Mouse macrophages completely lacking Rho subfamily GTPases (RhoA, RhoB, and RhoC) have severe lamellipodial retraction defects, but robust chemotactic navigation and altered motility

RHO subfamily of small GTPases in the development and function of hematopoietic cells

RHOA, RHOB, and RHOC comprise a subfamily of RHO GTPase proteins famed for controlling cytoskeletal dynamics. RHO proteins operate downstream of multiple signals emerging from the microenvironment, leading to diverse cell responses, such as proliferation, adhesion, and migration. Therefore, RHO signaling has been centrally placed in the regulation of blood cells. Despite their high homology, unique roles of RHOA, RHOB, and RHOC have been described in hematopoietic cells. In this article, we overview the contribution of RHO proteins in the development and function of each blood cell lineage. Additionally, we highlight the aberrations of the RHO signaling pathways found in hematological malignancies, providing clues for the identification of new therapeutic targets.

Mononuclear phagocyte morphological response to chemoattractants is dependent on geranylgeranyl pyrophosphate

Statins are used to treat hypercholesterolemia and function by inhibiting the production of the rate-limiting metabolite mevalonate. As such, statin treatment not only inhibits de novo synthesis of cholesterol but also isoprenoids that are involved in prenylation, the posttranslational lipid modification of proteins. The immunomodulatory effects of statins are broad and often conflicting. Previous work demonstrated that statins increased survival and inhibited myeloid cell trafficking in a murine model of sepsis, but the exact mechanisms underlying this phenomenon were unclear. Herein, we investigated the role of prenylation in chemoattractant responses. We found that simvastatin treatment abolished chemoattractant responses induced by stimulation by C5a and FMLP. The inhibitory effect of simvastatin treatment was unaffected by the addition of either farnesyl pyrophosphate (FPP) or squalene but was reversed by restoring geranylgeranyl pyrophosphate (GGPP). Treatment with prenyltransferase inhibitors showed that the chemoattractant response to both chemoattractants was dependent on geranylgeranylation. Proteomic analysis of C15AlkOPP-prenylated proteins identified several geranylgeranylated proteins involved in chemoattractant responses, including RHOA, RAC1, CDC42, and GNG2. Chemoattractant responses in THP-1 human macrophages were also geranylgeranylation dependent. These studies provide data that help clarify paradoxical findings on the immunomodulatory effects of statins. Furthermore, they establish the role of geranylgeranylation in mediating the morphological response to chemoattractant C5a.NEW & NOTEWORTHY The immunomodulatory effect of prenylation is ill-defined. We investigated the role of prenylation on the chemoattractant response to C5a. Simvastatin treatment inhibits the cytoskeletal remodeling associated with a chemotactic response. We showed that the chemoattractant response to C5a was dependent on geranylgeranylation, and proteomic analysis identified several geranylgeranylated proteins that are involved in C5a receptor signaling and cytoskeletal remodeling. Furthermore, they establish the role of geranylgeranylation in mediating the response to chemoattractant C5a.

Novel cardiovascular protective effects of RhoA signaling and its therapeutic implications

Ras homolog gene family member A (RhoA) belongs to the Rho GTPase superfamily, which was first studied in cancers as one of the essential regulators controlling cellular function. RhoA has long attracted attention as a key molecule involved in cell signaling and gene transcription, through which it affects cellular processes. A series of studies have demonstrated that RhoA plays crucial roles under both physiological states and pathological conditions in cardiovascular diseases. RhoA has been identified as an important regulator in cardiac remodeling by regulating actin stress fiber dynamics and cytoskeleton formation. However, its underlying mechanisms remain poorly understood, preventing definitive conclusions being drawn about its protective role in the cardiovascular system. In this review, we outline the characteristics of RhoA and its related signaling molecules, and present an overview of RhoA classical function and the corresponding cellular responses of RhoA under physiological and pathological conditions. Overall, we provide an update on the novel signaling under RhoA in the cardiovascular system and its potential clinical and therapeutic targets in cardiovascular medicine.

Migration and differentiation of muscle stem cells are coupled by RhoA signalling during regeneration

Skeletal muscle is highly regenerative and is mediated by a population of migratory adult muscle stem cells (muSCs). Effective muscle regeneration requires a spatio-temporally regulated response of the muSC population to generate sufficient muscle progenitor cells that then differentiate at the appropriate time. The relationship between muSC migration and cell fate is poorly understood and it is not clear how forces experienced by migrating cells affect cell behaviour. We have used zebrafish to understand the relationship between muSC cell adhesion, behaviour and fate in vivo. Imaging of pax7-expressing muSCs as they respond to focal injuries in trunk muscle reveals that they migrate by protrusive-based means. By carefully characterizing their behaviour in response to injury we find that they employ an adhesion-dependent mode of migration that is regulated by the RhoA kinase ROCK. Impaired ROCK activity results in reduced expression of cell cycle genes and increased differentiation in regenerating muscle. This correlates with changes to focal adhesion dynamics and migration, revealing that ROCK inhibition alters the interaction of muSCs to their local environment. We propose that muSC migration and differentiation are coupled processes that respond to changes in force from the environment mediated by RhoA signalling.

Methylated dialkylphosphate metabolites of the organophosphate pesticide malathion modify actin cytoskeleton arrangement and cell migration via activation of Rho GTPases Rac1 and Cdc42

The non-cholinergic molecular targets of organophosphate (OP) compounds have recently been investigated to explain their role in the generation of non-neurological diseases, such as immunotoxicity and cancer. Here, we evaluated the effects of malathion and its dialkylphosphate (DAP) metabolites on the cytoskeleton components and organization of RAW264.7 murine macrophages as non-cholinergic targets of OP and DAPs toxicity. All OP compounds affected actin and tubulin polymerization. Malathion, dimethyldithiophosphate (DMDTP) dimethylthiophosphate (DMTP), and dimethylphosphate (DMP) induced elongated morphologies and the formation of pseudopods rich in microtubule structures, and increased filopodia formation and general actin disorganization in RAW264.7 cells and slightly reduced stress fibers in the human fibroblasts GM03440, without significantly disrupting the tubulin or vimentin cytoskeleton. Exposure to DMTP and DMP increased cell migration in the wound healing assay but did not affect phagocytosis, indicating a very specific modification in the organization of the cytoskeleton. The induction of actin cytoskeleton rearrangement and cell migration suggested the activation of cytoskeletal regulators such as small GTPases. We found that DMP slightly reduced Ras homolog family member A activity but increased the activities of Ras-related C3 botulinum toxin substrate 1 (Rac1) and cell division control protein 42 (Cdc42) from 5 min to 2 h of exposure. Chemical inhibition of Rac1 with NSC23766 reduced cell polarization and treatment with DMP enhanced cell migration, but Cdc42 inhibition by ML-141 completely inhibited the effects of DMP. These results suggest that methylated OP compounds, especially DMP, can modify macrophage cytoskeleton function and configuration via activation of Cdc42, which may represent a potential non-cholinergic molecular target for OP compounds.

