Endocytic Trafficking of Integrins in Cell Migration

An Arf6- and caveolae-dependent pathway links hemidesmosome remodeling and mechanoresponse

Hemidesmosomes are epithelial-specific cell-matrix adhesions stably anchoring the intracellular keratin network to the extracellular matrix and providing mechanical resilience to epithelia. The small GTPase Arf6 and caveolae are essential for their remodeling, notably in response to external mechanical cues.

Hemidesmosomes (HDs) are epithelial-specific cell–matrix adhesions that stably anchor the intracellular keratin network to the extracellular matrix. Although their main role is to protect the epithelial sheet from external mechanical strain, how HDs respond to mechanical stress remains poorly understood. Here we identify a pathway essential for HD remodeling and outline its role with respect to α6β4 integrin recycling. We find that α6β4 integrin chains localize to the plasma membrane, caveolae, and ADP-ribosylation factor-6+ (Arf6+) endocytic compartments. Based on fluorescence recovery after photobleaching and endocytosis assays, integrin recycling between both sites requires the small GTPase Arf6 but neither caveolin1 (Cav1) nor Cavin1. Strikingly, when keratinocytes are stretched or hypo-osmotically shocked, α6β4 integrin accumulates at cell edges, whereas Cav1 disappears from it. This process, which is isotropic relative to the orientation of stretch, depends on Arf6, Cav1, and Cavin1. We propose that mechanically induced HD growth involves the isotropic flattening of caveolae (known for their mechanical buffering role) associated with integrin diffusion and turnover.

Activation of Rho-kinase and focal adhesion kinase regulates the organization of stress fibers and focal adhesions in the central part of fibroblasts

Specific regulation and activation of focal adhesion kinase (FAK) are thought to be important for focal adhesion formation, and activation of Rho-kinase has been suggested to play a role in determining the effects of FAK on the formation of stress fibers and focal adhesions. To clarify the role of FAK in stress fiber formation and focal adhesion organization, the author examined the formation of new stress fibers and focal adhesions by activation of Rho-kinase in FAK knockout (FAK^–/–) fibroblasts. FAK^–/– cells were elliptical in shape, and showed reduced numbers of stress fibers and focal adhesions in the central part of the cells along with large focal adhesions in the peripheral regions. Activation of Rho-kinase in FAK^–/– cells transiently increased the actin filaments in the cell center, but these did not form typical thick stress fibers. Moreover, only plaque-like structures as the origins of newly formed focal adhesions were observed in the center of the cell. Furthermore, introduction of an exogenous GFP-labeled FAK gene into FAK^–/– cells resulted in increased numbers of stress fibers and focal adhesions in the center of the cells, which showed typical fibroblast morphology. These results indicated that FAK plays an important role in the formation of stress fibers and focal adhesions as well as in regulation of cell shape and morphology with the activation of Rho-kinase.

Retriever fetches integrins from endosomes

Recycling from endosomes to the plasma membrane is an important step in cell homeostasis. The retromer/SNX27/WASH complex recycles numerous receptors, but key ones are still unaccounted for. Now a related conserved heterotrimer, called retriever, has been identified that, together with SNX17, the CCC complex and WASH, mediates the recycling of α₅β₁ integrins.

Mammalian Eps15 homology domain 1 promotes metastasis in non-small cell lung cancer by inducing epithelial-mesenchymal transition

The identification of the earliest molecular events responsible for the metastatic dissemination of non-small cell lung cancer (NSCLC) remains critical for early detection, prevention, and treatment interventions. In this study, we hypothesized that Mammalian Eps15 homology domain 1 (EHD1) might be responsible for the metastatic behavior of cells in NSCLC. We demonstrated that upregulation of EHD1 is associated with lymph nodes metastasis and unfavorable survival in patients with NSCLC. EHD1 knockdown inhibited the invasion and migration of human NSCLC cells, and overexpression of EHD1 increased the metastatic potential of lung cancer cells. Using the Affymetrix Human Gene 1.0 ST platform, microarray analysis revealed that an association between EHD1 and epithelial-mesenchymal transition (EMT), supported by downregulation of mesenchymal markers and upregulation of epithelial markers following knockdown of EHD1 in cell lines. Moreover, overexpression of EHD1 induced the EMT and increased the metastatic potential of lung cancer cells in vitro and in vivo. These results provide a model to illustrate the relationship between EHD1 expression and lung cancer metastasis, opening up new avenues for the prognosis and therapy of lung cancer.

