Regulation of cell volume is critical for the body’s cells, f. e. during cellular exposure to fluids of varying salt concentrations, in cell division, cell growth, but also in diseases such as cancer, stroke and myocardial infarction.
A certain chloride channel, a membrane protein that allows the passage of the chloride ion, is of crucial importance in volume regulation. It is activated by the swelling of the cell and then releases chloride ions and organic matter (osmolytes) from the cell. Researchers in Berlin-Buch have now succeeded for the first time in elucidating the molecular identity of this volume-regulated anion channel (VRAC) (Science Express, DOI: 10.1126/science.1252826)*.
Researchers led by Professor Thomas J. Jentsch (Max Delbrück Center for Molecular Medicine, MDC, Berlin-Buch/Leibniz-Institut für Molekulare Pharmakologie, FMP) identified a molecule, LRRC8A, which is an essential constituent of the volume-regulated anion channel (VRAC). This protein needs to be assembled with related proteins (LRRC8B to E) to form channels with probably six subunits.
They could also show for the first time that these chloride channels are also permeable to small organic molecules such as taurine or amino acids. For over 20 years, research groups across the globe have been seeking to elucidate the molecular structure of the volume-regulated anion channel (VRAC). It took Jentsch’s team almost four years to achieve this breakthrough.
The regulation of cell volume is important for many functions in the organism. The volume-regulated anion channel (VRAC) which Thomas Jentsch and his coworkers Felizia Voss and Tobias Stauber now identified at the molecular level is expressed in all vertebrate cells.
If a particular cell volume is exceeded, the channel opens and permits the outflow of osmolytes such as chloride ions as well as small organic molecules such as taurine and amino acids. By contrast, cations such as potassium or sodium cannot permeate.
Once the channel is opened, chloride and other osmolytes pass in a passive process called diffusion. Due to its biophysical properties the channel only allows anions and certain organic compounds to pass. Thus, the cell reduces the concentration of its osmolytically active constituents to (or even below) that of the surrounding fluid. At the same time, the water content of the cell decreases as the water molecules flow out via aquaporins in the cell membrane. The volume of the cell decreases again.
LRRC8A was discovered as a VRAC component using a genome-wide RNA interference (siRNA) screen in collaboration with Katina Lazarow and Jens von Kries from the FMP Screening Unit. By means of short RNA snippets, the translation of the genetic information into the corresponding proteins can be suppressed. Using a one-by-one approach in a large-scale cell culture experiment, the Berlin group transiently silenced the products of all approximately 20,000 human genes.
In an automated screening process the researchers investigated which of the genes are required for the swelling-activated anion flux across the cell membrane. The approximately 130,000 time-dependent ion flux measurements were statistically analyzed with help from the Bioinformatics Group of the MDC (Nancy Mah/Miguel Andrade-Navarro).
The essential role of LRRC8 proteins in the volume-regulated anion channel was verified using CRISPR/Cas technology, which just became available during the past two years. With this method, specific genes on the chromosomes can be disrupted completely. Different combinations of LRRC8 proteins, all including the obligate LRRC8A, – either by omitting some of the family members from gene disruption or by reconstituting different combinations – led to different electrophysiological properties of the channel. “This allows us to explain the behavior of the channel in different tissues which until now had remained elusive,” Thomas Jentsch said.
"Cells can swell or in the worst case even burst. Water transport and content must therefore be tightly regulated," he added. Water transport is always driven by the osmotic gradient. Cells take up chloride from their surroundings, whereas organic substances such as taurine or amino acids are produced within the cells.
Deciphering the molecular structure of this chloride channel may also pave the way for better medical treatments, for example, after stroke. "In the case of damage in the brain, cells swell and release glutamate, which acts upon receptors on nerve cells. The subsequent inflow of calcium raises the intracellular concentration of this ion to toxic levels," Jentsch said. With the onset of programmed cell death (apoptosis) during cancer chemotherapy, however, there is a strong reduction in cell volume. The volume-regulated chloride channel also appears to be involved in this process.
*Identification of LRRC8 Heteromers as Essential Component of the Volume-regulated Anion Channel VRAC.
