Two mutations that collectively occur in 71 percent of malignant melanoma tumors have been discovered in what scientists call the “dark matter” of the cancer genome, where cancer-related mutations haven’t been previously found.
Harvard Medical School (HMS) researchers at the Dana-Farber Cancer Institute and researchers at the Broad Institute said the highly “recurrent” mutations — occurring in the tumors of many people — may be the most common mutations in melanoma cells found to date.
The researchers said these cancer-associated mutations are the first to be discovered in the vast regions of DNA in cancer cells that do not contain genetic instructions for making proteins. The mutations are located in non-protein-coding DNA that regulates the activity of genes.
This non-coding DNA, much of which was previously dismissed as “junk,” accounts for 99 percent of a cell’s genome. A large number of oncogenic mutations in cancer have been identified in the past several decades, but all have been found within the actual genetic blueprints for proteins.
“This new finding represents an initial foray into the ‘dark matter’ of the cancer genome,” said Levi Garraway, HMS associate professor of medicine and the article’s senior author.
A human melanoma cell line growing in tissue culture is pictured. The study of cancer cell lines such as this one allows scientists to investigate cancer cell biological processes and ways to modify them in order to design and test new treatments.
“In addition, this represents the discovery of two of the most prevalent melanoma gene mutations. Considered as a whole, these two TERT promoter mutations are even more common than BRAF mutations in melanoma. Altogether, this discovery could cause us to think more creatively about the possible benefits of targeting TERT in cancer treatment or prevention,” Garraway said.
The mutations affect a promoter region — a stretch of DNA code that regulates the expression of a gene — adjacent to the TERT gene. TERT contains the recipe for making telomerase reverse transcriptase, an enzyme that can make cells virtually immortal, and is often found overexpressed in cancer cells. A promoter region of DNA controls the rate of a gene’s transcription — the copying of its DNA recipe into a message used by the cell to manufacture a protein.
“We think these mutations in the promoter region are potentially one way the TERT gene can be activated,” said Franklin Huang, an HMS clinical fellow in medicine and co-first author of the report along with Harvard M.D.-Ph.D. student Eran Hodis.