A dual role for the class III PI3K, Vps34, in platelet production and thrombus growth

To uncover the role of Vps34, the sole class III phosphoinositide 3-kinase (PI3K), in megakaryocytes (MKs) and platelets, we created a mouse model with Vps34 deletion in the MK/platelet lineage (Pf4-Cre/Vps34^lox/lox). Deletion of Vps34 in MKs led to the loss of its regulator protein, Vps15, and was associated with microthrombocytopenia and platelet granule abnormalities. Although Vps34 deficiency did not affect MK polyploidisation or proplatelet formation, it dampened MK granule biogenesis and directional migration toward an SDF1α gradient, leading to ectopic platelet release within the bone marrow. In MKs, the level of phosphatidylinositol 3-monophosphate (PI3P) was significantly reduced by Vps34 deletion, resulting in endocytic/trafficking defects. In platelets, the basal level of PI3P was only slightly affected by Vps34 loss, whereas the stimulation-dependent pool of PI3P was significantly decreased. Accordingly, a significant increase in the specific activity of Vps34 lipid kinase was observed after acute platelet stimulation. Similar to Vps34-deficient platelets, ex vivo treatment of wild-type mouse or human platelets with the Vps34-specific inhibitors, SAR405 and VPS34-IN1, induced abnormal secretion and affected thrombus growth at arterial shear rate, indicating a role for Vps34 kinase activity in platelet activation, independent from its role in MKs. In vivo, Vps34 deficiency had no impact on tail bleeding time, but significantly reduced platelet prothrombotic capacity after carotid injury. This study uncovers a dual role for Vps34 as a regulator of platelet production by MKs and as an unexpected regulator of platelet activation and arterial thrombus formation dynamics.

The functions of Reelin in membrane trafficking and cytoskeletal dynamics: implications for neuronal migration, polarization and differentiation

Reelin is a large extracellular matrix protein with relevant roles in mammalian central nervous system including neurogenesis, neuronal polarization and migration during development; and synaptic plasticity with its implications in learning and memory, in the adult. Dysfunctions in reelin signaling are associated with brain lamination defects such as lissencephaly, but also with neuropsychiatric diseases like autism, schizophrenia and depression as well with neurodegeneration. Reelin signaling involves a core pathway that activates upon reelin binding to its receptors, particularly ApoER2 (apolipoprotein E receptor 2)/LRP8 (low-density lipoprotein receptor-related protein 8) and very low-density lipoprotein receptor, followed by Src/Fyn-mediated phosphorylation of the adaptor protein Dab1 (Disabled-1). Phosphorylated Dab1 (pDab1) is a hub in the signaling cascade, from which several other downstream pathways diverge reflecting the different roles of reelin. Many of these pathways affect the dynamics of the actin and microtubular cytoskeleton, as well as membrane trafficking through the regulation of the activity of small GTPases, including the Rho and Rap families and molecules involved in cell polarity. The complexity of reelin functions is reflected by the fact that, even now, the precise mode of action of this signaling cascade in vivo at the cellular and molecular levels remains unclear. This review addresses and discusses in detail the participation of reelin in the processes underlying neurogenesis, neuronal migration in the cerebral cortex and the hippocampus; and the polarization, differentiation and maturation processes that neurons experiment in order to be functional in the adult brain. In vivo and in vitro evidence is presented in order to facilitate a better understanding of this fascinating system.

Integrins as architects of cell behavior

Integrins are cell surface receptors that bind cells to their physical external environment, linking the extracellular matrix to cell function. They are essential in the biology of all animals. In the late 1980s, we discovered that integrins are required for the ability of breast epithelia to do what they are programmed to do, which is to differentiate and make milk. Since then, integrins have been shown to control most other aspects of phenotype: to stay alive, to divide, and to move about. Integrins also provide part of the mechanism that allows cells to form tissues. Here I discuss how we discovered that integrins control mammary gland differentiation and explore the role of integrins as central architects of other aspects of cell behavior.