RHOA Therapeutic Targeting in Hematological Cancers

Primarily identified as an important regulator of cytoskeletal dynamics, the small GTPase Ras homolog gene family member A (RHOA) has been implicated in the transduction of signals regulating a broad range of cellular functions such as cell survival, migration, adhesion and proliferation. Deregulated activity of RHOA has been linked to the growth, progression and metastasis of various cancer types. Recent cancer genome-wide sequencing studies have unveiled both RHOA gain and loss-of-function mutations in primary leukemia/lymphoma, suggesting that this GTPase may exert tumor-promoting or tumor-suppressive functions depending on the cellular context. Based on these observations, RHOA signaling represents an attractive therapeutic target for the development of selective anticancer strategies. In this review, we will summarize the molecular mechanisms underlying RHOA GTPase functions in immune regulation and in the development of hematological neoplasms and will discuss the current strategies aimed at modulating RHOA functions in these diseases.

Impaired microtubule dynamics contribute to microthrombocytopenia in RhoB-deficient mice

Megakaryocytes are large cells in the bone marrow that give rise to blood platelets. Platelet biogenesis involves megakaryocyte maturation, the localization of the mature cells in close proximity to bone marrow sinusoids, and the formation of protrusions, which are elongated and shed within the circulation. Rho GTPases play important roles in platelet biogenesis and function. RhoA-deficient mice display macrothrombocytopenia and a striking mislocalization of megakaryocytes into bone marrow sinusoids and a specific defect in G-protein signaling in platelets. However, the role of the closely related protein RhoB in megakaryocytes or platelets remains unknown. In this study, we show that, in contrast to RhoA deficiency, genetic ablation of RhoB in mice results in microthrombocytopenia (decreased platelet count and size). RhoB-deficient platelets displayed mild functional defects predominantly upon induction of the collagen/glycoprotein VI pathway. Megakaryocyte maturation and localization within the bone marrow, as well as actin dynamics, were not affected in the absence of RhoB. However, in vitro-generated proplatelets revealed pronouncedly impaired microtubule organization. Furthermore, RhoB-deficient platelets and megakaryocytes displayed selective defects in microtubule dynamics/stability, correlating with reduced levels of acetylated α-tubulin. Our findings imply that the reduction of this tubulin posttranslational modification results in impaired microtubule dynamics, which might contribute to microthrombocytopenia in RhoB-deficient mice. Importantly, we demonstrate that RhoA and RhoB are localized differently and have selective, nonredundant functions in the megakaryocyte lineage.

Plasmodium berghei-Released Factor, PbTIP, Modulates the Host Innate Immune Responses

The Plasmodium parasite has to cross various immunological barriers for successful infection. Parasites have evolved mechanisms to evade host immune responses, which hugely contributes to the successful infection and transmission by parasites. One way in which a parasite evades immune surveillance is by expressing molecular mimics of the host molecules in order to manipulate the host responses. In this study, we report a Plasmodium berghei hypothetical protein, PbTIP (PbANKA_124360.0), which is a Plasmodium homolog of the human T-cell immunomodulatory protein (TIP). The latter possesses immunomodulatory activities and suppressed the host immune responses in a mouse acute graft-versus-host disease (GvHD) model. The Plasmodium berghei protein, PbTIP, is expressed on the merozoite surface and exported to the host erythrocyte surface upon infection. It is shed in the blood circulation by the activity of an uncharacterized membrane protease(s). The shed PbTIP could be detected in the host serum during infection. Our results demonstrate that the shed PbTIP exhibits binding on the surface of macrophages and reduces their inflammatory cytokine response while upregulating the anti-inflammatory cytokines such as TGF-β and IL-10. Such manipulated immune responses are observed in the later stage of malaria infection. PbTIP induced Th2-type gene transcript changes in macrophages, hinting toward its potential to regulate the host immune responses against the parasite. Therefore, this study highlights the role of a Plasmodium-released protein, PbTIP, in immune evasion using macrophages, which may represent the critical strategy of the parasite to successfully survive and thrive in its host. This study also indicates the human malaria parasite TIP as a potential diagnostic molecule that could be exploited in lateral flow-based immunochromatographic tests for malaria disease diagnosis.

Temporal Quantitative Phosphoproteomics Profiling of Interleukin-33 Signaling Network Reveals Unique Modulators of Monocyte Activation

Interleukin-33 (IL-33), a member of the IL-1 superfamily cytokines, is an endogenous danger signal and a nuclear-associated cytokine. It is one of the essential mediators of both innate and adaptive immune responses. Aberrant IL-33 signaling has been demonstrated to play a defensive role against various infectious and inflammatory diseases. Although the signaling responses mediated by IL-33 have been previously reported, the temporal signaling dynamics are yet to be explored. To this end, we applied quantitative temporal phosphoproteomics analysis to elucidate pathways and proteins induced by IL-33 in THP-1 monocytes. Employing a TMT labeling-based quantitation and titanium dioxide (TiO₂)-based phosphopeptide enrichment strategy followed by mass spectrometry analysis, we identified and quantified 9448 unique phosphopeptides corresponding to 3392 proteins that showed differential regulation. Of these, 171 protein kinases, 60 phosphatases and 178 transcription factors were regulated at different phases of IL-33 signaling. In addition to the confirmed activation of canonical signaling modules including MAPK, NFκB, PI3K/AKT modules, pathway analysis of the time-dependent phosphorylation dynamics revealed enrichment of several cellular processes, including leukocyte adhesion, response to reactive oxygen species, cell cycle checkpoints, DNA damage and repair pathways. The detailed quantitative phosphoproteomic map of IL-33 signaling will serve as a potentially useful resource to study its function in the context of inflammatory and pathological conditions.

