Three Americans Share Nobel Prize for Medicine

The Nobel Prize in Physiology or Medicine was awarded this year to three American scientists who solved a problem of cell biology with deep relevance to cancer and aging. The three will receive equal shares of a prize worth around $1.4 million.

The recipients solved a longstanding puzzle involving the ends of chromosomes, the giant molecules of DNA that embody the genetic information. These ends, called telomeres, get shorter each time a cell divides and so serve as a kind of clock that counts off the cell’s allotted span of life.

The three winners are Elizabeth H. Blackburn of the University of California, San Francisco, Carol W. Greider of Johns Hopkins University School of Medicine and Jack W. Szostak of Massachusetts General Hospital.

Their discoveries were made some 20 years ago in pursuit of a purely scientific problem that seemingly had no practical relevance. But telomeres have turned out to play a role in two medical areas of vast importance, those of aging and cancer, because of their role in limiting the number of times a cell can divide.

Dr. Greider said in an interview Monday that she saw the prize as a celebration of the value of basic research. Eight women have previously won the Nobel prize in Medicine or Physiology.

Though Americans have once again made a clean sweep of the Nobel medicine prize, two of the three winners are immigrants. Dr. Blackburn was born in Tasmania, Australia, and has dual citizenship; Dr. Szostak was born in London. Dr. Blackburn came to the United States in the 1970s because it was “notably attractive” as a place to do science.

Despite ups and downs in recent years, America is still a magnet for foreign scientists, she said, “but one shouldn’t take that for granted.”

Dr. Szostak said the world was now more competitive in terms of scientific research. “So maybe we have to work a little harder to attract people from around the world and make sure they stay here,” he said.

All three of the prize-winners seem to have had science in their genes, and certainly in their home environment. Dr. Greider is the daughter of two scientists with doctorates from the University of California, Berkeley, and she, too, has a Ph.D. from that school. Dr. Szostak’s father was an engineer, which had some influence on his choice of career, he said. Both of Dr. Blackburn’s parents were family physicians, and her grandfather and great-grandfather were geologists in Australia.

The study of telomeres is notable as a field of research in which female scientists are particularly prominent. Dr. Greider said she ascribed this to a “founder effect,” the founder being Dr. Joseph Gall of Yale University. Dr. Gall was very supportive of women in science, Dr. Greider said. He trained Dr. Blackburn and other women, and they recruited others to the field “because there is a slight tendency for women to work with other women,” Dr. Greider said. She herself trained with Dr. Blackburn.

The field of telomere research grew out of a puzzle in the mechanics of copying DNA. The copying enzyme works in such a way that one of the two strands of the double helix is left a little shorter after each division. Work by the three winners and others led to the discovery of telomerase, a special enzyme that can prevent the shortening by adding extra pieces of DNA.

Dr. Blackburn addressed this problem by working with a single-celled organism found in pond water known as Tetrahymena. It was particularly suitable because its genome is divided into many small chromosomes so each cell has a large number of telomeres.

While she and Dr. Greider were working with Tetrahymena, Dr. Szostak was studying the same problem in yeast. The two groups in collaboration worked out the basic mechanism of how telomerase works and the special piece of RNA it carries to help elongate the chromosomes. RNA is a close chemical cousin of DNA.

This piece of basic biology soon turned out to have important implications for aging and cancer. Telomerase is usually active only at the beginning of life; thereafter the telomeres get shorter each time a cell divides. When they get too short, a cell is thrown into senescence, meaning that it is prevented from dividing again.

Short telomeres are known to play a role in certain diseases of aging, and may be of more general importance. Telomeres are also important in cancer, a disease in which control of cell proliferation is lost. Cancer cells need to reactivate the telomerase gene, or their telomeres will get steadily shorter, forcing them into senescence. In some 80 to 90 percent of human cancer cells, the telomerase gene has been switched back on, Dr. Blackburn said. Clinical trials are under way to see if cancers can be treated by inhibiting telomerase.