A protein known for turning on genes to help cells survive low-oxygen conditions also slows down the copying of new DNA strands, thus shutting down the growth of new cells, Johns Hopkins researchers report. Their discovery has wide-ranging implications, they say, given the importance of this copying — known as DNA replication — and new cell growth to many of the body's functions and in such diseases as cancer.
"We've long known that this protein, HIF-1á, can switch hundreds of genes on or off in response to low oxygen conditions," says Gregg Semenza, M.D., Ph.D., a molecular biologist who led the research team and has long studied the role of low-oxygen conditions in cancer, lung disease and heart disorders. "We've now learned that HIF-1á is even more versatile than we thought, as it can work directly to stop new cells from forming." A report on the discovery appears in the Feb. 12 issue of Science Signaling.
With his team, Semenza, who is the C. Michael Armstrong Professor of Medicine at the Johns Hopkins University School of Medicine's Institute for Cell Engineering and Institute for Genomic Medicine, discovered HIF-1á in the 1990s and has studied it ever since, pinpointing a multitude of genes in different types of cells that have their activity ramped up or down by the activated protein. These changes in so-called "gene expression" help cells survive when oxygen-rich blood flow to an area slows or stops temporarily; they also allow tumors to build new blood vessels to feed themselves.
To learn how HIF-1á's own activity is controlled, the team looked for proteins from human cells that would attach to HIF-1á. They found two, MCM3 and MCM7, that limited HIF-1á's activity, and were also part of the DNA replication machinery. Those results were reported in 2011.
In the new research, Semenza and his colleagues further probed HIF-1á's relationship to DNA replication by comparing cells in low-oxygen conditions to cells kept under normal conditions. They measured the amount of DNA replication complexes in the cells, as well as how active the complexes were. The cells kept in low-oxygen conditions, which had stopped dividing, had just as much of the DNA replication machinery as the normal dividing cells, the researchers found; the difference was that the machinery wasn't working. It turned out that in the nondividing cells, HIF-1á was binding to a protein that loads the DNA replication complex onto DNA strands, and preventing the complex from being activated.
"Our experiments answered the long-standing question of how, exactly, cells stop dividing in response to low oxygen," says Maimon Hubbi, Ph.D., a member of Semenza's team who is now working toward an M.D. degree. "It also shows us that the relationship between HIF-1á and the DNA replication complex is reciprocal — that is, each can shut the other down."
Other authors on the report are Kshitiz, Daniele M. Gilkes, Sergio Rey, Carmen C. Wong, Weibo Luo, Chi V. Dang and Andre Levchenko, all of the Johns Hopkins University School of Medicine, and Deok-Ho Kim of the University of Washington, Seattle.
The study was funded by the U.S. Public Health Service (contracts N01-HV28180 and HHS-N268201000032c), the National Heart, Lung, and Blood Institute (grant number T32-HL007525), the National Institute of General Medical Sciences (grant number T32-GM008752), the American Heart Association (predoctoral fellowship 10PRE4160120), the Susan G. Komen Foundation (postdoctoral fellowship KG111254), the Foundation for Advanced Research in the Medical Sciences and the Johns Hopkins Institute for Cell Engineering.
Link to the paper: http://stke.sciencemag.org/cgi/content/full/sigtrans;6/262/ra10
Shawna Williams | Newswise
Water forms 'spine of hydration' around DNA, group finds
26.05.2017 | Cornell University
How herpesviruses win the footrace against the immune system
26.05.2017 | Helmholtz-Zentrum für Infektionsforschung
Staphylococcus aureus is a feared pathogen (MRSA, multi-resistant S. aureus) due to frequent resistances against many antibiotics, especially in hospital infections. Researchers at the Paul-Ehrlich-Institut have identified immunological processes that prevent a successful immune response directed against the pathogenic agent. The delivery of bacterial proteins with RNA adjuvant or messenger RNA (mRNA) into immune cells allows the re-direction of the immune response towards an active defense against S. aureus. This could be of significant importance for the development of an effective vaccine. PLOS Pathogens has published these research results online on 25 May 2017.
Staphylococcus aureus (S. aureus) is a bacterium that colonizes by far more than half of the skin and the mucosa of adults, usually without causing infections....
Physicists from the University of Würzburg are capable of generating identical looking single light particles at the push of a button. Two new studies now demonstrate the potential this method holds.
The quantum computer has fuelled the imagination of scientists for decades: It is based on fundamentally different phenomena than a conventional computer....
An international team of physicists has monitored the scattering behaviour of electrons in a non-conducting material in real-time. Their insights could be beneficial for radiotherapy.
We can refer to electrons in non-conducting materials as ‘sluggish’. Typically, they remain fixed in a location, deep inside an atomic composite. It is hence...
Two-dimensional magnetic structures are regarded as a promising material for new types of data storage, since the magnetic properties of individual molecular building blocks can be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute published their findings in the journal Nature Communications.
Ferrimagnets are composed of two centers which are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets...
An Australian-Chinese research team has created the world's thinnest hologram, paving the way towards the integration of 3D holography into everyday...
24.05.2017 | Event News
23.05.2017 | Event News
22.05.2017 | Event News
26.05.2017 | Life Sciences
26.05.2017 | Life Sciences
26.05.2017 | Physics and Astronomy