Rho signaling inhibition mitigates lung injury via targeting neutrophil recruitment and selectin-AKT signaling

Neutrophils, the early responders of the immune system, eliminate intruders, but their over-activation can also instigate tissue damage leading to various autoimmune and inflammatory disease conditions. As approaches causing neutropenia are associated with immunodeficiency, targeting aberrant neutrophil infiltration offers an attractive strategy in neutrophil-centered diseases including acute lung injury. Rho GTPase family proteins Rho, Rac and Cdc42 play important role as regulators of chemotaxis in diverse systems. Rho inhibitors protected against lung injuries, while genetic Rho-deficiency exhibited neutrophil hyperactivity and exacerbated lung injury. These differential outcomes might be due to distinct effects on different cell types or activation/ inhibition of specific signaling pathways responsible for neutrophil polarity, migration and functions. In this study, we explored neutrophil centric effects of Rho signaling mitigation. Consistent with previous reports, Rho signaling inhibitor Y-27632 provided protection against acute lung injury, but without regulating LPS mediated systemic increase of neutrophils in the circulation. Interestingly, the adoptive transfer approach identified a specific defect in neutrophil migration capacity after Rho signaling mitigation. These defects were associated with loss of polarity and altered actin dynamics identified using time-lapse in vitro studies. Further analysis revealed a rescue of stimulation-dependent L-selectin shedding on neutrophils with Rho signaling inhibitor. Surprisingly, functional blocking of L-selectin (CD62L) led to defective recruitment of neutrophils into inflamed lungs. Further, single-cell level analyses identified MAPK signaling as downstream mechanism of Rho signaling and L-selectin mediated effects. p-AKT levels were diminished in detergent resistance membrane-associated signalosome upon Rho signaling inhibition and blockade of selectin. Moreover, inhibition of AKT signaling as well as selectin blocking led to defects in neutrophil polarity. Together, this study identified Rho-dependent distinct L-selectin and AKT signaling mediated regulation of neutrophil recruitment to inflamed lung tissue.

Thiopurines correct the effects of autophagy impairment on intestinal healing - a potential role for ARHGAP18/RhoA

The ATG16L1 T300A single-nucleotide polymorphism (SNP) is associated with Crohn's disease and causes an autophagy impairment. We have previously shown that this SNP is involved in the migration and hyperactivation of Rac1 in dendritic cells. Mucosal healing, currently the main target for inflammatory bowel disease treatment, depends on restoration of the epithelial barrier and requires appropriate migration of epithelial cells towards and over mucosal lesions. Therefore, we here further investigated the impact of autophagy on epithelial migration. ATG16L1 knockdown was established in the HT29 human colonic epithelial cell line using lentiviral transduction. Migratory capacity was evaluated using scratch assays and RhoAGTP was measured using G-LISA. Immunofluorescent ARHGAP18 and sequestome 1 (SQSTM1; also known as p62) staining was performed on HT29 cells and primary colonic tissue of Crohn's disease patients. We observed that ATG16L1 knockdown cells exhibited decreased autophagy and decreased migration capacity. Furthermore, activity of RhoA was decreased. These characteristics were phenocopied using ATG5 knockdown and pharmacological inhibition of autophagy. The migration defect was dependent on accumulation of SQSTM1 and was alleviated upon SQSTM1 knockdown. Strikingly, thiopurines also mitigated the effects of impaired autophagy. RhoA dysregulation appeared mediated through accumulation of the upstream regulator ARHGAP18, which was observed in cell lines, human foetal organoids and primary colonic tissue. Our results indicate that the ATG16L1 T300A Crohn's disease-associated SNP causes a decrease in migration capacity in epithelial cells, mediated by an increase in SQSTM1 and ARHGAP18 protein and subsequent reduced RhoA activation.

Functional and Therapeutic Relevance of Rho GTPases in Innate Immune Cell Migration and Function during Inflammation: An In Silico Perspective

Systematic regulation of leukocyte migration to the site of infection is a vital step during immunological responses. Improper migration and localization of immune cells could be associated with disease pathology as seen in systemic inflammation. Rho GTPases act as molecular switches during inflammatory cell migration by cycling between Rho-GDP (inactive) to Rho-GTP (active) forms and play an essential role in the precise regulation of actin cytoskeletal dynamics as well as other immunological functions of leukocytes. Available reports suggest that the dysregulation of Rho GTPase signaling is associated with various inflammatory diseases ranging from mild to life-threatening conditions. Therefore, it is crucial to understand the step-by-step activation and inactivation of GTPases and the functioning of different Guanine Nucleotide Exchange Factors (GEFs) and GTPase-Activating Proteins (GAPs) that regulate the conversion of GDP to GTP and GTP to GDP exchange reactions, respectively. Here, we describe the molecular organization and activation of various domains of crucial elements associated with the activation of Rho GTPases using solved PDB structures. We will also present the latest evidence available on the relevance of Rho GTPases in the migration and function of innate immune cells during inflammation. This knowledge will help scientists design promising drug candidates against the Rho-GTPase-centric regulatory molecules regulating inflammatory cell migration.

RhoA- and Actin-Dependent Functions of Macrophages from the Rodent Cardiac Transplantation Model Perspective -Timing Is the Essence

Simple Summary

The functions of animal and human cells depend on the actin cytoskeleton and its regulating protein called the RhoA. The actin cytoskeleton and RhoA also regulate the response of the immune cells such as macrophages to the microbial invasion and/or the presence of a non-self, such as a transplanted organ. The immune response against transplant occurs in several steps. The early step occurring within days post-transplantation is called the acute rejection and the late step, occurring months to years post-transplantation, is called the chronic rejection. In clinical transplantation, acute rejection is easily manageable by the anti-rejection drugs. However, there is no cure for chronic rejection, which is caused by the macrophages entering the transplant and promoting blockage of its blood vessels and destruction of tissue. We discuss here how the inhibition of the RhoA and actin cytoskeleton polymerization in the macrophages, either by genetic interference or pharmacologically, prevents macrophage entry into the transplanted organ and prevents chronic rejection, and also how it affects the anti-microbial function of the macrophages. We also focus on the importance of timing of the macrophage functions in chronic rejection and how the circadian rhythm may affect the anti-chronic rejection and anti-microbial therapies.

Abstract

The small GTPase RhoA, and its down-stream effector ROCK kinase, and the interacting Rac1 and mTORC2 pathways, are the principal regulators of the actin cytoskeleton and actin-related functions in all eukaryotic cells, including the immune cells. As such, they also regulate the phenotypes and functions of macrophages in the immune response and beyond. Here, we review the results of our and other’s studies on the role of the actin and RhoA pathway in shaping the macrophage functions in general and macrophage immune response during the development of chronic (long term) rejection of allografts in the rodent cardiac transplantation model. We focus on the importance of timing of the macrophage functions in chronic rejection and how the circadian rhythm may affect the anti-chronic rejection therapies.

