PTEN received its name because of its similarity to phosphatases and tensin. The similarity between PTEN and protein phosphatases, which remove phosphates from proteins, is significant because many oncogenes-genes that help to transform normal cells into cancer cells-encode tyrosine kinases, which add phosphates to proteins. Tensin is part of a complex of proteins that sits below the cell surface and controls cell shape. Thus, PTEN may also be involved in the spread of tumors, by localizing to the cell surface and removing phosphates from key signaling proteins. In a productive collaboration between the Wigler laboratory and Nicholas Tonks' laboratory at CSHL, the two groups quickly confirmed that PTEN is a phosphatase and have identified proteins with which it interacts. These studies should point to the pathway in which PTEN functions in normal cells and which is altered in tumor cells.

Representational difference analysis (RDA), an advanced genetic technology developed by Mike and Nikolai Lisitsyn, then at CSHL, played a key role in the identification of a PTEN tumor suppressor gene. RDA is a procedure used to analyze the differences between two genomes. (A genome is the entire DNA sequence of an organism.) By comparing DNA from diseased and normal cells from the same person, scientists can use RDA to identify DNA sequences that differ between the cancer cells and normal cells. In the case of PTEN, RDA was used to find unique DNA sequences present in normal tissue but missing in breast cancer. To date, the Wigler lab has located about a dozen genetic loci potentially involved in breast cancer. Each of these discoveries represents a vital step forward in the path to earlier diagnosis and improved treatment for breast cancer patients, and it illustrates the growing realization of the genetic complexity of cancer.

In 1994, to further utilize RDA in the search for cancer-related genes, the Laboratory and Mike formed Amplicon Corporation. In October 1997, the Laboratory announced the acquisition of Amplicon by biotech leader Tularik, Inc. Tularik is the largest privately held biotechnology company in the nation, and its scientists are enthusiastic about continuing collaborations with CSHL scientists while using RDA in an extensive cancer research program. Although Tularik, Inc. is located in California, the oncology division of the company will continue to operate on Long Island for at least 5 years and will continue to collaborate with CSHL scientists.

There was good news and bad news from Carol Greider's lab in 1997: The good news was the report of a line of telomerase knock-out mice. The bad news was that Carol left Cold Spring Harbor after 9 years to accept a position as Associate Professor in the Department of Molecular Biology and Genetics at Johns Hopkins University School of medicine in Baltimore, Maryland, to follow her historian husband to his new faculty position at George Washington University.

In October, Carol's group published a report about mice that lack telomerase, an enzyme that she discovered in 1985 and has continued to study. Telomerase is necessary for maintaining chromosome integrity. Several studies have suggested that telomerase also plays a role in cancer and cell senescence. The ends of chromosomes, called telomeres, shorten each time a cell divides. It is thought that when telomeres reach a critically short length, the cell division cycle arrests and cells enter into a senescent state after which they never divide again. Telomerase appears to sustain telomeres against this shortening.

In collaboration with Ron DePinho's lab at Albert Einstein College of Medicine, Carol's group bred a line of mice that lacked the telomerase enzyme. The results showed that mice can survive for six generations without telomerase. The studies also proved telomerase's role in chromosome stability; mice that lacked telomerase showed telomere shortening and loss of telomere function, and they eventually developed chromosomal abnormalities. After five or six generations, telomere loss in mice leads to sterility and loss of cell viability in certain highly proliferative tissues. The work confirms the suspected role for this important enzyme in cell proliferation and demonstrates that when telomeres reach a critically short length, cell and tissue viability are progressively lost. Interestingly, cells that lacked telomerase could still form tumors, demonstrating that telomerase is not essential for tumor formation in mice. As predicted, however, recent results indicate that the rate of tumor formation is lower in mice that lack telomerase. Thus, although telomerase is not essential for the development of cancer, it may play an important role in tumor formation.

Scott Lowe and David Beach made a surprising new discovery about the transformation of normal cells into cancer cells. Usually, most human cells undergo senescence, or permanent cell cycle arrest, after a restricted number of cell divisions. This, in effect, limits the cells' life span. Cancer occurs when cells continue dividing beyond the normal limit or fail to die when they should. In 1981, scientists, including Mike Wigler at CSHL, discovered that a gene called ras was involved in some human cancers. This was the first discovery of a human oncogene that was derived from a tumor. In 1983, Earl Ruley-then at CSHL, now at Vanderbilt University School of Medicine-showed that ras acts in concert with other oncogenes to cause cancer. It was determined that most of these cooperative oncogenes can independently extend the life span of-or even immortalize-cells. Recently, Scott and David reported the surprising observation that when the oncogenic form of ras is overexpressed in normal cells, it immediately induces the same sort of cell senescence that occurs during cell aging. two other genes, p16 and p53, both extensively studied at CSHL and elsewhere, are necessary for this type of cell cycle arrest. When p53 or p16 are absent from the cell, ras now stimulates uncontrolled cell division, rather than cell division arrest. This research provides important information about the multistep nature of cancer and suggests that, in the right context, it may be possible to exploit oncogenes to reverse tumor cell growth.