Myosin II isoforms promote internalization of spatially distinct clathrin-independent endocytosis cargoes through modulation of cortical tension downstream of ROCK2

Prickle2 regulates apical junction remodeling and tissue fluidity during vertebrate neurulation

The process of folding the flat neuroectoderm into an elongated neural tube depends on tissue fluidity, a property that allows epithelial deformation while preserving tissue integrity. Neural tube folding also requires the planar cell polarity (PCP) pathway. Here, we report that Prickle2 (Pk2), a core PCP component, increases tissue fluidity by promoting the remodeling of apical junctions (AJs) in Xenopus embryos. This Pk2 activity is mediated by the unique evolutionarily conserved Ser/Thr-rich region (STR) in the carboxyterminal half of the protein. Mechanistically, the effects of Pk2 require Rac1 and are accompanied by increased dynamics of C-cadherin and tricellular junctions, the hotspots of AJ remodeling. Notably, Pk2 depletion leads to the accumulation of mediolaterally oriented cells in the neuroectoderm, whereas the overexpression of Pk2 or Pk1 containing the Pk2-derived STR promotes cell elongation along the anteroposterior axis. We propose that Pk2-dependent regulation of tissue fluidity contributes to anteroposterior tissue elongation in response to extrinsic cues.

VopX, a novel Vibrio cholerae T3SS effector, modulates host actin dynamics

Pathogenic Vibrio cholerae strains cause cholera using different mechanisms. O1 and O139 serogroup strains use the toxin-co-regulated pilus (TCP) and cholera toxin (CT) for intestinal colonization and to promote secretory diarrhea, while non-O1/non-O139 serogroup strains are typically non-toxigenic and use alternate virulence factors to cause a clinically similar disease. An O39 serogroup, TCP/CT-negative V. cholerae strain, named AM-19226, uses a type III secretion system (T3SS) to translocate more than 10 effector proteins into the host cell cytosol. Effectors VopF and VopM directly interact with the host actin and contribute to colonization. Our previous studies using the Saccharomyces cerevisiae model system identified VopX as a third effector that alters cytoskeletal dynamics. Herein, we used complementary approaches to translate yeast findings to a mammalian system and determined the target and mechanism of VopX activity. VopX overexpression in HeLa cells caused dramatic cell rounding. Co-culture of strain AM-19226 with polarized Caco-2/BBE monolayers increased formation of stress fibers and focal adhesions, as well as Caco-2/BBE adherence to extracellular matrix in a VopX-dependent manner. Finally, we demonstrate in vitro that VopX can act as a guanine nucleotide exchange factor for RhoA, which functions upstream of a mitogen-activated protein kinase (MAPK) signaling pathway regulating cytoskeletal dynamics. Our results suggest that VopX activity initiates a signaling cascade resulting in enhanced cell-extracellular matrix adhesion, potentially preventing detachment of host cells, and facilitating sustained bacterial colonization during infection. VopX function is therefore part of a unique pathogenic strategy employed by T3SS-positive V. cholerae, which involves multiple cytoskeletal remodeling mechanisms to support a productive infection.

IMPORTANCE

Despite different infection strategies, enteric pathogens commonly employ a T3SS to colonize the human host and cause disease. Effector proteins are unique to each T3SS-encoding bacterial species and generally lack conserved amino acid sequences. However, T3SS effectors from diverse pathogens target and manipulate common host cell structures and signaling proteins, such as the actin cytoskeleton and MAPK pathway components. T3SS-encoding Vibrio cholerae strains and effectors have been relatively recently identified, and the mechanisms used to mediate colonization and secretory diarrhea are poorly understood. Two V. cholerae effectors that modify the host actin cytoskeleton were shown to be important for colonization. We therefore sought to determine the target(s) and mechanism of a third actin-reorganizing effector, VopX, based on results obtained from a yeast model system. We recapitulated actin-based phenotypes in multiple mammalian model systems, leading us to identify the molecular function of the V. cholerae VopX effector protein.

