Re: RAD51D

[The Fool]

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From: Z Fool

Secret of eternal life may give cancer cure 
 
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RAD51D

[The Fool]

Secret of eternal life may give cancer cure 
 
  
15:36 30 April 04 
 
A new system that helps cells stave off the ravages of time has been
discovered by scientists. The find may help explain how some cancer cells
live forever - and provide a new route of attack for up to one in 10
tumours, they say.

The system keeps cells youthful by adding thimble-like caps to the ends
of chromosomes to protect them from damage and ageing, says the
international team led by scientists at Cancer Research UK.

They estimate that up to 10 per cent of cancer cells may rely on this
capping system to grow and divide well past their natural life
expectancy.

The system is based on a molecule called RAD51D, which the team show
protects DNA from damage. But the molecule also stops the protective ends
of chromosomes from wearing away naturally, the process that normally
allows a cell to grow old and die gracefully.

"Cancer has an amazing ability to shake off the shackles of ageing and
death, which is one of the reasons why it can be so hard to treat, " says
Madalena Tarsounas, who led the study at Cancer Research UK's London
Research Institute 

"Understanding how cancer cells remain eternally young has been a key
focus of research for more than a decade, so it's particularly exciting
to have made such a striking discovery," she says. "We think as many as
10 per cent of tumours may be heavily reliant on the new mechanism to
keep their cells alive and these may also be highly susceptible to drugs
targeted against it."


Structure and stability 


The ends of chromosomes are capped by repetitive sequences of DNA called
telomeres. They are important in maintaining the structure and stability
of chromosomes as they divide and replicate during cell growth. 

As cells grow and divide many times, these telomeres shorten until they
are so short they trigger the cell ageing process, and the cell dies. But
in tumours, this natural ageing mechanism is somehow blocked, and cells
grow and divide uncontrollably.

Tarsounas and her colleagues used immunofluorescence to light up various
molecules in cancer cells. They consistently found RD51D near the
chromosomes' telomeres.
  
And when they used a technique called RNA interference to block the
action of this molecule, the cancer cells suffered substantial damage.
Most of those treated with a blocker died within seven days, but cells
treated with a "placebo" were unaffected. Blocking the action of RD51D
also caused the ends of different chromosomes to fuse together more often
when cells divided.

Blocking this crucial molecule also increased the number of chromosomes
with short telomeres, less than 6 kilobases in length, and decreased the
number of long telomeres, over 20 kilobases in length.

"Cancer cells are adept at slipping the constraints of the ageing
process, but this highly significant study points to ways of making them
mortal, and vulnerable, once more," says Robert Souhami, Cancer Research
UK's Director of Clinical and External Affairs.
 

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