A biosensor of local kinesin activity reveals roles of PKC and EB1 in KIF17 activation

Neurons dispose of hyperactive kinesin into glial cells for clearance

Microtubule-based kinesin motor proteins are crucial for intracellular transport, but their hyperactivation can be detrimental for cellular functions. This study investigated the impact of a constitutively active ciliary kinesin mutant, OSM-3CA, on sensory cilia in C. elegans. Surprisingly, we found that OSM-3CA was absent from cilia but underwent disposal through membrane abscission at the tips of aberrant neurites. Neighboring glial cells engulf and eliminate the released OSM-3CA, a process that depends on the engulfment receptor CED-1. Through genetic suppressor screens, we identified intragenic mutations in the OSM-3CA motor domain and mutations inhibiting the ciliary kinase DYF-5, both of which restored normal cilia in OSM-3CA-expressing animals. We showed that conformational changes in OSM-3CA prevent its entry into cilia, and OSM-3CA disposal requires its hyperactivity. Finally, we provide evidence that neurons also dispose of hyperactive kinesin-1 resulting from a clinic variant associated with amyotrophic lateral sclerosis, suggesting a widespread mechanism for regulating hyperactive kinesins.

In Vitro FRET- and Fluorescence-Based Assays to Study Protein Conformation and Protein-Protein Interactions in Mitosis

Proper cell division and the equal segregation of genetic material are essential for life. Cell division is mediated by the mitotic spindle, which is composed of microtubules (MTs) and MT-associated proteins that help align and segregate the chromosomes. The localization and characterization of many spindle proteins have been greatly aided by using GFP-tagged proteins in vivo, but these tools typically do not allow for understanding how their activity is regulated biochemically. With the recent explosion of the pallet of GFP-derived fluorescent proteins, fluorescence-based biosensors are becoming useful tools for the quantitative analysis of protein activity and protein-protein interactions. Here, we describe solution-based Förster resonance energy transfer (FRET) and fluorescence assays that can be used to quantify protein-protein interactions and to characterize protein conformations of MT-associated proteins involved in mitosis.

Rab23/Kif17 regulate oocyte meiotic progression by modulating tubulin acetylation and actin dynamics

Cytoskeletal dynamics are involved in multiple cellular processes during oocyte meiosis, including spindle organization, actin-based spindle migration, and polar body extrusion. Here, we report that the vesicle trafficking protein Rab23, a GTPase, drives the motor protein Kif17 and that this is important for spindle organization and actin dynamics during mouse oocyte meiosis. GTP-bound Rab23 accumulated at the spindle and promoted migration of Kif17 to the spindle poles. Depletion of Rab23 or Kif17 caused polar body extrusion failure. Further analysis showed that depletion of Rab23/Kif17 perturbed spindle formation and chromosome alignment, possibly by affecting tubulin acetylation. Kif17 regulated tubulin acetylation by associating with αTAT and Sirt2, and depletion of Kif17 altered expression of these proteins. Moreover, depletion of Kif17 decreased the level of cytoplasmic actin, which abrogated spindle migration to the cortex. The tail domain of Kif17 associated with constituents of the RhoA-ROCK-LIMK-cofilin pathway to modulate assembly of actin filaments. Taken together, our results demonstrate that the Rab23-Kif17-cargo complex regulates tubulin acetylation for spindle organization and drives actin-mediated spindle migration during meiosis.

