Apoptosis regulation by the mitochondrial chaperone TRAP-1/HSP-75

Modulation of death is a pathogen strategy to establish residence and promote survival in host cells and tissues. Shigella spp. are human pathogens that invade colonic mucosa, where they provoke lesions caused by their ability to manipulate the host cell responses. Shigella spp. induce various types of cell death in different cell populations. However, they are equally able to protect host cells from death. Here, we have investigated on the molecular mechanisms and cell effectors governing the balance between survival and death in epithelial cells infected with Shigella. To explore these aspects, we have exploited both, the HeLa cell invasion assay and a novel ex vivo human colon organ culture model of infection that mimics natural conditions of shigellosis. Our results definitely show that Shigella induces a rapid intrinsic apoptosis of infected cells, via mitochondrial depolarization and the ensuing caspase-9 activation. Moreover, for the first time we identify the eukaryotic stress-response factor growth arrest and DNA damage 45a as a key player in the induction of the apoptotic process elicited by Shigella in epithelial cells, revealing an unexplored role of this molecule in the course of infections sustained by invasive pathogens. Type II hexokinase (HKII) is overexpressed in the outer mitochondrial membrane of most neoplastic cells. Current work postulates that HKII release from its mitochondrial interactor, the voltage-dependent anion channel, prompts outer mitochondrial membrane permeabilization and the ensuing release of apoptogenic proteins, and that these events are inhibited by growth factors. Here we show that a HKII Nterminal peptide selectively detaches HKII from mitochondria transduces a permeability transition pore opening signal that results in cell death, does not require the voltage-dependent anion channel and is not affected by insulin stimulation. These findings have implications for our understanding of the pathways of outer mitochondrial membrane permeabilization and their inactivation in tumors. TRAP1 is a mitochondrial chaperone also known as heat shock protein 75, which is overexpressed in several tumor cell types. Herewe analyze whether mitochondrial TRAP1 elicits cytoprotective functions in a model of human osteosarcoma, SAOS-2 cells, either wild-type or in which TRAP1 expressionwas knocked down by RNA interference. Cells were exposed to different kinds of pro-apoptotic stimuli: chemotherapeutics, oxidative stress or death ligands, and several apoptotic parameters were measured in order to dissect whether and how TRAP1 impacts on these stress-induced transduction pathways. TRAP1 displays a general antiapoptotic role in all the examined conditions, whereas TRAP1 interference increases cell sensitivity to death. Serine phosphorylation and mitochondrial localization are required for TRAP1 cytoprotective function. In fact, a deletion mutant lacking the mitochondrial import sequence is not phosphorylated and is unable to counteract apoptosis induction in all conditions. Preliminary data showthat TRAP1 interacts with Bcl-2 family proteins and is involved in the regulation of the mitochondrial permeability transition pore opening. Altogether, these results suggest that TRAP1 acts as a key anti-apoptotic molecule in mitochondria of neoplastic cells.