Felizia K. Voss1,2,3, Florian Ullrich1,2,3, Jonas Münch1,2,3, Katina Lazarow1, Darius Lutter1,2,3, Nancy Mah2, Miguel A. Andrade-Navarro2, Jens P. von Kries1, Tobias Stauber1,2 * and Thomas J. Jentsch1,2,4 *
*Correspondence to: Jentsch@fmp-berlin.de (T.J.J.); email@example.com (T.S.).
1Leibniz-Institut für Molekulare Pharmakologie (FMP), Berlin
2Max Delbrück Center for Molecular Medicine (MDC), Berlin
3Graduate program of the Freie Universität Berlin
4Neurocure, Charité Universitätsmedizin, Berlin
Science Express, 10. April 2014; DOI: 10.1126/science.1252826
Max Delbrück Center for Molecular Medicine (MDC) Berlin-Buch
in the Helmholtz Association
Phone: +49 (0) 30 94 06 - 38 96
Fax: +49 (0) 30 94 06 - 38 33
Leibniz-Institut für Molekulare Pharmakologie
im Forschungsverbund Berlin e.V. (FMP)
13125 Berlin, Germany
The Max Delbrück Center for Molecular Medicine (MDC) is one of 18 research centers of the Helmholtz Association. It was founded in 1992 to link basic molecular basic research with clinical research. The MDC is working closely with the Charité - University Medicine in the Berlin Institute of Health (BIH) and has evolved in recent years into an internationally recognized research institute.
The Leibniz-Institut für Molekulare Pharmakologie (FMP) is part of the Forschungsverbund Berlin e.V. (FVB), a federation of eight institutes in Berlin in the field of natural, life and environmental sciences with a staff of more than 1500 employees. The multiple award-winning institutions are members of the Leibniz Association. The Forschungsverbund came into being in 1992 in a unique historical situation as the successor organization of the former Academy of Sciences of the GDR.
Barbara Bachtler | Max-Delbrück-Centrum
Family tree for orchids explains their astonishing variability
04.09.2015 | University of Wisconsin-Madison
Gone with the wind: A new project focusses on atmospheric input of phosphorus into the Baltic Sea
04.09.2015 | Leibniz-Institut für Ostseeforschung Warnemünde
In a survey of NASA's Hubble Space Telescope images of 2,753 young, blue star clusters in the neighboring Andromeda galaxy (M31), astronomers have found that M31 and our own galaxy have a similar percentage of newborn stars based on mass.
By nailing down what percentage of stars have a particular mass within a cluster, or the Initial Mass Function (IMF), scientists can better interpret the light...
Researchers at the Fraunhofer Institute for Solar Energy Systems ISE have developed a highly compact and efficient inverter for use in uninterruptible power...
China's Loess Plateau was formed by wind alternately depositing dust or removing dust over the last 2.6 million years, according to a new report from University of Arizona geoscientists. The study is the first to explain how the steep-fronted plateau formed.
China's Loess Plateau was formed by wind alternately depositing dust or removing dust over the last 2.6 million years, according to a new report from...
The leaves of the lotus flower, and other natural surfaces that repel water and dirt, have been the model for many types of engineered liquid-repelling surfaces. As slippery as these surfaces are, however, tiny water droplets still stick to them. Now, Penn State researchers have developed nano/micro-textured, highly slippery surfaces able to outperform these naturally inspired coatings, particularly when the water is a vapor or tiny droplets.
Enhancing the mobility of liquid droplets on rough surfaces could improve condensation heat transfer for power-plant heat exchangers, create more efficient...
Longer, more severe, and hotter droughts and a myriad of other threats, including diseases and more extensive and severe wildfires, are threatening to transform some of the world's temperate forests, a new study published in Science has found. Without informed management, some forests could convert to shrublands or grasslands within the coming decades.
"While we have been trying to manage for resilience of 20th century conditions, we realize now that we must prepare for transformations and attempt to ease...
03.09.2015 | Event News
20.08.2015 | Event News
20.08.2015 | Event News
04.09.2015 | Power and Electrical Engineering
04.09.2015 | Machine Engineering
04.09.2015 | Materials Sciences