By Patricia Reaney
LONDON, Jun 15 (Reuters) - Scientists issued a warning on Wednesday about
the potential danger of using an enzyme to immortalize cells for research or
grow tissue to treat disease.
They found that telomerase, the so-called fountain of youth enzyme that
helps cells live longer, is linked to a cancer-causing gene and could increase
the risk of disease.
"The previous notion that using telomerase to immortalize cells in culture
and then assuming that no further genetic changes occur as a result of that is
now shown to be incorrect," David Beach a professor of cancer biology at
University College London, said in a telephone interview.
Telomerase extends the cell's life by preventing the ends of chromosomes
called telomeres, which contain specialized repeated sequences of DNA, from
fraying each time the cell divides. Without telomerase, telomeres shorten with
each cell division and when they are too short the cell stops dividing. With it,
they continue to thrive.
Initial experiments with the enzyme found no evidence that extending the
cell's normal life with telomerase could increase the risk of cancer. But new
research by Beach and his colleagues, reported in the science journal Nature,
showed telomerase activated the c-myc oncogene, which causes cancer.
"The oncogene has been known for years. It is involved in all sorts of
different tumors. This is the first time that it has been shown that you are
selecting for further oncogenic changes with immortalized cells," Beach
explained.
In experiments using human mammary epithelial cells--a type of breast
cell--the scientists showed that telomerase activity in the cells was high after
the telomerase gene was introduced into the cell and then eliminated. It showed
the cells' own telomerase gene had been switched on.
They found that the expression levels of c-myc was two-to-three fold higher
in cells that had been immortalized to live beyond their normal lifespan.
"There are a number of different areas in which you can imagine the utility
of propagating human cells in vitro and then putting them back. In a way the
most graphic, if it could be achieved, would be pancreatic islets (for
diabetes)," Beach explained.
"The idea that you could take a patient's own cells, propagate them, maybe
genetic modify them and put them back is very appealing," he said.
But he said the findings indicate that the expansion of normal human cells
for therapeutic purposes must be approached with caution.
