F-actin disassembly factor MICAL1 binding to Myosin Va mediates cargo unloading during cytokinesis

TBC1D20 coordinates vesicle transport and actin remodeling to regulate ciliogenesis

TBC1D20 deficiency causes Warburg Micro Syndrome in humans, characterized by multiple eye abnormalities, severe intellectual disability, and abnormal sexual development, but the molecular mechanisms remain unknown. Here, we identify TBC1D20 as a novel Rab11 GTPase-activating protein that coordinates vesicle transport and actin remodeling to regulate ciliogenesis. Depletion of TBC1D20 promotes Rab11 vesicle accumulation and actin deconstruction around the centrosome, facilitating the initiation of ciliogenesis even in cycling cells. Further investigations reveal enhanced Rab11-MICAL1 interaction upon TBC1D20 loss, activating the monooxygenase domain of MICAL1 and inducing F-actin depolymerization around the centrosome. This actin network reorganization facilitates vesicle trafficking and docking, ultimately promoting ciliogenesis. In summary, our work uncovers a coordinated ciliogenesis initiation mechanism via Rab11 activation. These findings underscore a pivotal role for TBC1D20 in early ciliogenesis, advancing our understanding of its spatiotemporal regulation and offering insights into the disease pathogenesis associated with TBC1D20 mutations.

Structural basis of MICAL autoinhibition

MICAL proteins play a crucial role in cellular dynamics by binding and disassembling actin filaments, impacting processes like axon guidance, cytokinesis, and cell morphology. Their cellular activity is tightly controlled, as dysregulation can lead to detrimental effects on cellular morphology. Although previous studies have suggested that MICALs are autoinhibited, and require Rab proteins to become active, the detailed molecular mechanisms remained unclear. Here, we report the cryo-EM structure of human MICAL1 at a nominal resolution of 3.1 Å. Structural analyses, alongside biochemical and functional studies, show that MICAL1 autoinhibition is mediated by an intramolecular interaction between its N-terminal catalytic and C-terminal coiled-coil domains, blocking F-actin interaction. Moreover, we demonstrate that allosteric changes in the coiled-coil domain and the binding of the tripartite assembly of CH-L2α1-LIM domains to the coiled-coil domain are crucial for MICAL activation and autoinhibition. These mechanisms appear to be evolutionarily conserved, suggesting a potential universality across the MICAL family.

Methionine oxidation of actin cytoskeleton attenuates traumatic memory retention via reactivating dendritic spine morphogenesis

Post-traumatic stress disorder (PTSD) is characterized by hypermnesia of the trauma and a persistent fear response. The molecular mechanisms underlying the retention of traumatic memories remain largely unknown, which hinders the development of more effective treatments. Utilizing auditory fear conditioning, we demonstrate that a redox-dependent dynamic pathway for dendritic spine morphogenesis in the basolateral amygdala (BLA) is crucial for traumatic memory retention. Exposure to a fear-induced event markedly increased the reduction of oxidized filamentous actin (F-actin) and decreased the expression of the molecule interacting with CasL 1 (MICAL1), a methionine-oxidizing enzyme that directly oxidizes and depolymerizes F-actin, leading to cytoskeletal dynamic abnormalities in the BLA, which impairs dendritic spine morphogenesis and contributes to the persistence of fearful memories. Following fear conditioning, overexpression of MICAL1 in the BLA inhibited freezing behavior during fear memory retrieval via reactivating cytokinesis, whereas overexpression of methionine sulfoxide reductase B 1, a key enzyme that reduces oxidized F-actin monomer, increased freezing behavior during retrieval. Notably, intra-BLA injection of semaphorin 3A, an endogenous activator of MICAL1, rapidly disrupted fear memory within a short time window after conditioning. Collectively, our results indicate that redox modulation of actin cytoskeleton in the BLA is functionally linked to fear memory retention and PTSD-like memory.

