCA2 protein levels and thus ER Ca2+ stores.
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