Microtubule Motors in Establishment of Epithelial Cell Polarity

Epithelial cells play a key role in insuring physiological homeostasis by acting as a barrier between the outside environment and internal organs. They are also responsible for the vectorial transport of ions and fluid essential to the function of many organs. To accomplish these tasks, epithelial cells must generate an asymmetrically organized plasma membrane comprised of structurally and functionally distinct apical and basolateral membranes. Adherent and occluding junctions, respectively, anchor cells within a layer and prevent lateral diffusion of proteins in the outer leaflet of the plasma membrane and restrict passage of proteins and solutes through intercellular spaces. At a fundamental level, the establishment and maintenance of epithelial polarity requires that signals initiated at cell-substratum and cell-cell adhesions are transmitted appropriately and dynamically to the cytoskeleton, to the membrane-trafficking machinery, and to the regulation of occluding and adherent junctions. Rigorous descriptive and mechanistic studies published over the last 50 years have provided great detail to our understanding of epithelial polarization. Yet still, critical early steps in morphogenesis are not yet fully appreciated. In this review, we discuss how cytoskeletal motor proteins, primarily kinesins, contribute to coordinated modification of microtubule and actin arrays, formation and remodeling of cell adhesions to targeted membrane trafficking, and to initiating the formation and expansion of an apical lumen.

Septin 9 interacts with kinesin KIF17 and interferes with the mechanism of NMDA receptor cargo binding and transport

Kinesin motor interactions with cargo and their regulation are not well understood. Septin 9 (SEPT9) interacts directly with kinesin KIF17 and interferes with binding of the cargo adaptor/scaffold mLin-10/Mint1, which links the NMDA receptor subunit 2B (NR2B) to KIF17. SEPT9 down-regulates NR2B transport without affecting the motile properties of KIF17.

Intracellular transport involves the regulation of microtubule motor interactions with cargo, but the underlying mechanisms are not well understood. Septins are membrane- and microtubule-binding proteins that assemble into filamentous, scaffold-like structures. Septins are implicated in microtubule-dependent transport, but their roles are unknown. Here we describe a novel interaction between KIF17, a kinesin 2 family motor, and septin 9 (SEPT9). We show that SEPT9 associates directly with the C-terminal tail of KIF17 and interacts preferentially with the extended cargo-binding conformation of KIF17. In developing rat hippocampal neurons, SEPT9 partially colocalizes and comigrates with KIF17. We show that SEPT9 interacts with the KIF17 tail domain that associates with mLin-10/Mint1, a cargo adaptor/scaffold protein, which underlies the mechanism of KIF17 binding to the NMDA receptor subunit 2B (NR2B). Significantly, SEPT9 interferes with binding of the PDZ1 domain of mLin-10/Mint1 to KIF17 and thereby down-regulates NR2B transport into the dendrites of hippocampal neurons. Measurements of KIF17 motility in live neurons show that SEPT9 does not affect the microtubule-dependent motility of KIF17. These results provide the first evidence of an interaction between septins and a nonmitotic kinesin and suggest that SEPT9 modulates the interactions of KIF17 with membrane cargo.

Kif26b controls endothelial cell polarity through the Dishevelled/Daam1-dependent planar cell polarity-signaling pathway

Angiogenesis involves the coordinated growth and migration of endothelial cells (ECs) toward a proangiogenic signal. The Wnt planar cell polarity (PCP) pathway, through the recruitment of Dishevelled (Dvl) and Dvl-associated activator of morphogenesis (Daam1), has been proposed to regulate cell actin cytoskeleton and microtubule (MT) reorganization for oriented cell migration. Here we report that Kif26b--a kinesin--and Daam1 cooperatively regulate initiation of EC sprouting and directional migration via MT reorganization. First, we find that Kif26b is recruited within the Dvl3/Daam1 complex. Using a three-dimensional in vitro angiogenesis assay, we show that Kif26b and Daam1 depletion impairs tip cell polarization and destabilizes extended vascular processes. Kif26b depletion specifically alters EC directional migration and mislocalized MT organizing center (MTOC)/Golgi and myosin IIB cell rear enrichment. Therefore the cell fails to establish a proper front-rear polarity. Of interest, Kif26b ectopic expression rescues the siDaam1 polarization defect phenotype. Finally, we show that Kif26b functions in MT stabilization, which is indispensable for asymmetrical cell structure reorganization. These data demonstrate that Kif26b, together with Dvl3/Daam1, initiates cell polarity through the control of PCP signaling pathway-dependent activation.