Autoinhibition and relief mechanisms for MICAL monooxygenases in F-actin disassembly

MICAL proteins represent a unique family of actin regulators crucial for synapse development, membrane trafficking, and cytokinesis. Unlike classical actin regulators, MICALs catalyze the oxidation of specific residues within actin filaments to induce robust filament disassembly. The potent activity of MICALs requires tight control to prevent extensive damage to actin cytoskeleton. However, the molecular mechanism governing MICALs' activity regulation remains elusive. Here, we report the cryo-EM structure of MICAL1 in the autoinhibited state, unveiling a head-to-tail interaction that allosterically blocks enzymatic activity. The structure also reveals the assembly of C-terminal domains via a tripartite interdomain interaction, stabilizing the inhibitory conformation of the RBD. Our structural, biochemical, and cellular analyses elucidate a multi-step mechanism to relieve MICAL1 autoinhibition in response to the dual-binding of two Rab effectors, revealing its intricate activity regulation mechanisms. Furthermore, our mutagenesis study of MICAL3 suggests the conserved autoinhibition and relief mechanisms among MICALs.

The Dilute domain in Canoe is not essential for linking cell junctions to the cytoskeleton but supports morphogenesis robustness

Robust linkage between adherens junctions and the actomyosin cytoskeleton allows cells to change shape and move during morphogenesis without tearing tissues apart. The Drosophila multidomain protein Canoe and its mammalian homolog afadin are crucial for this, as in their absence many events of morphogenesis fail. To define the mechanism of action for Canoe, we are taking it apart. Canoe has five folded protein domains and a long intrinsically disordered region. The largest is the Dilute domain, which is shared by Canoe and myosin V. To define the roles of this domain in Canoe, we combined biochemical, genetic and cell biological assays. AlphaFold was used to predict its structure, providing similarities and contrasts with Myosin V. Biochemical data suggested one potential shared function - the ability to dimerize. We generated Canoe mutants with the Dilute domain deleted (CnoΔDIL). Surprisingly, they were viable and fertile. CnoΔDIL localized to adherens junctions and was enriched at junctions under tension. However, when its dose was reduced, CnoΔDIL did not provide fully wild-type function. Furthermore, canoeΔDIL mutants had defects in the orchestrated cell rearrangements of eye development. This reveals the robustness of junction-cytoskeletal connections during morphogenesis and highlights the power of natural selection to maintain protein structure.

Cytokinetic abscission requires actin-dependent microtubule severing

Cell division is completed by the abscission of the intercellular bridge connecting the daughter cells. Abscission requires the polymerization of an ESCRT-III cone close to the midbody to both recruit the microtubule severing enzyme spastin and scission the plasma membrane. Here, we found that the microtubule and the membrane cuts are two separate events that are regulated differently. Using HeLa cells, we uncovered that the F-actin disassembling protein Cofilin-1 controls the disappearance of a transient pool of branched F-actin which is precisely assembled at the tip of the ESCRT-III cone shortly before the microtubule cut. Functionally, Cofilin-1 and Arp2/3-mediated branched F-actin favor abscission by promoting local severing of the microtubules but do not participate later in the membrane scission event. Mechanistically, we propose that branched F-actin functions as a physical barrier that limits ESCRT-III cone elongation and thereby favors stable spastin recruitment. Our work thus reveals that F-actin controls the timely and local disassembly of microtubules required for cytokinetic abscission.

Myosin Va: Capturing cAMP for synaptic plasticity

The plus-end directed actin-dependent motor protein, myosin Va, is of particular relevance for outward vesicular protein trafficking and for restraining specific cargo vesicles within the actin cortex. The latter is a preferred site of cAMP production, and the specificity of cAMP signaling is largely mediated through the formation of microdomains that spatially couple localized metabotropic receptor activity and cAMP production to selected effectors and downstream targets. This review summarizes the core literature on the role of myosin Va for the creation of such a cAMP microdomain at the mammalian nerve-muscle synapse that serves the activity-dependent recycling of nicotinic acetylcholine receptors (nAChRs)-a principal ligand-gated ion channel which is imperative for voluntary muscle contraction. It is discussed that i) the nerve-muscle synapse is a site with a unique actin-dependent microstructure, ii) myosin Va and protein kinase A regulatory subunit Iα as well as nAChR and its constitutive binding partner, rapsyn, colocalize in endocytic/recycling vesicles near the postsynaptic membrane, and iii) impairment of myosin Va or displacement of protein kinase A regulatory subunit Iα leads to the loss of nAChR stability. Regulation of this signaling process and underlying basic pieces of machinery were covered in previous articles, to which the present review refers.

