In mammals, multiple retrograde signaling mechanisms exist that are functionally similar to the yeast RTG system in that they alter nuclear gene expression in response to mitochondrial dysfunction, stress and other cues. For example, NFkB signaling is activated by mitochondrial stress. NFkB activity is regulated by multiple mechanisms, including altered transcription of NFkB components. To address the possibility that the NFkB pathway is engaged by genetic Meth-R, we used qRT-PCR to assess Vitamin C relative expression levels, in human MTR-KD and control cells, of transcripts encoding three factors involved in NFkB signaling. Our analyses demonstrated that the levels of transcripts encoding the NFkB family members RelA and RelB were 2-fold higher in long-lived MTR-KD cells, whereas NFKBIA, which encodes the NFkB inhibitor IkB, was downregulated nearly 4-fold. Together, these results suggest that NFkB signaling is activated by genetic Meth-R, and further, support the hypothesis that Meth-R promotes the stress tolerance and extended replicative lifespan of mammalian fibroblasts STF-118804 through NFkB-dependent changes in gene expression. Although it has been suggested that increased cellular stress resistance contributes to the extended lifespan imparted by longevity-promoting manipulations, few studies provide evidence for such a mechanism in the case of Meth-R. A key study characterizing Meth-R in mice showed that a methioninerestricted diet improves the resistance of hepatocytes to oxidative stress injury by acetaminophen injection in vivo, while a more recent report found that methionine-restricted rats have reduced blood levels of oxidative stress biomarkers. Consistent with these findings, a third group reported that mitochondrial ROS are decreased in methionine-restricted rats, along with oxidative damage to mtDNA. It remains unclear, however, whether such effects are due to an increased resistance to oxidative stress, per se, or simply the generation of lower basal levels of ROS in methionine-restricted animals.To explore in detail the mechanisms connecting Meth-R, cellular stress resistance and longevity, we developed two novel genetic systems using yeast and mammalian cells.