Jumping Genes May Play An Important Role in GI Cancers

    Gastrointestinal cancer (GI cancer) refers to malignant conditions of the gastrointestinal tract (GI tract) and accessory organs of digestion, including the esophagus, stomach, biliary system, pancreas, small intestine, large intestine, rectum and anus.  The studies state that a jumping gene may play a critical role in the GI cancer.

    Results of a trio of studies done on human cancer tissue biopsies have added to growing evidence that a so-called jumping gene called LINE-1 is active during the development of many gastrointestinal cancers. The John Hopkins scientists who conducted the studies caution there is no proof that the numerous new "insertions" of these rogue genetic elements in the human genome actually cause cancers, but they say their experiments do suggest that these transposons might one day serve as a marker for early cancer diagnosis.

    Collectively, the studies focus on insertions of a stretch of DNA, the LINE-1 transposon, that, as its name suggests, can produce copies of itself that hop into new areas of the genome and may interrupt normal DNA sequences. This particular genetic interloper, the investigators say, has been in the human genome for so long that an estimated 17% of it is made up of LINE-1 copies, the vast majority of which are now “rusty hulks" of their former selves, unable to move at all. A few, however, are still mobile. Summaries of two of the studies appeared in Nature Medicine and Genome Research, and a report on the third appears this week in PNAS.

    Researchers previously reported cases in which new LINE-1 insertions disabled cancer-fighting genes inside tumors, but no one knew how common it was for jumping genes to play a role in cancer development, says Haig Kazazian, M.D., professor of molecular biology and genetics at the Johns Hopkins University School of Medicine's McKusick-Nathans Institute for Genetic Medicine, who participated in two of the studies. "A challenge we had to overcome to begin to answer that question was detecting new copies of LINE-1 when the human genome already contains so many. It was like finding a needle in a haystack," he adds.

    After Dr. Kazazian and then-graduate student Adam Ewing devised a method to find LINE-1 insertions using genetic sequencing technology, the two worked with research fellow Szilvia Solyom, Ph.D., and other colleagues to analyze the insertions in several types and stages of gastrointestinal cancer tissues biopsies. They compared the DNA insertions they found in colon, pancreatic, and gastric cancer to those in healthy tissue from the same people.

    Results showed that new insertions of the still-mobile LINE-1 transposons tended to occur early in cancer development, Dr. Solyom says. For example, she says, a total of 29 new insertions were found in colon polyps, and 24 new insertions were found in samples from seven patients with pancreatic ca

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