New Link In Liver Cancer

Liver damage can be triggered by various insults, including hepatitis infection or alcohol-induced cirrhosis. In severe cases, this damage can lead to cancer. A new study by researchers at the National Institutes of Health and Osaka University reveals how one protein helps decide the fate of damaged livers in mice.Liver cells rely on signals triggered by growth hormone to survive and multiply—functions that go haywire in cancer. Normally, growth hormone works by activating a signaling network inside liver cells that includes a protein called STAT5. When the researchers removed STAT5 from liver cells, cancer ensued.

The normally protective effect of STAT5 was traced to its ability to hitch itself to a damage-inducing protein called TGFbeta and trigger its destruction. Without STAT5, TGFbeta levels soared, and growth hormone activated a related protein, STAT3, which is known to promote tumor growth.

TGFbeta and STAT5 appear to be adversaries in the liver, according to the study. STAT5 protects the liver by breaking down TGFbeta. But when TGFbeta is abundant—as occurs in people with chronic liver damage—growth hormone activates the cancer-promoting STAT3 instead of the protective STAT5. These results might help explain how chronic liver damage can eventually lead to cancer.

The study will be published online on March 30th in the Journal of Experimental Medicine.

Sleep May Help Clear Brain For New Learning

A new theory about sleep's benefits for the brain gets a boost from fruit flies in the journal Science. Researchers at Washington University School of Medicine in St. Louis found evidence that sleep, already recognized as a promoter of long-term memories, also helps clear room in the brain for new learning.The critical question: How many synapses, or junctures where nerve cells communicate with each other, are modified by sleep? Neurologists believe creation of new synapses is one key way the brain encodes memories and learning, but this cannot continue unabated and may be where sleep comes in.

"There are a number of reasons why the brain can't indefinitely add synapses, including the finite spatial constraints of the skull," says senior author Paul Shaw, Ph.D., assistant professor of neurobiology at Washington University School of Medicine in St. Louis. "We were able to track the creation of new synapses in fruit flies during learning experiences, and to show that sleep pushed that number back down."

Scientists don't yet know how the synapses are eliminated. According to theory, only the less important connections are trimmed back, while connections encoding important memories are maintained.

Many aspects of fly sleep are similar to human sleep; for example, flies and humans deprived of sleep one day will try to make up for the loss by sleeping more the next day. Because the human brain is much more complex, Shaw uses the flies as models for answering questions about sleep and memory.

Sleep is a recognized promoter of learning, but three years ago Shaw turned that association around and revealed that learning increases the need for sleep in the fruit fly. In a 2006 paper in Science, he and his colleagues found that two separate scenarios, each of which gave the fruit fly's brain a workout, increased the need for sleep.

The first scenario was inspired by human research linking an enriched environment to improved memory and other brain functions. Scientists found that flies raised in an enhanced social environment—a test tube full of other flies—slept approximately 2-3 hours longer than flies raised in isolation.

Researchers also gave male fruit flies their first exposure to female fruit flies, but with a catch—the females were either already mated or were actually male flies altered to emit female pheromones. Either fly rebuffed the test fly's attempts to mate. The test flies were then kept in isolation for two days and exposed to receptive female flies. Test flies that remembered their prior failures didn't try to mate again; they also slept more. Researchers concluded that these flies had encoded memories of their prior experience, more directly proving the connection between sleep and new memories.

Scientists repeated these tests for the new study, but this time they used flies genetically altered to make it possible to track the development of new synapses, the junctures at which brain cells communicate.

"The biggest surprise was that out of 200,000 fly brain cells, only 16 were required for the formation of new memories, " says first author Jeffrey Donlea, a graduate student. "These sixteen are lateral ventral neurons, which are part of the circadian circuitry that let the fly brain perform certain behaviors at particular times of day."

When flies slept, the number of new synapses formed during social enrichment decreased. When researchers deprived them of their sleep, the decline did not occur.

Donlea identified three genes essential to the links between learning and increased need for sleep: rutabaga, period and blistered. Flies lacking any of those genes did not have increased need for sleep after social enrichment or the mating test.

Blistered is the fruit fly equivalent to a human gene known as serum response factor (SRF). Scientists have previously linked SRF to plasticity, a term for brain change that includes both learning and memory and the general ability of the brain to rewire itself to adapt to injury or changing needs.

The new study shows that SRF could offer an important advantage for scientists hoping to study plasticity: unlike other genes connected to plasticity, it's not also associated with cell survival.

"That's going to be very helpful to our efforts to study plasticity, because it removes a large confounding factor," says co-author Naren Ramanan, Ph.D., assistant professor of neurobiology. "We can alter SRF activity and not have to worry about whether the resulting changes in brain function come from changes in plasticity or from dying cells."

