Kinesin-3 KIF1A functions as a diligent worker and its functionality is regulated by the ubiquitin-proteasome system

Long-distance intracellular transport is driven by motor proteins that walk along microtubule tracks. The fate of the motor protein after transport is unclear. Classically, motor proteins have been thought to function as Diligent Workers (DW) that remain attached to cargo during the entire transport event and are degraded at the end of the journey. In contrast, previous work suggests that kinesin-1 transport can be described by a Loose Bucket Brigade (LBB) model in which individual motor proteins participate in multiple rounds of transport. Here, we used live-cell imaging in iNeurons to test whether the kinesin-3 KIF1A functions as a DW during axonal transport. We demonstrate that the fluorescence intensity of KIF1A on particles undergoing axonal transport does not change over time, suggesting that KIF1A remains attached to its cargo for the entire transport event. We determined that KIF1A has a relatively short protein half-life, consistent with KIF1A being degraded at the end of the journey. Moreover, protein turnover appears to be tightly controlled in iNeurons, as treating cells with inhibitors of the ubiquitin/proteasome system results in a cessation of KIF1A-driven transport, the appearance of KIF1A aggregates in the cell body, and their subsequent degradation through aggrephagy. These results suggest that KIF1A transport fits the DW model and that KIF1A protein levels may play a role in signaling proteostatic stress in neuronal cells. [Media: see text].