In this post we bring you a Q & A from Alexander Palazzo, Department of Biochemistry, University of Toronto. Alex may one day find the answers to our ANE questions.
Q: Tell us a bit about yourself.
A: I am an Associate Professor of Biochemistry at the University of Toronto. Although I do teach undergraduate courses at U of T, I primarily run a laboratory that studies how mRNA is used to synthesize proteins in human cells.
Q: What is mRNA?
A: In each of the cells of your body you have a complete set of all the DNA you inherited from your mother and father. This complete set of DNA is called your genome and it lives in the nucleus, a small membrane-bound compartment found inside each cell. Small segments of this DNA, called genes, contain the information to make different types of proteins. In humans there are about 20,000 different genes, each making a different protein. These proteins are important for the proper functioning of your cells and your body. Some genes constantly make proteins, while others respond to your body’s needs. For example you have one gene that codes for the insulin protein and when your blood sugar rises after a meal, that gene is “turned on” in your pancreas cells, and as a result these cells make and secrete insulin into your blood stream. The insulin protein is a signal to the rest of your body that you need to absorb all that excess sugar that is in your bloodstream. Diabetic patients have problems either secreting insulin, or detecting insulin, and this defect can cause problems.
Q: What does mRNA have to do with protein production?
A: When a gene is “turned on”, that segment of DNA that lives in the nucleus is copied into many strands of a related molecule called “messenger RNAs”, or mRNA. Thus the information from the DNA has been copied into the mRNA and this information is then used to make one particular protein. There is one problem –the mRNA is made inside the nucleus and the machinery that uses the mRNA to make proteins is only found on the outside in another compartment of the cell called the cytoplasm. To get from the nucleus to the cytoplasm, the mRNA must be packaged into a large assembly and it must cross the nuclear envelope using a passageway called the nuclear pore. Once in the cytoplasm, the mRNA can come out of its packaging, and then it can be used to make new proteins. Now this whole process is what we would call “gene expression” and it uses many molecular machines, most of these machines are proteins themselves.
To help you out I’ll give you an analogy. Imagine that you manage many bakeries around your neighbourhood and because tomorrow is the rabbit festival they all need to bake a particular rabbit festival cake. However the information on how to bake that cake is on one page of a certain cookbook found only at the local library. Moreover, the cookbook is in the reference section and cannot be taken out of the building. This being the library, there is no kitchen, no oven.
Q: So how is this all supposed to work?
A: In this analogy, the library, where all the information is stored, is like the nucleus, the version of the recipe in the cookbook is like a gene, and the cake is a protein (with your employees being the cake/protein making machines). To start the whole process, you make copies of the recipe – this would be the equivalent of making mRNA copies of a gene. To be of any use, these mRNA copies need to exit the library, so you stuff them into envelopes and walk out the front door. Since the library is the equivalent of the nucleus, this would make its walls analogous to the nuclear membrane (also known as the nuclear envelope) and the door would be the nuclear pore. Once outside the library you deliver the recipes to your bakers, and they rip open the envelopes ad use the recipes to make the rabbit festival cakes.
Q: What does this have to do with RanBP2? (Genetic mutation associated with ANE)
A: RanBP2, also known as Nup358, is a protein that sits at the exit of the nuclear pore. It would be hang around, right outside the door of the library. A few years back my lab discovered that RanBP2 plays an important role in the gene expression process. Our work suggests that just after a packaged mRNA crosses the nuclear pore, RanBP2 briefly holds onto the mRNA and modifies how it is packaged. This either makes the mRNA more efficiently used to make proteins or less efficiently used. So getting back to our analogy, RanBP2 sits right outside the library’s front door and scans every envelope that exits the building. In some cases it changes the envelope making it easier for your bakers to open the envelope and make cakes. In other cases RanBP2 stiffens the envelope, preventing your bakers from opening it up and stopping them from baking any cakes.
We suspect that RanBP2 may affect the expression of these cytokine genes. Cells that are attacked by viruses turn on cytokine genes to mount an immune response – in other words cytokine genes are copied into mRNAs which are then packaged and sent to the nuclear pore. In normal individuals, data from my lab suggests that these mRNA packages are intercepted by RanBP2 as they exit the pore, and are modified so that they are not efficiently used to make cytokine proteins. Cytokine proteins act as a an alert signal that the body is under viral attack, and RanBP2 acts in the end to dial down this signal. If the cytokine signal is too strong then this can cause the problems that are seen in ANE1 patients.
Q: What does the ANE1-associated mutations do?
A: We are not completely sure. It is likely that mutated RanBP2 can’t do its job properly and can’t supress the production of cytokine proteins from these mRNAs. It is important to stress that in the end that the details of the role of RanBP2 in this disease will differ substantially from what I just described. But the more work we do in the lab, the more we will learn about how RanBP2 functions, and the closer we will get to understanding what is going on. Knowing the players at the molecular level, and figuring out how this all works, is the first step in developing a therapy. With new advances in molecular medicine, the biomedical community will come up with new therapeutic strategies. So I’m hopeful that we will one day be able to treat ANE1 patients. In addition, it is likely that we will learn basic concepts about how gene expression works, and this can lead to new insights that may have relevance to many other diseases.
To learn more about my lab, you can check out our website: www.palazzolab.com
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