The enzyme Dicer cleaves long precursors into short RNA molecules called microRNAs. A new study reveals how Dicer enhances energy metabolism and reduces levels of fat storage in macrophages, thus slowing the progression of atherosclerosis.
Atherosclerosis is one of the primary causes of premature death in modern societies. The condition is characterized by the deposition of fat-soluble molecules – principally cholesterol and triglycerides – on the inner walls of major blood vessels. This process triggers vascular inflammation and the formation of atherosclerotic plaques, which ultimately lead to narrowing of the arteries, thus impeding the flow of blood. Cells called macrophages are responsible for the uptake and disposal of the fatty deposits that induce plaque formation. However, depending on how they have been activated, macrophages can play an insidious role in the development of atherosclerosis. Inflammatory activation promotes inflammation, while ‘alternatively activated’ macrophages suppress inflammation reactions. The latter degrade triglycerides by means of fatty acid oxidation, but if this pathway operates sub-optimally – due to local inflammation, for example – they accumulate the engulfed fats, thus contributing to plaque development and increasing the risk of blood vessel blockage. A team of researchers in the Institute for Prophylaxis and Epidemiology of Cardiovascular Diseases at the LMU Medical Center, led by Professor Andreas Schober, has now shown that the enzyme Dicer plays an important role in the breakdown of triglycerides in alternatively activated macrophages.
Dicer slices long precursor RNAs into short snippets, which are known as microRNAs (miRNAs). miRNAs make a significant contribution to the regulation of gene activity. By binding to complementary nucleotide sequences in messenger RNAs (mRNAs), miRNAs prevent the synthesis of specific proteins. The Munich researchers used a mouse model system to study the impact of functional deletion of the Dicer gene in macrophages on energy metabolism. “We found that lack of Dicer in macrophages impairs their capacity for oxidative degradation of triglycerides. As a result, they accumulate more fat and develop into what are called foam cells“, Schober explains. Foam cells die at a higher rate than normal macrophages, which stimulates progression of atherosclerosis.
Schober and his colleagues went on to show that the effects of Dicer knockout on macrophage function are attributable to the loss of a single microRNA, named miR-10a, which is required for normal regulation of energy metabolism in these cells, and boosts the oxidative breakdown of the fatty acids in triglycerides. In addition, they identified the relevant target of miR-10a as the mRNA that codes for the ligand-dependent nuclear co-repressor protein (Lcor). “When the interaction between the two RNAs” (which reduces levels of the Lcor protein) “is inhibited, progression of atherosclerosis is accelerated, as in the case of the knockout of Dicer,” says Schober.
The discovery of this specific regulation of fatty acid metabolism in macrophages could lead to a novel therapeutic strategy for the treatment of atherosclerosis.

LMU Medical Center
www.en.uni-muenchen.de/news/newsarchiv/2018/schober_dicer.html

Genetic mutations in blood cells that have made their way into tumours could be red herrings that mislead physicians looking for genetic changes in tumours that are helping to drive the cancer. This finding is significant because physicians could make misinformed treatment decisions.
University of North Carolina Lineberger Comprehensive Cancer Center researchers and colleagues will report findings at the 2018 American Society of Clinical Oncology Annual Meeting on Monday, June 4, that show that blood cell mutations accounted for as many as 8 percent of the mutations identified in large-scale genetic sequencing efforts at two major academic centres.
“Next-generation sequencing of solid tumours is intended to identify acquired mutations within tumour tissue,” said the study’s first author Catherine C. Coombs, an associate member of UNC Lineberger and an assistant professor in the UNC School of Medicine Division of Hematology/Oncology. “The identification of acquired mutations in blood cells could lead to errors in interpretation of sequencing results.”
For the study, researchers reviewed data from patients with solid tumour cancers who had genetic sequencing tests performed by Foundation Medicine as part of their routine clinical care at the N.C. Cancer Hospital and the Moffitt Cancer Center between 2013 and 2017. They also analysed sequencing results for blood samples. A subset of patients at the N.C. Cancer Hospital had their tumours and their blood sequenced through UNCseq, a genetic sequencing clinical trial run by UNC Lineberger researchers. For patients at Moffitt Cancer Center, they compared Foundation Medicine results to sequencing results from banked blood samples.
The researchers analysed the data to identify mutations more commonly seen in blood cells. They found that “clonal haematopoiesis,” which are acquired mutations in blood cells, accounted for 8 percent of the mutations.
“The presence of clonal haematopoiesis mutations on next-generation sequencing reports from solid tumour biopsies can confound assay interpretation with the risk of misguided application of targeted therapies,” Coombs said.
Researchers say further work must be done to develop standard processes for differentiating mutations that occur in the blood versus the tumour in order to ensure accuracy in the tests for physicians who are using the sequencing results to choose personalized treatments for patients. In addition, the study shows an advantage to “paired” sequencing tests, which evaluate mutations in both the blood and the tumour.

