Ubiquitin sets the timer: impacts on aging and longevity

Protein homeostasis is essential for cellular function, organismal growth and viability. Damaged and aggregated proteins are turned over by two major proteolytic routes of the cellular quality-control pathways: the ubiquitin-proteasome system and autophagy. For both these pathways, ubiquitination provides the recognition signal for substrate selection. This Commentary discusses how ubiquitin-dependent proteolytic pathways are coordinated with stress- and aging-induced signals

Silencing of Hsp90 chaperone expression protects against 6-hydroxydopamine toxicity in PC12 cells

Parkinson's disease (PD) is the second most common age-related neurodegenerative disorder that has been shown to be associated with oxidative stress. This phenomenon occurs primarily via generation of 6-hydroxydopamine (6-OHDA) in catecholaminergic neurons leading to activation of apoptosis. The 90-kDa heat shock protein (Hsp90) functions as a chaperone in maintaining the functional stability and viability of cells under a transforming pressure. Since Hsp90 binds to inactive transcription factor heat shock factor-1 (HSF-1), inhibition of Hsp90 could activate HSF-1 and transcription of heat shock element containing genes subsequently, like Hsp70 as an anti-apoptotic factor. Our trial of silencing Hsp90 expression through transfection of Hsp90 siRNAs into neuronal PC12 cells being exposed to 6-OHDA resulted in the inhibition of pro-apoptotic factors, Bax, caspase-3, and PARP and upregulation of anti-apoptotic factor, Bcl2. In this manner, our data suggest a protective role for Hsp70 as it was observed to be induced upon Hsp90 knockdown. Furthermore, our results showed that Hsp90 silencing against 6-OHDA-induced oxidative stress may associate with upregulation of nuclear factor-erythroid 2-related factor 2. In summary, we found that silencing of Hsp90 expression leads to induction of cytoprotective pathways which can protect neurons against apoptosis in a PD model. © 2013 Springer Science+Business Media New York

Silencing of Hsp70 Intensifies 6-OHDA-Induced Apoptosis and Hsp90 Upregulation in PC12 Cells

By the current study, we tried to find out the interactive mechanisms enrolled by Hsp70 and Hsp90 following the 6-hydroxydopamine (6-OHDA)-induced oxidative stress. Of heat shock protein (Hsp) family, we have previously evaluated the effects of Hsp90 gene silencing on in vitro model of Parkinson�s disease and its influence on controlling the mechanisms of cell survival. Here, we extended our study to Hsp70 silencing short interfering RNA (siRNA) oligonucleotides, transfected into Pheochromocytoma (PC12) cells with/without exposure to 6-OHDA stress. In order to determine the probable effects of Hsp70 silencing on apoptotic factors, we assessed Bcl2/Bax ratio, nuclear level of PARP, and cleavage of caspase-3 under 6-OHDA stress condition. The results showed deteriorated effect of Hsp70 siRNA on apoptosis in cells exposed to only 6-OHDA. This is, at least in part, in consequence of upregulation of Hsp90, both at messenger RNA (mRNA) and protein levels. These data highlight the critical role of Hsp70 for cell survival under 6-OHDA stress condition. It could be a suggestive issue for supervision of caspase cascades by survival roles of Hsps as Hsp70 silencing resulted in apoptosis phenomenon. Convergence of Hsp70 anti-apoptotic and 6-OHDA pro-apoptotic pathways may explain intensified apoptosis following Hsp70 silencing. In addition, nuclear factor erythroid-2-related factor 2 (Nrf2), a transcription factor, has been previously studied in detoxification of oxidative stress. For this issue, we tried to elucidate Hsp70 silencing impact on Nrf2, which has been shown to regulate the transcription of Hsp70, unspecifically. Besides, our investigations revealed that Hsp70 siRNA did not affect the level of Nrf2 during 6-OHDA exposure. But, it is still a dealing question and other investigations are needed to have a comprehensive perception of Hsp family signaling functions. © 2014, Springer Science+Business Media New York