CD177 modulates human neutrophil migration through activation-mediated integrin and chemoreceptor regulation

CD177 is a glycosylphosphatidylinositol (GPI)-anchored protein expressed by a variable proportion of human neutrophils that mediates surface expression of the antineutrophil cytoplasmic antibody antigen proteinase 3. CD177 associates with β2 integrins and recognizes platelet endothelial cell adhesion molecule 1 (PECAM-1), suggesting a role in neutrophil migration. However, CD177^pos neutrophils exhibit no clear migratory advantage in vivo, despite interruption of in vitro transendothelial migration by CD177 ligation. We sought to understand this paradox. Using a PECAM-1-independent transwell system, we found that CD177^pos and CD177^neg neutrophils migrated comparably. CD177 ligation selectively impaired migration of CD177^pos neutrophils, an effect mediated through immobilization and cellular spreading on the transwell membrane. Correspondingly, CD177 ligation enhanced its interaction with β2 integrins, as revealed by fluorescence lifetime imaging microscopy, leading to integrin-mediated phosphorylation of Src and extracellular signal-regulated kinase (ERK). CD177-driven cell activation enhanced surface β2 integrin expression and affinity, impaired internalization of integrin attachments, and resulted in ERK-mediated attenuation of chemokine signaling. We conclude that CD177 signals in a β2 integrin-dependent manner to orchestrate a set of activation-mediated mechanisms that impair human neutrophil migration.

Fibronectin promotes directional persistence in fibroblast migration through interactions with both its cell-binding and heparin-binding domains

The precise mechanisms through which insoluble, cell-adhesive ligands induce and regulate directional cell migration remain obscure. We recently demonstrated that elevated surface density of physically adsorbed plasma fibronectin (FN) promotes high directional persistence in fibroblast migration. While cell-FN association through integrins α₅β₁ and α_vβ₃ was necessary, substrates that selectively engaged these integrins did not support the phenotype. We here show that high directional persistence necessitates a combination of the cell-binding and C-terminal heparin-binding domains of FN, but does not require the engagement of syndecan-4 or integrin α₄β₁. FN treatment with various fixation agents indicated that associated changes in fibroblast motility were due to biochemical changes, rather than alterations in its physical state. The nature of the coating determined the ability of fibroblasts to assemble endogenous or exogenous FN, while FN fibrillogenesis played a minor, but significant, role in regulating directionality. Interestingly, knockdown of cellular FN abolished cell motility altogether, demonstrating a requirement for intracellular processes in enabling fibroblast migration on FN. Lastly, kinase inhibition experiments revealed that regulation of cell speed and directional persistence are decoupled. Hence, we have identified factors that render full-length FN a promoter of directional migration and discuss the possible, relevant mechanisms.

Isoprenylcysteine carboxylmethyltransferase function is essential for RAB4A-mediated integrin β3 recycling, cell migration and cancer metastasis

Isoprenylcysteine carboxylmethyltransferase (ICMT) catalyzes the post-translational modification of RAB GTPases that contain C-terminal CXC motifs. However, the functional impact of this modification on RAB proteins has not been actively explored. We found that inhibition of ICMT significantly reduced cell migration in vitro and cancer invasion and metastasis in vivo. This role of ICMT was found to be mediated by RAB4A, an essential regulator of the fast recycling of integrin β3. Integrin β3 regulates cell polarity and migration when localized appropriately to the plasma membrane, thereby having an essential role in cancer metastasis. ICMT catalyzed carboxylmethylation is critical for RAB4A activation and interaction with effectors, its localization to endosomes and recycling vesicles, and hence important for RAB4A-dependent integrin β3 recycling to plasma membrane. These findings bring attention to the effects of C-terminal carboxylmethylation on RAB GTPases and provide a rationale for targeting ICMT in the treatment of metastatic cancer.

