The brain-specific protein, p42IP4 (ADAP 1) is localized in mitochondria and involved in regulation of mitochondrial Ca2+

In brain, p42(IP4) (centaurin-alpha 1; recently named ADAP 1, which signifies ADP ribosylation factor GTPase activating protein with dual PH domains 1, within the large family of Arf-GTPase activating proteins) is mainly expressed in neurons. p42(IP4) operates as a dual receptor recognising two second messengers, the soluble inositol(1,3,4,5)tetrakisphosphate and the lipid phosphatidylinositol(3,4,5)trisphosphate. We show here for the first time that p42(IP4) is localized in mitochondria, isolated from rat brain and from cells transfected with p42(IP4). In rat brain mitochondria we additionally found interaction of p42(IP4) with 2', 3'-cyclic nucleotide 3'-phosphodiesterase and alpha-tubulin by pull-down binding assay and by immunoprecipitation. In mitochondria from Chinese hamster ovary cells, p42(IP4) is predominantly associated with the intermembrane space and the inner membrane. This localization of p42(IP4) indicates that p42(IP4) might have a still unknown mitochondrial function. We studied whether p42(IP4) is involved in Ca2+-induced permeability transition pore opening, which is important in mitochondrial events leading to programmed cell death. We used mouse neuroblastoma cells as a model for the functional studies of p42(IP4) in mitochondria. In mitochondria isolated from p42(IP4)-transfected mouse neuroblastoma cells, over-expression of p42(IP4) significantly decreased Ca2+ capacity and lag time for Ca2+ retention. Thus, we suggest that p42(IP4) is involved in the regulation of Ca2+ transport in mitochondria. We propose that p42(IP4) promotes Ca2+-induced permeability transition pore opening and thus destabilizes mitochondria.