Fasudil inhibits α-synuclein aggregation through ROCK-inhibition-mediated mechanisms

ROCK inhibitors such as fasudil protected against dopaminergic degeneration and other neurodegenerative processes in several experimental models through inhibition of neuroinflammation and activation of survival signaling pathways, and clinical trials have been initiated. More recently, fasudil has been suggested to inhibit α-synuclein aggregation. However, this is controversial, particularly if it is a consequence of direct binding of the fasudil molecule to α-synuclein. We studied the mechanisms involved in the effects of fasudil on α-synuclein aggregation using the α-synuclein-T/V5-synphilin-1 model. Molecule-molecule interactions were studied using real time quaking inducing conversion (RT-QuiC). Fasudil decreased the number of cells with inclusions and the size of inclusions in dopaminergic neurons and glial cells, and inhibited α-synuclein aggregation and microglial endocytosis of aggregates. These changes were not due to changes in α-synuclein protein expression or phosphorylation and were related to ROCK inhibition rather than direct interaction with α-synuclein, as confirmed with a second ROCK inhibitor (Y27632) and ROCK gene silencing. We observed that ROCK inhibition downregulates several factors that are known to promote α-synuclein aggregation such as NADPH-oxidase-derived oxidative stress, intracellular calcium increase, and α-synuclein endocytosis, and promotes autophagy. The present results support that fasudil is a useful drug against Parkinson's disease progression. In addition to other reported neuroprotective properties, fasudil inhibits α-synuclein aggregation and microglial endocytosis of aggregates, which enhances the microglial inflammatory response. The effects of fasudil are mostly related to ROCK inhibition, which we have shown using two structurally different ROCK inhibitors and knockdown data, and further supported by using RT-QuiC.

Arp2/3 mediated dynamic lamellipodia of the hPSC colony edges promote liposome-based DNA delivery

Cationic liposome-mediated delivery of drugs, DNA, or RNA plays a pivotal role in small molecule therapy, gene editing, and immunization. However, our current knowledge regarding the cellular structures that facilitate this process remains limited. Here, we used human pluripotent stem cells (hPSCs), which form compact colonies consisting of dynamically active cells at the periphery and epithelial-like cells at the core. We discovered that cells at the colony edges selectively got transfected by cationic liposomes through actin-related protein 2/3 (Arp2/3) dependent dynamic lamellipodia, which is augmented by myosin II inhibition. Conversely, cells at the core establish tight junctions at their apical surfaces, impeding liposomal access to the basal lamellipodia and thereby inhibiting transfection. In contrast, liposomes incorporating mannosylated lipids are internalized throughout the entire colony via receptor-mediated endocytosis. These findings contribute a novel mechanistic insight into enhancing therapeutic delivery via liposomes, particularly in cell types characterized by dynamic lamellipodia, such as immune cells or those comprising the epithelial layer.

MT-125 Inhibits Non-Muscle Myosin IIA and IIB, Synergizes with Oncogenic Kinase Inhibitors, and Prolongs Survival in Glioblastoma

We have identified a NMIIA and IIB-specific small molecule inhibitor, MT-125, and have studied its effects in GBM. MT-125 has high brain penetrance and retention and an excellent safety profile; blocks GBM invasion and cytokinesis, consistent with the known roles of NMII; and prolongs survival as a single agent in murine GBM models. MT-125 increases signaling along both the PDGFR- and MAPK-driven pathways through a mechanism that involves the upregulation of reactive oxygen species, and it synergizes with FDA-approved PDGFR and mTOR inhibitors in vitro . Combining MT-125 with sunitinib, a PDGFR inhibitor, or paxalisib, a combined PI3 Kinase/mTOR inhibitor significantly improves survival in orthotopic GBM models over either drug alone, and in the case of sunitinib, markedly prolongs survival in ∼40% of mice. Our results provide a powerful rationale for developing NMII targeting strategies to treat cancer and demonstrate that MT-125 has strong clinical potential for the treatment of GBM.

