Papers of the Month
By Nicholas Alagna, Victoria Placentra, Prashant Rai, Janelle Weaver, and Qing Xu
NTP uses metabolomics to assess toxicity
Scientists from the Division of the National Toxicology Program (DNTP) uncovered a new strategy that could estimate the safety of chemicals. Using benchmark concentration (BMC) analysis with human liver cells, the team determined that different concentrations of compounds caused changes in detectable metabolites produced by liver cells. The project used metabolomics, which is the large-scale detection and measurement of metabolites — the molecules that are intermediates or end products after the body breaks down food, drugs, or chemicals.
The researchers applied concentration-response modeling using BMC analysis to interpret mass spectrometry-based untargeted metabolomics data. Concentration-response modeling assesses how exposure to various concentrations of toxic chemicals and other compounds leads to changes in metabolites. The team exposed cultures of human liver cells to compounds that included relatively toxic drugs such as the cancer drug tamoxifen and the antiretroviral medication ritonavir.
Rising concentrations of drugs known to cause liver injury resulted in sharp increases in metabolic responses that were expected based on past research. By contrast, this effect did not occur for nontoxic compounds, such as sucrose and potassium chloride. According to the authors, the study shows that concentration-response modeling applied to untargeted metabolomics data accurately captures the potential of chemicals to cause liver injury. (JW)
Citation: Crizer DM, Ramaiahgari SC, Ferguson SS, Rice JR, Dunlap PE, Sipes NS, Auerbach SS, Merrick BA, DeVito MJ. 2021. Benchmark concentrations for untargeted metabolomics vs. transcriptomics for liver injury compounds in in vitro liver models. Toxicol Sci; doi: 10.1093/toxsci/kfab036 [Online 22 March 2021].
AEG12 inhibits mosquito-borne flavivirus by disrupting viral envelope
According to NIEHS researchers and their collaborators, the mosquito protein AEG12 disrupts the lipid envelope that covers some viruses. The study sheds light on the molecular mechanism AEG12 uses to inhibit virus infection, as well as offering potential new strategies to treat dangerous diseases caused by flaviviruses.
Flaviviruses — a class that includes dengue, yellow fever, and zika virus — are important public health concerns. These viruses are mainly transmitted by mosquitos and typically covered by a protective coating of lipids. Mosquitos produce AEG12 in response to a blood meal or flavivirus infection.
After solving the three-dimensional structure of AEG12 by X-ray crystallography, the researchers identified AEG12 as a lipid-binding protein. They further demonstrated that AEG12 was capable of rupturing membranes of red blood cells and inhibiting the replication of flaviviruses and other enveloped viruses, including human coronaviruses. AEG12 breaks open the cells or virus by swapping the lipid it carries with those in the cell membrane or virus envelop. By doing so, AEG12 contributes to both insect digestion and the antiviral immune response. The study suggests that AEG12, if engineered to target the virus only, may provide a useful tool to treat diseases caused by flaviviruses or coronaviruses. (QX)
Citation: Foo ACY, Thompson PM, Chen SH, Jadi R, Lupo B, DeRose EF, Arora S, Placentra VC, Premkumar L, Perera L, Pedersen LC, Martin N, Mueller GA. 2021. The mosquito protein AEG12 displays both cytolytic and antiviral properties via a common lipid transfer mechanism. Proc Natl Acad Sci U S A 118(11):e2019251118. (Story)
Preterm birth, prolonged labor influenced by progesterone balance
The progesterone receptor isoform B (PGR-B) mediates suppression of uterine contractibility via the Oxtr-Plcl2-Trpc3 pathway, according to NIEHS researchers and their collaborators. In humans, the progesterone receptor is a nuclear receptor with two isoforms: PGR-A and PGR-B. Elevated PGR-B gives rise to longer gestational periods, extended labor time, greater incidence of labor dystocia, or difficult birth, and a reduction in uterine contractility. PGR-A, however, promotes contractility of the uterus, without altering gestation length. To explore the in vivo role of progesterone signaling and progesterone receptor (PGR) isoforms in childbirth, the team employed transgenic mice with an overexpression of PGR-A or PGR-B in their myometrial smooth muscle.
