Isik, Meltem et al. (2015) International Worm Meeting "Investigation of TORC1-inhibition dependent SKN-1/Nrf activity and its effect on longevity ."

Isik, Meltem, Blackwell, Keith T

[International Worm Meeting, 2015]

The target of rapamycin (TOR) signaling is one of the pathways that regulate cell growth and metabolism in response to food availability and it has been broadly implicated in aging. Rapamycin, a TOR inhibitor, is the only drug studied so far that has unambiguously been shown to slow mammalian aging. However, in addition to its beneficial effects, it comes with harmful secondary effects, such as diabetic symptoms and suppression of immune system. It is therefore critical to identify specific mechanisms downstream of rapamycin that affect aging. The findings of our lab suggest that SKN-1/Nrf transcription factor is required for lifespan extensions associated with genetic inhibition of either TORC1 or TORC2, or rapamycin treatment indicating that it plays a central role in the influence of TOR pathways on aging. Interference with TOR signaling results in increased SKN-1/Nrf induced transcription, which seems to be critical for its effects on aging and stress resistance. Therefore, novel findings about the TORC1-SKN-1/Nrf-longevity axis might be useful for development of agents that promote particular SKN-1/Nrf activities, and would specifically reinforce beneficial effects of TOR inhibition by avoiding unwanted effects related to immunity, insulin sensitivity or inhibition of critical TOR functions. Here, we used high-throughput RNAi screens to determine the genes that have an effect on SKN-1 activity and also interacts with TOR signaling pathway. The tested 1451 clones consisted of genes that are available in TOR phosphoproteome data from six previous studies done in mammalian and yeast cells and the related genes in associated pathways. Each of these clones were tested for their effect on expression of a SKN-1/Nrf target gene reporter, Pgst-4::gfp, in WT, raga-1(ok386) (a TORC1 inhibition background) and skn-1(lax188) gain of function worms. This analysis has revealed already known as well as previously unidentified activators and repressors of SKN-1/Nrf activity, which also phenotypically interacted with TOR signaling pathway. Highly represented pathways included lin-35/Rb, chromatin factors, ubiquitin-proteosome, RNA processing/spliceosome, and endocytosis pathways. Therefore, these identified pathways can be responsible for TOR inhibition dependent SKN-1/Nrf activity and related genes will be analyzed further for their effect on lifespan and stress resistance of C. elegans. The findings of this research study may lead to development of agents that specifically reinforce beneficial effects of TOR inhibition by avoiding unwanted effects.

Wu, Ziyun et al. (2017) International Worm Meeting "Longevity from dietary restriction and reduced insulin/IGF-1 signaling requires modulation of p38/ATF-7 innate immunity."

Blackwell, Keith, Steinbaugh, Michael, Wu, Ziyun, Isik, Meltem, Moroz, Natalie

[International Worm Meeting, 2017]

Dietary restriction (DR) and reduced insulin/IGF-1 signaling (rIIS) are the most robust environmental and genetic interventions, respectively, that to extend healthy lifespan in diverse organisms. In mammals, through unknown mechanisms DR reduces chronic inflammation, a cause of aging-related disease. Here we show that in C. elegans, DR and rIIS promote longevity by modulating innate immunity. For DR and rIIS lifespan extension, the conserved innate immunity pathway TIR-1(SARM)-NSY-1(ASK1)- SEK-1(MKK3)-PMK-1(p38)-ATF-7(ATF2) must be intact. However, in contrast to other protective mechanisms, p38/ATF-7 immune activity is reduced to a basal level by DR and rIIS, which mobilize other pathogen resistance programs. Elevated p38/ATF-7 immunity accelerates aging, but can be reversed by DR or rIIS to allow lifespan extension. We conclude that innate immunity modulation is critical for longevity assurance, and that regulation of immunity by anabolic signals may have contributed to immune system evolution.

Zhang, Peng et al. (2017) International Worm Meeting "Phosphorylation by MPK-1/ERK regulates the SKN-1/Nrf1 proteasomal stress response."

Walhout, Albertha J.M., Zhang, Peng, Blackwell, T. Keith, Na, Huimin, Hourihan, John, Zhang, Fang, Isik, Meltem

[International Worm Meeting, 2017]

Protein degradation by the ubiquitin-proteasome system is vital to cellular homeostasis and survival, and mechanisms that promote healthy aging. The proteasome is also a critical therapeutic target in cancers that rely on the endoplasmic reticulum (ER) secretory system. An isoform of SKN-1 (SKN-1a; Nrf1 in mammals) regulates essentially all proteasome subunit genes, and mediates a pathway that maintains proteasome levels. Under conditions of proteasome inhibition, this recovery pathway generates additional proteasomes. In this little-understood pathway, SKN-1a/Nrf1 is processed through a complex mechanism that involves localization to and extrusion from the ER, and cleavage. Here, we performed a genome-scale RNAi screen in C. elegans to identify genes required to detect proteasome dysfunction, and activate SKN-1a/Nrf1. We show that a critical regulator in the proteasome recovery pathway is the kinase MPK-1/ERK, which responds to growth signals. We find that this pathway is regulated distinctly from the PMK-1/p38-dependent oxidative stress response that is mediated by a different SKN-1 isoform. MPK-1/ERK1 is activated by proteasomal stress, and inhibition of this kinase blocks the proteasome recovery pathway, and sensitizes C. elegans and human tumor cells to proteasome inhibition. In human tumor cells, phosphorylation by ERK on a single residue is required for Nrf1/SKN-1 to localize to nuclei and activate proteasome genes. Our data indicate that SKN-1a/ERK is directly regulated by MPK-1/ERK in the proteasomal recovery/synthesis pathway, suggesting that it is responsive to growth factor signaling. They also identify ERK/MPK-1 and possibly other hits from our screen as potential therapeutic targets for blocking compensatory proteasome synthesis in cancers that depend upon the proteasome.