University of North Carolina Lineberger Comprehensive Cancer Center
unclineberger.org/news/mutations-could-contaminate-genetic-analyses

 New findings from the groundbreaking Trial Assigning Individualized Options for Treatment (Rx), or TAILORx trial, show no benefit from chemotherapy for 70 percent of women with the most common type of breast cancer. The study found that for women with hormone receptor (HR)-positive, HER2-negative, axillary lymph node-negative breast cancer, treatment with chemotherapy and hormone therapy after surgery is not more beneficial than treatment with hormone therapy alone. The new data will help inform treatment decisions for many women with early-stage breast cancer.
The trial was supported by the National Cancer Institute (NCI), part of the National Institutes of Health, and designed and led by the ECOG-ACRIN Cancer Research Group.
“The new results from TAILORx give clinicians high-quality data to inform personalized treatment recommendations for women,” said lead author Joseph A. Sparano, M.D., associate director for clinical research at the Albert Einstein Cancer Center and Montefiore Health System in New York City and vice chair of the ECOG-ACRIN Cancer Research Group. “These data confirm that using a 21-gene expression test to assess the risk of cancer recurrence can spare women unnecessary treatment if the test indicates that chemotherapy is not likely to provide benefit.”
TAILORx, a phase 3 clinical trial, opened in 2006 and was designed to provide an evidence-based answer to the question of whether hormone therapy alone is not inferior to hormone therapy plus chemotherapy. The trial used a molecular test (Oncotype DX Breast Recurrence Score) that assesses the expression of 21 genes associated with breast cancer recurrence to assign women with early-stage, HR- positive, HER2-negative, axillary lymph node–negative breast cancer to the most appropriate and effective post-operative treatment. The trial enrolled 10,273 women with this type of breast cancer at 1,182 sites in the United States, Australia, Canada, Ireland, New Zealand, and Peru.
When patients enrolled in the trial, their tumours were analysed using the 21-gene expression test and assigned a risk score (on a scale of 0–100) for cancer recurrence. Based on evidence from earlier trials, women in the trial who had a score in the low-risk range (0–10) received hormone therapy only, and those who had a score in the high-risk range (26 and above) were treated with hormone therapy and chemotherapy.
Women in the trial who had a score in the intermediate range (11–25) were randomly assigned to receive hormone therapy alone or hormone therapy with adjuvant chemotherapy. The goal was to assess whether women who received hormone therapy alone had outcomes that were as good as those among women who received chemotherapy in addition to hormone therapy.
“Until now, we’ve been able to recommend treatment for women with these cancers at high and low risk of recurrence, but women at intermediate risk have been uncertain about the appropriate strategy to take,” said Jeffrey Abrams, M.D., associate director of NCI’s Cancer Therapy Evaluation Program. “These findings, showing no benefit from receiving chemotherapy plus hormone therapy for most patients in this intermediate-risk group, will go a long way to support oncologists and patients in decisions about the best course of treatment.”
The researchers found that the primary endpoint of the trial, invasive disease-free survival—the proportion of women who had not died or developed a recurrence or a second primary cancer—was very similar in both groups. Five years after treatment, the rate of invasive disease-free survival was 92.8 percent for those who had hormone therapy alone and 93.1 percent for those who also had chemotherapy. At nine years, the rate was 83.3 percent for those with hormone therapy alone and 84.3 percent for the group that had both therapies. None of these differences were considered statistically significant.
The rates of overall survival were also very similar in the two groups. At five years, the overall survival rate was 98.0 percent for those who received hormone therapy alone and 98.1 percent for those who received both therapies, and at nine years the respective overall survival rates were 93.9 percent and 93.8 percent.
The researchers also found that women with a score of 0–10 had very low recurrence rates with hormone therapy alone at nine years (3 percent). This confirms similar findings from earlier studies. In addition, they found that women with a score of 26–100 had a distant recurrence rate of 13 percent despite receiving both chemotherapy and hormone therapy. This finding indicates the need to develop more effective therapies for women at high risk of recurrence.

