Papers of the Month
By Aidin Alejo Abdala, Kiri Hoff, Victoria Placentra, Payel Sil, and Salahuddin Syed
NTP compares chemical and biological profiles of botanical supplements
National Toxicology Program (NTP) researchers used chemical and biological response profiles to evaluate the similarity of two botanical supplements with well-established NTP test articles. The approaches they used could be applied to other types of complex mixtures with unidentified active components. The scientists suggested that confirming similarity was an important step in selecting test articles and extrapolating from a tested mixture to related samples.
Researchers chose two botanical supplements, black cohosh (Actaea racemosa) and Echinacea purpurea, to analyze variability between samples. The scientists used nontargeted chemical analysis to create chemical profiles and gene expression of toxicologically important receptor pathways in human liver cells to assess bioactivity.
The combined chemical and biological data for black cohosh identified nine of 14 samples that were similar to the control. Five of 14 samples were similar in terms of both chemistry and bioactivity for Echinacea purpurea. Together, these results indicated that the approaches for determining sufficient similarity were useful for evaluating both black cohosh and Echinacea purpurea. The authors asserted that multiple techniques must be used to confirm sample similarity. (KH)
Citation: Ryan KR, Huang MC, Ferguson SS, Waidyanatha S, Ramaiahgari S, Rice JR, Dunlap PE, Auerbach SS, Mutlu E, Cristy T, Peirfelice J, DeVito MJ, Smith-Roe SL, Rider CV. 2019. Evaluating sufficient similarity of botanical dietary supplements: combining chemical and in vitro biological data. Toxicol Sci; doi: 10.1093/toxsci/kfz189 [Online 27 August 2019].
Replacing red meat with poultry may reduce breast cancer risk
According to NIEHS scientists, women in the Sister Study who consumed the most red meat had a higher risk of developing breast cancer, whereas those who ate more poultry — turkey, chicken, duck, for example, — had reduced risk. This work adds to the growing literature on health effects of eating red meat and suggests that substituting poultry for red meat may further reduce breast cancer risk.
The research team analyzed information on meat consumption from 42,012 women enrolled in the Sister Study. Participants were followed for an average of 7.6 years, and during that time, 1,536 women developed invasive breast cancer. Women who ate the highest amount of red meat had a 23% higher risk of breast cancer compared with women who consumed the lowest amount. The study reported that women who ate the most poultry had a 15% lower risk compared with those who did not eat poultry. In a theoretical model, if red meat eaters switched to eating poultry exclusively, they could reduce their risk of breast cancer by 28%.
Although the authors stated further studies were needed to understand the association of meat with breast cancer, they proposed that it might be beneficial to replace red meat with poultry to reduce the overall risk of breast cancer. (PS)
Citation: Lo JJ, Park YM, Sinha R, Sandler DP. 2019. Association between meat consumption and risk of breast cancer: findings from the Sister Study. Int J Cancer; doi: 10.1002/ijc.32547 [Online 6 August 2019].
Cryo-EM reveals crosstalk during ribosomal assembly
Using cryo-electron microscopy (Cryo-EM), NIEHS researchers revealed the first structural snapshots of key proteins important in processing pre-rRNA in the thermophilic filamentous fungus Chaetomium thermophilum. Processing pre-rRNA, one of the first steps necessary for making ribosomes, occurs in a multienzyme complex composed of the RNA degrading enzyme, Las1, and an enzyme that adds phosphate groups to nucleotides, called Grc3. Because ribosomes serve as protein factories for cells, this research provides additional insight into the mechanism involved in ribosomal assembly and how dysfunction in the pathway can lead to human disease.
