PHILADELPHIA - Double-strand breaks in DNA happen every time a cell divides and replicates. Depending on the type of cell, that can be pretty often. Many proteins are involved in everyday DNA repair, but if they are mutated, the repair system breaks down and cancer can occur. Cells have two complicated ways to repair these breaks, which can affect the stability of the entire genome.
Roger A. Greenberg, M.D., Ph.D., associate investigator, Abramson Family Cancer Research Institute and associate professor of Cancer Biology at the Perelman School of Medicine, University of Pennsylvania, together with postdoctoral researcher Jiangbo Tang Ph.D. and colleagues, found a key determinant in the balance between two proteins, BRCA1 and 53BP1, in the DNA repair machinery. Breast and ovarian cancer are associated with a breakdown in the repair systems involving these proteins. Their findings appear in the latest online issue of Nature Structural & Molecular Biology.
The two proteins, BRCA1 and 53BP1, control which of two cell-repair mechanisms will be used: homologous recombination or non-homologous end-joining, technically speaking. This competition has proven to be a key factor in determining whether a cell becomes cancer prone as well as how a cancer cell will respond to chemotherapy.
The key step of the balance is acetylation, the chemical process of adding a compound called an acetyl group to other cellular molecules.
The researchers asked what cell signals determine whether BRCA or 53BP1 predominates at a DNA break site.
DNA in the nucleus is tightly packed around proteins called histones. Acetylation at a specific spot on histone H4 determines the answer. If H4 is acetylated at a specific location, then 53BP1 binding near the broken DNA region is strongly reduced. This leaves BRCA1 free to do the work, kicking in the homologous recombination tool to repair the break.
On the other hand, if acetylation is reduced, 53BP1 outcompe
|Contact: Karen Kreeger|
University of Pennsylvania School of Medicine