Highlights

MT-125 is a highly specific small molecule inhibitor of non-muscle myosin IIA and IIB, is well-tolerated, and achieves therapeutic concentrations in the brain with systemic dosing.Treating preclinical models of glioblastoma with MT-125 produces durable improvements in survival.MT-125 stimulates PDGFR- and MAPK-driven signaling in glioblastoma and increases dependency on these pathways.Combining MT-125 with an FDA-approved PDGFR inhibitor in a mouse GBM model synergizes to improve median survival over either drug alone, and produces tumor free, prolonged survival in over 40% of mice.

SCRIB controls apical contractility during epithelial differentiation

Although mutations in the SCRIB gene lead to multiple morphological organ defects in vertebrates, the molecular pathway linking SCRIB to organ shape anomalies remains elusive. Here, we study the impact of SCRIB-targeted gene mutations during the formation of the gut epithelium in an organ-on-chip model. We show that SCRIB KO gut-like epithelia are flatter with reduced exposed surface area. Cell differentiation on filters further shows that SCRIB plays a critical role in the control of apical cell shape, as well as in the basoapical polarization of myosin light chain localization and activity. Finally, we show that SCRIB serves as a molecular scaffold for SHROOM2/4 and ROCK1 and identify an evolutionary conserved SHROOM binding site in the SCRIB carboxy-terminal that is required for SCRIB function in the control of apical cell shape. Our results demonstrate that SCRIB plays a key role in epithelial morphogenesis by controlling the epithelial apical contractility during cell differentiation.

Actin-dependent recruitment of AGO2 to the zonula adherens

Adherens junctions are cadherin-based structures critical for cellular architecture. E-cadherin junctions in mature epithelial cell monolayers tether to an apical actomyosin ring to form the zonula adherens (ZA). We have previously shown that the adherens junction protein PLEKHA7 associates with and regulates the function of the core RNA interference (RNAi) component AGO2 specifically at the ZA. However, the mechanism mediating AGO2 recruitment to the ZA remained unexplored. Here, we reveal that this ZA-specific recruitment of AGO2 depends on both the structural and tensile integrity of the actomyosin cytoskeleton. We found that depletion of not only PLEKHA7, but also either of the three PLEKHA7-interacting, LIM-domain family proteins, namely LMO7, LIMCH1, and PDLIM1, results in disruption of actomyosin organization and tension, as well as disruption of AGO2 junctional localization and of its miRNA-binding ability. We also show that AGO2 binds Myosin IIB and that PLEKHA7, LMO7, LIMCH1, and PDLIM1 all disrupt interaction of AGO2 with Myosin IIB at the ZA. These results demonstrate that recruitment of AGO2 to the ZA is sensitive to actomyosin perturbations, introducing the concept of mechanosensitive RNAi machinery, with potential implications in tissue remodeling and in disease.

MYL3 protects chondrocytes from senescence by inhibiting clathrin-mediated endocytosis and activating of Notch signaling

As the unique cell type in articular cartilage, chondrocyte senescence is a crucial cellular event contributing to osteoarthritis development. Here we show that clathrin-mediated endocytosis and activation of Notch signaling promotes chondrocyte senescence and osteoarthritis development, which is negatively regulated by myosin light chain 3. Myosin light chain 3 (MYL3) protein levels decline sharply in senescent chondrocytes of cartilages from model mice and osteoarthritis (OA) patients. Conditional deletion of Myl3 in chondrocytes significantly promoted, whereas intra-articular injection of adeno-associated virus overexpressing MYL3 delayed, OA progression in male mice. MYL3 deficiency led to enhanced clathrin-mediated endocytosis by promoting the interaction between myosin VI and clathrin, further inducing the internalization of Notch and resulting in activation of Notch signaling in chondrocytes. Pharmacologic blockade of clathrin-mediated endocytosis-Notch signaling prevented MYL3 loss-induced chondrocyte senescence and alleviated OA progression in male mice. Our results establish a previously unknown mechanism essential for cellular senescence and provide a potential therapeutic direction for OA.

