Findings could lead to new biomarkers clinical laboratories would use for identifying cancer in patients and monitoring treatments
As DNA “dark matter” (the DNA sequences between genes) continues to be studied, researchers are learning that so-called “junk DNA” (non-functional DNA) may influence multiple health conditions and diseases including cancer. This will be of interest to pathologists and clinical laboratories engaged in cancer diagnosis and may lead to new non-invasive liquid biopsy methods for identifying cancer in blood draws.
This technique could enable non-invasive monitoring of cancer treatment and cancer diagnosis, Technology Networks noted.
“Our study shows that ARTEMIS can reveal genomewide repeat landscapes that reflect dramatic underlying changes in human cancers,” said study co-leader Akshaya Annapragada (above), an MD/PhD student at the Johns Hopkins University School of Medicine, in a news release. “By illuminating the so-called ‘dark genome,’ the work offers unique insights into the cancer genome and provides a proof-of-concept for the utility of genomewide repeat landscapes as tissue and blood-based biomarkers for cancer detection, characterization, and monitoring.” Clinical laboratories may soon have new biomarkers for the detection of cancer. (Photo copyright: Johns Hopkins University.)
Detecting Early Lung, Liver Cancer
Artemis is a Greek word meaning “hunting goddess.” For the Johns Hopkins researchers, ARTEMIS also describes a technique “to analyze junk DNA found in tumors” and which float in the bloodstream, Financial Times explained.
“It’s like a grand unveiling of what’s behind the curtain,” said geneticist Victor Velculescu, MD, PhD, Professor of Oncology and co-director of the Cancer Genetics and Epigenetics Program at Johns Hopkins Kimmel Cancer Center, in the news release.
“Until ARTEMIS, this dark matter of the genome was essentially ignored, but now we’re seeing that these repeats are not occurring randomly,” he added. “They end up being clustered around genes that are altered in cancer in a variety of different ways, providing the first glimpse that these sequences may be key to tumor development.”
ARTEMIS could “lead to new therapies, new diagnostics, and new screening approaches for cancer,” Velculescu noted.
Repeats of DNA Sequences Tough to Study
For some time technical limitations have hindered analysis of repetitive genomic sequences by scientists.
“Genetic changes in repetitive sequences are a hallmark of cancer and other diseases, but characterizing these has been challenging using standard sequencing approaches,” the study authors wrote in their Science Translational Medicine paper.
“We developed a de novok-mer (short sequences of DNA)-finding approach called ARTEMIS to identify repeat elements from whole-genome sequencing,” the researchers wrote.
The scientists put ARTEMIS to the test in laboratory experiments.
The first analysis involved 1,280 types of repeating genetic elements “in both normal and tumor tissues from 525 cancer patients” who participated in the Pan-Cancer Analysis of Whole Genomes (PCAWG), according to Technology Networks, which noted these findings:
A median of 807 altered elements were found in each tumor.
About two-thirds (820) had not “previously been found altered in human cancer.”
Second, the researchers explored “genomewide repeat element changes that were predictive of cancer,” by using machine learning to give each sample an ARTEMIS score, according to the Johns Hopkins news release.
The scoring detected “525 PCAWG participants’ tumors from the healthy tissues with a high performance” overall Area Under the Curve (AUC) score of 0.96 (perfect score being 1.0) “across all cancer types analyzed,” the Johns Hopkins’ release states.
Liquid Biopsy Deployed
The scientists then used liquid biopsies to determine ARTEMIS’ ability to noninvasively diagnose cancer. Researchers used blood samples from:
ARTEMIS classified patients with lung cancer with an AUC of 0.82.
ARTEMIS detected people with liver cancer, as compared to others with cirrhosis or viral hepatitis, with a score of AUC 0.87.
Finally, the scientists used their “ARTEMIS blood test” to find the origin of tumors in patients with cancer. They reported their technique was 78% accurate in discovering tumor tissue sources among 12 tumor types.
“These analyses reveal widespread changes in repeat landscapes of human cancers and provide an approach for their detection and characterization that could benefit early detection and disease monitoring of patients with cancer,” the researchers wrote in Science Translational Medicine.
Large Clinical Trials Planned
Velculescu said more research is planned, including larger clinical trials.
“While still at an early stage, this research demonstrates how some cancers could be diagnosed earlier by detecting tumor-specific changes in cells collected from blood samples,” Hattie Brooks, PhD, Research Information Manager, Cancer Research UK (CRUK), told Financial Times.
