New information about DNA repair mechanism could lead to better cancer drugs

July 16, 2009,

Researchers at Washington University School of Medicine in St. Louis have shed new light on a process that fixes breaks in the genetic material of the body's cells. Their findings could lead to ways of enhancing chemotherapy drugs that destroy cancer cells by damaging their DNA.

Using yeast cells, the scientists studied protein molecules that have an important role in homologous recombination, which is one way that cells repair breaks in the DNA double helix. The process in yeast is similar to that in humans and other organisms.

Earlier research had established that a named Srs2 regulates homologous recombination by counteracting the work of another protein, Rad51. Reporting in the July 10 issue of the journal Molecular Cell, the research team reveals the mechanism of how Srs2 removes Rad51 from DNA and thereby prevents it from making repairs to broken strands.

"Our findings may make it possible to uncover ways to augment the effect of DNA-damaging agents that are used for cancer chemotherapy," says senior author Tom Ellenberger, D.V.M, Ph.D., the Raymond H. Wittcoff Professor and head of the Department of Biochemistry and Molecular Biophysics. "Many chemotherapeutic agents work by causing DNA damage in cancer cells, leading to their death, and tumors can become resistant to chemotherapy by using DNA repair mechanisms to keep the cells alive. Drugs that inhibit the DNA repair process could help increase the efficiency of chemotherapeutic agents."

Ellenberger is also co-director of the Pharmacology Core at Siteman Cancer Center at Barnes-Jewish Hospital and Washington University. The facility aids in the development of anti-cancer agents.

Srs2 is a helicase molecule — a motor protein that's able to walk or slide along a strand of DNA and remove other proteins from DNA or separate the two strands of the twisted double helix. For studies of Srs2, Ellenberger's laboratory collaborated with Timothy Lohman, Ph.D., the Marvin A. Brennecke Professor of Biochemistry and Molecular Biophysics, a prominent expert in the biochemistry of motor proteins like Srs2.

Rad51's job in the cell is to promote the exchange of sequences between two related DNA molecules, which can be used to repair breaks in DNA where both strands of the are compromised. As a DNA matchmaker, Rad51 forms long filaments on DNA. Srs2 can remove these to prevent unwanted exchanges of DNA sequences. Without Srs2, cells lose their ability to maintain the normal structure of chromosomes, and DNA sequences become shuffled.

The biochemists found that Srs2 possesses a small arm that interacts with Rad51 and triggers a chemical reaction within the Rad51 protein causing it to fall off the DNA.

"Scientists had assumed that as Srs2 moved along the DNA strand, it just pushed off everything in its path," says lead author Edwin Antony, Ph.D., a postdoctoral research associate in biochemistry and molecular biophysics. "This isn't the case — we showed that Srs2 has a specialized structure that allows it to interact specifically with Rad51."

This finding shows how a motor protein like Srs2 can perform the specialized task of remodeling a protein-DNA complex without interference by other similar helicases, he adds.

Because they now know more precisely the nature of this interaction between Srs2 and Rad51, the researchers can narrow their search for drugs that will block DNA repair by Rad51. This type of drug could make a lower dose of a DNA-damaging drug effective in treating cancer.

The research team is now trying to identify the Srs2 homologue in human cells and will study its structure in combination with Rad51. That will allow a more rational approach to understanding how cells cope with and how some tumors evade cancer therapeutics, they say.

"In the long-term, my laboratory will look for drug-like molecules that influence this interaction," Ellenberger says. "We are using the Chemical Genetics Screening Center here at the University ( It has vast libraries of molecules that may have the activity we want. Edwin's work on Srs2 and Rad51 will allow us to develop an assay to screen for agents that augment or supersede Srs2's interference with DNA repair."

More information: Antony E, Tomko EJ, Xiao Q, Krejci L, Lohman TM, Ellenberger T. Srs2 disassembles Rad51 filaments by a protein-protein interaction triggering ATP turnover and dissociation of Rad51 from . Molecular Cell. 2009;35(1):105-115.

Source: Washington University School of Medicine (news : web)

Explore further: Yale scientists to study DNA repair in cancer cells

Related Stories

Enhanced DNA-repair mechanism can cause breast cancer

October 15, 2007

Although defects in the "breast cancer gene," BRCA1, have been known for years to increase the risk for breast cancer, exactly how it can lead to tumor growth has remained a mystery. In the October 15, 2007, issue of the ...

Human DNA repair process recorded in action (Video)

January 29, 2009

( -- A key phase in the repair process of damaged human DNA has been observed and visually recorded by a team of researchers at the University of California, Davis. The recordings provide new information about ...

How cells handle broken chromosomes

February 13, 2009

( -- After being recognized and initially processed by the cellular machinery, the broken chromosome is extensively scanned for homology and the break itself is later tethered to the nuclear envelope. Thus the ...

Recommended for you

Scientists shed light on biological roots of individuality

February 16, 2018

Put 50 newborn worms in 50 separate containers, and they'll all start looking for food at roughly the same time. Like members of other species, microscopic C. elegans roundworms tend to act like other individuals their own ...

Plants are given a new family tree

February 16, 2018

A new genealogy of plant evolution, led by researchers at the University of Bristol, shows that the first plants to conquer land were a complex species, challenging long-held assumptions about plant evolution.


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.