Plants Repel Bacteria’s Assaults by Spying on Their Chatter

04.17.2012
Researchers discover an impressive ability never seen in plants before.
by Veronique Greenwood

Some rice plants have evolved a leg up on their microbial adversaries by
breaking the chemical code bacteria use to communicate.


Bacteria are quite the talkers. Lying low inside their hosts, they scheme up attacks through coded biochemical messages that are largely imperceptible to the immune systems of plants and animals. But in December researchers published the first evidence that some plants have broken the code, allowing them to listen in on chatter and thwart infection.

Evidence for this reconnaissance emerged in 2009, when University of California, Davis, plant pathologist Pamela Ronald discovered a bacterial protein called Ax21 in some strains of rice. Whenever Ax21 was present, the plants flooded their tissues with antibacterial chemicals. The mere presence of an immunity-inducing protein like Ax21 was not that unusual—the immune systems of most organisms identify a microbial intruder through proteins protruding from its outer membrane. But last year Ronald discovered that Ax21 is not part of the bacterial cells themselves. Instead, it is a secreted chemical rallying cry. When Ax21 chatter reaches a certain level, the microbes pack into a thin layer called a biofilm that protects them from immune defenses and many antibiotics. These rice plants are the only known organisms able to intercept the messages and act before the bacteria can form their biological bunker.

Ronald’s discovery may spark similar finds. University of North Carolina plant immunologist Jeff Dangl says plants have many immune receptors with unknown functions: “There may be a vast listening apparatus just waiting to be discovered.”

Cellular Communicators for Cancer Virus Identified

ScienceDaily (Nov. 8, 2010)

A new discovery by UNC scientists describes how cells infected by the Epstein-Barr virus (EBV) produce small vesicles or sacs called exosomes, changing their cellular “cargo” of proteins and RNA. This altered exosome enters cells and can change the growth of recipient cells from benign to cancer-producing.

In this way, virus-infected cells can have wide-ranging effects and potentially manipulate other cells throughout the body. The findings are reported in the Nov. 8 early online edition of the Proceedings of the National Academy of Sciences.

Nancy Raab-Traub, PhD, professor of microbiology and Immunology, said, “Exosomes may be the Trojan Horse through which EBV gains control of cells that are not even infected. Importantly, the production of exosomes may provide a new therapeutic target that can be blocked to reduce cancer growth.” Raab-Traub is a Sarah Graham Kenan Professor and member of UNC Lineberger Comprehensive Cancer Center.

Epstein-Barr Virus (EBV) is perhaps the world’s most successful virus as almost everyone is infected with it for life. EBV cannot be eliminated by the immune system and is constantly secreted into saliva where it is effectively transmitted. Infection with the virus rarely causes disease; however, EBV is found in several major cancers, including lymphoma and cancer of the nose and throat, where its proteins hijack the cell’s growth regulatory mechanisms to induce uncontrolled cell growth characteristic of cancer.

Through exosomes, a protein called latent membrane protein 1, that is considered the EBV oncogene, can be delivered to uninfected cells. Significantly, EBV also changes the entire contents of the exosomes to deliver cellular proteins that are also activated in cancers. This surprising finding reveals that one infected cell can have wide-ranging effects and induce the unchecked growth of neighboring cells.

The immune system is constantly on guard to identify foreign viral proteins. Through exosomal uptake, cancer cells would be stimulated to grow without the expression of proteins that “announce” infection to the immune system, thus allowing unchecked growth. The study also showed that the cells that produce blood vessels, the process called angiogenesis, readily take in the altered exosomes and are potentially induced to grow.

“The next step,” explains David Meckes, PhD, postdoctoral fellow in the Raab-Traub lab and first author of the paper, “is to determine how the virus controls which proteins are sorted into exosomes and how this process could be inhibited.”

Other UNC Lineberger authors, all members of the Raab-Traub laboratory, are: Kathy Shair, PhD;Aron Marquitz, PhD; Patrick Kung, PhD ; and Rachel Edwards, BS. The research was supported by a grant from the National Cancer Institute.

