A jumping gene with the fairy tale name “Sleeping Beauty” has helped to unlock vital clues for researchers investigating the genetics of colorectal cancer.
A study published today used the Sleeping Beauty transposon system to profile the repertoire of genes that can drive colorectal cancer, identifying many more than previously thought. Around one third of these genes are mutated in human cancer, which provides strong evidence that they are driver mutations in human tumours.
The collaborative project funded by Cancer Research UK and the Wellcome Trust was led by Dr David Adams from the Wellcome Trust Sanger Institute, and Dr Douglas Winton, of the Cancer Research-UK Cambridge Research Institute.
“These findings, when combined with mutation data from human colon cancers, will drive forward our understanding of the processes that lead to colorectal cancer,” says Dr Adams, senior author from the Sanger Institute. “They demonstrate how many genes can contribute to this cancer and how these genes work together in the development of this disease”.
The Sleeping Beauty transposon system induces genetic mutations at random, identifying and tagging candidate cancer genes, the drivers that cause colorectal cancer. This system has become critical in uncovering the genetic pathways that cause cancer, and, in this study, the team identify more than 200 genes that can be disrupted in human colorectal cancers.
Colorectal (bowel) cancer is the third most common cancer in the UK, and the second most common cause of cancer deaths after lung cancer; just under 40,000 people were diagnosed with bowel cancer in the UK in 2008 – around 110 people every day – a figure which has shown little improvement over the last decade.
Case Western Reserve University School of Medicine researchers published a study identifying the hereditary components of colorectal cancer (CRC.) It is the first large linkage study of families with CRC and colon polyps in the country.
Because only five percent of CRC cases are due to known gene defects, this study is designed to identify the remaining CRC-related susceptibility genes. The team built on a previous study which identified a specific region on chromosome 9q that harbors a CRC susceptibility gene. Upon review of a whole genome scan of all chromosome pairs in 194 families, the researchers were able to identify additional CRC gene regions on chromosomes 1p, 15q, and 17p.
While the overall Case Western Reserve University School of Medicine study looked at families with colon cancer and colon polyps, the study also analyzed families with different clusters of cancer, such as CRC with multiple polyps and CRC with breast cancer. These different phenotypes appeared to link to different chromosomal regions, which the study teams says supports the idea of multiple susceptibility genes causing different types of cancers. These links will be further investigated in the next phase of the study.
“The goal of our study is to identify the CRC genes in susceptible patients to better understand who may be prone to develop CRC and why,” said Georgia L. Wiesner, M.D., lead author of the study. “This study is step towards future the of genetic CRC testing.”
Case Western Reserve University
“Our research provides a rich source of candidate genes that represent potential diagnostic, prognostic and therapeutic targets, and defines the breadth of genes that can contribute to cancer of the intestine,” says Dr Winton, senior author from the Cancer Research UK Cambridge Research Institute. “It is becoming increasingly clear that cancers are driven by mutations in disparate collections of genes and it is essential that we tease apart the important changes.”
Current thinking is that perhaps around 50 major drivers are mutated in any one cancer cell, but the number and identity of all of the cancer drivers, and how many drivers are found in each type of cancer, is largely unknown. By performing screens for cancer genes in the mouse and by then comparing them to data from human tumours the team identified a rich catalogue of new candidate genes helping to refine the genes that genetic pathways that drive bowel cancer development.
What role do genes play in colorectal cancer?
Many cancers begin when one or more genes in a cell are mutated (changed), creating an abnormal protein or no protein at all. The information provided by an abnormal protein is different from that of a normal protein, which can cause cells to multiply uncontrollably and become cancerous.
A person may either be born with a genetic mutation in all of their cells (germline mutation) or acquire a genetic mutation in a single cell during his or her lifetime. An acquired mutation is passed on to all cells that develop from that single cell (called a somatic mutation). Somatic mutations can sometimes be caused by environmental factors, such as cigarette smoke. Most colorectal cancers (about 95%) are considered sporadic, meaning that the damage to the genes occurs by chance after a person is born and there is no risk of passing on the gene to a person’s children. Inherited colorectal cancers are less common (about 5%) and occur when gene mutations are passed within a family from one generation to the next.
What are the chances a damaged gene is inherited?
Every cell usually has two copies of each gene: one inherited from a person’s mother and one inherited from a person’s father. Hereditary colorectal cancer usually follows an autosomal dominant inheritance pattern, in which a mutation needs to happen in only one copy of the gene for the person to have an increased risk of getting the disease. This means that a parent with a gene mutation may pass on a copy of the normal gene or a copy of the gene with a mutation. Therefore, a child who has a parent with a mutation has a 50% chance of inheriting that mutation. A brother, sister, or parent of a person who has a gene mutation also has a 50% chance of having the same mutation.
“At its heart, cancer is a disease driven by faulty genes,” says Dr Lesley Walker, director of cancer information at Cancer Research UK. “Research suggests that each cancer cell has a number of ‘driver’ faults that make them grow out of control, as well as ‘passenger’ faults that they pick up as the disease develops. This technique is helping us to tease out the key drivers of bowel cancer, laying the foundations for more effective, targeted treatments for the disease in the future.”
The research complements studies by The Cancer Genome Atlas and the International Cancer Genome Consortium, which are cataloguing the mutations responsible for cancer development using next generation DNA sequencing.
Note to Editors
March HN et al. (2011) Insertional mutagenesis reveals multiple networks of co-operating genes driving intestinal tumorigenesis. Nature Genetics, published online on Sunday 6 November 2011
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The Wellcome Trust Sanger Institute, which receives the majority of its funding from the Wellcome Trust, was founded in 1992. The Institute is responsible for the completion of the sequence of approximately one-third of the human genome as well as genomes of model organisms and more than 90 pathogen genomes. In October 2006, new funding was awarded by the Wellcome Trust to exploit the wealth of genome data now available to answer important questions about health and disease.
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