Environmental Factor – August 2020: Inside Papers of the Month

internal
Written by Nicholas Elgna, Mimi Huang, Sania Mehta, Arif Rahman, Dhahia Yu

New 5-day NTP assay speeds up chemical toxicity screening

NTP scientists evaluated a high-throughput transcription approach using liver and kidney tissues from five-day assays in male rats to estimate the toxicological potency of chemicals. Toxicity and carcinogenicity are usually evaluated by a resource-intensive two-year bioassay for cancer. In the five-day assays, the authors determined the toxicological potency based on the groups of the most sensitive genes that are active in the liver and kidneys. For most chemicals, the results approached the toxicological potency derived from the most sensitive histopathological effects—regardless of target tissue or organ—observed in male rats in long-term assays. Notably, these estimates were similar in female rats, as well as in male and female rats. The results indicate that transcription-based efficacy estimates are short-term in vivo Assays, in the absence of other data, can provide a rapid and efficient estimation of the potency of toxins.

Driven by the need for alternative, more rapid and efficient assays, the authors used standardized dose analysis (BMD) to compare the toxicological potency between the short-term and the long-term. in vivo metrics. Regulatory agencies such as the US Environmental Protection Agency use the lower bound BMD as the preferred measure for calculating exposure levels to chemicals that may pose little risk to humans. (EN)

the quote: Gwen WM, Auerbach SS, Parham F, Stout MD, Widianata S, Mutlo E, Collins B, Pulse RS, Merrick PA, Ferguson S, Ramayahgari S, Bucher GR, Sparrow B, Tui H, Gorosby G , Machisky N., Shah R.; , Balik-Meisner MR, Mav D, Phadke DP, Roberts G, DeVito MJ. 2020. Evaluation of rat liver and kidneys in vivo for 5 days with high-throughput transcription for estimation of standard doses for apical outcomes. Toxicol Sciences. doi: 10.1093/Toxsci/kfaa081 [Online 3 June 2020].

CLP1 is a critical negative regulator of RNA processing

The NIEHS researchers have shown that an enzyme called CLP1 plays an important role in processing transfer tRNA by regulating tRNA binding. They also showed that mature, functional RNA is created by RNA through a process called TSEN, or (stranding RNA endonuclease) mediated by introns. Mutations in CLP1 and the TSEN complex often lead to severe neurological disorders.

Using technology allowed Escherichia coli To produce several proteins simultaneously, the scientists expressed and reconstituted the TSEN protein complex, which was able to cleave the tRNA. The TSEN complex alone was sufficient to remove tRNA introns but CLP1, a TSEN-binding partner, was required to properly regulate the splicing step that generates mature tRNA and circular intronic tRNAs (tricRNAs). Gene knockdown of CLP1 led to increases in mature tRNAs and tricRNAs, indicating that CLP1 acts as a negative modifier of tRNA processing. Based on these observations, the authors suggest that disruption of tRNA processing may cause distinct subtypes of neurodegenerative diseases, such as cerebellar hypoplasia that occurs when CLP1 or TSEN is mutated.

Taken together, this study expanded our knowledge of RNA splicing Regulation and created a recombinant system that generates the biochemically active compound TSEN useful for future studies. (DY)

the quote: Hayne CK, Schmidt CA, Haque MI, Matera AG, Stanley RE. 2020. Reconstitution of the human RNA exonuclease complex: an insight into the regulation of pre-RNA cleavage. nucleic acids precision; doi: 10.1093/nar/gkaa438 [Online 1 June 2020].

Inner neurons alpha7 nAChRs serve a function in theta wave production

Alpha 7 nicotinic acetylcholine receptors (alpha7 nAChRs) located on the surface of interneurons, a type of neuron, are involved in producing electrical oscillations known as theta waves, according to the NIEHS researchers and collaborators. Theta waves, which originate from the hippocampus and other areas, are involved in many crucial cognitive functions and processes, such as spatial learning, memory, and navigation. The team previously showed that muscarinic acetylcholine receptors (mAChRs) facilitated the generation of theta oscillations in physically active mice, but they also noted findings that implicate nAChRs in their regulation.

