Human Cells Evolved To Reduce Cancer Risk

Main Category: Cancer / Oncology
Article Date: 10 Jul 2009 - 4:00 PDT

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The cells of humans and other animals have likely evolved to reduce the chance of triggering cancers and other diseases, according to research published in the journal Science.

Dr Rune Linding at The Institute of Cancer Research in the UK, working with scientists in the US and Canada, found that as animals moved up the evolutionary chain they progressively shed molecules that are linked to cancer development.

Chris Tan, then a PhD student working under Dr Linding's supervision, investigated whether complex organisms shed these molecules to compensate for acquiring new molecules that could increase the risk of disease, but are necessary for the animals to function.

As animals have become more biologically complex they have acquired more variants of tyrosine kinases, a class of enzymes that control the behaviour of cells. Tyrosine kinases are necessary for survival as their effect on an amino acid called tyrosine alters proteins, sending instructions to cells about when to move, grow and die - but they can also become damaged and send the wrong signals, causing cancer and other diseases.

The scientists found that, in an apparent effort to compensate for this increased risk, the cells of more complex animals have reduced the amount of tyrosine they allow in their proteins - leaving less opportunity for the kinases to malfunction.

Tyrosine levels in animals - including a worm, sea squirt, fly, mosquito, two species of pufferfish, frog, chicken, dog, cow, mouse, rat, chimpanzee and humans - were evaluated relative to other amino acids. A "striking" progressive reduction in tyrosine concentrations was found to occur higher up the evolutionary chain.

"Tyrosine loss has been strongly favoured in human protein evolution," Dr Linding says. "Reducing the number of potentially harmful tyrosine kinase interactions is important to avoid cancer, and losing these tyrosines seems to be a deliberate effort by the cells to reduce the risk of malfunction and disease. It looks like we've found an example of co-ordinated, adaptive evolution occurring at a cellular level."

The cells are following a pattern of behaviour also recognised in humans on a population level, Dr Linding adds.

"Adaptive evolution that can be seen in human society - such as when local populations adjust to the influx of immigrants contributing to societies' economic development - also appears to be operating at a cellular and molecular level," Dr Linding says.

The research was a collaboration between researchers at The Institute of Cancer Research, United Kingdom, the Samuel Lunenfeld Research Institute of Mount Sinai Hospital, Toronto, Canada, the University of Toronto, Canada, and the University of California, San Francisco, US.

Source
The Institute of Cancer Research