A fountain of youth for individual cells, the enzyme telomerase keeps cells living longer by preventing their chromosomes from eroding. But scientists report in today's Proceedings of the National Academy of Sciences that telomerase can freshen up cancer cells in a second, more mysterious way.
When a cell divides, its genetic machinery faces a problem: It can't copy the chromosomes all the way to their very tips. After each division, the chromosomes get shorter and shorter until the cells stop dividing, a process called senescence. Telomerase maintains chromosome ends, allowing embryonic tissues, immune cells, and certain other cells to divide with abandon. When added to aging cells, telomerase makes them immortal. Because this is also a hallmark of cancer, a team led by Elizabeth Blackburn, a cell and molecular biologist at the University of California, San Francisco, wondered what role the enzyme plays in the molecular transformation from normal cell to tumor cell.
The team inserted telomerase into skin and lung cells that are predisposed to become cancerous but lack telomerase activity. As expected, the telomerase prevented the cells from dividing themselves into oblivion. But the chromosome ends kept getting shorter--even shorter than the ones in senescent cells. Blackburn speculates that in cancer cells, at least, telomerase may form part of a protective sheath around the chromosome ends that prevents them from swapping genetic material. Although recombination is usually a healthy process that maintains a diverse gene pool, if the chromosome ends were to recombine the chromosomes themselves would fuse.
The study offers a fresh look at telomerase, says molecular geneticist Arthur Lustig of Tulane University in New Orleans. "There appear to be truly two functions for telomerase," he says. Telomerase, if it acts as a genetic bodyguard for cancer cells, is a promising target for anticancer therapies, Lustig adds, noting that the enzyme is found in an estimated 80% to 90% of all cancer types.