Featured Research

from universities, journals, and other organizations

Rare, childhood neurodegenerative diseases linked to common problem in DNA repair

Date:
May 9, 2014
Source:
St. Jude Children's Research Hospital
Summary:
Two rare, inherited childhood neurodegenerative disorders are being studied by researchers who have identified a new, possibly common source of DNA damage that may play a role in other neurodegenerative diseases, cancer and aging. Researchers showed for the first time that an enzyme required for normal DNA functioning causes DNA damage in the developing brain. DNA is the molecule found in nearly every cell that carries the instructions needed to assemble and sustain life.

St. Jude Children's Research Hospital scientists studying two rare, inherited childhood neurodegenerative disorders have identified a new, possibly common source of DNA damage that may play a role in other neurodegenerative diseases, cancer and aging. The findings appear in the current issue of the scientific journal Nature Neuroscience.

Researchers showed for the first time that an enzyme required for normal DNA functioning causes DNA damage in the developing brain. DNA is the molecule found in nearly every cell that carries the instructions needed to assemble and sustain life.

The enzyme is topoisomerase 1 (Top1). Normally, Top1 works by temporarily attaching to and forming a short-lived molecule called a Top1 cleavage complex (Top1cc). Top1ccs cause reversible breaks in one strand of the double-stranded DNA molecule. That prompts DNA to partially unwind, allowing cells to access the DNA molecule in preparation for cell division or to begin production of the proteins that do the work of cells.

Different factors, including the free radicals that are a byproduct of oxygen metabolism, result in Top1ccs becoming trapped on DNA and accumulating in cells. This study, however, is the first to link the buildup to disease. The results also broaden scientific understanding of the mechanisms that maintain brain health.

Investigators made the connection between DNA damage and accumulation of Top1cc while studying DNA repair problems in the rare neurodegenerative disorders ataxia telangiectasia (A-T) and spinocerebellar ataxia with axonal neuropathy 1(SCAN1). The diseases both involve progressive difficulty with walking and other movement. This study showed that A-T and SCAN1 also share the buildup of Top1ccs as a common mechanism of DNA damage. A-T is associated with a range of other health problems, including an increased risk of leukemia, lymphoma and other cancers.

"We are now working to understand how this newly recognized source of DNA damage might contribute to tumor development or the age-related DNA damage in the brain that is associated with neurodegenerative disorders like Alzheimer's disease," said co-corresponding author Peter McKinnon, Ph.D., a member of the St. Jude Department of Genetics. The co-corresponding author is Sachin Katyal, Ph.D., of the University of Manitoba Department of Pharmacology and Therapeutics and formerly of St. Jude.

A-T and SCAN1 are caused by mutations in different enzymes involved in DNA repair. Mutations in the ATM protein lead to A-T. Alterations in the Tdp1 protein cause SCAN1.

Working in nerve cells growing in the laboratory and in the nervous system of specially bred mice, researchers showed for the first time that ATM and Tdp1 work cooperatively to repair breaks in DNA. Scientists also demonstrated how the proteins accomplish the task.

The results revealed a new role for ATM in repairing single-strand DNA breaks. Until this study, ATM was linked to double-strand DNA repair. ATM was also known to work exclusively as a protein kinase. Kinases are enzymes that use chemicals called phosphate groups to regulate other proteins.

Scientists reported that when Top1ccs are trapped ATM functions as a protein kinase and alert cells to the DNA damage. But researchers found ATM also serves a more direct role by marking the trapped Top1ccs for degradation by the protein complex cells use to get rid of damaged or unnecessary proteins. ATM accomplishes that task by promoting the addition of certain proteins called ubiquitin and SUMO to the Top1cc surface.

Tdp1 then completes the DNA-repair process by severing the chemical bonds that tether Top1 to DNA.

Mice lacking either Atm or Tdp1 survived with apparently normal neurological function. But compared to normal mice, the animals missing either protein had elevated levels of Top1cc. Those levels rose sharply during periods of rapid brain development and in response to radiation, oxidation and other factors known to cause breaks in DNA.

When researchers knocked out both Atm and Tdp1, Top1cc accumulation rose substantially as did a form of programmed cell death called apoptosis. Investigators reported that apoptosis was concentrated in the developing brain and few mice survived to birth. McKinnon said the results add to evidence that the brain is particularly sensitive to DNA damage.

Researchers then used the anti-cancer drug topotecan to link elevated levels of Top1cc to the cell death and other problems seen in mice lacking Atm and Tdp1. Topotecan works by trapping Top1ccs in tumor cells, resulting in the DNA damage that triggers apoptosis. Investigators showed that the impact of Top1cc accumulation was strikingly similar whether the cause was topotecan or the loss of Atm and Tdp1.


Story Source:

The above story is based on materials provided by St. Jude Children's Research Hospital. Note: Materials may be edited for content and length.


Journal Reference:

  1. Sachin Katyal, Youngsoo Lee, Karin C Nitiss, Susanna M Downing, Yang Li, Mikio Shimada, Jingfeng Zhao, Helen R Russell, John H J Petrini, John L Nitiss, Peter J McKinnon. Aberrant topoisomerase-1 DNA lesions are pathogenic in neurodegenerative genome instability syndromes. Nature Neuroscience, 2014; DOI: 10.1038/nn.3715

Cite This Page:

St. Jude Children's Research Hospital. "Rare, childhood neurodegenerative diseases linked to common problem in DNA repair." ScienceDaily. ScienceDaily, 9 May 2014. <www.sciencedaily.com/releases/2014/05/140509172549.htm>.
St. Jude Children's Research Hospital. (2014, May 9). Rare, childhood neurodegenerative diseases linked to common problem in DNA repair. ScienceDaily. Retrieved September 2, 2014 from www.sciencedaily.com/releases/2014/05/140509172549.htm
St. Jude Children's Research Hospital. "Rare, childhood neurodegenerative diseases linked to common problem in DNA repair." ScienceDaily. www.sciencedaily.com/releases/2014/05/140509172549.htm (accessed September 2, 2014).

Share This




More Health & Medicine News

Tuesday, September 2, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Get on Your Bike! London Cycling Popularity Soars Despite Danger

Get on Your Bike! London Cycling Popularity Soars Despite Danger

AFP (Sep. 1, 2014) Wedged between buses, lorries and cars, cycling in London isn't for the faint hearted. Nevertheless the number of people choosing to bike in the British capital has doubled over the past 15 years. Duration: 02:27 Video provided by AFP
Powered by NewsLook.com
Can You Train Your Brain To Eat Healthy?

Can You Train Your Brain To Eat Healthy?

Newsy (Sep. 1, 2014) New research says if you condition yourself to eat healthy foods, eventually you'll crave them instead of junk food. Video provided by Newsy
Powered by NewsLook.com
We've Got Mites Living In Our Faces And So Do You

We've Got Mites Living In Our Faces And So Do You

Newsy (Aug. 30, 2014) A new study suggests 100 percent of adult humans (those over 18 years of age) have Demodex mites living in their faces. Video provided by Newsy
Powered by NewsLook.com
Liberia Continues Fight Against Ebola

Liberia Continues Fight Against Ebola

AFP (Aug. 30, 2014) Authorities in Liberia try to stem the spread of the Ebola epidemic by raising awareness and setting up sanitation units for people to wash their hands. Duration: 00:41 Video provided by AFP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins