Axonal transport in neurons is essential for the delivery of functional proteins to the synapse, for clearance of damaged or misfolded proteins, and for long-distance signaling from the distal axon to the cell body. However, regulation of axonal transport in terms cargo recognition and transport behavior (speed, direction, pausing) is poorly understood. This study proposes the idea that transport of organelles can be modulated by changes in intracellular signaling, such as activation of JNK (c-Jun N-terminal kinase), which has been implicated in stress response and neuronal death. My preliminary data from neuronal cultures shows that pharmacological inhibition of JNK inhibits vesicular transport in both directions and that activation of JNK increases the speed of retrograde transport. An excellent candidate for mediating these transport responses is JIP1 (JNK-interacting protein), which has the ability to associate with JNK, both anterograde and retrograde motor proteins, and vesicles (via transmembrane proteins). In addition, the preliminary observation that JNK activation also leads to phosphorylation of JIP1 supports the hypothesis that JNK-induced phosphorylation of JIP1 leads to changes in axonal transport by altering the interaction between JIP1 and motor proteins. To verify this hypothesis, the proposed experiments will use live-cell microscopy to characterize the effects of pharmacological manipulation of JNK signaling on the transport of specific fluorescently labeled vesicle populations. Also, siRNA knockdown experiments will be used to determine whether these JNK-induced changes are mediated by JIP1. Further, coimmunoprecipitations will more clearly elucidate the interaction between JIP1 and the retrograde motor complex, dynein/dynactin. Finally, mutant nonphosphorylatable JIP1 constructs will be used to determine whether JIP1 phosphorylation is the mechanism responsible for these JNK-induced changes in transport. These experiments will further the idea that axonal transport can be regulated at the cargo level via post-translational modification in response to signaling pathway activation. A better understanding of the connection between injury signaling and transport will provide new insight into the role of transport dysregulation in neurodegenerative diseases.
Neurons are specialized cells that contain long processes called axons along which electrical information travels. In order to maintain normal neuronal function, proteins and organelles must be transported at great distances along these axons to and from the cell body. This project investigates the role of an injury signaling pathway in regulating axonal transport properties, such as which cargos are transported and how fast they move, and will provide insight into understanding the role of axonal transport in neuronal injury and neurodegeneration.
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