Nobel Prize focused on life-giving cellular cargo delivery system

A Nobel Prize was recently awarded to three researchers who discovered bubbles within bubbles that have tentacles. Award winners James Rothman, Randy Schekman and Thomas Südhof were pioneers in the study of vesicles, which are like bubbles inside human cells whose outer layers are made of the same stuff that separates cell insides from the outside world. Because the bubbles’ insides are kept separate from the rest of the cell’s interior, they can store, organize and deliver highly reactive biochemicals and proteins, releasing them only when and where they’re needed.

Electron microscope images of vesicles near Golgi complex in a cell.

Furthermore, the outer membranes of vesicles can fuse to outer cell membranes or to the membranes surrounding other cellular machines. This lets them take in contents from one compartment, move them to another walled-off area, and deposit them there. It also lets a cell start manufacturing a hormone or an antibody in one spot, truck it somewhere else for finishing, move it to the cell's surface, and secrete it to do a job elsewhere in the body.

To ensure that it dumps its contents into the right compartment, each vesicle has “tentacles,” squiggly proteins that “taste” the surface of other vesicles to make sure they have reached the right destination. Without vesicle formation and fusion, cells could neither live nor signal to each other as part of complex tissues. Vesicles are so central to cellular function that they are most likely involved in almost every disease when things go wrong, although we don’t yet know their role.

For his share of the prize, Dr. Rothman, a professor at Yale, discovered a protein complex that lets vesicles fuse with membranes to deliver their molecular cargo. He has a UAB connection in his former student, Dr. Elizabeth Sztul, Ph.D., professor in the UAB Department of Cell, Developmental and Integrative Biology and a vesicle expert in her own right. Dr. Sztul said she was “thrilled” to see vesicle research be recognized in the form of a Nobel Prize, and we thought to ask her why her field deserves notice.

Show notes from the podcast

1:56  A Nobel Prize win for vesicle research underscores just how vital basic scientific research is, along with the fundamental importance of vesicles in human life, said Dr. Sztul. Cells are made of compartments, and the prize went to the three-scientist team for discovering how proteins and genes work together to move key substances from one compartment to another.

3:02  Vesicular traffic has implication for all of life. Genetic mistakes that occur in genes that control this delivery system mean that an embryo does not often survive, and if so, with severe disabilities. The Nobel Prize winners designed tests that identified the cogs (proteins) that make possible the machinery behind vesicle formation and transport.

4:15 Specifically, Dr. Rothman, a biochemist, identified the proteins required for vesicle transport and then re-created vesicle trafficking in a test tube. Dr. Schekman identified some of the genes that control vesicle transport, and that have done so throughout evolution. He works one-celled organisms like yeast that share vesicle pathways with human cells. Dr Sudhof, a neurobiologist, showed how vesicles deliver proteins, not just to the right place, but also with perfect timing, to make cellular life possible. Together, the pioneers outlined how a vesicle "knows" where to go and when to fuse.

5:47  Genetic mutations, random changes in that occur in genes as they constantly get copied, are usually fatal within a few days when they occur within the central machinery proteins of vesicle trafficking in a human embryo. Dr. Stzul describes one key vesicle protein type as snares, which help a vesicle grab on to the outside of another compartment they want to fuse with. Genetic defects in snares are fatal, but people are born with genetic changes in less essential machinery related to vesicles and survive.

6:22 For instance, proteins on the sides of vesicles that are nicknamed tethers or tentacles, touch and "sample" the outer membranes of surrounding vesicles to determine which they should target for fusion.  A mutation in one these protein tentacles causes a very serious, rare disease called congenital disorder of glycosylation. Tethers and snares represent two ways that any vesicle chooses a specific vesicle that it will deliver its cargo into.

8:40 There are many types of payloads delivered by vesicle in human cells. The immune system uses them to swallow invading bacteria, and then to deliver chemicals to that vesicle that destroy the bacteria.  Nerve cells use them to deliver signaling molecules to the next cell in line as a nerve message runs along a nerve pathway. After you eat a meal, cells in your pancreas packs digestive enzymes into vesicles and ship them off to the gut.