Should ARTEMIS prove to be a viable, non-invasive blood test for cancer, it could provide pathologists and clinical laboratories with new biomarkers and the opportunity to work with oncologists to promptly diagnosis cancer and monitor patients’ response to treatment.
Research findings could lead to new biomarkers for genetic tests and give clinical laboratories new capabilities to diagnose different health conditions
New insights continue to emerge about “junk DNA” (aka, non-coding DNA). For pathologists and clinical laboratories, these discoveries may have value and eventually lead to new biomarkers for genetic testing.
One recent example comes from researchers at Stanford Medicine in California who recently learned how non-coding DNA—which makes up 98% of the human genome—affects gene expression, the function that leads to observable characteristics in an organism (phenotypes).
The research also could lead to a better understanding of how short tandem repeats (STRs)—the number of times a gene is copied into RNA for protein use—affect gene expression as well, according to Stanford.
“We’ve known for a while that short tandem repeats or STRs, aren’t junk because their presence or absence correlates with changes in gene expression. But we haven’t known how they exert these effects,” said study lead Polly Fordyce, PhD (above), Associate Professor of Bioengineering and Genetics at Stanford University, in a news release. The research could lead to new clinical laboratory biomarkers for genetic testing. (Photo copyright: Stanford University.)
To Bind or Not to Bind
In their Science paper, the Stanford researchers described an opportunity to explore a new angle to transcription factors binding to some sequences, also known as sequence motifs.
“Researchers have spent a lot of time characterizing these transcription factors and figuring out which sequences—called motifs—they like to bind to the most,” said the study lead Polly Fordyce, PhD, Associate Professor of Bioengineering and Genetics at Stanford University, in a Stanford Medicine news release.
“But current models don’t adequately explain where and when transcription factors bind to non-coding DNA to regulate gene expression. Sometimes, no transcription factor is attached to something that looks like a perfect motif. Other times, transcription factors bind to stretches of DNA that aren’t motifs,” the news release explains.
Transcription factors are “like light switches that can turn genes on or off depending on what cells need,” notes a King’s College LondonEDIT Labblog post.
But why do transcription factors target some places in the genome and not others?
“To solve the puzzle of why transcription factors go to some places in the genome and not to others, we needed to look beyond the highly preferred motifs,” Fordyce added. “In this study, we’re showing that the STR sequence around the motif can have a really big effect on transcription factor binding, providing clues as to what these repeated sequences might be doing.”
Such information could aid in understanding certain hereditary conditions and diseases.
“Variations in STR length have been associated with changes in gene expression and implicated in several complex phenotypes such as schizophrenia, cancer, autism, and Crohn’s disease. However, the mechanism by which STRs affect transcription remains unknown,” the researchers wrote in Science.
Special Assays Explore Binding
According to their paper, the research team turned to the Fordyce Lab’s previously developed microfluidic binding assays (MITOMI, k–MITOMI, and STAMMP) to analyze the impact of different DNA sequences on transcription factor binding.
“In the experiment we asked, ‘How do these changes impact the strength of transcription factor binding?’ We saw a surprisingly large effect. Varying the STR sequence around a motif can have a 70-fold impact on the binding,” Fordyce wrote.
In an accompanying Science article titled, “Repetitive DNA Regulates Gene Expression,” Thomas Kuhlman, PhD, Assistant Professor, Physics and Astronomy, University of California, Riverside, wrote that the study “demonstrates that STRs exert their effects by directly binding transcription factor proteins, thus explaining how STRs might influence gene expression in both normal and diseased states.”
“This research unveils, for the first time, the intricate connection between how variants in the non-coding genome affect genes that are associated with blood pressure and with hypertension. What we’ve created is a kind of functional map of the regulators of blood pressure genes, “said Philipp Maass, PhD, Lead Researcher and Assistant Professor Molecular Genetics, University of Toronto, in a news release.
The research team used massively parallel reporter assay (MPRA) technology to analyze 4,608 genetic variants associated with blood pressure.
The findings could aid precision medicine for cardiovascular health and may possibly be adopted to other conditions, according to The Hospital for Sick Children.
“The variants we have characterized in the non-coding genome could be used as genomic markers for hypertension, laying the groundwork for future genetic research and potential therapeutic targets for cardiovascular disease,” Maass noted.
Why All the ‘Junk’ DNA?
Clinical laboratory scientists may wonder why genetic research has primarily focused on 20,000 genes within the genome, leaving the “junk” DNA for later investigation. So did researchers at Harvard University.
