|Ph.D Student||Lotan Rona|
|Subject||Elucidation of ARTS Apoptotic Signaling Pathway|
|Department||Department of Medicine||Supervisors||Professor Emeritus John Finberg|
|Ms. Sarit Larisch|
The aims of this work were to characterize the ARTS protein, and to elucidate
its apoptotic signaling pathway.
We found that, ARTS is essential for transmitting the apoptotic signal in the cell, and that over-expression of ARTS sensitizes cells to undergo apoptosis induced by different apoptotic stimuli. ARTS is localized to the mitochondria, inducing apoptosis through activation of the mitochondrial pathway characterized by cytochrome c release to the cytosol, down-regulation of Bcl-xL levels, and caspase 9 activation, which in turn causes caspase 3 activation and apoptosis. Following 1 hour of induction, ARTS protein is released from the mitochondria to the cytosol, and this release precedes cytochrome c massive release to the cytosol. ARTS protein has a half-life of less than 30 minutes, and it's mitochondrial and cytosolic levels are tightly regulated through the ubiquitin-proteosome system. Following apoptotic induction, ARTS protein levels increases significantly (x 4), and this increase occurs probably through two different mechanisms: 1. Inhibition of ARTS protein degradation, and 2. Increase in ARTS transcription levels.
In structure / function analysis, we found that different domains are essential for the protein localization and apoptotic activity.
In summary, we demonstrate that ARTS is a central mitochondrial pro-apoptotic protein, which is essential for promoting apoptosis in living cells. ARTS cellular levels are kept at low levels, tightly regulated through ubiquitination. Upon pro-apoptotic trigger, a combination of transcriptional up-regulation, and inhibition of the ubiquitination result in increased levels of ARTS leading to activation of the mitochondrial pathway, and apoptosis.