Complement receptor 3 mediates both sinking phagocytosis and phagocytic cup formation via distinct mechanisms

A long-standing hypothesis is that complement receptors (CRs), especially CR3, mediate sinking phagocytosis, but evidence is lacking. Alternatively, CRs have been reported to induce membrane ruffles or phagocytic cups, akin to those induced by Fcγ receptors (FcγRs), but the details of these events are unclear. Here we used real-time 3D imaging and KO mouse models to clarify how particles (human red blood cells) are internalized by resident peritoneal F4/80⁺ cells (macrophages) via CRs and/or FcγRs. We first show that FcγRs mediate highly efficient, rapid (2-3 min) phagocytic cup formation, which is completely abolished by deletion or mutation of the FcR γ chain or conditional deletion of the signal transducer Syk. FcγR-mediated phagocytic cups robustly arise from any point of cell-particle contact, including filopodia. In the absence of CR3, FcγR-mediated phagocytic cups exhibit delayed closure and become aberrantly elongated. Independent of FcγRs, CR3 mediates sporadic ingestion of complement-opsonized particles by rapid phagocytic cup-like structures, typically emanating from membrane ruffles and largely prevented by deletion of the immunoreceptor tyrosine-based activation motif (ITAM) adaptors FcR γ chain and DAP12 or Syk. Deletion of ITAM adaptors or Syk clearly revealed that there is a slow (10-25 min) sinking mode of phagocytosis via a restricted orifice. In summary, we show that (1) CR3 indeed mediates a slow sinking mode of phagocytosis, which is accentuated by deletion of ITAM adaptors or Syk, (2) CR3 induces phagocytic cup-like structures, driven by ITAM adaptors and Syk, and (3) CR3 is involved in forming and closing FcγR-mediated phagocytic cups.

MicroRNA-20b-5p aggravates neuronal apoptosis induced by β-Amyloid via down-regulation of Ras homolog family member C in Alzheimer's disease

Recent studies have reported that microRNAs are abnormally expressed in brain tissues of Alzheimers disease (AD) patients. However, the accurate function of miR-20b-5p in AD has not been elucidated. We intended to investigate the role and underlying mechanism of miR-20b-5p in AD. The expression of miR-20b-5p was increased, and the expression of RhoC was decreased in the hippocampus of Appswe/PS△E 9 mice. In order to construct a cell model in vitro to study the underlying action mechanism, PC12 cells were treated with Aβ_25-35. The cell apoptosis detected by flow cytometry and the expression of cleaved-caspase-3 detected by western blot were both remarkably increased in PC12 cells treated with Aβ_25-35, but they were reduced by miR-20b-5p inhibitor. In addition, MTT test showed that the cell survival rate in Aβ_25-35 + miR-20b-5p inhibitor group was higher than that in Aβ_25-35 + NC inhibitor group. Double luciferase reporter gene analysis confirmed that the binding site of miR-20b-5p was in 3'- UTR of RhoC mRNA. Knockdown of RhoC increased neuronal apoptosis induced by Aβ25-35 and the expression of cleaved-caspase-3, while miR-20b-5p inhibitor reversed these effects. Knockdown of RhoC aggravated the inhibition effect on cell viability induced by Aβ_25-35, while miR-20b-5p inhibitor diminished these effects. In conclusion, inhibition of miR-20b-5p attenuates apoptosis induced by Aβ_25-35 in PC12 cells through targeting RhoC. Therefore, miR-20b-5p may be a perspective curative target for AD.

Cell Tracking Profiler - a user-driven analysis framework for evaluating 4D live-cell imaging data

Accurate measurements of cell morphology and behaviour are fundamentally important for understanding how disease, molecules and drugs affect cell function in vivo Here, by using muscle stem cell (muSC) responses to injury in zebrafish as our biological paradigm, we established a 'ground truth' for muSC behaviour. This revealed that segmentation and tracking algorithms from commonly used programs are error-prone, leading us to develop a fast semi-automated image analysis pipeline that allows user-defined parameters for segmentation and correction of cell tracking. Cell Tracking Profiler (CTP) is a package that runs two existing programs, HK Means and Phagosight within the Icy image analysis suite, to enable user-managed cell tracking from 3D time-lapse datasets to provide measures of cell shape and movement. We demonstrate how CTP can be used to reveal changes to cell behaviour of muSCs in response to manipulation of the cell cytoskeleton by small-molecule inhibitors. CTP and the associated tools we have developed for analysis of outputs thus provide a powerful framework for analysing complex cell behaviour in vivo from 4D datasets that are not amenable to straightforward analysis.

MicroRNA-1253 Regulation of WASF2 (WAVE2) and its Relevance to Racial Health Disparities

The prevalence of hypertension among African Americans (AAs) in the US is among the highest of any demographic and affects over two-thirds of AA women. Previous data from our laboratory suggest substantial differential gene expression (DGE) of mRNAs and microRNAs (miRNAs) exists within peripheral blood mononuclear cells (PBMCs) isolated from AA and white women with or without hypertension. We hypothesized that DGE by race may contribute to racial differences in hypertension. In a reanalysis of our previous dataset, we found that the Wiskott-Aldrich syndrome protein Verprolin-homologous protein 2 (WASF2 (also known as WAVE2)) is differentially expressed in AA women with hypertension, along with several other members of the actin cytoskeleton signaling pathway that plays a role in cell shape and branching of actin filaments. We performed an in silico miRNA target prediction analysis that suggested miRNA miR-1253 regulates WASF2. Transfection of miR-1253 mimics into human umbilical vein endothelial cells (HUVECs) and human aortic endothelial cells (HAECs) significantly repressed WASF2 mRNA and protein levels (p < 0.05), and a luciferase reporter assay confirmed that miR-1253 regulates the WASF2 3' UTR (p < 0.01). miR-1253 overexpression in HUVECs significantly increased HUVEC lamellipodia formation (p < 0.01), suggesting the miR-1253-WASF2 interaction may play a role in cell shape and actin cytoskeleton function. Together, we have identified novel roles for miR-1253 and WASF2 in a hypertension-related disparities context. This may ultimately lead to the discovery of additional actin-related genes which are important in the vascular-related complications of hypertension and influence the disproportionate susceptibility to hypertension among AAs in general and AA women in particular.

