New clues to genetic link in growth of cancers are discovered
New York Times
June 9, 2005
By Andrew Pollack
A recently discovered genetic mechanism appears to play an important role in the development of cancer, scientists are reporting today in findings that may eventually lead to new ways to diagnose and treat the disease.
The discoveries "change the landscape in cancer genetics," Dr. Paul S. Meltzer of the National Human Genome Research Institute wrote in a commentary in the journal Nature, which is publishing three papers on the findings.
Other scientists cautioned that the new findings merely add detail to the already complex picture of how tumors arise and grow.
The findings concern micro-RNAs, which are tiny snippets of genetic material that help dampen the activity of other genes. The material was discovered in the early 1990s in the roundworm, and in recent years, scientists have been finding them everywhere, including 200 in human cells.
The mere discovery has altered views of RNA's importance in regulating the working of genes. The previous view was that genes, which are made of DNA, are the recipes for protein, which make up much of the structure of cells and perform most of the functions. In this scheme, RNA, a sort of chemical cousin of DNA, acted mainly as a messenger dispatched by DNA to carry the recipe for a protein to the cell's protein-making machinery.
But with micro-RNAs, the RNA itself is the end product of a gene, not merely an intermediate product on the way to making a protein. These RNA snippets help control the activity of protein-making genes.
But in most cases the specific function of the snippets has not been found. The papers are a start in that direction.
In one paper, scientists at the Cold Spring Harbor Laboratory, the University of North Carolina and the Memorial Sloan-Kettering Cancer Center found that a particular set of micro-RNAs may help cause B-cell lymphoma, a blood cancer.
The scientists altered stem cells from mouse blood to make the micro-RNAs more active. When the cells were then put into mice, the animals developed lymphomas that could be traced to the altered cells. The scientists also found that micro-RNAs were active in human tumor biopsies.
"This is perhaps the first example that a gene that doesn't produce any protein at all can contribute to cancer," said Dr. Gregory J. Hannon, a senior author of the paper.
In a second paper, scientists at Johns Hopkins found evidence that a well-known cancer-promoting gene called c-Myc activates six micro-RNAs.
The third paper found that patterns of activity of the 200 or so known human micro-RNAs may be used to distinguish healthy cells from tumor cells or one type of tumor from another. The technique may prove useful in diagnosing the small fraction of tumors that cannot be diagnosed clearly.