“After the Human Genome Project, scientists found that there were around 20,000 genes within the genome, a number that some researchers had already predicted. Remarkably, these genes comprise only about 1-2% of the three billion base pairs of DNA. This means that anywhere from 98-99% of our entire genome must be doing something other than coding for proteins,” they wrote in a blog post.
“Imagine being given multiple volumes of encyclopedias that contained a coherent sentence in English every 100 pages, where the rest of the space contained a smattering of uninterpretable random letters and characters. You would probably start to wonder why all those random letters and characters were there in the first place, which is the exact problem that has plagued scientists for decades,” they added.
Not only is junk DNA an interesting study subject, but ongoing research may also produce useful new biomarkers for genetic diagnostics and other clinical laboratory testing. Thus, medical lab professionals may want to keep an eye on new developments involving non-coding DNA.
Recent research into transposons within DNA dark matter may produce new biomarkers for clinical laboratory testing and diagnostics
There’s been another interesting development in the study of genetic “dark matter” which may give rise to new biomarkers for clinical laboratory diagnostics and testing. This is worth noting, because biological dark matter has long been considered non-critical and immaterial to the human organism or human evolution. Researchers often refer to it as junk DNA.
However, newly-released research suggests that transposons (aka, transposable elements) contained within our genetic dark matter may play a “critical role in mammalian development,” according to a UC Berkeley news release. Transposons, the release notes, are “viral elements [that] have invaded mammalian genomes for millions of years and currently make up nearly half the DNA in the genomes of all living mammals.”
The study, led by researchers at the University of California, Berkeley, and Washington University in St. Louis, found at least one family of transposons that affected the viability of test mice. They believe the transposon could play a similar role in all mammals—including humans.
Molecular biologist Lin He, PhD (above), led the study conducted at the University of California, Berkeley, and Washington University in St. Louis, which found that bits of DNA once considered “junk” may actually perform important functions, such as ensuring fertility. These findings may one day confirm new biomarkers for clinical laboratory testing. (Photo copyright: MacArthur Foundation.)
How Removal of a Transposon Led to Death
The researchers found that the function of one type of transposon affected whether a mouse fetus could form properly and survive birth. The transposon “regulates the proliferation of cells in the early fertilized embryo and the timing of implantation in the mother’s uterus,” the news release notes.
To perform the research, the scientists removed a specific transposon that controls the proliferation of cells in the early fertilization of an embryo from the mice. After extracting that transposon, half of the mouse pups died before birth.
The researchers then looked at other mammalian species—including humans—and “found virus-derived regulatory elements linked to cell proliferation and timing of embryo implantation, suggesting that ancient viral DNA has been domesticated independently to play a crucial role in early embryonic development in all mammals,” UC Berkeley noted.
The researchers suggest that some of our dark matter DNA has an important function in our embryonic maturation and survival.
“The mouse and humans share 99% of their protein coding genes in their genomes—we are very similar with each other,” said molecular biologist and senior author of the study Lin He, PhD, Associate Professor, Department of Molecular and Cell Biology, UC Berkeley, in the news release.
“So, what constitutes the differences between mice and humans? One of the major differences is gene regulation—mice and humans have the same genes, but they can be regulated differently. Transposons have the capacity to generate a lot of gene regulatory diversity and could help us to understand species-specific differences in the world.”
“The real significance of this story is it tells us how evolution works in the most unexpected manner possible,” said geneticist and study co-author Ting Wang, PhD, Sanford and Karen Loewentheil Distinguished Professor of Medicine, Department of Genetics, Washington University School of Medicine, in the UC Berkeley news release.
“Transposons were long considered useless genetic material, but they make up such a big portion of the mammalian genome. A lot of interesting studies illustrate that transposons are a driving force of human genome evolution. Yet, this is the first example that I know of where deletion of a piece of junk DNA leads to a lethal phenotype, demonstrating that the function of specific transposons can be essential,” he added.
Their research could have implications for human fertility as many miscarriages in humans are due to undiagnosed conditions or have no apparent genetic component.
“If 50% of our genome is non-coding or repetitive—this dark matter—it is very tempting to ask the question whether or not human reproduction and the causes of human infertility can be explained by junk DNA sequences,” he said.
Thus, the UC Berkeley/Washington University study is building on prior research demonstrating that dark matter DNA may not be “junk” after all. More specifically, transposons may eventually have value as biomarkers for clinical laboratory tests and diagnostics.
Of course, additional research and studies are needed to validate these findings and provide greater knowledge about the function of specific transposons. But it’s an intriguing development that’s worth following.
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