Editor’s Note: This article is not intended to provide medical advice, diagnosis or treatment.

The Lucky Genetic Variants That Protect Some People From HIV

by Richard Knox

Wednesday morning Harvard AIDS researcher Bruce Walker called one of his long-time patients with an announcement: “We’ve found the needle in the haystack!”

Actually, Walker and his colleagues have found a half-dozen needles. They pinpointed genetic variations that change amino acid building blocks in key proteins in the immune system. These differences help explain why some patients can be infected with HIV for decades, never get treatment and yet never progress to AIDS.

“We’ve found the five or six amino acids that explain the difference between people doing well or doing badly,” Walker says.

The discovery is being published online by the journal Science.

The patient Walker called Wednesday morning is a 54-year-old Episcopalian priest named Robert Massie who’s a fellow at Harvard’s Kennedy School of Government. Massie inspired Walker’s 17-year search for the secret of these HIV controllers.

Massie got infected with HIV way back in 1978 – several years before AIDS was recognized — from the constant injections of Factor VIII clotting factor he needed to treat his hemophilia.

Hemophiliacs were a bellwether group that helped scientists zero in on the AIDS virus. Many of them got infected early in the pandemic because Factor VIII was made from the blood of hundreds of donors. If even one was carrying HIV, the clotting concentrate was an efficient way to transmit the virus to unsuspecting hemophiliacs.

It turns out that the half-dozen amino acid variants that have protected Massie against AIDS are the same ones the Harvard-led team has found in others of European descent, those of African descent and Hispanics.

With the discovery, a number of other findings are falling neatly into place.

For instance, scientists have previously shown that people whose immune systems can control HIV are more likely to have certain “flavors” of an important immune trait called HLA (for Human Leukocyte Antigen). The HLA system allows the body to distinguish between its own healthy cells and those infected by foreign invaders, such as viruses.

But until now, scientists didn’t know what it was about the more favorable HLA subtypes that conferred protection against HIV.

The genetic instructions for the newly found amino acid variants resides in a region of chromosome 6 that codes for the HLA system. Five of the six variants are within a protein that controls how certain immune cells, called CD4s, display bits and pieces of viral protein on their outer shell – if they happen to be infected with a virus. HIV has a special affinity for infecting CD4 cells, and without constant antiviral treatment the virus slowly destroys the immune systems of most infected people.

But if a person has the newly discovered amino acid variants, his CD4 cells will be especially good at displaying pieces of HIV in a binding groove, or pocket of their outer coat. That enables killer cells, immune cells called CD8s, to target and kill the infected cells before they can spew forth more viruses.

For most people, the lack of these protective variants renders their HIV-infected cells invisible to their immune system.

“What we know for absolute certain is that these variants alter the way the viral protein sits in the binding groove,” Walker says. “Now we’re working on exactly how the protein is presented to induce a protective immune response.

“The exciting part of this finding,” he continues, “is that it helps us focus on something that clearly is important and hopefully will allow us to manipulate the immune response” of people without the protective trait.

Walker acknowledges that “we have a long ways to go before we can turn this finding into something that will prevent someone from becoming infected with HIV or augment their immunity. But this takes us a step closer to defining and effective immune response.”

Vaccines are one way to manipulate the immune response. But nobody has ever used a vaccine in such a targeted way.

Massie says he was “very, very happy” to hear of the discovery. “I know they’ve devoted a huge amount of time, money, effort and emotion to try and unlock this puzzle,” he says.

Meanwhile, Massie is keenly aware of his own good fortune – and not only at being born with the genetic talismans that have protected him from HIV.

He wasn’t protected, it turns out, against hepatitis C, also acquired from injections of Factor VIII concentrate. Hep-C destroyed his liver.

A year ago, he had a liver transplant. And, there’s a silver lining: The transplant has cured his hemophilia, because his new liver can make the Factor VIII he needs to prevent bleeding.

“I used to have four or five injections a day to maintain the right level of Factor VIII in my blood, ” Massie says. “All that’s behind me.”