10:38 Vesicle delivery of proteins by cells is tightly regulated and very precise, Dr. Sztul said. Even small genetic errors in the genes that make the vesicle proteins can cause disease, including one called craniofacial disorder. These patients have bones that don't form properly because the structural protein collagen, which makes the lion's share of skin and bones, is not delivered properly by vesicles.

12:37  Dr. Sztul's lab is trying to figure out all of the steps needed to move all important proteins in the cell from where they are made, through every required vesicle stop along the way and to a final destination.  Each stop in this journey involves a web of interacting proteins, and Dr. Sztul would like to map all of these interactions precisely in time and space. She believe that this map, once complete, will reveal links between mutations in vesicle trafficking genes and many diseases, both common and rare. These patterns will emerge, she said, as more and more patients routinely get their DNA sequenced as part of personalized medicine.

15:00 With the map in place, researchers will have a basis for the design of treatments that compensate for problems with specific vesicle proteins. At least theoretically, every protein that regulates trafficking will become targets for drug design. In cancer for instance, vesicles may be used by tumors to deliver proteins that cause cancer cells to spread or that encourage the growth of blood vessels that feed tumors. Drugs might be designed to keep vesicles from making these harmful deliveries.

18:15 The field is working to invent imaging technologies that can track the movement and action in a living cell, not just of a couple of interacting proteins at a time, but that can watch perhaps 60 vesicle trafficking proteins at work during one stage of trafficking. Also on the horizon, an in-depth understanding of the interaction between vesicle trafficking and outer key cellular actions. How do hormones effect vesicle trafficking in cells that secrete hormones? How vesicles in immune cells become filled with antibodies when the body senses that it has been infected with a bacterium or a virus, or in response to a vaccine?

Advice for scientists from a Nobel Prize winner

The UAB School of Medicine recently played host to its leading regional forum, the Spring Immunology Symposium. Proof of the event's growing influence can be seen in  this year's keynote, Nobel Prize Laureate Rolf Zinkernagel, M.D., Ph.D., Professor in the Institute of Experimental Immunology at the University of Zurich. Dr. Zinkernagel won in his Nobel prize in 1996 for discoveries that helped to explain how the human immune system recognizes that one of its cells has been infected by a virus.

Included here is a brief video of Dr. Zinkernagel talking about his life's work, what young scientists should be thinking about and frontiers in immunology.



Dr. Rolf Zinkernagel, UAB Immunology Symposium, June 2013 from UAB School of Medicine on Vimeo.

Below is a summary of the video discussion in a Q&A format.

Q1. What should young people keep in mind who want to get into science and immunology?

• Success requires a scientist to be prepared for a ratio of 1 percent success to 99 percent failure and that a researcher perservere. 
• Young scientists should be prepared to work long hours because "the harder you work the luckier you get,"  
• It is important to find a research subject that you feel is extremely important and one where you burn to know the answer.  

Q2. What were the key decisions that led you to success in your field?

• Among Dr. Zinkernagel's important early decisions as a scientist was to first become a medical doctor. It enabled him to learn study a complex bodily system, the immune system, in its entirety as a foundation. 
• Dr. Zinkernagel started as a surgeon, but then got interested in immunology because of the immune rejections seen with transplanted organs. His focus remained on infectious disease from there on out, and not entirely by design.

Q3. What are your thoughts about how science differs around the word (e.g. in the U.S. versus Europe)?

• The United States, and the UK as well, treat research like a sport in some ways, with a spirit of "fierce, competitive openness" that gives new researchers an opportunity to show what they can do, and with relatively few restrictions. Of his native Switzerland, Dr. Zinkernagel said it has a good research environment, but its small size limits opportunities when compared to larger nations. 
• He also lauded the opportunistic outlook of the average American. That becomes important as researchers face seemingly unsolvable science problems, but just keep trying. 