ROCK inhibition enhanced hepatocyte liver engraftment by retaining membrane CD59 and attenuating complement activation

Hepatocyte transplantation can be an effective treatment for patients with certain liver-based metabolic disorders and liver injuries. Hepatocytes are usually infused into the portal vein, from which hepatocytes migrate into the liver and integrate into the liver parenchyma. However, early cell loss and poor liver engraftment represent major hurdles to sustaining the recovery of diseased livers after transplantation. In the present study, we found that ROCK (Rho-associated kinase) inhibitors significantly enhanced in vivo hepatocyte engraftment. Mechanistic studies suggested that the isolation of hepatocytes caused substantial degradation of cell membrane proteins, including the complement inhibitor CD59, probably due to shear stress-induced endocytosis. ROCK inhibition by ripasudil, a clinically used ROCK inhibitor, can protect transplanted hepatocytes by retaining cell membrane CD59 and blocking the formation of the membrane attack complex. Knockdown of CD59 in hepatocytes eliminates ROCK inhibition-enhanced hepatocyte engraftment. Ripasudil can accelerate liver repopulation of fumarylacetoacetate hydrolase-deficient mice. Our work reveals a mechanism underlying hepatocyte loss after transplantation and provides immediate strategies to enhance hepatocyte engraftment by inhibiting ROCK.

Nanoparticle Spikes Enhance Cellular Uptake via Regulating Myosin IIA Recruitment

Spike-like nanostructures are omnipresent in natural and artificial systems. Although biorecognition of nanostructures to cellular receptors has been indicated as the primary factor for virus infection pathways, how the spiky morphology of DNA-modified nanoparticles affects their cellular uptake and intracellular fate remains to be explored. Here, we design dually emissive gold nanoparticles with varied spikiness (from 0 to 2) to probe the interactions of spiky nanoparticles with cells. We discovered that nanospikes at the nanoparticle regulated myosin IIA recruitment at the cell membrane during cellular uptake, thereby enhancing cellular uptake efficiency, as revealed by dual-modality (plasmonic and fluorescence) imaging. Furthermore, the spiky nanoparticles also exhibited facilitated endocytosis dynamics, as revealed by real-time dark-field microscopy (DFM) imaging and colorimetry-based classification algorithms. These findings highlight the crucial role of the spiky morphology in regulating the intracellular fate of nanoparticles, which may shed light on engineering theranostic nanocarriers.

Endosomal sorting sorted - motors, adaptors and lessons from in vitro and cellular studies

Motor proteins are key players in exerting spatiotemporal control over the intracellular location of membrane-bound compartments, including endosomes containing cargo. In this Review, we focus on how motors and their cargo adaptors regulate positioning of cargoes from the earliest stages of endocytosis and through the two main intracellular itineraries: (1) degradation at the lysosome or (2) recycling back to the plasma membrane. In vitro and cellular (in vivo) studies on cargo transport thus far have typically focussed independently on either the motor proteins and adaptors, or membrane trafficking. Here, we will discuss recent studies to highlight what is known about the regulation of endosomal vesicle positioning and transport by motors and cargo adaptors. We also emphasise that in vitro and cellular studies are often performed at different scales, from single molecules to whole organelles, with the aim to provide a perspective on the unified principles of motor-driven cargo trafficking in living cells that can be learned from these differing scales.

Assembly and disassembly dynamics of nonmuscle myosin II control endosomal fission

Endocytic vesicular trafficking requires merging of two lipid bilayers, but how the two lipid bilayers can come close together during fusion and fission in endocytic trafficking is not well explored. Here, we establish that knocking down nonmuscle myosin IIs (NM IIs) by small interfering RNA (siRNA) or inhibition of their activities by (-) blebbistatin causes the formation of a ring-like assembly of early endosomes (raEE). Inhibition of NM II assembly by an inhibitor of regulatory light-chain (RLC) kinase results in the formation of raEE, whereas inhibition of NM II disassembly by inhibitors of heavy chain kinases, protein kinase C (PKC) and casein kinase 2 (CK2), causes the dispersion of early endosomes. The raEEs retain EEA1, Rab7, and LAMP2 markers. Overexpression of an assembly incompetent form, RLC-AA, and disassembly incompetent form, NMHCIIB-S6A or NMHCIIA-1916A, induces such defects, respectively. Altogether, these data support that NM II assembly and disassembly dynamics participate in endocytic trafficking by regulating fission to maintain the size of early endosomes.

