Regulation of KIF1A-Driven Dense Core Vesicle Transport: Ca2+/CaM Controls DCV Binding and Liprin-α/TANC2 Recruits DCVs to Postsynaptic Sites

Abstract

SummaryTight regulation of neuronal transport allows for cargo binding and release at specific cellular locations. The mechanisms by which motor proteins are loaded on vesicles and how cargoes are captured at appropriate sites remain unclear. To better understand how KIF1A-driven dense core vesicle (DCV) transport is regulated, we identified the KIF1A interactome and focused on three binding partners, the calcium binding protein calmodulin (CaM) and two synaptic scaffolding proteins: liprin-α and TANC2. We showed that calcium, acting via CaM, enhances KIF1A binding to DCVs and increases vesicle motility. In contrast, liprin-α and TANC2 are not part of the KIF1A-cargo complex but capture DCVs at dendritic spines. Furthermore, we found that specific TANC2 mutations—reported in patients with different neuropsychiatric disorders—abolish the interaction with KIF1A. We propose a model in which Ca2+/CaM regulates cargo binding and liprin-α and TANC2 recruit KIF1A-transported vesicles.

Synapsin is required for dense core vesicle capture and cAMP-dependent neuropeptide release

“…Possibly, activity causes a redistribution of DCVs but no proper recruitment at release sites occurs, thus DCVs may be ‘dropped’ in these regions of the axon when no synapsin-based tethering of DCVs to the actin cytoskeleton can occur. This supports two conclusions: 1) Contrary to previous publications that attributed ‘capture’ merely to a tightly regulated balance of antero- and retrograde molecular motors of the tubulin cytoskeleton (Bharat et al, 2017; Morrison et al, 2018; Stucchi et al, 2018), our data suggest that also a direct tethering of DCVs occurs by synapsin, as established for SVs, to keep them near synaptic release sites. 2) This process appears to depend on S9, where phosphorylation leads to release of the captured DCVs from the actin cytoskeleton to enable their PM localization and fusion.…”

“…However, also actin was found to play a role, such that localization of DCVs at neuronal terminals may involve a handover from microtubules to the actin cytoskeleton. In line with this, a requirement for the scaffold proteins α-liprin and TANC2 was shown in DCV capture at postsynaptic spines, and these proteins interact with actin as well to modulate function of kinesin motors, which also involves calmodulin (Stucchi et al, 2018). Last, in C. elegans , a complex of proteins involving sentryn, α-liprin and the SAD kinase were shown to regulate antero- vs. retrograde traffic of DCVs, thus ‘capture’ could be determined by a balance of the two processes (Morrison et al, 2018).…”

A novel strategy to visualize vesicle‐bound kinesins reveals the diversity of kinesin‐mediated transport

“…The mechanism by which such regulation is achieved is not known, but several models have been proposed. One possibility is that multiple motors—dynein, myosins, or other kinesins—bind vesicles together and that transport behavior is the sum of their activities, which may be regulated in a vesicle‐specific way. A second possibility is that adaptor proteins selectively activate or inhibit kinesins and that the regulatory proteins that associate with a given kinesin are vesicle‐specific.…”

Disease-associated mutations hyperactivate KIF1A motility and anterograde axonal transport of synaptic vesicle precursors

“…To precisely regulate KIF1A activity, a currently unknown molecular mechanism must monitor the number of synaptic vesicles and this information must feed back to the autoinhibition of the UNC-104/KIF1A motor. A CaM-dependent mechanism is a candidate for this regulation (4). Another mechanism that may be involved is BORC-dependent regulation, which is involved in lysosomal transport and relies on KIF1Bb, another mammalian ortholog of UNC-104 (44,45).…”