|M.Sc Student||Bayaa Doaa|
|Subject||The Possible Interactions between Steroids and TSPO in|
Relation to Glioblastoma Cells Death
|Department||Department of Medicine||Supervisor||Professor Emeritus Moshe Gavish|
|Full Thesis text|
The 18kDa Translocator Protein (TSPO), formerly known as the peripheral-type benzodiazepine receptor, is located at the outer mitochondrial membrane. Previous studies suggested that activation of TSPO by the toxic agent CoCl2, the pro-apoptotic agent Erucylphosphohomocholine (ErPC3), and the nitric oxide (NO) donor Sodium nitroprusside (SNP), leading to cell death, including initiation of the mitochondrial apoptosis cascade. One question is by which agent the TSPO may be activated to perform its cell death functions. Our study investigated the possibility that steroids may activate the TSPO to induce cell death of glioblastoma cells. We applied various steroids including: dexamethasone, estradiol and pregnenolone. We investigated whether steroids modulated cell death rates as induced by exogenous cytotoxic agents, including CoCl2, ErPC3, and SNP. For this study we used the human glioblastoma cell lines U118MG and T98G. We found that dexamethasone reduced the basal cell death rate in U118MG and T98G cells. Pregnenolone also reduced basal cell death rates in U118MG cells. In contrast, estradiol induced cell death in U118MG cells. Application of dexamethasone to T98G cells reduced the expression of TSPO in these cells. Treatment of T98G cells with dexamethasone also resulted in inhibition of cell death otherwise induced by ErPC3, including initiation of the mitochondrial apoptosis cascade.
Application of 0.5 mM of the NO donor SNP to U118MG cells reduces their metabolic activity. When the cells received dexamethasone 24 hours before the application of 0.5 mM SNP, and then also together with SNP for another 24 hrs, this attenuated the increase in metabolic activity otherwise induced by SNP alone. We found that the TSPO ligands PK 11195 and FGIN-1-27 significantly counteracted the decrease in metabolic activity of U118MG cells otherwise caused by CoCl2. PK 11195 significantly counteracted the lethal effect of ErPC3 on T98G cells.
Dexamethasone, estradiol, and pregnenolone did not interfere with binding of the TSPO specific ligand [3H]PK 11195 in rat kidney homogenates. Interestingly, however, protein expression assayed by immunoblot showed decreases in TSPO protein expression following dexamethasone application to T98G cells.
In conclusion, our present study shows that the induction of cell death, including initiation of the mitochondrial apoptosis cascade, by TSPO is inhibited by dexamethasone probably by the capability of dexamethasone to cause a decrease in TSPO protein expression.