Humans develop cancer at a remarkably high rate in comparison to other animals. Many elements are attributed to the high cancer rate in humans, including environmental factors, errors in gene replication, and inherited mutations. Notably, the odds of developing cancer related to our environmental exposures or somatic mutations rise because of our relatively long lifespan. These factors explain, in part, why humans are more susceptible to cancer than other species (we previously explored the low cancer incidence in elephants.) However, there is significant interest in understanding the precise mechanisms dictating variable susceptibility between species. Researchers could eventually apply information on the mechanisms which protect other species from cancer to develop new therapies to treat cancer patients.
Humans (Homo sapiens) share over 98% of their genome with our evolutionary relatives, chimpanzees (Pan troglodytes); however, non-human primates exhibit very low cancer incidence rates. So, why are humans so much more susceptible to cancer than chimpanzees despite our similar genetic profiles? A group of researchers from Memorial Sloan Kettering Cancer Center and the American Museum of Natural History recently published an article in Cell Reports details a study that tackled this precise question.
The research team compared the gene profiles of humans to that of 12 different non-human primates. The comparison identified almost 400 gene substitutions present in human DNA, which emerged throughout the human evolutionary process. The researchers then performed bioinformatics analyses which revealed that one of the mutations was located on the breast cancer 2 (BRCA2) gene.
The BRCA2 gene codes for proteins pivotal for DNA repair, a biological process to correct the damage naturally arising in our genetic code. Pathogenic mutations can develop in the BRCA2 gene, inhibiting the DNA repair process and promoting cancer development. Because of this role in regulating a function closely linked to cancer development, BRCA2 is known as a tumor suppressor gene.
The analysis uncovered a substitution in codon 2662 of BRCA2. Notably, this substitution has become fixed in the human genome, meaning it has appeared through mutation and spread through the population. When the substitution was present, the ability of BRCA2 to promote DNA damage repair was reduced by about 20%.
The study suggests that a single mutation in codon 2662 of the BRCA2 gene could explain why humans remain more susceptible to cancer than other primates. The findings of this study may present a new target for drug and therapeutic development. Someday, with significant advances in gene editing, it may become feasible to manipulate the BRCA2 gene to resemble that of our non-human primate ancestors.
Sources: National Academies Press, Science, Hum Mutat, Nature, BMC Genomics, Cell Reports