SERCA1 truncated proteins unable to pump calcium reduce the endoplasmic reticulum calcium concentration and induce apoptosis.
By pumping calcium from the cytosol to the ER, sarco/endoplasmic reticulum calcium ATPases (SERCAs) play a major role in the control of calcium signaling. We describe two SERCA1 splice variants (S1Ts) characterized by exon 4 and/or exon 11 splicing, encoding COOH terminally truncated proteins, having only one of the seven calcium-binding residues, and thus unable to pump calcium. As shown by semiquantitative RT-PCR, S1T transcripts are differentially expressed in several adult and fetal human tissues, but not in skeletal muscle and heart. S1T proteins expression was detected by Western blot in nontransfected cell lines. In transiently transfected cells, S1T homodimers were revealed by Western blot using mildly denaturing conditions. S1T proteins were shown, by confocal scanning microscopy, to colocalize with endogenous SERCA2b into the ER membrane. Using ER-targeted aequorin (erAEQ), we have found that S1T proteins reduce ER calcium and reverse elevation of ER calcium loading induced by SERCA1 and SERCA2b. Our results also show that SERCA1 variants increase ER calcium leakage and are consistent with the hypothesis of a cation channel formed by S1T homodimers. Finally, when overexpressed in liver-derived cells, S1T proteins significantly induce apoptosis. These data reveal a further mechanism modulating Ca(2+) accumulation into the ER of nonmuscle cells and highlight the relevance of S1T proteins to the control of apoptosis.
Chami
M
M
The French Institute of Health and Medical Research Institut National de la Santé et de la Recherche Médicale (INSERM/Pasteur U370)/Necker Faculty Institute of Medicine, 75015 Paris, France.
Gozuacik
D
D
Lagorce
D
D
Brini
M
M
Falson
P
P
Peaucellier
G
G
Pinton
P
P
Lecoeur
H
H
Gougeon
M L
ML
le Maire
M
M
Rizzuto
R
R
Bréchot
C
C
Paterlini-Bréchot
P
P
D000328:Adult; D000595:Amino Acid Sequence; D017209:Apoptosis; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003001:Cloning, Molecular; D019281:Dimerization; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D015870:Gene Expression; D006367:HeLa Cells; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism; D008969:Molecular Sequence Data; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017433:Protein Structure, Secondary; D012326:RNA Splicing; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D014018:Tissue Distribution; D014407:Tumor Cells, Cultured
D020033:Protein Isoforms; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; C506943:ATP2A1 protein, human; D000252:Calcium-Transporting ATPases; D002118:Calcium