ECOG-ACRIN Cancer Research Group
ecog-acrin.org/news-and-info/press-releases/tailorx-trial-finds-most-women-with-early-breast-cancer-do-not-benefit-from-chemotherapy

Scientists have known for decades that the Hox family of transcription factors are key regulators in the formation of blood cells and the development of leukemia. Exactly how this large family of genes, which are distributed in four separate chromosomal clusters named A through D, is regulated has been less clear. Now, new research from the Stowers Institute for Medical Research reveals that a DNA regulatory element within the Hoxb cluster globally mediates signals to the majority of Hoxb genes to control their expression in blood-forming stem cells.
“It’s like we found a general control that simultaneously turns the lights on and off in many rooms, rather than having a single switch that controls each individual room,” says Stowers Investigator Linheng Li, PhD, who co-led the study along with Stowers Scientific Director and Investigator Robb Krumlauf, PhD. These findings also help explain why a particular form of leukemia resists treatment and points to potential new therapeutic avenues.
In mammals, the blood system contains a number of mature cell types — white blood cells, red blood cells, platelets — that arise from blood-forming, or hematopoietic, stem cells (HSCs). HSCs renew themselves and differentiate into other cells to replenish the body’s blood supply in a process called hematopoiesis. Hox genes, which are well known for their roles in establishing the body plan of developing organisms, are also important for HSCs to maintain their critical balancing act in the adult blood system, and have been implicated in the development of leukemia.
In an article Li, Krumlauf, and co-authors including first author Pengxu Qian, PhD, second author Bony De Kumar, PhD, and other collaborators provide new details as to how Hox genes are regulated in HSCs. They report that a single cis-regulatory element, DERARE, works over a long range to control the majority of Hoxb genes in HSCs in a coordinated manner. The researchers found that the loss of the DERARE decreased Hoxb expression and altered the types of blood cells arising from HSCs, whereas “turning on” DERARE allowed Hoxb cluster gene expression in progenitor cells and increased the progression of leukemia.
Genes can be regulated by non-coding DNA sequences termed cis-regulatory sequences. These sequences get input from multiple types of molecules, such as transcription factors, histone modifiers, or various morphogens. The DERARE, or distal element RARE (retinoic acid response element), is a cis-regulatory element that responds to signals from the vitamin A derivative retinoic acid and determines the fate of HSCs.
Using human leukemia cell lines and mouse models, the Stowers researchers and collaborators have identified a mechanism for how the retinoid-sensitive DERARE maintains normal hematopoiesis and prevents acute myeloid leukemia (AML) by regulating Hoxb cluster genes in a methylation-dependent manner.
Methylation is the process of adding methyl groups to the DNA molecule, which can change the activity of the DNA segment. The researchers demonstrated that DNA methyltransferases mediate DNA methylation on DERARE, leading to reduced Hoxb cluster expression. AML patients with mutations in the DNA methyltransferase DNMT3A exhibit reduced DERARE methylation, elevated Hoxb expression, and adverse outcomes.
“In two human AML cell lines carrying a DNMT3A mutation, we used an adaptation of genome editing technology called dCas9-DNMT3A to specifically increase the DNA methylation on DERARE. This targeted methylation technique was able to reduce Hoxb cluster expression and alleviate the progression of leukemia,” says Qian. “It is known that Hoxb cluster genes show a dramatic increase in expression in patients with DNMT3A-mutated AML. Our work provides mechanistic insights into the use of DNA methylation on the DERARE as a potential screening tool for therapeutic drugs that target DNMT3A-mutated AML, thus leading to the development of new drugs for treating AML, in which DNA methylation is abnormal.”

Stowers Institutehttps://tinyurl.com/yarf3xfd