The Dilute domain of Canoe is not essential for Canoe's role in linking adherens junctions to the cytoskeleton but contributes to robustness of morphogenesis

Robust linkage between cell-cell adherens junctions and the actomyosin cytoskeleton allows cells to change shape and move during morphogenesis without tearing tissues apart. The multidomain protein Drosophila Canoe and its mammalian homolog Afadin are critical for this linkage, and in their absence many events of morphogenesis fail. To define underlying mechanisms, we are taking Canoe apart, using Drosophila as our model. Canoe and Afadin share five folded protein domains, followed by a large intrinsically disordered region. The largest of these folded domains is the Dilute domain, which is found in Canoe/Afadin, their paralogs, and members of the MyosinV family. To define the roles of Canoe's Dilute domain we have combined biochemical, genetic and cell biological assays. Use of the AlphaFold tools revealed the predicted structure of the Canoe/Afadin Dilute domain, providing similarities and contrasts with that of MyosinV. Our biochemical data suggest one potential shared function: the ability to dimerize. We next generated Drosophila mutants with the Dilute domain cleanly deleted. Surprisingly, these mutants are viable and fertile, and CanoeΔDIL protein localizes to adherens junctions and is enriched at junctions under tension. However, when we reduce the dose of CanoeΔDIL protein in a sensitized assay, it becomes clear it does not provide full wildtype function. Further, canoeΔDIL mutants have defects in pupal eye development, another process that requires orchestrated cell rearrangements. Together, these data reveal the robustness in AJ-cytoskeletal connections during multiple embryonic and postembryonic events, and the power of natural selection to maintain protein structure even in robust systems.

MICAL-mediated oxidation of actin and its effects on cytoskeletal and cellular dynamics

Actin and its dynamic structural remodelings are involved in multiple cellular functions, including maintaining cell shape and integrity, cytokinesis, motility, navigation, and muscle contraction. Many actin-binding proteins regulate the cytoskeleton to facilitate these functions. Recently, actin's post-translational modifications (PTMs) and their importance to actin functions have gained increasing recognition. The MICAL family of proteins has emerged as important actin regulatory oxidation-reduction (Redox) enzymes, influencing actin's properties both in vitro and in vivo. MICALs specifically bind to actin filaments and selectively oxidize actin's methionine residues 44 and 47, which perturbs filaments' structure and leads to their disassembly. This review provides an overview of the MICALs and the impact of MICAL-mediated oxidation on actin's properties, including its assembly and disassembly, effects on other actin-binding proteins, and on cells and tissue systems.

Crystal Structure of the SH3 Domain of ASAP1 in Complex with the Proline Rich Motif (PRM) of MICAL1 Reveals a Unique SH3/PRM Interaction Mode

SH3 domains are common protein binding modules. The target sequence of SH3 domains is usually a proline-rich motif (PRM) containing a minimal "PxxP" sequence. The mechanism of how different SH3 domains specifically choose their targets from vast PxxP-containing sequences is still not very clear, as many reported SH3/PRM interactions are weak and promiscuous. Here, we identified the binding of the SH3 domain of ASAP1 to the PRM of MICAL1 with a sub-μM binding affinity, and determined the crystal structure of ASAP1-SH3 and MICAL1-PRM complex. Our structural and biochemical analyses revealed that the target-binding pocket of ASAP1-SH3 contains two negatively charged patches to recognize the "xPx + Px+" sequence in MICAL1-PRM and consequently strengthen the interaction, differing from the typical SH3/PRM interaction. This unique PRM-binding pocket is also found in the SH3 domains of GTPase Regulator associated with focal adhesion kinase (GRAF) and Src kinase associated phosphoprotein 1 (SKAP1), which we named SH3^AGS. In addition, we searched the Swiss-Prot database and found ~130 proteins with the SH3^AGS-binding PRM in silico. Finally, gene ontology analysis suggests that the strong interaction between the SH3^AGS-containing proteins and their targets may play roles in actin cytoskeleton regulation and vesicle trafficking.

High MICAL1 expression correlates with cancer progression and immune infiltration in renal clear cell carcinoma

BACKGROUND

Molecule interacting with CasL 1 (MICAL1), a multidomain flavoprotein monooxygenase, is strongly involved in the biological processes related to cancer cell proliferation and metastasis. However, there were few reports on the clinical significance of MICAL1 in renal clear cell carcinoma.

METHODS

The expression and prognostic value of MICAL1 in renal clear cell carcinoma were explored using immunohistochemical assays, public TCGA-KIRC databases and multiple analysis methods, including survival analysis, univariate and multivariate analyses, KEGG and GSEA. Wound healing and Transwell assays were performed to check the 786-O cell and Caki-1 cell migration abilities after knockdown of MICAL1. Western blotting was used to assess the regulatory effect of MICAL1 on the Rac1 activation. Additionally, the function of MICAL1 and the correlations between MICAL1 and immune infiltration levels in KIRC were investigated using TIMER and TISIDB.

