Bowhead Whales Exhibit Efficient DNA Repair
All large mammals must evolve ways to suppress cancer risk more effectively than their smaller relatives. More mass means more cells, and thus more chances for a cell to suffer the mutations that will lead to cancer. Elephants evolved additional copies of P53 and other tumor suppression genes, for example. Bowhead whales, on the other hand, appear to manage with more efficient DNA repair mechanisms. We can hope that some of these explorations may lead to ways to improve human resistance to cancer. Improved DNA repair in particular is an attractive goal, given that DNA damage is linked to aging in a number of ways, such as via somatic mosaicism and the possibility of causing detrimental epigenetic change.
At over 200 years, the maximum lifespan of the bowhead whale exceeds that of all other mammals. The bowhead is also the second-largest animal on Earth, reaching over 80,000 kg. In spite of its very large number of cells, the bowhead is not highly cancer-prone, an incongruity termed Peto's Paradox. This has been explained by the evolution of additional tumor suppressor genes in larger animals, which is supported by research on elephants demonstrating expansion of the p53 gene.
However, we show here that bowhead whale fibroblasts undergo oncogenic transformation after disruption of fewer tumor suppressors than required for human fibroblasts. Instead, analysis of DNA repair revealed that bowhead cells repair double-strand breaks with uniquely high efficiency and accuracy compared to other mammals. Further, we identified two proteins, CIRBP and RPA2, that are present at high levels in bowhead fibroblasts and increase the efficiency and fidelity of DNA repair in human cells.
These results suggest that rather than possessing additional tumor suppressor genes as barriers to oncogenesis, the bowhead whale relies on more accurate and efficient DNA repair to preserve genome integrity. This strategy, one that does not eliminate cells but repairs them, may be critical for the long and cancer-free lifespan of the bowhead whale. Our work demonstrates the value of studying long-lived organisms in identifying novel longevity mechanisms and their potential for translation to humans.