Coronin2A links actin-based endosomal processes to the EHD1 fission machinery

Fission of transport vesicles from endosomes is a crucial step in the recycling of lipids and receptors to the plasma membrane, but this process remains poorly understood. Although key components of the fission machinery, including the actin cytoskeleton and the ATPase Eps15 homology domain protein 1 (EHD1), have been implicated in endosomal fission, how this process is coordinately regulated is not known. We have identified the actin regulatory protein Coronin2A (CORO2A) as a novel EHD1 interaction partner. CORO2A localizes to stress fibers and actin microfilaments but also can be observed in partial overlap with EHD1 on endosomal structures. siRNA knockdown of CORO2A led to enlarged lamellae-like actin-rich protrusions, consistent with a role of other Coronin family proteins in attenuating actin-branching. Moreover, CORO2A depletion also caused a marked decrease in the internalization of clathrin-dependent cargo but had little impact on the uptake of clathrin-independent cargo, highlighting key differences in the role of branched actin for different modes of endocytosis. However, CORO2A was required for recycling of clathrin-independent cargo, and its depletion led to enlarged endosomes, supporting a role for CORO2A in the fission of endosomal vesicles. Our data support a novel role for CORO2A in coordinating endosomal fission and recycling with EHD1. [Media: see text].

Rac1, actin cytoskeleton and microtubules are key players in clathrin-independent endophilin-A3-mediated endocytosis

Endocytic mechanisms actively regulate plasma membrane composition and sustain fundamental cellular functions. Recently, we identified a clathrin-independent endocytic (CIE) modality mediated by the BAR domain protein endophilin-A3 (endoA3), which controls the cell surface homeostasis of the tumor marker CD166/ALCAM. Deciphering the molecular machinery of endoA3-dependent CIE should therefore contribute to a better understanding of its pathophysiological role, which remains so far unknown. Here, we investigate the role in this mechanism of actin, Rho GTPases and microtubules, which are major actors of CIE processes. We show that the actin cytoskeleton is dynamically associated with endoA3- and CD166-positive endocytic carriers and that its perturbation strongly inhibits the uptake process of CD166. We also reveal that the Rho GTPase Rac1, but not Cdc42, is a master regulator of this endocytic route. Finally, we provide evidence that microtubules and kinesin molecular motors are required to potentiate endoA3-dependent endocytosis. Of note, our study also highlights potential compensation phenomena between endoA3-dependent CIE and macropinocytosis. Altogether, our data deepen our understanding of this CIE modality and further differentiate it from other unconventional endocytic mechanisms.

Pancreatic Ductal Adenocarcinoma Cortical Mechanics and Clinical Implications

Pancreatic ductal adenocarcinoma (PDAC) remains one of the deadliest cancers due to low therapeutic response rates and poor prognoses. Majority of patients present with symptoms post metastatic spread, which contributes to its overall lethality as the 4th leading cause of cancer-related deaths. Therapeutic approaches thus far target only one or two of the cancer specific hallmarks, such as high proliferation rate, apoptotic evasion, or immune evasion. Recent genomic discoveries reveal that genetic heterogeneity, early micrometastases, and an immunosuppressive tumor microenvironment contribute to the inefficacy of current standard treatments and specific molecular-targeted therapies. To effectively combat cancers like PDAC, we need an innovative approach that can simultaneously impact the multiple hallmarks driving cancer progression. Here, we present the mechanical properties generated by the cell’s cortical cytoskeleton, with a spotlight on PDAC, as an ideal therapeutic target that can concurrently attack multiple systems driving cancer. We start with an introduction to cancer cell mechanics and PDAC followed by a compilation of studies connecting the cortical cytoskeleton and mechanical properties to proliferation, metastasis, immune cell interactions, cancer cell stemness, and/or metabolism. We further elaborate on the implications of these findings in disease progression, therapeutic resistance, and clinical relapse. Manipulation of the cancer cell’s mechanical system has already been shown to prevent metastasis in preclinical models, but it has greater potential for target exploration since it is a foundational property of the cell that regulates various oncogenic behaviors.