Jellyfish Cells ‘Diagnose’ Cancer, York Scientists Say

01 November 2010

Luminous cells from jellyfish can be used to diagnose cancers deep inside the body, scientists have said.

The process uses the green fluorescent protein (GFP) enabling jellyfish to glow in the dark.

Researchers in North Yorkshire found it can be targeted at cancer cells allowing them to be spotted using a special camera.

A team from the Yorkshire Cancer Research Laboratory at York University has developed the procedure.

The team’s leader, Professor Norman Maitland, believes it will revolutionise the way some cancers are diagnosed.

He said: “Cancers deep within the body are difficult to spot at an early stage, and early diagnosis is critical for the successful treatment of any form of cancer.

“What we have developed is a process which involves inserting proteins derived from luminous jellyfish cells into human cancer cells.

“Then, when we illuminate the tissue, a special camera detects these proteins as they light up, indicating where the tumours are.”

The process is an extension of the work done by American chemist Dr Roger Y Tsien, who won a Nobel Prize in 2008 for taking luminous cells from the crystal jelly species of jellyfish and isolating the GFP.

Prof Maitland said: “When we heard about Dr Tsien’s work, we realised how that advance might be useful in the diagnosis of cancer.

‘Flare up’
“X-rays, for example, struggle to penetrate well deeply into tissues and bone, so diagnosing dangerous microscopic bone cancer is difficult.

“Our process should allow earlier diagnosis to take place.”

The York team’s process uses an altered form of the protein so that it shows up as red or blue, rather than its original green.

Viruses containing the proteins are targeted to home in on tiny bundles of cancer cells scattered throughout the body which are too small to be seen by conventional scanning techniques.

But the viruses grow and, while doing so, make more and more of the fluorescent proteins.

“When a specially-developed camera is switched on, the proteins just flare up and you can see where the cancer cells are.” said Prof Maitland.

“We call the process ‘Virimaging’.”

Deep in body
The team expects the procedure to be ready for clinical trials within five years, if the research continues to go to plan.

Prof Maitland said one problem, however, may be the availability of the specialised cameras needed for the process.

A United States company is the only one which has so far designed and built a camera system which allows the jellyfish proteins to be seen with the desired resolution so deep in the body.

This kit costs about £500,000 and Prof Maitland said he was currently raising the funds to buy one.

Taken from: http://www.bbc.co.uk/news/uk-england-york-north-yorkshire-11667447

Plant’s Light Switch Could Be Used to Control Cells

Within milliseconds of a blue flash of light, a red fluorescent protein that typically sits in a cell (left) interacts with a plant protein attached to the cell membrane. The fluorescent protein then migrates to the cell's edge (right). (Credit: Chandra Tucker, Duke)

ScienceDaily (Oct. 31, 2010)
Chandra Tucker shines a blue light on yeast and mammalian cells in her Duke University lab and the edges of them start to glow. The effect is the result of a light-activated switch from a plant that has been inserted into the cell.

Researchers could use this novel “on-off switch” to control cell growth or death, grow new tissue or deliver doses of medication directly to diseased cells, said Tucker, an assistant research professor in the biology department at Duke.

She and colleagues created the switch by genetically inserting two proteins from a mustard plant, Arabidopsis thaliana, into yeast cells, kidney cells and cultured rodent brain tissue. The two proteins interact under light to provide the control over cell functions.

The switch is similar to one described last year where researchers genetically inserted a different light-receptive plant protein and its interacting protein partner from Arabidopsis into mammalian cells. In response to red light, these proteins interacted to cause mammalian cells to change shape, moving in the direction of the light.

Tucker’s switch uses Arabidopsis proteins that respond to blue light. Unlike the red-light activated proteins, which need an added cofactor, a chemical that is required for the light response, the blue-light switch doesn’t need any additional chemicals to work because it uses a cofactor that naturally exists in non-plant organisms.

“It’s hard to deliver a chemical to a fly or to individual cells. This new approach, with one of the molecules already in the mammalian or yeast cells, makes building a light-controlled switch a lot easier,” Tucker said. Her team describes the switch in the Oct. 31 Nature Methods.

