Regulation of stress-signalling by proteolysis of JIP scaffold proteins

We are trying to understand how the cells in our body sense their environment and transmit this information to ensure normal development and function. If this information is not transmitted or transmitted to the wrong place or at the wrong time, then the cells do not respond correctly and disease or developmental abnormalities may occur. It is therefore important to understand the precise function of proteins that regulate the transfer of information within cells in order to design treatments that interfere with or promote their function to combat disease. One such group of proteins act as molecular scaffolds by binding to particular enzymes involved in transmitting information. These scaffold proteins direct the location of the enzymes in the cell and can regulate their activities. We will investigate using rodent models how particular scaffold proteins and their associated signalling enzymes control normal neurone function and how these functions break down in response to stress, as can occur during stroke, brain injury, and neurodegenerative diseases. The project will therefore elucidate important mechanisms underlying neurone behaviour and thus contribute to finding future treatments for neuronal diseases and brain injury. Such treatments will be beneficial to patients suffering from these conditions both in terms of prevention and enhanced recovery.

The apoptosis of neurones occurs during embryogenesis to shape the developing nervous system but also underlies human neurological disorders including stroke and neurodegenerative diseases. The JNK MAP kinase pathway is a major component of neuronal apoptotic pathways. JNK activity in neurones can be regulated by the JIP family of scaffold proteins. We have evidence that JIP/JNK signalling is regulated by signal-dependent degradation of JIP proteins mediated by the ubiquitin-proteosome system. The objectives of the project are to (i) determine the molecular mechanism of JIP degradation, including elucidating the signalling events that prime JIPs for degradation, and (ii) address the functional consequences of JIP degradation for JNK signalling and stress-induced neuronal apoptosis. Primary neurone cultures will be used for the study as they represent an ideal model for functional studies of JIP/JNK signalling and neuronal apoptosis. A number of molecular tools will be employed including the ectopic expression of JIP mutants that are impaired for signal-dependent degradation, pharmacological inhibition of intracellular signalling pathways, and knockdown of the expression of signalling pathways or components of the ubiquitin-proteosome system that regulate JIP stability. Overall, the study will enhance our understanding of the JIP/JNK signalling pathway and will provide important new insights into the molecular mechanisms of signal integration that contribute to neurone fate. In addition, the regulation of JNK activity by manipulating JIP protein levels may provide a therapeutic target for the prevention of neurone loss following injury or disease.