Cancer breakthrough at Westmead

Research into cancer, anticancer treatments, and ageing has been advanced through the identification of the composition of human telomerase - an enzyme integral to 85% of all cancers.
Cancer researchers around the world have studied telomerase since its discovery 18 years ago but they were working somewhat in the dark.
The actual protein composition was unknown, scientists believing it contains any mixture of 32 proteins.
A study, headed by Dr Scott Cohen of the Childrens Medical Research Institute reveals that telomerase contains just 2 proteins.
Until now, researchers studying telomerase have not been sure what they’re working with, said Dr Cohen, whose study was supported by The Cancer Council NSW and the National Health and Medical Research Council Australia, and published by leading journal Science.
Dr Roger Reddel, acting director of CMRI and an international cancer research expert, believes the identification ‘switches on a light’ for basic cell biology and cancer research.
"Telomerase is the target of an extensive global effort to develop anti-cancer treatments.
This discovery sharpens the focus of these efforts and no doubt will speed up the process of delivering successful treatment," said Dr Reddel.
Dr Cohen developed a brilliant new purification technique that made the telomerase identification possible and will be useful for scientists requiring purified telomerase, a step towards development of anti-telomerase drugs.
"No-one has previously been able to purify telomerase because, within each cell, its a very rare enzyme. Each cell has about 20 molecules of telomerase – compared to about 20 million molecules each of some abundant enzymes," said Dr Cohen.
"I had to pull out one part in 100 million, which is roughly a teacup of water from an Olympic swimming pool."
These findings will significantly enhance the ability of cancer researchers to further study telomerase.

Dr Cohens identification of the composition also makes research methods such as x-ray crystallography possible for telomerase, which would be another major step towards identifying new anti-cancer drugs.


How active telomerase enables cancer:Active telomerase allows cancer cells to divide and reproduce indefinitely.

Telomeres are the protective DNA caps on the ends of chromosomes. In most normal human cells, telomeres get shorter with every cell division.

Telomere shortening contributes to ageing and also prevents normal cells from becoming cancerous.

Shortening telomeres act like a "molecular clock", with time they get too short and the cell stops dividing.

Most human tumour cells overcome telomere shortening by activating the telomerase enzyme.

Telomerase works by adding DNA to the ends of chromosomes to lengthen them. Telomerase activity is not detected in most normal cells.



Telomerases components identified by Dr Cohens team

1) Telomerase Reverse Transcriptase (hTERT) is the known catalytic protein component - this is the protein that actually catalyses the chemical reaction - addition of nucleotides onto the ends of telomeres. hTERT is 1100 amino acids in length, 127 kDa.

2) dyskerin is an RNA binding protein, 57 kDa. Dyskerin is the protein identified by Dr Cohen, ruling out the other 31 candidate proteins.

3) Telomerase RNA (referred to as hTR or hTER) is the third component of telomerase.
The RNA is an integral component that is necessary for the activity of the enzyme. hTR is 450 nucleotides in length, 150 kDa.



Dr Cohens method

Because of the vanishingly small quantities of telomerase in each cell, Dr Cohen enlisted the help of CSIROs Dr George Lovrecz in Melbourne to grow "industrial" quantities of cancer cells in a bioreactor.

Then he had a piece of good luck. CMRI researcher Dr Lorel Colgin had previously arranged for a sheep to be vaccinated against human telomerase, and the antibodies produced by the sheep proved very useful for partly purifying the enzyme.

Dr Cohen next exploited the ability of telomerase to bind to the end of chromosomes to purify telomerase further.

The final step was simply brilliant. Dr Cohen had noticed a study buried in the scientific literature that reported an unusual property of telomerase.

Its affinity for a chromosome end depends on the precise "letter" of the genetic code at the very end.

He therefore supplied the partly purified telomerase with exactly the right "letters", so it would alter the chromosome end that it was bound to, change its affinity for the chromosome from very strong to very weak, and fall off.

This allowed him to collect highly purified telomerase.

The head of CMRIs Cancer Research Unit and senior author of the Science paper, Dr Roger Reddel said "The purification process Scott Cohen has invented is one of the cleverest Ive seen. In about 12 hours he can purify telomerase more than 100-million fold."

Identifying the molecules in the purified enzyme was still a challenge, because the amount of telomerase Scott Cohen extracted from 100 grams of cancer cells was only 100 nanograms!
The identification was achieved by Drs Mark Graham, Nicolai Bache and Phillip Robinson in CMRI's mass spectrometry unit which is funded by the popular Jeans for Genes campaign.

The answer was surprisingly simple. Apart from the two components telomerase is already known to contain, there is only one more protein present in the active enzyme.



More advanced structural studies for telomerase

The combined structural information advances research into the functions of telomerase in cells.

Cohen has also demonstrated the dimeric structure of the enzyme. When he added the molecular weights of hTERT, dyskerin, and the RNA, he came up with 334 kDa, (one kDa = 1,000 mass units).

The active telomerase enzyme complex is measured at 670 kDa, exactly twice the mass predicted by Cohens research.

There is other evidence to suggest that the telomerase enzyme exists as a dimer, being made up of two identical halves.

X-ray crystallography now possible for telomerase

Cohen used endogenous telomerase from human cells for his research, but in identifying telomerase’s composition he has opened the way for research based on "synthetic" telomerase, made with recombinant technology.

This will allow X-ray crystallography of telomerase which was not previously possible because X-ray crystallography requires much more protein than could be obtained from human cells.
X-ray crystallography would give the precise 3D structure of telomerase, the best starting point to design anti-cancer drugs that target telomerase.

source:www.parramattasun.com.au