To test the switch, the team fused one of the light-sensitive Arabidopsis proteins to a red fluorescent protein and the other to a green fluorescent protein, which was in turn attached to the cell membrane. When the researchers flashed blue light on the cell, the plant proteins interacted, causing the red fluorescent protein to rapidly move to the cell membrane, which then glowed yellow due to the merging of the red and green fluorescing proteins. The team found that this interaction was reversible and could be triggered repeatedly with light exposure.

The switch is one among several that have been designed to give researchers better control of different functions of the cell. The next step in developing the switch will be to make the interacting proteins more effective, Tucker said. The approach is expected to be applicable not only for studies in cultured cells and yeast, but also worms, fruit flies, mice and other model organisms. Eventually this method could allow researchers to test how cells in a tissue affect neighboring cells in a tissue, to guide axon growth in neurons to repair brain tissue, or even to kill cancer cells.

Tucker’s new approach will be a “major boon” to those who wish to apply light activation to their own experimental systems, said Klaus Hahn, a pharmacologist at the University of North Carolina at Chapel Hill, whose lab reported on another blue-light responsive protein to control movement of mammalian cells last year.

Hahn said the “elegant work will likely see broad use, in many fields and for applications that will surprise us,” and it is already going to be applied to important areas of research, such as control of gene expression.

Taken from: http://www.sciencedaily.com/releases/2010/10/101031154011.htm

Anticancer protein might combat HIV

Anticancer protein might combat HIV

Tumor suppressor p21 found in abundance in people impervious to developing AIDS
Web edition : Thursday, October 21st, 2010

VANCOUVER — A protein best known as a cancer suppressor may enable some people infected with HIV to fend off the virus indefinitely, a new study shows. Copious production of this protein, called p21, shows up in a select group of HIV-positive people who rarely develop AIDS, scientists reported October 21 at a meeting of the Infectious Diseases Society of America.

Some HIV patients, dubbed long-term nonprogressors, get infected with HIV yet seem impervious to its effects. While research has suggested factors that could separate these lucky few from most HIV patients, the specifics underlying their resistance are still an area of keen interest. “This is a specific group of patients who are spontaneously able to control HIV and don’t get sick from it,” says infectious disease physician Mathias Lichterfeld of Harvard Medical School and Massachusetts General Hospital in Boston, who presented the new data.

In the new study, researchers compared four groups of people — 14 who were HIV negative, 16 with HIV that had progressed, 10 with HIV who were undergoing treatment and 15 whose HIV infection had totally stalled. This last group included nonprogressors so adept at halting an HIV infection that they didn’t even have any virus detectable by routine tests. (Researchers ascertained infection by testing for antibodies to HIV.) Scientists call this subset of patients elite controllers. “They comprise 1 percent or fewer of HIV-infected people,” Lichterfeld says.

The researchers obtained immune cells called CD4 T cells — the prime targets of HIV — from all the volunteers and subjected these cells to lab tests. The tests showed that elite controllers had CD4 T cells that made 10 to 100 times more p21 than did people in the other three groups. “It’s not a subtle difference. It’s quite striking,” Lichterfeld says.

When the researchers put these cells in lab dishes and subjected them to an HIV assault, the cells loaded with p21 held off the virus.

“These data suggest that this protein can inhibit HIV,” Lichterfeld says. But he notes that the mechanism by which p21 does this and even how these cells make extra amounts of the protein are not yet fully understood. There may be genetic variations involved, he says.

“It might offer an alternative way to control HIV if we can find a way to manipulate this p21 protein in patients,” he says. But using p21 as a tool probably won’t be as simple as giving the protein to people.

“The fact that it occurs in nature is encouraging — that you have a natural model,” says Joel Gallant, an infectious disease physician who specializes in HIV at Johns Hopkins University in Baltimore. Although many questions need to be answered before finding a way to use p21 clinically, he says, “this could be critical someday in getting better control of HIV.”