Molecular regulation of apoptosis and cell cycle by Bcl-2 and FKBP38
The anti-apoptotic protein Bcl-2 is a central player in apoptosis. It is mainly localized at the mitochondrial outer membrane and keeps the mitochondria intact. In addition, the biological function of Bcl-2 has been shown to delay the cell cycle progression, especially by retarding G 1 →S transition. Bcl-2 also acts as an antioxidant to reduce the generation of reactive oxygen species (ROS) inside cells. Taken together, the known functions of Bcl-2 make the anti-apoptotic protein an essential
... ayer in apoptosis and important molecular target for development of anti-cancer drugs. In this study, by using siRNA-mediated RNA interference, we studied the molecular regulation of Bcl-2. The silencing of Bcl-2 led to the increase of the expression of pro-apoptotic protein such as Bax and the activation of caspase-3, which acted as the executor in apoptosis. Also an increase of the mitochondrial outer membrane permeabilization was detected. In addition, we examined the role of Bcl-2 in the cell cycle transition. We demonstrated that the down-regulation of Bcl-2 initiated the cell cycle progression with cells arrested in the early S-phase accompanying with an increase of ROS. FKBP38 is a novel molecular chaperon, which has been shown to bind Bcl-2 and help Bcl-2 localizing at the mitochondrial outer membrane. Currently, molecular mechanism how these two proteins communicate to each other remains unclear. In this study, to define the molecular interaction between Bcl-2 and FKBP38, several plasmids with Bcl-2 loop deletion mutants were constructed and co-transfected with ATTENTION: The Singapore Copyright Act applies to the use of this document. Nanyang Technological University Library Summary Ph.D. Thesis, School of Biological Sciences, NTU iii the plasmids expressing FKBP38 into Hela cells. We demonstrated that the region of P65-V89 in the long flexible loop was mainly responsible for the molecular interaction with FKBP38. Deleting this region weakened the binding with FKBP38 significantly, and resulted in the misdistribution and degradation of Bcl-2 inside cells. In addition, the silencing of FKBP38 by RNA interference also resulted in the initiation of cell cycle progression and apoptosis. However, compared to Bcl-2, the silencing of FKBP38 resulted in a greater number of cells arrested in S-or G 2 /Mphase with a significant increase of cyclin A and activation of CDK2. The antioxidant protected the mitochondrial membrane from damage and inhibited the apoptotic cell death initiated by FKBP38 suppression, while the antioxidant didn't inhibit Bcl-2suppression-induced mitochondrial damage and apoptosis. Thus, besides its chaperone function anchoring Bcl-2 to the mitochondria, FKBP38 acts as a novel link between apoptosis and cell cycle through the ROS-mediated damage on the mitochondria, independent of Bcl-2.