RIG-I–like receptor LGP2 protects tumor cells from ionizing radiation

An siRNA screen targeting 89 IFN stimulated genes in 14 different cancer cell lines pointed to the RIG-I (retinoic acid inducible gene I)–like receptor Laboratory of Genetics and Physiology 2 (LGP2) as playing a key role in conferring tumor cell survival following cytotoxic stress induced by ionizing radiation (IR). Studies on the role of LGP2 revealed the following: (i) Depletion of LGP2 in three cancer cell lines resulted in a significant increase in cell death following IR, (ii) ectopic expression of LGP2 in cells increased resistance to IR, and (iii) IR enhanced LGP2 expression in three cell lines tested. Studies designed to define the mechanism by which LGP2 acts point to its role in regulation of IFNβ. Specifically (i) suppression of LGP2 leads to enhanced IFNβ, (ii) cytotoxic effects following IR correlated with expression of IFNβ inasmuch as inhibition of IFNβ by neutralizing antibody conferred resistance to cell death, and (iii) mouse embryonic fibroblasts from IFN receptor 1 knockout mice are radioresistant compared with wild-type mouse embryonic fibroblasts. The role of LGP2 in cancer may be inferred from cumulative data showing elevated levels of LGP2 in cancer cells are associated with more adverse clinical outcomes. Our results indicate that cytotoxic stress exemplified by IR induces IFNβ and enhances the expression of LGP2. Enhanced expression of LGP2 suppresses the IFN stimulated genes associated with cytotoxic stress by turning off the expression of IFNβ.Several studies have shown that the response of tumor cells to ionizing radiation (IR) is associated with IFN-mediated signaling (1–6). IFN signaling leads to the induction of multiple IFN stimulated genes (ISGs) (7, 8) and activates growth arrest and cell death in exposed cell populations (9). The precise mechanism of IR-mediated induction of IFN signaling is unknown. Tumor cell clones that survive an initial cytotoxic insult are subsequently resistant to exposure to both IR and prodeath components of IFN signaling (10). These clones express IFN-dependent enhanced levels of constitutively expressed ISGs, which overlap in part with ISGs initially induced by cytotoxic stress. Many of these constitutively expressed ISGs have been characterized as antiviral genes (11). Recently, enhanced levels of constitutively expressed ISGs have been reported in advanced cancers and were often associated with a poor prognosis related to aggressive tumor growth, metastatic spread, resistance to IR/chemotherapy, or combinations of these factors (11–18). The studies presented in this report are based on the hypothesis that a specific set of constitutively expressed ISGs, whose enhanced expression is by cytotoxic stress, confers a selective advantage to individual tumor clones (5, 9, 10, 13, 19).To test this hypothesis, we designed a targeted siRNA screen against 89 ISGs selected from two sources. The first included ISGs identified in our earlier screen and designated the IFN-Related DNA Damage Signature (IRDS) (1, 13). The second set included related ISG signatures that have been reported in the literature (as described in Methods and Dataset S1). The 89 genes were individually targeted in 14 tumor cell lines derived from malignant gliomas, lung, breast, colon, head and neck, prostate, and bladder cancers.The most significant finding from this screen was that the RNA helicase Laboratory of Genetics and Physiology 2 (LGP2) encoded by DHX58 [DEXH (Asp-Glu-X-His) box polypeptide 58] confers survival and mediates the response to IR of multiple tumor cell lines. LGP2 acts as a suppressor of the RNA-activated cytoplasmic RIG-I RIG-I (retinoic acid inducible gene I)–like receptor’s pathway (20, 21). This pathway is a subtype of pattern recognition receptors responsible for primary recognition of pathogen and host-associated molecular patterns and the subsequent activation of type I IFN production that orchestrates an innate immune response (22–24). In addition to its role in inhibiting IFNβ expression, Suthar et al. recently demonstrated that LGP2 governs CD8+ T-cell fitness and survival by inhibiting death-receptor signaling (25). Here we demonstrate that suppression of LGP2 leads to an enhanced IFNβ expression and increased killing of tumor cells. Our results thereby provide a mechanistic connection between IR-induced cytotoxic response in tumor cells and the LGP2–IFNβ pathway.     

Cassia tora prevents Aβ1-42 aggregation,inhibits acetylcholinesterase activity and protects against Aβ1-42-induced cell death and oxidative stress in human neuroblastoma cells

BackgroundAlzheimer’s is a complex neurodegenerative disease and is characterized by extraneuronal accumulation of β-amyloid peptide. Because of its complex nature, multi-target directed ligands (MTDLs) are increasingly being considered as promising anti-Alzheimer therapeutic agents. This study is aimed at determining the effects of Cassia tora ethyl acetate fraction on several Alzheimer-associated deleterious events in test tubes as well as in human neuroblastoma SK-N-SH and SH-SY5Y cell lines.MethodEthyl acetate fraction of C. tora was purified by chromatography, characterized by ¹H and ¹³C NMR, and tested for its ability to prevent Aβ _1-42 aggregation by thioflavin-T fluorescence and transmission electron microscopy. We also analyzed the intracellular ROS level and cytotoxicity in SK-N-SH and SH-SY5Y cell lines.ResultsThe extract inhibits the formation of Aβ _1-42 aggregation from monomers and oligomers, as also acetylcholinesterase activity, Aβ _1-42 -induced cell death, and Aβ _1-42 -dependent intracellular ROS production in both SK-N-SH and SH-SY5Y cells. In-depth chromatographic and spectroscopic analysis of the extract revealed that the active molecules are most likely triglycerides of oleic acid (C₁₈H₃₄O₂).ConclusionWe demonstrate for the first time that Cassia tora fraction prevents Aβ _1-42 aggregation, inhibits acetylcholinesterase and alleviates Aβ _1-42 -induced oxidative stress in human neuroblastoma cells. We further suggest the possible use of triglycerides of oleic acid as efficient anti-Alzheimer agents.