Shaw plans further investigations of the connections between memory and sleep, including the question of how increased synapses induce the need for sleep.

"Right now a lot of people are worried about their jobs and the economy, and some are no doubt losing sleep over these concerns," Shaw says. "But these data suggest the best thing you can do to make sure you stay sharp and increase your chances of keeping your job is to make getting enough sleep a top priority."

Improved Antibiotic: Genes For Synthesizing Thiostrepton Identified

Researchers at the Georgia Institute of Technology have identified the genetic machinery responsible for synthesizing thiostrepton, a powerful antibiotic produced by certain bacteria. Though effective against the dangerous MRSA (methicillin-resistant Staphylococcus aureus) and vancomycin-resistant enterococci, thiostrepton currently has only limited applications in humans because it is not water soluble.dentification of the gene cluster responsible for producing thiostrepton sets the stage for genetic manipulations that could make the drug more useful by improving its water solubility, potentially providing a new tool in the high-stakes battle against bacteria. Beyond the possible medical applications, the research produced a scientific surprise: thiostrepton is derived from a genetically encoded peptide that undergoes no fewer than 19 different modifications, one of the most complex such processes known – and a surprising capability for a single-celled bacterium.

"We are interested in making derivatives of this peptide drug that retain their potency and are efficiently processed by biochemical machinery," said Wendy L. Kelly, an assistant professor in Georgia Tech's School of Chemistry and Biochemistry and the Parker Petit Institute for Bioengineering and Bioscience. "We want to put in substitutions to the genetic machinery that may create a more water soluble analog and could potentially be used for development of a new class of antibacterial agent."

Kelly, graduate student Lisa Pan and postdoctoral fellow Chaoxuan Li began their study of thiostrepton by having the genome of one bacterium that produces it -- Streptomyces laurentii – sequenced by a commercial laboratory. They then studied different parts of the genome, searching for the genes responsible for producing the drug.

"It was a combination of DNA sequencing, bioinformatic analysis of the encoded proteins and biochemical characterization," said Kelly. "We didn't really know where on the chromosome this would be localized. Instead of taking a single shot and looking only at one location, we used a shotgun strategy that gave us insight into many different regions on the chromosome at the same time."

Fortunately, in simple organisms like bacteria, genes responsible for a particular task tend to be located close together, so when the researchers found one relevant gene, they knew the rest would be nearby. The researchers produced a knockout mutant to confirm that the genes they had identified were the correct ones.

The mechanism by which the bacterium produces thiostrepton turned out to be of considerable interest. Because peptides produced directly by ribosomal synthesis tend to be comparably simple, researchers had expected the complex thiostrepton molecule to be produced by a non-ribosomal route.

However, the Georgia Tech team showed that the drug results from a process controlled by the ribosome – which makes it a good target for genetic manipulation.

"The fact that we have a gene that produces a peptide that undergoes post-translational modification makes this a simpler target for biosynthetic engineering," Kelly noted. "Before this finding, we didn't know that such extensive modifications could be made to a peptide. Finding this mechanism completely changes how we look at this and similar systems, and changes the potential for biosynthetically engineering effective new systems."

Kelly's research team will next seek to understand the complex pathway used to synthesize the drug, then attempt to modify the right component of that machinery to create a variant of thiostrepton that is water soluble.

"You can think about this in terms of an assembly line for manufacturing cars, with the changes occurring in stages during construction," she said. "The same would be true of a microorganism building up a complex molecule. Some modifications that occur later in the process may require certain key elements to be present first. We need to understand what modifications are necessary and what features of the structure are important for recognition and processing down the line."

Produced by certain terrestrial and marine bacteria, thiostrepton was identified in the 1950s, and first synthesized in the laboratory in 2004. Thiostrepton and related thiopeptide antibiotics fight bacteria by disabling their protein biosynthesis, and also have promising anti-malarial and anti-cancer activity.

Though researchers face many challenges in attempting to modify the genes and enzymes required to produce the drug, the potential benefits are significant.

"With the development of resistance and pathogens such as MRSA, there's a crisis developing in anti-microbial treatments," she noted. "If they were to become resistant to the few drugs that are currently available to fight them, they would become untreatable. There is a big push to identify new drugs for clinical use in humans that are effective against these strains."

With an undergraduate degree in pharmacy and graduate degrees in chemistry, Kelly has focused on natural systems that produce useful drugs.

"I have a profound appreciation for nature's chemistry and how nature makes complex metabolites from very simple building blocks," she said. "If you compare the kinds of transformations that can be done inside a bacterium against what a synthetic chemist can do, you see the power of nature in its ability to catalyze highly specialized reactions under very mild conditions."

Details of the work were published online in the Journal of the American Chemical Society on March 5. The research was sponsored by the Camille and Henry Dreyfus Foundation, the American Society of Pharmacognosy and Georgia Tech.