KIF17 regulates RhoA-dependent actin remodeling at epithelial cell-cell adhesions

The kinesin KIF17 localizes at microtubule plus-ends where it contributes to regulation of microtubule stabilization and epithelial polarization. We now show that KIF17 localizes at cell-cell adhesions and that KIF17 depletion inhibits accumulation of actin at the apical pole of cells grown in 3D organotypic cultures and alters the distribution of actin and E-cadherin in cells cultured in 2D on solid supports. Overexpression of full-length KIF17 constructs or truncation mutants containing the N-terminal motor domain resulted in accumulation of newly incorporated GFP-actin into junctional actin foci, cleared E-cadherin from cytoplasmic vesicles and stabilized cell-cell adhesions to challenge with calcium depletion. Expression of these KIF17 constructs also increased cellular levels of active RhoA, whereas active RhoA was diminished in KIF17-depleted cells. Inhibition of RhoA or its effector ROCK, or expression of LIMK1 kinase-dead or activated cofilin(S3A) inhibited KIF17-induced junctional actin accumulation. Interestingly, KIF17 activity toward actin depends on the motor domain but is independent of microtubule binding. Together, these data show that KIF17 can modify RhoA-GTPase signaling to influence junctional actin and the stability of the apical junctional complex of epithelial cells.

Studying Kinetochores In Vivo Using FLIM-FRET

Kinetochores play essential roles in coordinating mitosis, as a mechanical connector between chromosome and microtubule and as a source of numerous biochemical signals. These mechanical and biochemical behaviors of kinetochores change dynamically in cells during mitosis. Therefore, understanding kinetochore function requires an imaging tool that quantifies the protein-protein interactions or biochemical changes with high spatiotemporal resolution. FRET has previously been used in combination with biosensors to probe protein-protein interactions and biochemical activity. In this chapter, we introduce FLIM-FRET, a lifetime-based method that quantifies FRET, and describe the use of FLIM-FRET as a method for studying dynamic kinetochore behavior in cells with high spatiotemporal resolution.

A direct interaction between fascin and microtubules contributes to adhesion dynamics and cell migration

Fascin is an actin-binding and bundling protein that is highly upregulated in most epithelial cancers. Fascin promotes cell migration and adhesion dynamics in vitro and tumour cell metastasis in vivo. However, potential non-actin bundling roles for fascin remain unknown. Here, we show for the first time that fascin can directly interact with the microtubule cytoskeleton and that this does not depend upon fascin-actin bundling. Microtubule binding contributes to fascin-dependent control of focal adhesion dynamics and cell migration speed. We also show that fascin forms a complex with focal adhesion kinase (FAK, also known as PTK2) and Src, and that this signalling pathway lies downstream of fascin-microtubule association in the control of adhesion stability. These findings shed light on new non actin-dependent roles for fascin and might have implications for the design of therapies to target fascin in metastatic disease.

Direct regulation of microtubule dynamics by KIF17 motor and tail domains

KIF17 is a kinesin-2 family motor that interacts with EB1 at microtubule (MT) plus-ends and contributes to MT stabilization in epithelial cells. The mechanism by which KIF17 affects MTs and how its activity is regulated are not yet known. Here, we show that EB1 and the KIF17 autoinhibitory tail domain (KIF17-Tail) interacted competitively with the KIF17 catalytic motor domain (K370). Both EB1 and KIF17-Tail decreased the K0.5MT of K370, with opposing effects on MT-stimulated ATPase activity. Importantly, K370 had independent effects on MT dynamic instability, resulting in formation of long MTs without affecting polymerization rate or total polymer mass. K370 also inhibited MT depolymerization induced by dilution in vitro and by nocodazole in cells, suggesting that it acts by protecting MT plus-ends. Interestingly, KIF17-Tail bound MTs and tubulin dimers, delaying initial MT polymerization in vitro and MT regrowth in cells. However, neither EB1 nor KIF17-Tail affected K370-mediated MT polymerization or stabilization significantly in vitro, and EB1 was dispensable for MT stabilization by K370 in cells. Thus, although EB1 and KIF17-Tail may coordinate KIF17 catalytic activity, our data reveal a novel and direct role for KIF17 in regulating MT dynamics.