title: Presenilin-2 dampens intracellular Ca2+ stores by increasing Ca2+ leakage and reducing Ca2+ uptake.
abstract: We have previously shown that familial Alzheimer's disease mutants of presenilin-2 (PS2) and, to a lesser extent, of presenilin-1 (PS1) lower the Ca(2+) concentration of intracellular stores. We here examined the mechanism by which wild-type and mutant PS2 affect store Ca(2+) handling. By using HeLa, SH-SY5Y and MEFs as model cells, and recombinant aequorins as Ca(2+) probes, we show evidence that transient expression of either wild-type or mutant PS2 increases the passive Ca(2+) leakage: both ryanodine- and IP(3)-receptors contribute to Ca(2+) exit out of the ER, whereas the ribosome translocon complex is not involved. In SH-SY5Y cells and MEFs, wild-type and mutant PS2 potently reduce the uptake of Ca(2+) inside the stores, an effect that can be counteracted by over-expression of SERCA-2B. On this line, in wild-type MEFs, lowering the endogenous level of PS2 by RNA interference, increases the Ca(2+)-loading capability of intracellular stores. Furthermore, we show that in PS double knockout MEFs, reduction of Ca(2+) stores is mimicked by the expression of PS2-D366A, a loss-of-function mutant, uncleaved because also devoid of presenilinase activity but not by co-expression of the two catalytic active fragments of PS2. In summary, both physiological and increased levels of wild-type and mutant PS2 reduce the Ca(2+) uptake by intracellular stores. To exert this newly described function, PS2 needs to be in its full-length form, even if it can subsequently be cleaved.
authors.affiliation: Department of Biomedical Sciences, University of Padova, Padova, Italy.
authors.forename: Lucia
authors.initials: L
authors.lastname: Brunello
authors.forename: Enrico
authors.initials: E
authors.lastname: Zampese
authors.forename: Cristina
authors.initials: C
authors.lastname: Florean
authors.forename: Tullio
authors.initials: T
authors.lastname: Pozzan
authors.forename: Paola
authors.initials: P
authors.lastname: Pizzo
authors.forename: Cristina
authors.initials: C
authors.lastname: Fasolato
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D007700:Kinetics; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D008954:Models, Biological; D009154:Mutation; D009474:Neurons / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D053766:Presenilin-2 / Q000378:metabolism*; D034622:RNA Interference
chemical_list: D008565:Membrane Proteins; D053766:Presenilin-2; D002118:Calcium