Q4. What will the future of immunology look like?

• The next few years will see scientists gain a more and more detailed understanding of the processes and pathways involved in the immune system. He said that the field may go so deep that it identities a set of uniform processes because, at the root of everything, cells are cells despite their different functions.  
• That said, how cells and organs interact, the province of systems biology, still has a long way to go before researchers understand the sum of complex interactions that result in health or disease.
• In addition, immunology is a relatively "soft" science compared to physics, said Dr. Zinkernagel. There are yet many unknowns and presumptions that persist despite a lack of evidence to back them up, and many will turn out to be wrong. In that light, those involved in teaching the next generation of immunologists should take care to instill a combination of open-mindedness and critical thinking in their students.   

For a look back, here is another video created by Nobelprize.org after Dr. Zinkernagel won his award.

Nobel Prizes recall promise of and obstacles to stem cell medicine

Sir John Gurdon of the University of Cambridge and Shinya Yamanaka of Kyoto University were recently awarded Nobel Prizes for their work with induced pluripotent stem cells.

We used the occasion to ask Tim Townes, Ph.D., chair of UAB’s Department of Biochemistry and Molecular Genetics, for his comment on the state of the iPSC field, its wondrous potential and the remaining obstacles to human treatment.

Gurdon discovered in 1962 that an entire living tadpole could be created from an already mature frog intestine cell using a technique called nuclear transfer. But his technique required the use of an embryo, and led to the controversy over the potential use of human embryonic stem cells. Yamanaka’s work ended the controversy by showing you could turn skin cells into stem cells just using proteins called transcription factors (no embryos needed).

“Proving that a fully differentiated bodily cell could be turned back into a stem cell, and determining all the steps necessary to do so, were absolutely phenomenal accomplishments worthy of a Nobel Prize,” says Townes.

Just after Yamanaka did his Nobel-winning work in 2006, Townes’ team, in collaboration with scientists at the Massachusetts Institute of Technology (MIT), "cured” sickle-cell disease in mice using genetically altered induced pluripotent stem cells. This was the very first demonstration that researchers could not only take a differentiated cell back to a stem cell, but could also fix a genetic problem in iPS cells and transplant them to cure a disease.

In a perfect world, says Townes, you could take a few skin cells from a patient and coax them back along the differentiation pathway to become stem cells, which are capable of becoming many kinds of cells. Then you would program the stem cells to become, say, red blood cells to treat sickle cell anemia, or white blood cells to replace those causing leukemia. You might be able to make stem cells that attack tumors, or even keep them on ice for years to fight a disease you don’t have yet.

The problem is that the field must prove such cells are safe and potentially effective in humans before they are ever given to humans, even in clinical trials. Stem cells in our body rarely move backward from being fully mature differentiated cells to immature stem cells. Some kinds of tumor cells are among the exceptions, so it pays to tread carefully.

The traditional solution is to create a model of the disease in mice — for instance, ones genetically engineered to have a human gene responsible for a disease. But mice and humans have evolved to have considerable differences, and many treatments that work in one do not work in the other. Researchers are currently debating whether or not studies in a larger animal like a pig are needed to better ensure safety. Furthermore, how long do you wait after giving stem cells to an animal before you declare the treatment to be safe? It may be a few years, says Townes.

In the meantime, he and others are studying whether they can make the treatments safer by using more mature stem cells. After a certain point in the process of maturing, stem cells can no longer move backwards along the pathway to become immature (potentially cancerous) again. Treatments based on mature stem cells would not provide a permanent cure for a disease like sickle cell. Patients might need a monthly infusion, but it could potentially still bring considerable relief.

For those interested in learning more about induced pluripotent stem cells, Townes recommends the National Institutes of Health's stem cell website and its research site. Also see Yamanaka’s recent GEN article, which warns against putting stem cell treatments into human patients too soon, or without proper proof in place. Then there is the iPSC content offered by Genetic Engineering & Biotechnology News.