Cancer researchers have discovered a new genetic abnormality in tumor cells that distinguishes them from normal cells. In mice and humans, the angled cancer cells in large quantities of a specific type of RNA that has been ignored so far. This discovery could shed light on how cancer develops and could give pathologists a new marker for detecting cancer cells in a biopsy.
Postdoctoral researcher David Ting and his colleagues in the laboratory of geneticist Cancer Daniel Haber of Massachusetts General Hospital in Boston have found their new marker using next generation sequencing machine to measure RNA molecules, or transcripts which are encoded by the DNA of a cancer cell. Unlike traditional microarray dotted with DNA probes that measure the activity of a subset of the 20,000 genes of a cell, this gene expression analysis "digital" has collected all of the transcripts of RNA.
To the surprise of scientists, a significant fraction of the RNA transcripts in the first sample they tested a mouse-pancreatic tumor was encoded by a DNA sequence type called repetitions satellite. These are short, repeated DNA stretches that do not encode proteins. Because the satellite repeats are not considered important, do not test microarrays for expression, said Haber.
In eight of the 10 pancreatic tumors in mice, the level of transcribed satellite was a stunning 40 times higher than in normal mouse pancreatic cells, the team announced today online science . The findings were similar in human tumors. high levels of a particular satellite RNA in 15 of 15 human pancreatic cancers as well as in a small sample of the prostate, lung, kidney and ovarian tumors compared to normal human cells
When team Haber stained this satellite RNA in tissues of the pancreas had been removed for biopsy, they showed that cancer cells are clearly (see image), even in the early stages of the disease. The marker could improve diagnosis of cancer, the researchers say. Often, doctors who suspect cancer in an organ will use a needle to collect a few cells and examine their form. Although this test is less invasive than a surgical biopsy, it is not as accurate-ting said that only 60% to 80% of pancreatic samples obtained in this manner are correctly diagnosed. Pathologist Ralph Hruban of Johns Hopkins University School of Medicine in Baltimore, Maryland, says that cell staining is "pretty impressive," recognizes that it might help with biopsies that are difficult to interpret.
The Haber group hopes to use the marker to improve tumor cell (CTC) chip in circulation, a device that captures cancer cells floating in a blood sample of a patient. The method is based on protein markers to distinguish cancer cells from normal cells trapped by the chip, but no existing markers cutting all types of cancer. (Although the cancer cells still carry mutations and abnormally expressed genes, so far no individual cancer cells genetic glitch distinguished from normal cells.) "This seems to be so radically different," said Haber. However, his group n has not yet worked out how to detect the satellite RNA in the cells trapped by a CTC chip.
on the road, the high expression levels by satellite could help reveal how cancer develops . "It is surprising and it means something. But at this stage we do not know what that means, "says Tyler Jacks cancer biologist at the Massachusetts Institute of Technology in Cambridge. The group Haber found that high RNA levels correlate with the expression of certain genes involved in embryonic development, suggesting that cancer could be using normal development programs to evolve. But researchers still need to understand why satellite RNA levels are so high and whether they contribute to cancer or are simply a side effect of another process.
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