The authors referred to the enzyme complex made up of Las1 and Grc3 as RNase PNK. In general, Las1 generates a cut in the pre-rRNA transcript, whereas Grc3 phosphorylates it. The high-resolution Cryo-EM structure showed that RNase PNK adopts a butterfly-like structure, with the nuclease active site surrounded by RNA kinase sites. This unique configuration allows for communication between distant active sites and global conformational changes, allowing RNase PNK to coordinate its enzymatic activity. (SS)
Citation: Pillon MC, Hsu AL, Krahn JM, Williams JG, Goslen KH, Sobhany M, Borgnia, MJ, Stanley RE. 2019. Cryo-EM reveals active site coordination within a multienzyme pre-rRNA processing complex. Nat Struct Mol Biol 26(9):830–839.
New roles for Pol delta in DNA replication
Scientists at NIEHS uncovered new roles for polymerase delta (Pol delta), which is responsible for building DNA molecules during DNA replication. The canonical model suggests that polymerase alpha (Pol alpha) initiates the replication process. Then, polymerase epsilon (Pol epsilon) works on the leading strand and Pol delta synthesizes Okazaki fragments of the lagging strand. Okazaki fragments are short pieces of DNA that are joined to make an entire strand. The new findings suggest that Pol delta is also involved in leading strand synthesis and provides a novel mechanism of replication termination involving this enzyme.
Researchers improved upon the Hydrolytic End sequencing (HydEn-seq) technique to more accurately map polymerase activity across the genome. Using the budding yeast Saccharomyces cerevisiae, they found that Pol delta was highly involved in leading strand initiation as an intermediary between Pol alpha and Pol epsilon. Furthermore, they found that Pol epsilon switched to Pol delta at termination zones, a previously unknown mechanism of DNA replication. The researchers also suggested that the mechanism was conserved among eukaryotes, because they obtained similar results when working with fission yeast Schizosaccharomyces pombe. (AAA)
Citation: Zhou ZX, Lujan SA, Burkholder AB, Garbacz MA, Kunkel TA. 2019. Roles for DNA polymerase delta in initiating and terminating leading strand DNA replication. Nat Commun 10(1):3992.
Carbon nanotube exposure leads to mitochondrial dysfunction
Mitochondria in lung cells exposed to multiwalled carbon nanotubes (MWCNTs) undergo severe damage and are recycled by a process called mitophagy, according to NIEHS researchers and their collaborators. MWCNTs, a type of nanomaterial, are incorporated into consumer products. These studies will help scientists understand how MWCNT exposure affects humans.
Mitochondria are the sites of energy production within cells, and therefore, important to cell function. Because humans are primarily exposed to MWCNTs by inhalation, the team conducted experiments with cells isolated from human lung tissue, or primary bronchial epithelial cells (BECs). After exposing BECs to MWCNTs, the researchers analyzed the effects on mitochondria. They were surprised to find that although the number of mitochondria in BECs decreased, levels of mitochondrial gene expression increased. The scientists hypothesized the increase in gene expression was an attempt by the cell to recover mitochondria lost to MWCNT exposure. They also determined that MWCNTs were found in the cytoplasm, which indicated MWCNTs were likely able to penetrate the cell membrane, which damaged mitochondria and triggered mitophagy. Although further study is needed, this work is an important contribution toward gaining an understanding of MWCNT exposure. (VP)
Citation: Snyder RJ, Verhein KC, Vellers HL, Burkholder AB, Garantziotis S, Kleeberger SR. 2019. Multi-walled carbon nanotubes upregulate mitochondrial gene expression and trigger mitochondrial dysfunction in primary human bronchial epithelial cells. Nanotoxicology 3:1−18.
(Aidin Alejo Abdala is an Intramural Research Training Award [IRTA] postbaccalaureate fellow in the NIEHS Clinical Investigation of Host Defense Group. Kiri Hoff, Ph.D., is an IRTA fellow in the NIEHS Mitochondrial DNA Replication Group. Victoria Placentra is an IRTA postbaccalaureate fellow in the NIEHS Mutagenesis and DNA Repair Regulation Group. Payel Sil, Ph.D., is an IRTA fellow in the NIEHS Inflammation and Autoimmunity Group. Salahuddin Syed, Ph.D., is an IRTA fellow in the NIEHS DNA Replication Fidelity Group.)