Abstract
In this study, Bax inhibitor-1 (BI-1) overexpression reduces the ER pool of Ca2+ released by thapsigargin. Cells overexpressing BI-1 also showed lower intracellular Ca2+ release induced by the Ca2+ ionophore ionomycin as well as agonists of ryanodine receptors and inositol trisphosphate receptors. In contrast, cells expressing carboxyl-terminal deleted BI-1 (CΔ-BI-1 cells) displayed normal intracellular Ca2+ mobilization. Basal Ca2+ release rates from the ER were higher in BI-1-overexpressing cells than in control or CΔ-BI-1 cells. We determined that the carboxyl-terminal cytosolic region of BI-1 contains a lysine-rich motif (EKDKKKEKK) resembling the pH-sensing domains of ion channels. Acidic conditions triggered more extensive Ca2+ release from ER microsomes from BI-1-overexpressing cells and BI-1-reconsituted liposomes. Acidic conditions also induced BI-1 protein oligomerization. Interestingly subjecting BI-1-overexpressing cells to acidic conditions induced more Bax recruitment to mitochondria, more cytochrome c release from mitochondria, and more cell death. These findings suggest that BI-1 increases Ca2+ leak rates from the ER through a mechanism that is dependent on pH and on the carboxyl-terminal cytosolic region of the BI-1 protein. The findings also reveal a cell death-promoting phenotype for BI-1 that is manifested under low pH conditions.
Original language | English |
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Pages (from-to) | 15946-15955 |
Number of pages | 10 |
Journal | Journal of Biological Chemistry |
Volume | 283 |
Issue number | 23 |
DOIs | |
State | Published - 6 Jun 2008 |