RESULTS

MICAL1 expression was significantly higher in carcinoma tissue compared with non-cancerous tissue. A survival analysis revealed that patients with high MICAL1 expression had shorter overall survival (OS) and disease-specific survival (DSS) compared with patients with low MICAL1 expression. ROC analysis also confirmed that MICAL1 has a high diagnostic value in KIRC. Importantly, the univariate and multivariate Cox analysis further confirmed that high MICAL1 expression was an independent risk factor for OS in patients with KIRC. In accordance with this, knockdown of MICAL1 expression decreased Rac1 activation and cell migration. KEGG and GSEA analysis revealed that the immune infiltration and Ras signaling pathways were significantly upregulated in the high MICAL1 expression group. In terms of immune infiltrating levels, MICAL1 expression was positively associated with CD8+/Treg cell infiltration levels. Specifically, bioinformatic analysis showed that MICAL1 expression had strong relationships with various T cell exhaustion markers.

CONCLUSIONS

MICAL1 expression may act as a prognostic biomarker for determining the prognosis in renal clear cell carcinoma and plays an important role in regulating tumor immune microenvironment and cell migratory capacity.

Autoinhibition and activation mechanisms revealed by the triangular-shaped structure of myosin Va

As the prototype of unconventional myosin motor family, myosin Va (MyoVa) transport cellular cargos along actin filaments in diverse cellular processes. The off-duty MyoVa adopts a closed and autoinhibited state, which can be relieved by cargo binding. The molecular mechanisms governing the autoinhibition and activation of MyoVa remain unclear. Here, we report the cryo-electron microscopy structure of the two full-length, closed MyoVa heavy chains in complex with 12 calmodulin light chains at 4.78-Å resolution. The MyoVa adopts a triangular structure with multiple intra- and interpolypeptide chain interactions in establishing the closed state with cargo binding and adenosine triphosphatase activity inhibited. Structural, biochemical, and cellular analyses uncover an asymmetric autoinhibition mechanism, in which the cargo-binding sites in the two MyoVa heavy chains are differently protected. Thus, specific and efficient MyoVa activation requires coincident binding of multiple cargo adaptors, revealing an intricate and elegant activity regulation of the motor in response to cargos.

Mechanics and regulation of cytokinetic abscission

Cytokinetic abscission leads to the physical cut of the intercellular bridge (ICB) connecting the daughter cells and concludes cell division. In different animal cells, it is well established that the ESCRT-III machinery is responsible for the constriction and scission of the ICB. Here, we review the mechanical context of abscission. We first summarize the evidence that the ICB is initially under high tension and explain why, paradoxically, this can inhibit abscission in epithelial cells by impacting on ESCRT-III assembly. We next detail the different mechanisms that have been recently identified to release ICB tension and trigger abscission. Finally, we discuss whether traction-induced mechanical cell rupture could represent an ancient alternative mechanism of abscission and suggest future research avenues to further understand the role of mechanics in regulating abscission.

MICAL1 activation by PAK1 mediates actin filament disassembly

The MICAL1 monooxygenase is an important regulator of filamentous actin (F-actin) structures. Although MICAL1 has been shown to be regulated via protein-protein interactions at the autoinhibitory carboxyl terminus, a link between actin-regulatory RHO GTPase signaling pathways and MICAL1 has not been established. We show that the CDC42 GTPase effector PAK1 associates with and phosphorylates MICAL1 on two serine residues, leading to accelerated F-actin disassembly. PAK1 binds to the amino-terminal catalytic monooxygenase and calponin homology domains, distinct from the autoinhibitory carboxyl terminus. Extracellular ligand stimulation leads to PAK-dependent phosphorylation, linking external signals to MICAL1 phosphorylation. Mass spectrometry indicates that MICAL1 co-expression with CDC42 and PAK1 increases MICAL1 association with hundreds of proteins, including the previously described MICAL1-interacting proteins RAB10 and RAB7A. These results provide insights into a redox-mediated pathway linking extracellular signals to cytoskeleton regulation via a RHO GTPase and indicate a means of communication between RHO and RAB GTPases.

