The Associated Press

A new study suggests that an enzyme treatment used to grow cells for transplant into people may also trigger a gene that promotes cancer.

The enzyme, called telomerase, has been called a potential fountain of youth for cells. It made headlines in 1998, when researchers reported that it let human cells remain young and continue to divide indefinitely.

Speculation that the treatment might also keep people young captured public attention, but the scientific focus has largely been elsewhere.

For example, researchers have been hoping to use telomerase to treat conditions like diabetes or liver disease. They envision taking tissue from a patient and using the enzyme to build up a population of rejuvenated cells that could be implanted in the patient.

That idea has been shadowed by concerns that telomerase treatment might promote cancer, even after other research in 1998 found no sign of that connection.

The new result doesn't mean scientists should abandon hopes for telomerase, said study author David Beach of University College London in England. Instead, he said, it suggests the enzyme isn't the whole answer.

Beach and two colleagues in the United States present their work in Thursday's issue of the journal Nature.

The researchers worked with human breast cells. After they inserted a gene to make the cells produce telomerase, and the cells were grown in a lab, scientists found the cells had activated a gene called "c-myc." That gene is active in a wide variety of cancers.

The cells in the experiment were not cancerous, but they had "moved one step closer to becoming tumor cells," Beach said. That suggests a risk of cancer if telomerase-treated cells were used in therapy, he said.

So "we have got to do a bit more biology" to overcome that problem, he said.

Telomerase itself apparently didn't switch on the gene. Instead, the prolonged cell life in the lab apparently set the stage for the gene to be turned on by something else.

Jerry Shay of the University of Texas Southwestern Medical Center in Dallas, an author of the original 1998 study, said he had not seen the cancer gene activated in other kinds of cells treated with telomerase.

Whether the gene gets turned on or not may depend on what kind of cell is under study, he said.

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