The human body has so many millions of cells that when things go awry in one, it's best to kill off the offender.

Changes in DNA that would lead to cancer if unchecked are common in the body, but when cells notice that their DNA is damaged, they will tidily commit suicide in the best interest of the organism.

A new study published in this month's edition of the journal Nature by Associate Professor of Medicine William G. Kaelin Jr. sheds new light on the contents of the cell's bottle of hemlock.

Scores of chemicals participate in the intricate web of interactions that control cell suicide. Fifty percent of all human cancers cause defects in one, the drably named p53. Without this protein, cells have trouble killing themselves to save the body from cancer.

Because of its key role, p53 has been a major subject of the search for a cancer cure. In 1997, immune system researchers at a French pharmaceutical company surprised the cancer research community with their serendipitous discovery of a close cousin of p53 which they named p73.

P73's pedigree suggests that it should be important in fighting cancer but it has proved surprisingly hard to pin down its function.

In some of the most interesting research on the subject, Kaelin showed a few years ago that p73 can be coaxed into involvement in cell suicide. In his latest paper he reports the surprising discovery that both p53 and p73 are activated by the same protein.

Lives of a Cell