Important how cells copy chromosomes for fighting cancer

As we find out more and more about what goes wrong inside cells, the better we become at killing cancer without harming the rest of the body. Now, scientists have discovered a key step in how cells copy their 

chromosomes when they divide that promises to be very useful for cancer research.

Karim Labib, a professor in life sciences at the University of Dundee in Scotland, and colleagues report how they solved an important mystery in cell biology in the journal Science.

Life depends on cells being able to multiply, a key part of which is copying chromosomes, the tightly packed bundles of DNA that carry the genetic blueprint of the individual.

The chromosome copying process has to copy the genetic information perfectly for new cells to grow and carry out their function normally. The more mistakes that are made, the more likely that cells will behave abnormally and triggercancer.

We do not know enough about how chromosome copying works

The researchers say one of the fundamental biological processes that go wrong in cancer is that the chromosome copying machinery has not worked properly. Their new study sheds light on this process.

Prof. Labib says ever since Watson and Crick first revealed the structure of DNA, scientists have been fascinated by how cells copy chromosomes, yet "we are still quite a way from having a complete picture of how it works."

He and his colleagues focused on the stage when the cells finish copying their chromosomes. Scientists already know something about this; it is vital that this happens correctly for the genetic blueprint to be passed on to the next generation of cells.

"We already knew that 11 proteins in the cell combine to build a molecular 'machine' called the DNA helicase, which plays a vital role in copying the double helix of DNA that is at the heart of each chromosome," Prof. Labib adds.

He explains that the DNA helicase unwinds the two strands of the double helix of DNA, so they can each be copied, and that:

"It is vital that the helicase is only built once during the life of each cell, and then is taken apart or disassembled once it has done its job, so that cells just make one single copy of each chromosome."

Understanding disassembly of the DNA helicase is important for cancer research

Until now, scientists did not know how the helicase disassembled. This is what the team at Dundee discovered. They found, because of a process called "ubiquitylation," one of the 11 components of the helicase falls out when chromosome copying is complete.

Because this one component falls out, the other proteins are unable to stick together, and the DNA helicase falls apart.

"It turns out that this is a very good thing," says Prof. Labib, "as genetic studies show that if the helicase does not come apart but instead remains glued to the chromosomes, then this leads to major problems."

He says this is one of the fundamental biological processes that go wrong in cancer, "almost any time that we see cancer developing, one of the things that has gone wrong early in the process is that the chromosome copying machinery has not worked properly."

The research was funded by the Medical Reseach Council, Cancer Research UK and the Wellcome Trust.

Meanwhile, in another area of cancer research, Medical News Today recently learned that researchers have found a molecule that helps cancer cells evade the immune system.

Written by Catharine Paddock PhD