Doering, Kelsie et al. (2017) International Worm Meeting "Dissecting NHR-49's role in stress response regulation."

Doering, Kelsie, Taubert, Stefan, Goh, Grace

[International Worm Meeting, 2017]

Cells and organisms constantly experience harmful environmental stresses ranging from suboptimal temperatures to foreign substances such as nutrient contaminants or drugs. Oxidative stress occurs when reactive oxygen species (ROS), obligate and ubiquitous by-products of aerobic respiration, accumulate within the cell. This accumulation is toxic, and high ROS levels are hypothesized to cause and/or exacerbate diseases such as diabetes, cancers, and neurodegenerative disorders. MDT-15, a subunit of the Mediator complex, is a transcriptional coregulator which controls oxidative stress response gene programs in C. elegans. For example, SKN-1, the master regulator of oxidative stress responses in C. elegans, binds to MDT-15 and both proteins are necessary to activate SKN-1-dependent genes and to survive oxidative stress. Surprisingly, responses to the oxidative stressor tert-butyl hydroperoxide (tBOOH), which causes ROS accumulation, are SKN-1 independent. This suggests that additional, parallel mechanisms must exist that protect against excess ROS. We have discovered that the transcription factor NHR-49, which is required to express genes involved in lipid metabolism, including beta-oxidation and fatty acid desaturation, is also involved in this response pathway to induce tBOOH response genes such as fmo-2. To identify new players acting in this pathway, I am performing a reverse genetic screen using RNAi. As readout, I am using a transcriptional reporter, composed of the GFP reporter fused to the promoter of fmo-2. Targeted RNAi will identify which of the ~900 transcription factors, ~400 kinases and ~500 transcriptional coregulators are required for tBOOH-dependent induction of fmo-2, and thus might map into the NHR-49 pathway. In addition, we have also begun to explore whether mdt-15 and nhr-49 participate in other stress and defence responses, and/or whether they interact genetically with factors known to coordinate environmental adaptation.

Doering, Kelsie et al. (2021) International Worm Meeting "Nuclear Hormone Receptor NHR-49 controls a HIF-1-independent hypoxia adaptation pathway in Caenorhabditis elegans"

Cheng, Xuanjin, Taubert, Stefan, Ghazi, Arjumand, Ratnappan, Ramesh, Doering, Kelsie, Miller, Dana, Milburn, Luke

[International Worm Meeting, 2021]

Cells encounter many harmful stresses, and their ability to mount responses specific to each stress is critical for survival. The response to insufficient oxygen (hypoxia) is orchestrated by the conserved Hypoxia-Inducible Factor (HIF). However, HIF-independent hypoxia response pathways exist that act in parallel to HIF to mediate the physiological hypoxia response. We have found a HIF-independent hypoxia response pathway controlled by Caenorhabditis elegans Nuclear Hormone Receptor NHR-49, an orthologue of mammalian lipid metabolism regulator Peroxisome Proliferator-Activated Receptor alpha (PPARalpha). We show that nhr-49 is required for worm survival in hypoxia and is synthetic lethal with hif-1 in this context, demonstrating that these factors act independently. Our RNA-seq analysis shows that in hypoxia nhr-49 regulates a set of genes that are hif-1-independent, including autophagy genes that promote hypoxia survival. We further show that Nuclear Hormone Receptor nhr-67 and Homeodomain-interacting Protein Kinase hpk-1 act in the NHR-49 pathway. The former acts during normoxia to repress NHR-49; however, during hypoxia, an increase in NHR-49 protein levels in turn represses nhr-67 levels, forming a feedback loop that may serve to reinforce NHR-49 activity. In contrast to nhr-67, the upstream kinase HPK-1 positively regulates the NHR-49 hypoxia response, as it is required to activate the NHR-49 regulated hypoxia response genes and to survive hypoxia. Together, our experiments define a new, essential hypoxia response pathway that acts in parallel to the well-known HIF-mediated hypoxia response.