Scientists do know that satellites are expressed during fetal development, and they are thought to help chromosomes to divide normally. That similarity between cancer cells and embryonic cells—both can proliferate extensively—may hint at the role satellites play in cancer. “Somehow cancer has found a way to go backwards, to hijack a program from early in development for malicious use,” says Ting.
However, researchers don’t yet know whether satellites play a central role in the development of cancer or merely reflect some other malignant process. It might be analogous to, for example, prostate-specific antigen (PSA), which is found in high levels in prostate-cancer cells but doesn’t play a role in cancer. Either way, they hope the repetitive sequences will provide a new biomarker for diagnosing cancer.
If scientists confirm that satellite expression is highly concentrated only in cancer cells in adult tissue, they may be able to diagnose cancer accurately from very small amounts of tissue, such as the cells collected during needle biopsies. Ting’s team has already done some initial testing on cells collected in needle biopsies of pancreatic cancer. With a fluorescent molecular probe designed to bind to the satellites, “you can see cancer cells light up, while non-cancer cells do not,” says Ting. Currently, pathologists analyze cells based mainly on their appearance under the microscope, and their assessment can vary widely.
Ting’s team also found high concentrations of satellites in a type of precancerous cell that precedes pancreatic cancer. “That implies satellites are turned on relatively early in cancer development,” says Ting. If so, he hopes they can be used to detect cancer early. “Now we are trying to get a sense of the landscape. For what percentage of other cancers does this phenomenon occur? It seems to be prevalent, but we don’t have numbers.”
Researchers say they were able to make this discovery in part because of the type of sequencer they used—one from Helicos Biosciences that reads single molecules of DNA and RNA allowed scientists to count the number of RNA molecules present in the samples. Most other sequencers on the market have to replicate the RNA or DNA molecules under study before sequencing them.
Ting says he hopes other scientists will start to look for satellites in their own samples. “We think this is an initial step towards a new area of research for cancer,” he says.