NEW YORK (Reuters Health) - A protein that has long been known to play a key role in normal immune system function may also have a dark side--encouraging cancer spread, according to a preliminary report.

The finding could one day lead to therapies that block the effects of the protein in cancers of the breast, colon and possibly other organs, said study author Dr. Alex Toker, an assistant professor of pathology at Harvard Medical School in Boston, Massachusetts.

"I think this presents an entirely novel target for cancer treatment," he told Reuters Health.

The protein, known as NFAT, for nuclear factor of activated T cells, was unexpectedly found in high levels in both breast cancer and colon cancer tissue, Toker and colleagues report in the June 24th online issue of Nature Cell Biology.

When the researchers examined the effects of NFAT in a laboratory model of cancer spread, they found that human breast cancer cells containing high levels of the protein could penetrate a wall of tissue designed to simulate a blood vessel wall. However, cancer cells engineered to produce low levels of the NFAT protein did not penetrate the tissue.

Toker explained that the NFAT protein "contributes to the ability of these cells to migrate and invade." Cancer spreads, or metastasizes, to other organs through either blood vessels or vessels of the lymphatic system.

What remains unclear is just how NFAT promotes cancer metastasis. Important next steps, the researchers said, are to identify which gene or genes the protein is "turning on" in the process of cancer spread and to study the effects of the protein in lab animals.

The investigators are also planning to explore whether the protein is present in other types of tumors. "I suspect we will find it in other cancers," Toker said.

While it has been known for two decades that NFAT functions in immune system cells, only recently did researchers discover that it also appears to be important for a developing heart, Toker noted. In addition, preliminary evidence suggests it may also be present in neurons in the brain, he added.

There is already a drug on the market that blocks the effects of NFAT in immune cells. And while there is some evidence to suggest that the drug, cyclosporin A, may have some anti-cancer activity, Toker said he doesn't believe the drug is a powerful cancer fighter because the NFAT protein functions differently in cancer cells than in immune cells. Cyclosporin A is given to organ-transplant patients to suppress the immune system and allow the foreign organ to be transplanted without the body rejecting it.

SOURCE: Nature Cell Biology 2002;10.1038/ncb816.

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