TCF11/Nrf1-Mediated Induction of Proteasome Expression Prevents Cytotoxicity by Rotenone

Abstract

Using the human dopaminergic neuroblastoma cell line SH-SY5Y and mouse nigrostriatal organotypic slice cultures, gene and protein expression analysis and functional assays revealed oxidative stress is induced by the proteasome inhibitor epoxomicin or the mitochondrial complex I inhibitor rotenone and promotes the upregulation of proteasome expression and function mediated by TCF11/Nrf1 activation. In addition, we show that these stress conditions induce the unfolded protein response. TCF11/Nrf1, thus, has a cytoprotective function in response to oxidative and proteotoxic stress. Innovation and Conclusion: We here demonstrate that adaption of the proteasome system in response to oxidative stress is dependent on TCF11/Nrf1 in this model system. We conclude that TCF11/Nrf1, therefore, plays a vital role in maintaining redox and protein homeostasis. This work provides a vital insight into the molecular mechanisms of neurodegeneration due to oxidative stress by rotenone, and further studies investigating the role of TCF11/Nrf1 in the human condition would be of considerable interest. Antioxid. Redox Signal. 25, 870-885.

Molecular mechanisms controlling the multistage post-translational processing of endogenous Nrf1α/TCF11 proteins to yield distinct proteoforms within the coupled positive and negative feedback circuits

“…Overall, it is important to note that a lower dose (1 µmol/L) of MG132 only gave rise to a dominant stimulation signal to activate the PERK-elF2 pathway (Figure 8, C4 to C7), with a weak signal of XBP-1s but not of ATF6-N. By contrast, striking signals of XBP-1s and ATF6-N appeared to be activated by a higher dose ( oxidative) besides ER stress. Together with the above results (as shown in Figure 3) and a previous report by another group [70], these findings demonstrate that distinct extents of oxidative stress and antioxidant response signaling are significantly induced by different concentrations of MG132, particularly at a higher dose of the proteasomal inhibitor, resulting in marked increases in the expression of Nrf2-target antioxidant genes (Figure 9). In addition, it is intriguing to note that the aspartic protease DDI-1 per se also appeared to be processed under modest ER stress induced by 1 µmol/L of TG or MG132 ( Figures 8C10, 8D10, S8C).…”

“…All together with the previous evidence provided by us and other groups from immunocytochemical staining of distinct Nrf1 isoforms, subcellular fractionation, and live-cell imaging combined with membrane protease protection assays [11,39,43,44,70], these demonstrated that protein- Nrf1/TCF11 and its aggregated proteins are also examined, particularly following treatment of cells with a higher concentration of proteasomal inhibitors [55,70,71].…”

“…In this study, a large bulk of laborious work has been focused on endogenous Nrf1/TCF11 and its post-translational processing, aiming to establish a general criterion acceptable for identification of multiple isoforms between 140-kDa and 100-kDa ( Table 1). The objective of building such a generally acceptable criterion is for an attempt to terminate the chaotic state of the literature on distinct Nrf1/TCF11 isoforms, which were defined confusedly by discrepant molecular weights of their endogenous proteins as inconsistently reported by those groups [27,29,35,37,55,57,61,70]. For example, immensely disparate sizes of Nrf1-derived proteoforms had been shown in three publications by Sha and Goldberg [37,55,71] (as the cropped images, Figure S1C to E).…”

“…Inhibition of proteasome-mediated ERAD pathway leads to accumulation and even aggregation of ubiquitinated and carbonylated proteins (e.g. ER-localized Nrf1/TCF11) [55,70]. The proteotoxic stress is also accompanied by secondary oxidative stress leading to activation of Nrf2-mediate signalling.…”

Proteasome subunitPSMC3variants cause neurosensory syndrome combining deafness and cataract due to proteotoxic stress

“…As shown in Figure 4, control cells exposed to carfilzomib could successfully compensate the applied proteotoxic stress by increasing their pools of intracellular proteasomes, as evidenced by elevated expression of all investigated β-and Rpt-subunits. As expected, this process was preceded by the processing of the ER membrane-resident protein TCF11/Nrf1 ( Figure 4A), which is the transcription factor acting on nuclear genes encoding 19S and 20S proteasome subunits (Steffen et al, 2010;Radhakrishnan et al, 2010;Sotzny et al, 2016). Strikingly, the level of processed TCF11/Nrf1 in response to carfilzomib was much lower in cells carrying the homozygous PSMC3 pathogenic variant than that observed in control cells.…”