Dr Mark Graham
Dr Mark Graham is a Group Leader and part of the Cell Signalling Unit. He’s also a father of four, two of them twins, and all of them born since he started at CMRI in 2002. “Work/life balance can be difficult,” Mark says, “especially as science is so demanding, but children do make you remember why research is important.”
Mark’s research focuses on a fundamental question: “Why and how do we get small packets of neurotransmitter in vesicles in the brain?” It’s probably not the first question most people think about when they wake up in the morning, but it is important for understanding how nerve cells communicate, for understanding learning and memory, and for finding new treatments for conditions as varied as Alzheimer’s disease and childhood leukaemia. Vesicles are structures that bud off of a cell membrane and carry things into or out of cells, anything from chemical signals telling the cells how to behave to invading viruses.
“Right now I’m interested in two clathrin assembly proteins, AP180 and CALM, both of which assemble clathrin coated vesicles.” Clathrin is a scaffolding material, a sort of microscopic version of a geodesic dome or piece of playground climbing equipment, that gives many vesicles their shape and helps them form.
“The AP180 protein is only found in brain and forms small vesicles in the synapses of neurons. CALM is found in all cells of the body and forms vesicles twice the size. You’d assume my interest in brain would make AP180 most appealing, but it turns out CALM has implications for both Alzheimer’s and leukaemia, and it’s captured my attention.” When you examine aggressive childhood leukaemia, you will find many have a genetic mutation, a rearrangement of chromosomes that alters the CALM protein. “We think CALM is what makes these cancers more aggressive,” Mark says. “CALM is needed to transport iron into blood cells. These leukaemias have too many immature blood cells with little iron, so CALM may exacerbate the anaemia in leukaemia patients.”
Polymorphisms in CALM (small mutations in the gene) have also been found in Alzheimer’s patients. “It may be that CALM is needed to clear the junk from brain cells. CALM probably has a role in transferring these deposits through the blood brain barrier in endothelial cells. If CALM isn’t working, plaques build up over time to cause late-onset Alzheimer’s. CALM is also known to be involved in amyloid precursor protein (APP)-trafficking, so it could also cause Alzheimer’s by bringing more APP into brain cells where it can break down and eventually form plaques.”
“We still need to discover how CALM works, but it is likely to be important in any disease where transfer of material between the blood and an organ is important (e.g. blood to kidney, in kidney disease),” Marks says, “so my goal is to find subtle ways to regulate endocytosis and modulate its function to treat diseases. We find that most proteins simply can’t be turned on or off. They’re involved in too many processes, and turning something off to treat one disease may cause more problems elsewhere in the body, especially with CALM, which is found everywhere.”
“Post-translational modification, which is the addition of other molecules to a protein, is a much better way to subtly affect a protein’s function. There are many types of post-translational modification (phosphorylation, acetylation, sumoylation, methylation, ubiquination) and these can be studied and used to determine the fine controls for a protein and for disease treatment. When Mark started at CMRI in 2002, they had one mass spectrometer to work with (an extremely specialised machine to help study proteins and post-translational modifications at the molecular level). Together with Val Valova, Manager of the Biomedical Proteomics Facility, and Prof Phil Robinson, Facility Director, Mark has helped to build up the facility over time, and now they have seven mass spectrometers.
“We just completed a broad study of phosphorylation-based signalling in axon terminals,” Mark says.
“This is where neurotransmitters are waiting to be released. The endocytic machinery sits there waiting to make vesicles. The only thing stopping it is phosphorylation, acting as chemical switches. We asked where are the sites of phosphorylation? Which ones are important for nerve signalling, which ones respond to a stimulus? Our most unexpected finding was that there were some phosphorylation changes that could last up to seven minutes. This is a long time in the neuron, where most signals are complete in seconds. This could be important for plasticity, for learning and memory. The longer a signal is carried, the more neurotransmitter is released, and the more likely the brain is to see it as a useful connection between nerve cells. A stimulated neuron is more likely to be stimulated in future, and this is the basis for learning and memory.”
The questions are many and varied, but his toolkit to answer those questions remains the same: mass spectrometry. “But,” Mark says, “bioinformatics is becoming more important now. We have so much data from mass spectrometry that we need faster ways of processing and understanding the data. This will bring us closer to clinical outcomes faster.” When asked what he thought about the importance of basic research and the current trend towards clinical-focused work, Mark says,
“We need ‘Super Teams’ able to do basic research and link it all the way to the clinic, to patients. We can’t do it without basic research—we need new avenues and discoveries—but the same people can’t necessarily take it to the clinic. Achieving a vision for a cure requires collaboration.”