Knockout mouse models reveal the contributions of G protein subunits to complement C5a receptor-mediated chemotaxis

G protein-coupled receptor signaling is required for the navigation of immune cells along chemoattractant gradients. However, chemoattractant receptors may couple to more than one type of heterotrimeric G protein, each of which consists of a Gα, Gβ, and Gγ subunit, making it difficult to delineate the critical signaling pathways. Here, we used knockout mouse models and time-lapse microscopy to elucidate Gα and Gβ subunits contributing to complement C5a receptor-mediated chemotaxis. Complement C5a-mediated chemokinesis and chemotaxis were almost completely abolished in macrophages lacking Gnai2 (encoding Gα_i2), consistent with a reduced leukocyte recruitment previously observed in Gnai2 ^-/- mice, whereas cells lacking Gnai3 (Gα_i3) exhibited only a slight decrease in cell velocity. Surprisingly, C5a-induced Ca²⁺ transients and lamellipodial membrane spreading were persistent in Gnai2 ^-/- macrophages. Macrophages lacking both Gnaq (Gα_q) and Gna11 (Gα₁₁) or both Gna12 (Gα₁₂) and Gna13 (Gα₁₃) had essentially normal chemotaxis, Ca²⁺ signaling, and cell spreading, except Gna12/Gna13-deficient macrophages had increased cell velocity and elongated trailing ends. Moreover, Gnaq/Gna11-deficient cells did not respond to purinergic receptor P2Y₂ stimulation. Genetic deletion of Gna15 (Gα₁₅) virtually abolished C5a-induced Ca²⁺ transients, but chemotaxis and cell spreading were preserved. Homozygous Gnb1 (Gβ₁) deletion was lethal, but mice lacking Gnb2 (Gβ₂) were viable. Gnb2 ^-/- macrophages exhibited robust Ca²⁺ transients and cell spreading, albeit decreased cell velocity and impaired chemotaxis. In summary, complement C5a-mediated chemotaxis requires Gα_i2 and Gβ₂, but not Ca²⁺ signaling, and membrane protrusive activity is promoted by G proteins that deplete phosphatidylinositol 4,5-bisphosphate.

The Transcription Factor Nfix Requires RhoA-ROCK1 Dependent Phagocytosis to Mediate Macrophage Skewing during Skeletal Muscle Regeneration

Macrophages (MPs) are immune cells which are crucial for tissue repair. In skeletal muscle regeneration, pro-inflammatory cells first infiltrate to promote myogenic cell proliferation, then they switch into an anti-inflammatory phenotype to sustain myogenic cells differentiation and myofiber formation. This phenotypical switch is induced by dead cell phagocytosis. We previously demonstrated that the transcription factor Nfix, a member of the nuclear factor I (Nfi) family, plays a pivotal role during muscle development, regeneration and in the progression of muscular dystrophies. Here, we show that Nfix is mainly expressed by anti-inflammatory macrophages. Upon acute injury, mice deleted for Nfix in myeloid line displayed a significant defect in the process of muscle regeneration. Indeed, Nfix is involved in the macrophage phenotypical switch and macrophages lacking Nfix failed to adopt an anti-inflammatory phenotype and interact with myogenic cells. Moreover, we demonstrated that phagocytosis induced by the inhibition of the RhoA-ROCK1 pathway leads to Nfix expression and, consequently, to acquisition of the anti-inflammatory phenotype. Our study identified Nfix as a link between RhoA-ROCK1-dependent phagocytosis and the MP phenotypical switch, thus establishing a new role for Nfix in macrophage biology for the resolution of inflammation and tissue repair.

ROCK and RHO Playlist for Preimplantation Development: Streaming to HIPPO Pathway and Apicobasal Polarity in the First Cell Differentiation

In placental mammalian development, the first cell differentiation produces two distinct lineages that emerge according to their position within the embryo: the trophectoderm (TE, placenta precursor) differentiates in the surface, while the inner cell mass (ICM, fetal body precursor) forms inside. Here, we discuss how such position-dependent lineage specifications are regulated by the RHOA subfamily of small GTPases and RHO-associated coiled-coil kinases (ROCK). Recent studies in mouse show that activities of RHO/ROCK are required to promote TE differentiation and to concomitantly suppress ICM formation. RHO/ROCK operate through the HIPPO signaling pathway, whose cell position-specific modulation is central to establishing unique gene expression profiles that confer cell fate. In particular, activities of RHO/ROCK are essential in outside cells to promote nuclear localization of transcriptional co-activators YAP/TAZ, the downstream effectors of HIPPO signaling. Nuclear localization of YAP/TAZ depends on the formation of apicobasal polarity in outside cells, which requires activities of RHO/ROCK. We propose models of how RHO/ROCK regulate lineage specification and lay out challenges for future investigations to deepen our understanding of the roles of RHO/ROCK in preimplantation development. Finally, as RHO/ROCK may be inhibited by certain pharmacological agents, we discuss their potential impact on human preimplantation development in relation to fertility preservation in women.

Myeloid HMG-CoA Reductase Determines Adipose Tissue Inflammation, Insulin Resistance, and Hepatic Steatosis in Diet-Induced Obese Mice

Adipose tissue macrophages (ATMs) are involved in the development of insulin resistance in obesity. We have recently shown that myeloid cell-specific reduction of HMG-CoA reductase (Hmgcr ^m-/m- ), which is the rate-limiting enzyme in cholesterol biosynthesis, protects against atherosclerosis by inhibiting macrophage migration in mice. We hypothesized that ATMs are harder to accumulate in Hmgcr ^m-/m- mice than in control Hmgcr ^fl/fl mice in the setting of obesity. To test this hypothesis, we fed Hmgcr ^m-/m- and Hmgcr ^fl/fl mice a high-fat diet (HFD) for 24 weeks and compared plasma glucose metabolism as well as insulin signaling and histology between the two groups. Myeloid cell-specific reduction of Hmgcr improved glucose tolerance and insulin sensitivity without altering body weight in the HFD-induced obese mice. The improvement was due to a decrease in the number of ATMs. The ATMs were reduced by decreased recruitment of macrophages as a result of their impaired chemotactic activity. These changes were associated with decreased expression of proinflammatory cytokines in adipose tissues. Myeloid cell-specific reduction of Hmgcr also attenuated hepatic steatosis. In conclusion, reducing myeloid HMGCR may be a promising strategy to improve insulin resistance and hepatic steatosis in obesity.

RhoA as a Key Regulator of Innate and Adaptive Immunity

RhoA is a ubiquitously expressed cytoplasmic protein that belongs to the family of small GTPases. RhoA acts as a molecular switch that is activated in response to binding of chemokines, cytokines, and growth factors, and via mDia and the ROCK signaling cascade regulates the activation of cytoskeletal proteins, and other factors. This review aims to summarize our current knowledge on the role of RhoA as a general key regulator of immune cell differentiation and function. The contribution of RhoA for the primary functions of innate immune cell types, namely neutrophils, macrophages, and conventional dendritic cells (DC) to (i) get activated by pathogen-derived and endogenous danger signals, (ii) migrate to sites of infection and inflammation, and (iii) internalize pathogens has been fairly established. In activated DC, which constitute the most potent antigen-presenting cells of the immune system, RhoA is also important for the presentation of pathogen-derived antigen and the formation of an immunological synapse between DC and antigen-specific T cells as a prerequisite to induce adaptive T cell responses. In T cells and B cells as the effector cells of the adaptive immune system Rho signaling is pivotal for activation and migration. More recently, mutations of Rho and Rho-modulating factors have been identified to predispose for autoimmune diseases and as causative for hematopoietic malignancies.

