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.

Notes:

Vafiadaki, ElizabethArvanitis, Demetrios APagakis, Stamatis NPapalouka, VasilikiSanoudou, DespinaKontrogianni-Konstantopoulos, AikateriniKranias, Evangelia GengHL26057/HL/NHLBI NIH HHS/R37 HL026057/HL/NHLBI NIH HHS/HL77101/HL/NHLBI NIH HHS/R01 HL026057/HL/NHLBI NIH HHS/HL64018/HL/NHLBI NIH HHS/R01 HL064018/HL/NHLBI NIH HHS/P50 HL077101/HL/NHLBI NIH HHS/Research Support, N.I.H., ExtramuralResearch Support, Non-U.S. Gov't2008/10/31 09:00Mol Biol Cell. 2009 Jan;20(1):306-18. doi: 10.1091/mbc.e08-06-0587. Epub 2008 Oct 29.