Cargo Recognition Mechanisms of Yeast Myo2 Revealed by AlphaFold2-Powered Protein Complex Prediction

Myo2, a yeast class V myosin, transports a broad range of organelles and plays important roles in various cellular processes, including cell division in budding yeast. Despite the fact that several structures of Myo2/cargo adaptor complexes have been determined, the understanding of the versatile cargo-binding modes of Myo2 is still very limited, given the large number of cargo adaptors identified for Myo2. Here, we used ColabFold, an AlphaFold2-powered and easy-to-use tool, to predict the complex structures of Myo2-GTD and its several cargo adaptors. After benchmarking the prediction strategy with three Myo2/cargo adaptor complexes that have been determined previously, we successfully predicted the atomic structures of Myo2-GTD in complex with another three cargo adaptors, Vac17, Kar9 and Pea2, which were confirmed by our biochemical characterizations. By systematically comparing the interaction details of the six complexes of Myo2 and its cargo adaptors, we summarized the cargo-binding modes on the three conserved sites of Myo2-GTD, providing an overall picture of the versatile cargo-recognition mechanisms of Myo2. In addition, our study demonstrates an efficient and effective solution to study protein-protein interactions in the future via the AlphaFold2-powered prediction.

Oxidation and reduction of actin: Origin, impact in vitro and functional consequences in vivo

Actin is among the most abundant proteins in eukaryotic cells and assembles into dynamic filamentous networks regulated by many actin binding proteins. The actin cytoskeleton must be finely tuned, both in space and time, to fulfill key cellular functions such as cell division, cell shape changes, phagocytosis and cell migration. While actin oxidation by reactive oxygen species (ROS) at non-physiological levels are known for long to impact on actin polymerization and on the cellular actin cytoskeleton, growing evidence shows that direct and reversible oxidation/reduction of specific actin amino acids plays an important and physiological role in regulating the actin cytoskeleton. In this review, we describe which actin amino acid residues can be selectively oxidized and reduced in many different ways (e.g. disulfide bond formation, glutathionylation, carbonylation, nitration, nitrosylation and other oxidations), the cellular enzymes at the origin of these post-translational modifications, and the impact of actin redox modifications both in vitro and in vivo. We show that the regulated balance of oxidation and reduction of key actin amino acid residues contributes to the control of actin filament polymerization and disassembly at the subcellular scale and highlight how improper redox modifications of actin can lead to pathological conditions.

Caveolae promote successful abscission by controlling intercellular bridge tension during cytokinesis

During cytokinesis, the intercellular bridge (ICB) connecting the daughter cells experiences pulling forces, which delay abscission by preventing the assembly of the ESCRT scission machinery. Abscission is thus triggered by tension release, but how ICB tension is controlled is unknown. Here, we report that caveolae, which are known to regulate membrane tension upon mechanical stress in interphase cells, are located at the midbody, at the abscission site, and at the ICB/cell interface in dividing cells. Functionally, the loss of caveolae delays ESCRT-III recruitment during cytokinesis and impairs abscission. This is the consequence of a twofold increase of ICB tension measured by laser ablation, associated with a local increase in myosin II activity at the ICB/cell interface. We thus propose that caveolae buffer membrane tension and limit contractibility at the ICB to promote ESCRT-III assembly and cytokinetic abscission. Together, this work reveals an unexpected connection between caveolae and the ESCRT machinery and the first role of caveolae in cell division.

MICAL1 inhibits colorectal cancer cell migration and proliferation by regulating the EGR1/β-catenin signaling pathway

MICAL1 has been reported to be involved in the malignant processes of several types of cancer cells, however, the roles of MICAL1 in colorectal cancer (CRC) have not been well-characterized. This study aims to investigate the cellular functions and molecular mechanisms of MICAL1 in CRC cells. Here, we found that both mRNA and protein levels of MICAL1 were down-regulated in colorectal cancer tissues compared with matched adjacent non-tumor tissues, and the expression level of MICAL1 was correlated with the metastatic status of colorectal cancer. Importantly, overexpression of MICAL1 significantly inhibited colorectal cancer cell migration and growth, and increased the level of E-cadherin and Occludin, and suppressed the expression level of Vimentin and N-cadherin; while silencing of MICAL1 promoted CRC cell migration and enhanced EMT. In addition, MICAL1 overexpression significantly inhibited the proliferation and growth of CRC in vitro and in vivo. Moreover, RNA sequencing and bioinformatics analysis identified that MICAL1 was closely correlated with "cell migration", "cell cycle" and "β-catenin signaling" genesets. Mechanistically, overexpression of MICAL1 downregulated the mRNA level of EGR1 and β-catenin, decreased the protein level and nuclear translocation of β-catenin, and inhibited the transcriptions of β-catenin downstream targets, c-myc and cyclin D1. The ectopic expression of EGR1 or β-catenin can significantly block the MICAL1-mediated inhibitory effects. Collectively, MICAL1 is down-regulated in CRC, and plays an inhibitory role in the migration and growth of CRC cells by suppressing the ERG1/β-catenin signaling pathway.