RhoGTPase in Vascular Disease

Ras-homologous (Rho)A/Rho-kinase pathway plays an essential role in many cellular functions, including contraction, motility, proliferation, and apoptosis, inflammation, and its excessive activity induces oxidative stress and promotes the development of cardiovascular diseases. Given its role in many physiological and pathological functions, targeting can result in adverse effects and limit its use for therapy. In this review, we have summarized the role of RhoGTPases with an emphasis on RhoA in vascular disease and its impact on endothelial, smooth muscle, and heart and lung fibroblasts. It is clear from the various studies that understanding the regulation of RhoGTPases and their regulators in physiology and pathological conditions is required for effective targeting of Rho.

E-cadherin loss in RMG-1 cells inhibits cell migration and its regulation by Rho GTPases

E-cadherin is an adherens junction protein that forms intercellular contacts in epithelial cells. Downregulation of E-cadherin is frequently observed in epithelial tumors and it is a hallmark of epithelial–mesenchymal transition (EMT). However, recent findings suggest that E-cadherin plays a more complex role in certain types of cancers. Previous studies investigating the role of E-cadherin mainly used gene-knockdown systems; therefore, we used the CRISPR/Cas9n system to develop E-cadherin-knockout (EcadKO) ovarian cancer RMG-1 cell to clarify the role of E-cadherin in RMG-1 cells. EcadKO RMG-1 cells demonstrated a complete loss of the adherens junctions and failed to form cell clusters. Cell–extracellular matrix (ECM) interactions were increased in EcadKO RMG-1 cells. Upregulation of integrin beta1 and downregulation of collagen 4 were confirmed. EcadKO RMG-1 cells showed decreased β-catenin levels and decreased expression of its transcriptional target cyclin D1. Surprisingly, a marked decrease in the migratory ability of EcadKO RMG-1 cells was observed and the cellular response to Rho GTPase inhibitors was diminished. Thus, we demonstrated that E-cadherin in RMG-1 cells is indispensable for β-catenin expression and β-catenin mediated transcription and Rho GTPase-regulated directionally persistent cell migration.

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E-cadherin loss diminished the formation of cell clusters in RMG-1 cells.

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E-cadherin loss depleted β-catenin expression in RMG-1 cells.

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E-cadherin loss markedly decreased cell migration and response to RhoGTPase inhibitors during cell migration in RMG-1 cells.

The impact of the rs8005161 polymorphism on G protein-coupled receptor GPR65 (TDAG8) pH-associated activation in intestinal inflammation

Background

Tissue inflammation in inflammatory bowel diseases (IBD) is associated with a decrease in local pH. The gene encoding G-protein-coupled receptor 65 (GPR65) has recently been reported to be a genetic risk factor for IBD. In response to extracellular acidification, proton activation of GPR65 stimulates cAMP and Rho signalling pathways. We aimed to analyse the clinical and functional relevance of the GPR65 associated single nucleotide polymorphism (SNP) rs8005161.

Methods

1138 individuals from a mixed cohort of IBD patients and healthy volunteers were genotyped for SNPs associated with GPR65 (rs8005161, rs3742704) and galactosylceramidase (rs1805078) by Taqman SNP assays. 2300 patients from the Swiss IBD Cohort Study (SIBDC) were genotyped for rs8005161 by mass spectrometry based SNP genotyping. IBD patients from the SIBDC carrying rs8005161 TT, CT, CC and non-IBD controls (CC) were recruited for functional studies. Human CD14+ cells were isolated from blood samples and subjected to an extracellular acidic pH shift, cAMP accumulation and RhoA activation were measured.

Results

In our mixed cohort, but not in SIBDC patients, the minor variant rs8005161 was significantly associated with UC. In SIBDC patients, we observed a consistent trend in increased disease severity in patients carrying the rs8005161-TT and rs8005161-CT alleles. No significant differences were observed in the pH associated activation of cAMP production between IBD (TT, CT, WT/CC) and non-IBD (WT/CC) genotype carriers upon an acidic extracellular pH shift. However, we observed significantly impaired RhoA activation after an extracellular acidic pH shift in IBD patients, irrespective of the rs8005161 allele.

Conclusions

The T allele of rs8005161 might confer a more severe disease course in IBD patients. Human monocytes from IBD patients showed impaired pH associated RhoA activation upon an acidic pH shift.

Electronic supplementary material

The online version of this article (10.1186/s12876-018-0922-8) contains supplementary material, which is available to authorized users.

The RhoB small GTPase in physiology and disease

RhoB is a Rho family GTPase that is highly similar to RhoA and RhoC, yet has distinct functions in cells. Its unique C-terminal region is subject to specific post-translational modifications that confer different localization and functions to RhoB. Apart from the common role with RhoA and RhoC in actin organization and cell migration, RhoB is also implicated in a variety of other cellular processes including membrane trafficking, cell proliferation, DNA-repair and apoptosis. RhoB is not an essential gene in mice, but it is implicated in several physiological and pathological processes. Its multiple roles will be discussed in this review.

Rho signaling research: history, current status and future directions

One of the main research areas in biology from the mid‐1980s through the 1990s was the elucidation of signaling pathways governing cell responses. These studies brought, among other molecules, the small GTPase Rho to the epicenter. Rho signaling research has since expanded to all areas of biology and medicine. Here, we describe how Rho emerged as a key molecule governing cell morphogenesis and movement, how it was linked to actin reorganization, and how the study of Rho signaling has expanded from cultured cells to whole biological systems. We then give an overview of the current research status of Rho signaling in development, brain, cardiovascular system, immunity and cancer, and discuss the future directions of Rho signaling research, with emphasis on one Rho effector, ROCK*.

Cobalt (II) ions and nanoparticles induce macrophage retention by ROS-mediated down-regulation of RhoA expression

Histological assessments of synovial tissues from patients with failed CoCr alloy hip prostheses demonstrate extensive infiltration and accumulation of macrophages, often loaded with large quantities of particulate debris. The resulting adverse reaction to metal debris (ARMD) frequently leads to early joint revision. Inflammatory response starts with the recruitment of immune cells and requires the egress of macrophages from the inflamed site for resolution of the reaction. Metal ions (Co²⁺ and Cr³⁺) have been shown to stimulate the migration of T lymphocytes but their effects on macrophages motility are still poorly understood. To elucidate this, we studied in vitro and in vivo macrophage migration during exposure to cobalt and chromium ions and nanoparticles. We found that cobalt but not chromium significantly reduces macrophage motility. This involves increase in cell spreading, formation of intracellular podosome-type adhesion structures and enhanced cell adhesion to the extracellular matrix (ECM). The formation of podosomes was also associated with the production and activation of matrix metalloproteinase-9 (MMP9) and enhanced ECM degradation. We showed that these were driven by the down-regulation of RhoA signalling through the generation of reactive oxygen species (ROS). These novel findings reveal the key mechanisms driving the wear/corrosion metallic byproducts-induced inflammatory response at non-toxic concentrations.