Gene signature analyses demonstrated that PGR-A acts in a proinflammatory fashion, while PGR-B causes uterine muscle relaxation. Transcriptomic investigation revealed that PGR-B mice exhibit repression of both the Oxtr and Trpc3 genes, which both have a positive effect on uterine contractility. Furthermore, PGR-B mice displayed increased expression of the Plcl2 gene, which can reduce uterine contraction. These findings further explain precise molecular mechanisms by which PGR isoforms govern childbirth, while contributing novel insights into the maintenance of uterine dormancy by progesterone during pregnancy. (NA)
Citation: Peavey MC, Wu SP, Li R, Liu J, Emery OM, Wang T, Zhou L, Wetendorf M, Yallampalli C, Gibbons WE, Lydon JP, DeMayo FJ. 2021. Progesterone receptor isoform B regulates the Oxtr-Plcl2-Trpc3 pathway to suppress uterine contractility. Proc Natl Acad Sci U S A 118(11):e2011643118. (Story)
A single metabolic enzyme supervises cancer cell proliferation
NIEHS scientists and collaborators at the National Cancer Institute and Duke University have uncovered the detailed mechanism by which a metabolic enzyme called PPIP5K can directly regulate tumor cell multiplication. The study helps explain the metabolic reprogramming required for multiplication of tumor cells and reveals potential targets for cancer treatment.
PPIP5K, a type of enzyme called a kinase, produces unique cellular metabolites called inositol pyrophosphates. The authors previously showed that colorectal cancer cells deficient in PPIP5K have reduced growth rate despite enhanced energy production. In this study, using high-resolution mass spectrometry and genetics, the authors demonstrated that in cancer cells, PPIP5K was critical to synthesizing nucleotides, which are universal building blocks of DNA and RNA. Absence of precursor materials to synthesize these fundamental biological units inhibits growth in PPIP5K-deficient cancer cells. Furthermore, PPIP5K kinase activity, which synthesizes inositol pyrophosphates, is critical for nucleotide synthesis and cancer cell growth.
In addition, the authors determined two specific pathways of nucleotide synthesis that are regulated by PPIP5K — the serine-glycine one-carbon pathway and the pentose phosphate pathway. These results provide insight on how a single metabolic enzyme can have an overarching impact on multiple metabolic processes during tumor development. (PR)
Citation: Gu C, Liu J, Liu X, Zhang H, Luo J, Wang H, Locasale JW, Shears SB. 2021. Metabolic supervision by PPIP5K, an inositol pyrophosphate kinase-phosphatase, controls proliferation of the HCT116 tumor cell line. Proc Natl Acad Sci U S A 118(10):e2020187118.
Breast cancer risk increases near age of sibling’s diagnosis
A team of NIEHS researchers found that breast cancer relative risk increases for women near the age that an older sister was previously diagnosed with breast cancer. This study was the first to model an age-time-dependent risk for a woman based on her proximity to a sibling’s age of breast cancer onset.
For this study, researchers used data from the NIEHS Sister Study, which examines familial and environmental risk factors for breast cancer and other diseases in women in the United States and Puerto Rico. The cohort of participants included more than 20,000 women who had one older sister previously diagnosed with breast cancer. Researchers employed several statistical models and methods to assess the pattern of risk over time for these women as they approached and passed their sister’s age of diagnosis. The risk increased by 80% when the participant reached the sister’s age of diagnosis. This familial clustering indicates there could be important genetic and early environmental factors that contribute to the timing of breast cancer onset. The findings have implications for patient counseling and personalized cancer screening. (VP)
Citation: Von Holle A, O'Brien KM, Sandler DP, Weinberg CR. 2021. Evidence for familial clustering in breast cancer age of onset. Int J Epidemiol 50(1):97–104.
(Nicholas Alagna is an Intramural Research Training Award [IRTA] postbaccalaureate fellow in the NIEHS Mechanisms of Mutation Group. Victoria Placentra is an IRTA postbaccalaureate fellow in the NIEHS Mutagenesis and DNA Repair Regulation Group. Prashant Rai, Ph.D., is a visiting fellow in the NIEHS Clinical Investigation of Host Defense Group. Janelle Weaver, Ph.D., is a contract writer for the NIEHS Office of Communications and Public Liaison. Qing Xu is a biologist in the NIEHS Metabolism, Genes, and Environment Group.)