Certain DNA sequences that do not code for proteins were never suspected of having a role in cancer—until now. Investigators have discovered that cells in the most common type of solid tumor—epithelial cancers—feature massive overexpression of these DNA sequences, which are called satellite repeats.
According to David Ting, MD, of the Massachusetts General Hospital Cancer Center and co-lead author of the research report (published online by Science), satellite repeats make up a large part of our genome but had been thought to be inactive. “We found that these regions are, in fact, very active in cancer but not in normal tissue,” he explained in a statement detailing his group’s work. “The findings may give us a novel cancer biomarker as well as new insights into how cancers behave.”
Satellite repeats are repetitive sequences often found near the centers or tips of chromosomes. Previously, significant expression of these DNA sequences had only been seen in embryonic tissues or embryonic stem cells. But Ting and colleagues found that in pancreatic cancer in a mouse model, satellite DNA was expressed at levels more than 100 times higher than what would be expected in normal tissues. Satellite expression was also greatly increased in mouse colon and lung tumors.
After observing similar results in human samples of tumors of the pancreas, lung, and prostate, the researchers concluded that increased satellite expression in lower-grade tumors suggests that overexpression begins early in tumor development. This finding has implications for early detection of cancer.