Statement of significance

Adverse tissue responses to metal wear and corrosion products from CoCr alloy implants remain a great challenge to surgeons and patients. Macrophages are the key regulators of these adverse responses to the ions and debris generated. We demonstrated that cobalt, rather than chromium, causes macrophage retention by restructuring the cytoskeleton and inhibiting cell migration via ROS production that affects Rho Family GTPase. This distinctive effect of cobalt on macrophage behaviour can help us understand the pathogenesis of ARMD and the cellular response to cobalt based alloys, which provide useful information for future implant design and biocompatibility testing.

Icmt inhibition exerts anti-angiogenic and anti-hyperpermeability activities impeding malignant pleural effusion

Small GTPases are pivotal regulators of several aspects of tumor progression. Their implication in angiogenesis, vascular permeability and tumor-associated inflammatory responses is relevant to the pathobiology of Malignant Pleural Effusion (MPE). Inhibition of isoprenylcysteine carboxylmethyltransferase (Icmt) abrogates small GTPase activation. We therefore hypothesized that cysmethynil, an Icmt inhibitor would limit pleural fluid accumulation in two models, a lung-adenocarcinoma and a mesothelioma-induced MPE. Cysmethynil significantly reduced MPE volume in both models and tumor burden in the adenocarcinoma model. It inhibited pleural vascular permeability and tumor angiogenesis in vivo and reduced endothelial cell proliferation, migration and tube formation in vitro. Cysmethynil also promoted M1 anti-tumor macrophage homing in the pleural space in vivo, and inhibited tumor-induced polarization of macrophages towards a M2 phenotype in vitro. In addition, the inhibitor promoted adenocarcinoma cell apoptosis in vivo. Inhibition of small GTPase might thus represent a valuable strategy for pharmacotherapy of MPE.

Genetic deletion of the Rho GEF Net1 impairs mouse macrophage motility and actin cytoskeletal organization

Macrophages are innate immune cells that constantly patrol an organism to fulfill protective and homeostatic roles. Previous studies have shown that Rho GTPase activity is required for macrophage mobility, yet the roles of upstream regulatory proteins controlling Rho GTPase function in these cells are not well defined. Previously we have shown that the RhoA GEF Net1 is required for human breast cancer cell motility and extracellular matrix invasion. To assess the role of Net1 in macrophage motility, we isolated bone marrow macrophage (BMM) precursors from wild type and Net1 knockout mice. Loss of Net1 did not affect the ability of BMM precursors to differentiate into mature macrophages in vitro, as measured by CD68 and F4/80 staining. However, Net1 deletion significantly reduced RhoA activation, F-actin accumulation, adhesion, and motility in these cells. Nevertheless, similar to RhoA/RhoB double knockout macrophages, Net1 deletion did not impair macrophage recruitment to the peritoneum in a mouse model of sterile inflammation. These data demonstrate that Net1 is an important regulator of RhoA signaling and motility in mouse macrophages in vitro, but that its function may be dispensable for macrophage recruitment to inflammatory sites in vivo.

Up-regulation of Rho-associated kinase 1/2 by glucocorticoids promotes migration, invasion and metastasis of melanoma

Although glucocorticoids (GCs) regulate proliferation, differentiation and apoptosis of tumor cells, their influence on metastasis of tumor cells is poorly understood. Melanoma is a type of skin cancers with high metastasis. We investigated the effect of GCs on metastasis of melanoma cells and its mechanism. We found that GCs significantly promoted the adhesion, migration, invasion of melanoma cells in vitro and lung metastasis in experimental melanoma metastasis mice. Dexamethasone (Dex), a synthetic GC, did not change the RhoA, RhoB and RhoC signalings, but significantly increased the expression and activity of Rho-associated kinase 1/2 (ROCK1/2). The effect of Dex was to increase ROCK1/2 stability mediated by glucocorticoid receptor. Inhibiting ROCK1/2 activity with Y-27632, a ROCK1/2 inhibitor abrogated the pro-migration and pro-metastasis effects of GCs in vitro and in vivo, indicating that ROCK1/2 mediated the pro-metastasis effects of GCs. Activation of PI3K/AKT also contributed to the pro-migration and pro-invasion effects of Dex partially through up-regulating ROCK1/2 expression. Additionally, Dex also down-regulated the expression of tissue inhibitors of matrix metalloproteinase-2. Taken together, our findings provide new data to understand the possible promoting roles and mechanisms of GCs in melanoma metastasis.

Cortactin deficiency causes increased RhoA/ROCK1-dependent actomyosin contractility, intestinal epithelial barrier dysfunction, and disproportionately severe DSS-induced colitis

The intestinal epithelium constitutes a first line of defense of the innate immune system. Epithelial dysfunction is a hallmark of intestinal disorders such as inflammatory bowel diseases (IBDs). The actin cytoskeleton controls epithelial barrier integrity but the function of actin regulators such as cortactin is poorly understood. Given that cortactin controls endothelial permeability, we hypothesized that cortactin is also important for epithelial barrier regulation. We found increased permeability in the colon of cortactin-KO mice that was accompanied by reduced levels of ZO-1, claudin-1, and E-cadherin. By contrast, claudin-2 was upregulated. Cortactin deficiency increased RhoA/ROCK1-dependent actomyosin contractility, and inhibition of ROCK1 rescued the barrier defect. Interestingly, cortactin deficiency caused increased epithelial proliferation without affecting apoptosis. KO mice did not develop spontaneous colitis, but were more susceptible to dextran sulfate sodium colitis and showed severe colon tissue damage and edema formation. KO mice with colitis displayed strong mucus deposition and goblet cell depletion. In healthy human colon tissues, cortactin co-localized with ZO-1 at epithelial cell contacts. In IBDs patients, we observed decreased cortactin levels and loss of co-localization with ZO-1. Thus, cortactin is a master regulator of intestinal epithelial barrier integrity in vivo and could serve as a suitable target for pharmacological intervention in IBDs.

