Image: Noa Lamm, CMRI
A protein called actin lets cancer cells repair their DNA, and it can even help them to resist chemotherapy, new research shows.
The finding in cell lines and animal models, published today in Nature Cell Biology, will spark efforts to produce new tailored therapies to kill cancer cells.
“Understanding that actin assembled within the nucleus helps overcome malfunctions in DNA replication opens the door to the development of new and more precisely targeted therapeutics that stop cancer cells from dividing,” says Maté Biro of EMBL Australia Node in Single Molecule Science at UNSW.
Westmead’s Dr Noa Lamm, lead scientist on this project, was inspired to become a cancer researcher after losing her mother to the disease. She spent more than four years working on this discovery that revealed an unexpected function for the protein actin. Actin is well known as the protein that interacts with another protein called myosin to make muscles contract, and it also forms cables inside cells that connect up and function like girders in a building, contributing to the structure and shape of cells.
While scientists have known for decades that actin plays this critical role in the main body of the cell, its role in the cell's control centre, the nucleus, has been controversial.
For cancers to grow, cancer cells need to make many new copies of themselves. Every time this happens, the DNA in the cancer cells' nuclei must be replicated.
“Whether actin played a role in DNA replication was not known,’’ Dr Lamm said. Her previous work as a PhD student suggested actin may have an unexpected nuclear function – and her new research has shown that this hunch was correct.
Putting the brakes on cancer cells’ growth
DNA replication in a cancer cell is like an old car travelling at its top speed – it frequently breaks down and has to get restarted. Cancer chemotherapy exploits this weakness in cancer cells by making the process break down even more frequently in an attempt to destroy them.
Dr Lamm found that when cancer cells encounter problems replicating their DNA, actin cables form inside the nucleus. This allows the nucleus to change shape, and it increases the ability of the cancer cell to repair its DNA and restart the replication process.
Using advanced super resolution microscopy, the researchers showed that damaged DNA slides along the actin network to move to areas in the nucleus where repair occurs most efficiently. Scientists were previously unaware that cancer cells protected themselves in this way. Critically, this research found that actin performed these unexpected functions in response to treatment with chemotherapy and helped cancer cells resist the treatment.
Dr Lamm says there are two ways this discovery will help cancer patients down the track. First, treatments that disable the actin cable mechanism could kill cancers that already have difficulty maintaining a high rate of DNA replication. Second, adding treatment that interferes with the actin cables to commonly used chemotherapies will enhance their success rate.
Motivated by personal journey
Part of Dr Lamm’s motivation to become a cancer researcher arose from her own personal story. Her mother died of cancer when she was young.
“It was extremely hard, especially as a kid, to watch the person you love and depend upon the most, dying – and there was nothing you could do about it,” she said.
Now she feels excited to have found a new approach for treating cancer.
“Science is very creative; you get the feeling that you are doing something that no one else is, because no two scientists will ask exactly the same questions. It’s exciting to understand something that was not known before. We are very hopeful this will be a big step forward, because all progress starts with basic discovery.’’
Dr Lamm is a part of the team from the University of Sydney’s Faculty of Medicine and Health.
CMRI researchers working on this project include Dr Lamm, Associate Professor Tony Cesare, Dr David Ly, Scott Page and Dr Pragathi Masamsetti. They worked with Dr Maté Biro from UNSW, Dr Mark Reed from The University of Sydney, and Dr Max Nobis and Prof Paul Timpson of The Garvan Institute (who is also a Conjoint Professor at UNSW).