Reduced insulin/IGF-1-like signaling (IIS) extends C. elegans lifespan by up-regulating stress response (Class I) and down-regulating development (Class II) genes through a mechanism that depends on the conserved transcription factor DAF-16/FOXO. By integrating a genomewide analysis of gene expression responsiveness to DAF-16 with genomewide in vivo binding data for a compendium of transcription factors, we discovered that the transcriptional activator PQM-1 directly controls Class II genes by binding to the DAF-16 associated element (DAE). DAF-16 directly regulates Class I genes only, through the DAF-16 binding element (DBE). Loss of PQM-1 suppresses daf-2 and eat-2 longevity as well as thermotolerance, and further slows development. The nuclear presence of PQM-1 and DAF- 16 is controlled by IIS in opposite ways, and, surprisingly, was found to be mutually exclusive. We also observe progressive loss of nuclear PQM-1 with age, explaining declining expression of PQM-1 targets. Together, our data suggest an elegant mechanism for switching between stress response and development. The overall goal of this project is to elucidate the mechanisms underlying the observed antagonistic relationship between PQM-1 and DAF-16. We will employ high-throughput screens based on reporter assays and microfluidics microscopy to identify genetic and small-molecule regulators of PQM-1 translocation. Additionally, we will use mass spectrometry to identify PQM-1's post-translational modifications and protein interactors, and determine how these affect nuclear translocation. We will also identify factors responsible for the nuclear exit of DAF-16 and PQM-1 with age. Finally, we will identify PQM-1 homologs in mammalian cells that exhibit a similar antagonism with FOXOs. Together, our results and insights will provide a framework for understanding how PQM-1 and DAF-16 and its mammalian counterparts allow cells to strike a balance between development and stress response.
The rate at which an organism matures and ages is carefully tuned to its environmental circumstances. The roundworm C. elegans has long served as a genetic model for aging, allowing the discovery and analysis of longevity regulating pathways. Mutant worms exist that live several times as long as normal worms. The balance between two types of key processes - stress response on one hand, growth and development on the other - is tuned differently in these mutants. Recent work by our laboratories uncovered a novel regulatory pathway centered at the DNA-binding transcription factor PQM-1, which turns out to play a crucial role both in mutant longevity and in normal aging. Many questions remain about how PQM-1 functions and interacts with DAF-16, another major regulator of aging. Intriguingly, PQM-1 behaves oppositely to DAF-16 in almost all respects. In this project, we will dissect the mechanisms that cause its activity to change in response to external conditions and genetic mutations. Additionally, we will use several complementary strategies to identify homologs of PQM-1 that play the same functional role in mammalian cells. Since the insulin/IGF-1 signaling pathway and FOXOs are conserved between worms and humans, and many human diseases are associated with aging, our findings could be highly relevant to human health.
| Bussemaker, Harmen J; Causton, Helen C; Fazlollahi, Mina et al. (2017) Network-based approaches that exploit inferred transcription factor activity to analyze the impact of genetic variation on gene expression. Curr Opin Syst Biol 2:98-102 |