MICAL2 fine-tunes Arp2/3 for actin branching

The ARP2/3 complex promotes branched actin networks, but the importance of specific subunit isoforms is unclear. In this issue, Galloni, Carra, et al. (2021. J. Cell Biol. https://doi.org/10.1083/jcb.202102043) show that MICAL2 mediates methionine oxidation of ARP3B, thus destabilizing ARP2/3 complexes and leading to disassembly of branched actin filaments.

Propagation of F-actin disassembly via Myosin15-Mical interactions

The F-actin cytoskeleton drives cellular form and function. However, how F-actin-based changes occur with spatiotemporal precision and specific directional orientation is poorly understood. Here, we identify that the unconventional class XV myosin [Myosin 15 (Myo15)] physically and functionally interacts with the F-actin disassembly enzyme Mical to spatiotemporally position cellular breakdown and reconstruction. Specifically, while unconventional myosins have been associated with transporting cargo along F-actin to spatially target cytoskeletal assembly, we now find they also target disassembly. Myo15 specifically positions this F-actin disassembly by associating with Mical and using its motor and MyTH4-FERM cargo-transporting functions to broaden Mical's distribution. Myo15's broadening of Mical's distribution also expands and directionally orients Mical-mediated F-actin disassembly and subsequent cellular remodeling, including in response to Semaphorin/Plexin cell surface activation signals. Thus, we identify a mechanism that spatiotemporally propagates F-actin disassembly while also proposing that other F-actin-trafficked-cargo is derailed by this disassembly to directionally orient rebuilding.

RAB11-Mediated Trafficking and Human Cancers: An Updated Review

Simple Summary

The small GTPase RAB11 is a master regulator of both vesicular trafficking and membrane dynamic defining the surface proteome of cellular membranes. As a consequence, the alteration of RAB11 activity induces changes in both the sensory and the transduction apparatuses of cancer cells leading to tumor progression and invasion. Here, we show that this strictly depends on RAB11′s ability to control the sorting of signaling receptors from endosomes. Therefore, RAB11 is a potential therapeutic target over which to develop future therapies aimed at dampening the acquisition of aggressive traits by cancer cells.

Abstract

Many disorders block and subvert basic cellular processes in order to boost their progression. One protein family that is prone to be altered in human cancers is the small GTPase RAB11 family, the master regulator of vesicular trafficking. RAB11 isoforms function as membrane organizers connecting the transport of cargoes towards the plasma membrane with the assembly of autophagic precursors and the generation of cellular protrusions. These processes dramatically impact normal cell physiology and their alteration significantly affects the survival, progression and metastatization as well as the accumulation of toxic materials of cancer cells. In this review, we discuss biological mechanisms ensuring cargo recognition and sorting through a RAB11-dependent pathway, a prerequisite to understand the effect of RAB11 alterations in human cancers.

Roles and regulation of myosin V interaction with cargo

A major question in cell biology is, how are organelles and large macromolecular complexes transported within a cell? Myosin V molecular motors play critical roles in the distribution of organelles, vesicles, and mRNA. Mis-localization of organelles that depend on myosin V motors underlie diseases in the skin, gut, and brain. Thus, the delivery of organelles to their proper destination is important for animal physiology and cellular function. Cargoes attach to myosin V motors via cargo specific adaptor proteins, which transiently bridge motors to their cargoes. Regulation of these adaptor proteins play key roles in the regulation of cargo transport. Emerging studies reveal that cargo adaptors play additional essential roles in the activation of myosin V, and the regulation of actin filaments. Here, we review how motor-adaptor interactions are controlled to regulate the proper loading and unloading of cargoes, as well as roles of adaptor proteins in the regulation of myosin V activity and the dynamics of actin filaments.