Enabling Replicative Immortality
In: Conger, K. Stanford Medicine: Telomere extension turns back aging clock in cultured human cells, study finds. January 22, 2015.
Telomeres are sections of DNA located at the end of chromosomes. They protect the inner DNA as they degrade first over time through cycles of cell division.
T he fourth Hallmark of Cancer is the cell’s ability to enable replicative immortality. This means that cancer cells are able to replicate unlimitedly. Healthy cells are able keep track of their age and how many times they divide. Just like how cells are pre-programmed for apoptosis, cells are also pre-programmed with a limit on the number of times they proceed through the cell cycle and divide. This limit is called the Hayflick Limit, in which most cells divide anywhere from 40 to 60 times before the cell slows down and comes to a stop. When senescence is reached, the loss of a cell’s ability to divide and grow, it is irreversible.
As mentioned previously, telomeres are located at the ends of chromosomes and have control over the cell division limit. They keep track of the number of divisions a cell undergoes. Each time a cell’s DNA is replicated, the telomeres act as caps that protect the internal regions of DNA as they get worn down first. Cancer cells often have longer telomeres that last through more rounds of DNA replication, allowing for the cells to divide more. These abnormally long telomeres exist by an overexpression of an enzyme called telomerase that oversees the length of telomeres and makes them longer.
Cancer cells are able to evade signals to isolate and continue on the growth pathway and are also able to break the limit of cellular replication, making these cancer cells virtually immortal. Cancer is more prevalent in the aging population as the amount of harmful mutations increases with age.
An example of this Hallmark of Cancer can be seen with pancreatic cancer. Cancer cells in the pancreas often have telomeres that become short due to repetitive replication. However, due to some kind of overexpression, the cancer cells are able to make more telomerases that will lengthen the telomeres once more. An abnormally large amount of telomerases can be a sign that a cell is cancerous. Scientists are looking for ways to reduce the amount of telomerases that cancer cells can produce to allow the cells to age and die naturally. However, getting rid of telomerases completely could cause infertility and interfere with healing processes. Telomeres would be too short and cause problems with replication of DNA as well as speed up the aging process. More research in this area could provide effective treatments for cancer in the future. [i]
[i] Are Telomeres the Key to Aging and Cancer. Learn Genetics: Genetic Science Learning Center. http://learn.genetics.utah.edu/content/basics/telomeres/ . March 1, 2016.