|M.Sc Student||Goldberg Shimrit|
|Subject||Involvement of the Translocator Protein (TSPO) in Cell Death|
Induced by Ultra Violet Light (UV) and Reactive
Oxygen Species (ROS) in Cancer
|Department||Department of Medicine||Supervisor||Professor Emeritus Moshe Gavish|
|Full Thesis text|
With the present Master Thesis, the effects of oxidative stress, including reactive oxygen species (ROS), on the Translocator Protein (TSPO), in correlation with cell viability and cell death, including initiation of the mitochondrial apoptosis pathway were studied. The TSPO is also known as the peripheral-type benzodiazepine receptor. The TSPO can be found in the mitochondrial membrane, where it can be closely associated with the voltage dependent anion channel and the adenine nucleotide transporter, which form the core components of the mitochondrial permeability transition pore (MPTP). We suggested that the TSPO can modulate the activity of the MPTP, affecting the mitochondrial membrane potential (Δψm). Some of the putative functions of TSPO may include involvement of apoptotic processes induced by oxidative stress. We found that application of 100 µM H2O2 to cells from the SHSY-5Y neuroblastoma cell line led to cell death. This cell death appeared to be primarily necrotic, while apoptosis appeared to play a minor part in cell death due to H2O2 exposure in our study. In addition, we found that H2O2 exposure did lead to a collapse of the Δψm. Furthermore, H2O2 exposure gave a nonstatistical increase in TSPO expression as determined using [3H]PK 11195 binding and Western blot analyses. Application of the antioxidant glutathione suggested that the effects of H2O2 on TSPO expression and cell viability were due to ROS. Nonetheless, no significant change in lipid peroxidation and protein carbonylation was found following H2O2 exposure. Thus, our studies suggest that ROS generation by H2O2, and possibly H2O2 itself, can affect TSPO expression and cause collapse of the Δψm leading to cell death. Since oxidative damage to cellular structure does not seem to play a major role in this form of cell death, we suggest that ROS may affect the TSPO in a more direct way. This may be part of TSPO's reported function as an oxygen sensor. The effect of H2O2 exposure on TSPO may include activation of TSPO's putative modulatory role regarding the Δψm and lead to a sustained collapse of the Δψm. This sustained collapse of the Δψm then may lead to necrotic cell death, by-passing apoptotic mechanisms.