To investigate the role that nAChRs play in hippocampal theta oscillations, the researchers introduced methylcaconitine (MLA), a selective antagonist of alpha7 nAChRs, into the hippocampus of live mice. They observed a significant decrease in the strength of theta waves in the turned mice, indicating that the inhibitory receptors contribute to theta wave production. In addition, by eliminating the expression of alpha7 nAChRs in a set of neuronal subtypes, the group determined which subpopulation of neurons expressing alpha7 nAChRs is responsible for regulating theta energy. They found that theta power is significantly impaired in mice with a knockdown of alpha7 nAChRs in interneurons, particularly in a type called oriens lacunosumoleculare interneurons. (not available)

the quote: Gu Z, Smith KG, Alexander GM, Guerreiro I, Dudek SM, Gutkin B, Jensen P, Yakel JL. 2020. Hippocampal alpha7 nAChRs modulate theta oscillations in free-moving mice. Cell Representative 31 (10): 107740.

New tool predicts chemical effects on the human body

Researchers at NIEHS and the National Toxicology Program have developed Tox21BodyMap To predict which organs in the human body may be affected by chemicals. The tool will help scientists develop new hypotheses for chemical testing, prioritize them for toxicity testing, and identify knowledge gaps.

To identify organs likely to be affected by chemicals, Tox21BodyMap uses data from 971 high-throughput screening tests that value nearly 10,000 unique chemicals. Specifically, it gathers information about the gene that the assay targets, how well that gene is expressed in a human organ, and what tested concentrations of a chemical generated a positive test result. The result is a comprehensive picture of biochemical activity. For example, estradiol is active in multiple assays targeting estrogen receptors. Organs in which these receptors are highly expressed, and therefore likely to be targeted by estradiol exposure, are the female urogenital tract, vagina, uterus, and breast tissue. In addition to allowing users to customize scan sensitivity and specificity of organ gene expression, Tox21BodyMap provides multiple data visualizations, highlights target organs on a body map, as well as shows network connections and provides downloadable data. (MH)

the quote: Borrell A, Auerbach SS, Hawk CA, Kleinstruer NC. 2020. Tox21BodyMap: A web tool for mapping chemical effects on the human body. Nucleic Acids Res 48 (W1): W472-W476.

Loss of the APE2 protein is a major weakness in BRCA1/2 .-deficient tumor cells

The NIEHS researchers, as part of an international team, determined that the APE2 protein is important for resolving the blocked 3′ DNA ends generated by topoisomerase 1. The scientists knew that the loss of the APE2 protein in breast cancer cells with BRCA1 and BRCA2 mutations was lethal, but they did not understand the mechanism behind it. The work may lead to the development of therapeutic agents against these types of tumors.

As tumor suppressor genes, BRCA1 and BRCA2 encode proteins that regulate processes that prevent DNA damage. In particular, BRCA1/2 proteins are important for facilitating repair of homologous recombination of lesions that inhibit DNA synthesis. Through genome-wide interaction studies combined with structural and biochemical analysis of APE2, the researchers demonstrated that APE2 acts as an exonuclease, or a type of protein that acts like a pair of molecular scissors. In BRCA1/2-deficient tumors, the APE2 protein is critical for cutting 3 blocks of DNA that arise endogenously from normal body processes involving topoisomerase 1 and serve as an essential backup for BRCA-mediated DNA repair.

The results highlight 3 DNA blocks as a major weakness in cancer cells that are deficient in homologous recombination due to the BRCA1/2 mutation. The development of an APE2 inhibitor to treat BRCA1/2-mediated breast cancers may be a promising personalized medical approach. (SM)

the quote: Alvarez-Quilon A, Wojtasek JL, Mateo MC, Patel T, Abel CD, Hostedt N, Rossi C, Wallace D, Setiaputra D, Adam S, Ohashi Y, Milo H, Cho T, Jervis C, Munoz M , Grazzini E, Young GTF, Ross J, Zinda M, Williams RS, Durocher D. 2020. Endogenous 3′ DNA blocks are vulnerabilities of BRCA1 and BRCA2 deficiency and are reversed by APE2 endonuclease. Cell Moll 78 (6): 1152–1165 AH. (a story)

(Nicholas Elgna is an internal research training award [IRTA] Fellow at the NIEHS Mutation Group Mechanisms. Mimi Huang, PhD, is an IRTA Fellow in the Division of Toxicology Systems Group of the National Toxicology Program (DNTP). Sania Mehta is an IRTA Post-Baccalaureate Fellow in the NIEHS Matrix Biology Group. Arif Rahman, Ph.D., is a visiting fellow at DNTP Toxicoinformatics Group. Dahea You, MD, PhD, is an IRTA Postdoctoral Fellow in the DNTP Group for Molecular Toxicology and Genomics.)

from San Jose News Bulletin https://sjnewsbulletin.com/environmental-factor-august-2020-inside-papers-of-the-month/