Study suggests enzyme vital for DNA replication can provide powerful anti-cancer Drug Target

An enzyme essential for DNA replication and repair in people works in a way that could be exploited as anti-cancer therapy, say researchers at The Scripps Research Institute and the Lawrence Berkeley National Laboratory.

The research, published in 15 April 2011 the issue of the journal cell, focused on a member of a group of enzymes, valve enzyme, which is essential for the life of a cell. The findings show new, clearly defined crystal structures of the enzyme FEN1 in action to show that it functions in a way contrary to accepted dogma.

"This work represents an important step forward in understanding FEN1," said team leader John Tainer, professor and member of the Skaggs Institute for chemical biology at Scripps Research and senior scientist at the Lawrence Berkeley National Lab. "the research produced very accurate structures displayed: DNA before and after the FEN1 activity is bezuinigddie a basis for the understanding of an entire superfamily of enzymes that cut DNA specific DNA structures must be replicated and repaired. "

This superfamily contains important objectives for the development of new cancer interventions, Tainer added. Many cancers Show high levels of FEN1 expression, which in some cases is correlated with tumor aggressiveness. For these cases may FEN1-specific inhibitors chemotherapeutic potential.

"A better understanding of the structure and function can FEN1 long-term positive effects on human health," did co-author Andy Arvai, a scientific associate at Scripps Research.

To quickly work with excellent precision

DNA to replicate, it has to unwind from the double helix, which is formed from two strands of amino acids spiral cord together. This settlement is done by a replication (DNA) where the two strands are separated. These businesses, which are two branching processes of the replication (DNA), serves as a template for the production of a new additional beach.

That task is pretty simple on what is known as the "lead" of the two strands. The replication (DNA) moved along from the so-called 3 ' (three prime) end to the 5 ' end (five prime) and DNA polymerase speech output a 5 ' to 3 ' additional beach.

But because the two strands are anti-parallel, meaning that they are oriented in opposite directions, the work of the DNA polymerase, which only in the 5 ' to 3 ' direction, can work is harder on the so-called lagging beach. This component must be replicated into pieces, which are known as Okazaki fragments, located near the replication (DNA). These fragments include a "primer," a component of RNA that as a starting point for DNA synthesis.

This is where FEN1 comes it removes that RNA primer at the 5 ', that every 100 base pairs or so on the lagging strand occurs, said Tainer. It is a daunting task that happen quickly and accurately to glue the ends of replicated DNA on the lagging strand together to ultimately an intact chromosome. "For replicating a DNA double helix in a single cell is to cut off a 5 '-valve so that you are not one base pair too much or too little one base pair, and you have to do this accurately with 50 million Okazaki primers in each cell cycle" said tainer. "It is always a mystery as to how exactly this flap can FEN1 as efficiently and as quickly. It's a great, efficient molecular machine for precise cutting DNA. "

To determine what FEN1 seemed in action, Arvai led the difficult but ultimately successful effort to grow crystals of the human FEN1 protein bound to DNA. The team then uses x-ray crystallography to determine the atomic structure of the complex. Using Lawrence Berkeley National Laboratory's advanced light source beamline, called SIBYLS, the scientists solved three different crystal structures.

The end result was a very detailed and accurate model showing the structure of DNA before and after FEN1 reductions.

Previous crystal structures proposed that FEN1 first grab onto the lid of the 5 ' DNA, one slides to the joint where DNA is duplicated stranded, cuts and the primer there patches. But the new study found that, in fact, bind, Fraisse FEN1, curves, and then the DNA cuts.

"The duplex DNA binds, bends it into a single-stranded DNA in the valve, flips out two base pairs and cuts between them," said Tainer. "This gives FEN1 very precise control a refinement that we had not expected."

Evidence of cancer

Researchers know that mutations in human FEN1 predispose to cancer growth because errors in valve can remove unstable DNA that promotes cell growth and Division. And studies in mice have shown that when one of the two genes are inherited FEN1 knock-out, the mice are prone to developing cancer if their DNA is damaged.

While other DNA repair systems can help compensate FEN1 errors or missing FEN1 activity, "you have a bunch of FEN1 for DNA repair and replication to work properly must," said Tainer.

This suggests that, in tumors already lacks a set of repair proteins, the function of selective braking FEN1 in replicating cells can quickly prove to be an effective anti-cancer therapy. Tainer, said "the achilles heel of cancer cells is defective DNA repair pathways,", "because that makes them more sensitive to traditional therapies, such as chemotherapy and radiation. As cancer cannot repair the damage caused by these therapies to tumors restore do, they will die. "

This is the paradox of DNA repair: while a defect in DNA repair can cause cancer, knocking off a number of back-repair systems can tumors vulnerable anti-cancer therapies.

"My hope is that our findings on the functioning of mechanistically FEN1 could form a basis for a next generation cancer drug," said Tainer. "We need to cut as many lifelines as possible in cancer cells in order to ensure an effective treatment."

The study was supported by grants from the National Institutes of Health and biotechnology and Biological Sciences Research Council (BBSRC) in the United Kingdom.

Sources: The Scripps Research Institute, AlphaGalileo Foundation.