Ceramide activation of RhoA/Rho kinase impairs actin polymerization during aggregated LDL catabolism

Macrophages use an extracellular, hydrolytic compartment formed by local actin polymerization to digest aggregated LDL (agLDL). Catabolism of agLDL promotes foam cell formation and creates an environment rich in LDL catabolites, including cholesterol and ceramide. Increased ceramide levels are present in lesional LDL, but the effect of ceramide on macrophage proatherogenic processes remains unknown. Here, we show that macrophages accumulate ceramide in atherosclerotic lesions. Using macrophages from sphingosine kinase 2 KO (SK2KO) mice to mimic ceramide-rich conditions of atherosclerotic lesions, we show that SK2KO macrophages display impaired actin polymerization and foam cell formation in response to contact with agLDL. C16-ceramide treatment impaired wild-type but not SK2KO macrophage actin polymerization, confirming that this effect is due to increased ceramide levels. We demonstrate that knockdown of RhoA or inhibition of Rho kinase restores agLDL-induced actin polymerization in SK2KO macrophages. Activation of RhoA in macrophages was sufficient to impair actin polymerization and foam cell formation in response to agLDL. Finally, we establish that during catabolism, macrophages take up ceramide from agLDL, and inhibition of ceramide generation modulates actin polymerization. These findings highlight a critical regulatory pathway by which ceramide impairs actin polymerization through increased RhoA/Rho kinase signaling and regulates foam cell formation.

Small GTPases and their guanine-nucleotide exchange factors and GTPase-activating proteins in neutrophil recruitment

PURPOSE OF REVIEW

The review describes the roles of Rho- and Rap-guanosine triphosphatases (GTPases) and of their activators, guanine-nucleotide exchange factors (GEFs), and inhibitors, GTPase activating proteins (GAPs), in neutrophil recruitment from the blood stream into inflamed tissues, with a focus on recently identified roles in neutrophils, endothelial cells, and platelets.

RECENT FINDINGS

Recent studies have identified important roles of Rho- and Rap-GTPases, and of their GEFs and GAPs, in the neutrophil recruitment cascade. These proteins control the upregulation and/or activation of adhesion molecules on the surface of neutrophils, endothelial cells, and platelets, and they alter cell/cell adhesion in the vascular endothelium. This enables the capture of neutrophils from the blood stream, their migration along and through the vessel wall, and their passage into the inflamed tissue. In particular, it has recently become clear that P-Rex and Vav family Rac-GEFs in platelets are crucial for neutrophil recruitment.

SUMMARY

These recent findings have contributed greatly to our understanding of the signalling pathways that control neutrophil recruitment to sites of inflammation and have opened up new avenues of research in this field.

ROCK inhibition enhances neurite outgrowth in neural stem cells by upregulating YAP expression in vitro

Spontaneous axonal regeneration of neurons does not occur after spinal cord injury because of inhibition by myelin and other inhibitory factors. Studies have demonstrated that blocking the Rho/Rho-kinase (ROCK) pathway can promote neurite outgrowth in spinal cord injury models. In the present study, we investigated neurite outgrowth and neuronal differentiation in neural stem cells from the mouse subventricular zone after inhibition of ROCK in vitro. Inhibition of ROCK with Y-27632 increased neurite length, enhanced neuronal differentiation, and upregulated the expression of two major signaling pathway effectors, phospho-Akt and phospho-mitogen-activated protein kinase, and the Hippo pathway effector YAP. These results suggest that inhibition of ROCK mediates neurite outgrowth in neural stem cells by activating the Hippo signaling pathway.

Real-time two- and three-dimensional imaging of monocyte motility and navigation on planar surfaces and in collagen matrices: roles of Rho

We recently found that macrophages from RhoA/RhoB double knockout mice had increased motility of the cell body, but severely impaired retraction of the tail and membrane extensions, whereas RhoA- or RhoB-deficient cells exhibited mild phenotypes. Here we extended this work and investigated the roles of Rho signaling in primary human blood monocytes migrating in chemotactic gradients and in various settings. Monocyte velocity, but not chemotactic navigation, was modestly dependent on Rho-ROCK-myosin II signaling on a 2D substrate or in a loose collagen type I matrix. Viewed by time-lapse epi-fluorescence microscopy, monocytes appeared to flutter rather than crawl, such that the 3D surface topology of individual cells was difficult to predict. Spinning disk confocal microscopy and 3D reconstruction revealed that cells move on planar surfaces and in a loose collagen matrix using prominent, curved planar protrusions, which are rapidly remodeled and reoriented, as well as resorbed. In a dense collagen type I matrix, there is insufficient space for this mode and cells adopt a highly Rho-dependent, lobular mode of motility. Thus, in addition to its role in tail retraction on 2D surfaces, Rho is critical for movement in confined spaces, but is largely redundant for motility and chemotaxis in loose matrices.

Rho GTPase signalling in cell migration

Cells migrate in multiple different ways depending on their environment, which includes the extracellular matrix composition, interactions with other cells, and chemical stimuli. For all types of cell migration, Rho GTPases play a central role, although the relative contribution of each Rho GTPase depends on the environment and cell type. Here, I review recent advances in our understanding of how Rho GTPases contribute to different types of migration, comparing lamellipodium-driven versus bleb-driven migration modes. I also describe how cells migrate across the endothelium. In addition to Rho, Rac and Cdc42, which are well known to regulate migration, I discuss the roles of other less-well characterized members of the Rho family.

Rho GTPase signalling in cell migration

Cells migrate in multiple different ways depending on their environment, which includes the extracellular matrix composition, interactions with other cells, and chemical stimuli. For all types of cell migration, Rho GTPases play a central role, although the relative contribution of each Rho GTPase depends on the environment and cell type. Here, I review recent advances in our understanding of how Rho GTPases contribute to different types of migration, comparing lamellipodium-driven versus bleb-driven migration modes. I also describe how cells migrate across the endothelium. In addition to Rho, Rac and Cdc42, which are well known to regulate migration, I discuss the roles of other less-well characterized members of the Rho family.

Front-signal-dependent accumulation of the RHOA inhibitor FAM65B at leading edges polarizes neutrophils

A hallmark of neutrophil polarization is the back localization of active RHOA and phosphorylated myosin light chain (pMLC, also known as MYL2). However, the mechanism for the polarization is not entirely clear. Here, we show that FAM65B, a newly identified RHOA inhibitor, is important for the polarization. When FAM65B is phosphorylated, it binds to 14-3-3 family proteins and becomes more stable. In neutrophils, chemoattractants stimulate FAM65B phosphorylation largely depending on the signals from the front of the cells that include those mediated by phospholipase Cβ (PLCβ) and phosphoinositide 3-kinase γ (PI3Kγ), leading to FAM65B accumulation at the leading edge. Concordantly, FAM65B deficiency in neutrophils resulted in an increase in RHOA activity and localization of pMLC to the front of cells, as well as defects in chemotaxis directionality and adhesion to endothelial cells under flow. These data together elucidate a mechanism for RHOA and pMLC polarization in stimulated neutrophils through direct inhibition of RHOA by FAM65B at the leading edge.