Deng, Xinzhu et al. (2009) International Worm Meeting "Targeting DNA Repair to Enhance Radio-sensitivity in Tumor Stem Cells of C. elegans."

Deng, Xinzhu, Fuks, Zvi, Rothenstein, Diana, Kolesnick, Richard

[International Worm Meeting, 2009]

The C. elegans germ line presents several biological features similar to those of human cancer stem cells (CSCs). First, the germ line contains a small population of self-renewing cells represented as germ stem cells. Second, the distal tip cell (DTC) provides a niche that expresses the LAG-2 proliferative signal to the germ stem cell GLP-1/Notch receptor ortholog. Further, the C. elegans glp-1 mutant glp-1(ar202) exhibits constitutive activity of GLP-1/Notch signaling, generating a germline tumor with a phenotype highly reminiscent of the behavior of human cancers. This germ stem cell population is resistant to apoptotic stimuli and has a high DNA repair capacity, resulting in resistance to the lethal effects of ionizing radiation (IR). The goal of this study is to identify and target genes that are responsible for the radiation resistance in the glp-1(ar202) CSC tumor model. In preliminary studies, we have developed an optimized readout system to assess IR-induced glp-1(ar202) tumor response, as a baseline for mechanistic studies to assess the role of DNA damage repair enzymes in the radioresistance phenotype. We also confirmed that glp-1(ar202) CSC death by IR is not through apoptosis, but rather appears akin to the mitotic death conferred by radiation treatment of most mammalian solid tumors. Further, we targeted rad-51 and mre-11, genes that regulate homologous recombination (HR) and found that their silencing by RNAi significantly increased sensitivity of the germline tumor to IR, reducing the IR dose required to eradicate glp-1(ar202) tumors by 50%. We are also using immunostaining of DNA repair foci to quantitatively study the role of HR and other DNA repair pathways in the glp-1(ar202)tumor model response to IR. We anticipate that some gene products on these pathways will have a major impact on radiation sensitivity, and may lead to discovery of new targets for enhancing radiotherapy sensitivity in human cancer.

Michaelson, David et al. (2013) International Worm Meeting "Mechanism of Germ Cell Loss by Ionizing Radiation in a C. elegans Tumor Model."

Rothenstein, Diana, Feldman, Regina, Deng, Xinzhu, Michaelson, David, Kolesnick, Richard, Powell, Simon, Fuks, Zvi, Hubbard, E. Jane Albert

[International Worm Meeting, 2013]

Ionizing radiation (IR) contributes to approximately 50% of cancer treatment protocols in the United States. It is well established that the main effect of ionizing radiation relevant to cancer treatment is the creation of double stranded breaks in DNA. The cellular response to DNA damage is well conserved across evolution and involves a cascade of proteins that sense and respond to DNA damage, whatever the source. Depending on the nature of the DNA damage as well as the cellular and genetic context of the damage, this conserved DNA damage pathway can trigger cell cycle arrest, DNA repair pathways, and, in some circumstances, apoptosis. The exact combination of these responses downstream of DNA damage largely determines the outcome of cancer treatment. We are using C. elegans to study the mechanisms of IR-induced effects on a germline "tumor" driven by hyperactive GLP-1/Notch signaling, using C. elegans genetics to better understand what determines the response of these cells to IR. Using this model we show that IR induces both G2 arrest and cell death, though the cell death mechanism is not dependent on classical apoptotic caspases. We show that the Homologous Recombination (HR), but not Non-Homologous End Joining (NHEJ) pathway of DNA repair partially protects these cells from the effects of ionizing radiation. We also compare the effects of IR in our worm tumor model to the effects on a human leukemia cell line driven by hyperactive Notch signaling and find that they both show a similar dependence on HR for surviving IR treatment.

Taylor R C et al. (2010) Aging, Metabolism, Stress, Pathogenesis, and Small RNAs, Madison, WI "The Role Of The Unfolded Protein Response In Aging and Protection Against Proteotoxicity"

Paulsson J F, Panowski S H, Kelly J W, Dillin A, Taylor R C, Liu Z

[Aging, Metabolism, Stress, Pathogenesis, and Small RNAs, Madison, WI, 2010]

A decline in protein homeostasis is a central hallmark of cellular aging. The Unfolded Protein Response (UPR) is a crucial element of the cell's protein quality control system, monitoring and responding to the level of protein misfolding within the endoplasmic reticulum (ER). We, and others1, have found that the ability of C. elegans to respond to a range of stimuli that induce ER stress declines with age, and we hypothesized that this loss of protein quality control is a causative factor in the aging process. Consistent with this, we found that reducing the function of one branch of the UPR, by RNAi against the ire-1 kinase and endoribonuclease or the downstream xbp-1 transcription factor, drastically reduces age-dependent protection against proteotoxicity in several C. elegans disease models. In addition, reduction of ire-1 and xbp-1 by RNAi or mutation reduces lifespan in wild type worms, and these genes are essential for lifespan extension by specific longevity signaling pathways. We are currently exploring the mechanistic basis for these roles in longevity and protection against proteotoxicity. 1Ben-Zvi et al, Proc Natl Acad Sci USA 106:14914-9.

Guasp, Ryan et al. (2019) International Worm Meeting "Trans-tissue signals from developing embryos instruct distant neurons to throw out their trash."

Guasp, Ryan, Salam, Sangeena, Harinath, Girish, Wang, Guoqiang, Driscoll, Monica, Melentijevic, Ilija

[International Worm Meeting, 2019]

The maintenance of proteostasis is critical for cell and organism function. We have reported that, in addition to internal protein quality control functions of chaperone action, proteasome-mediated degradation, and autophagy, certain C. elegans cells have the capacity to select, package and throw out their trash (Melentijevic et al., 2017). Large membrane-bound vesicles that contain protein aggregates and damaged organelles can be extruded by touch receptor neurons into the neighboring hypodermis, which attempts exopher degradation. The frequency of exopher production can be greatly exacerbated by internal proteo-stresses or by factors that disrupt mitochondrial quality. We have shown that in hermaphrodites, exophers produced by multiple neurons are generated in a distinct bi-modal pattern during adult life. We observe an initial peak in exopher production on adult day 2-3, followed by relatively low levels until around adult days 9-11 when a second peak can occur. The young adult exopher peak appears at about the time of a reconfiguration of proteostasis strategies (Ben-Zvi et al., 2009), and thus might reflect a developmental trash-elimination period in which deleterious materials accumulated during early life are collected and thrown away at one designated moment to clean house. What triggers this "trash day" is unclear. We have found that genetic and pharmacological interventions that disrupt embryogenesis can abrogate the early adult peak of exopher production. FuDR can inhibit the early peak; disruption of sperm maturation using the auxin-inducible spe-44 degron system blocks virtually all early exopher production; and genetic mutants in glp-4 and gld-1 that lack oocytes have very few early exophers. Similarly, the small-molecule drug C22, which causes embryonic lethality via increasing eggshell permeability (Weicksel et al., 2016) prevents early exopher generation. These data suggest signals associated with housing developing embryos act to ultimately increase neuronal exopher production in distant cells. Male C. elegans display a temporal and spatial distribution of exopher production distinct from hermaphrodites. In hermaphrodite touch neurons the highest rate of exopher production is from ALMR neurons with almost no production in the PLM neurons. This pattern is reversed in males. Furthermore, exophers in males increase progressively with age rather than occurring with the temporal peak pattern characteristic of hermaphrodites. These data suggest that signals associated with housing fertilized embryos modulate exopher production in hermaphrodites. We will discuss these studies with regard to understanding the molecular nature of the trans-tissue signaling.