Quadruple helix DNA discovered in human cells

Nearly sixty years after the discovery that DNA forms a double helix (by James Watson and Francis Crick), a quadruple stranded DNA was found in cancer cells by a team at the University of Cambridge.

Previously the quadruple helix had been formed in the laboratory by intertwining four strands of DNA however it was long believed that they did not exist in nature. The four-stranded DNA called the G-quadruplexes, are formed by the interaction of four guanine bases that together make a square, and appeared in cells that were ready divide. They form in the core of chromosomes and on telomeres (tips of chromosomes to protect them from damage), however since cancer cells have defects in telomeres and divide rapidly, this may be unique to cancer cells.

The study (published in Nature and New Scientist) was led by Shankar Balasubramanian, at the University of Cambridge, with the team using antibodies that could only attach to G-quadruplexes to locate the G-quadruplexes and then using pyridostatin (a molecule trapping the quadruple helices) to stop them from unraveling into ordinary DNA, enabling researchers to count the number formed at each stage of cell division. They found that these quadruple helices were most common in the S-phase (during Interphase) when cells replicate their DNA, before dividing.

Balasubramanian believes that the G-quadruplexes are triggered into action by chaotic genomic mutations and reorganizations typical of cancerous of precancerous cells. Using pyridostatin on human breast cancer cells, the team found that it stopped the cells from replicating and reduced the spread of cancer cells. The results, therefore, reinforce the possibility that blocking G-quadruplexes could combat cancers. However, currently the team is hoping to find out whether quadruple helices exist in healthy cells and whether they play a role in embryo development, being mistakenly reactivated in cancer cells.