Low-intensity pulsed ultrasound promotes cell motility through vinculin-controlled Rac1 GTPase activity

Low-intensity pulsed ultrasound (LIPUS) is a therapy used clinically to promote healing. Using live-cell imaging we show that LIPUS stimulation, acting through integrin-mediated cell-matrix adhesions, rapidly induces Rac1 activation associated with dramatic actin cytoskeleton rearrangements. Our study demonstrates that the mechanosensitive focal adhesion (FA) protein vinculin, and both focal adhesion kinase (FAK, also known as PTK2) and Rab5 (both the Rab5a and Rab5b isoforms) have key roles in regulating these effects. Inhibiting the link of vinculin to the actin-cytoskeleton abolished LIPUS sensing. We show that this vinculin-mediated link was not only critical for Rac1 induction and actin rearrangements, but was also important for the induction of a Rab5-dependent increase in the number of early endosomes. Expression of dominant-negative Rab5, or inhibition of endocytosis with dynasore, also blocked LIPUS-induced Rac1 signalling events. Taken together, our data show that LIPUS is sensed by cell matrix adhesions through vinculin, which in turn modulates a Rab5-Rac1 pathway to control ultrasound-mediated endocytosis and cell motility. Finally, we demonstrate that a similar FAK-Rab5-Rac1 pathway acts to control cell spreading upon fibronectin.

The small G protein Arf6 expressed in keratinocytes by HGF stimulation is a regulator for skin wound healing

The earlier step of cutaneous wound healing process, re-epithelialization of the wounded skin, is triggered by a variety of growth factors. However, molecular mechanisms through which growth factors trigger skin wound healing are less understood. Here, we demonstrate that hepatocyte growth factor (HGF)/c-Met signaling-induced expression of the small G protein Arf6 mRNA in keratinocytes is essential for the skin wound healing. Arf6 mRNA expression was dramatically induced in keratinocytes at the wounded skin, which was specifically suppressed by the c-Met inhibitor. Wound healing of the skin was significantly delayed in keratinocyte-specific Arf6 conditional knockout mice. Furthermore, Arf6 deletion from keratinocytes remarkably suppressed HGF-stimulated cell migration and peripheral membrane ruffle formation, but did not affect skin morphology and proliferation/differentiation of keratinocytes. These results are consistent with the notion that Arf6 expressed in skin keratinocytes through the HGF/c-Met signaling pathway in response to skin wounding plays an important role in skin wound healing by regulating membrane dynamics-based motogenic cellular function of keratinocytes.

Linking cortical microtubule attachment and exocytosis

Exocytosis is a fundamental cellular process whereby secreted molecules are packaged into vesicles that move along cytoskeletal filaments and fuse with the plasma membrane. To function optimally, cells are strongly dependent on precisely controlled delivery of exocytotic cargo. In mammalian cells, microtubules serve as major tracks for vesicle transport by motor proteins, and thus microtubule organization is important for targeted delivery of secretory carriers. Over the years, multiple microtubule-associated and cortical proteins have been discovered that facilitate the interaction between the microtubule plus ends and the cell cortex. In this review, we focus on mammalian protein complexes that have been shown to participate in both cortical microtubule capture and exocytosis, thereby regulating the spatial organization of secretion. These complexes include microtubule plus-end tracking proteins, scaffolding factors, actin-binding proteins, and components of vesicle docking machinery, which together allow efficient coordination of cargo transport and release.

Arf GAPs: A family of proteins with disparate functions that converge on a common structure, the integrin adhesion complex

ADP-ribosylation factors (Arfs) are members of the Ras GTPase superfamily. The function of Arfs is dependent on GTPase-activating proteins (GAPs) and guanine nucleotide exchange factors (GEFs), which allow Arfs to cycle between the GDP-bound and GTP-bound forms. Arf GAPs have been shown to be present in integrin adhesion complexes, which include focal adhesions. Integrin adhesion complexes are composed of integrins, scaffolding proteins and signaling proteins and regulate cell proliferation, survival, differentiation and migration. Understanding the role of Arf GAPs in the regulation of integrin adhesion complexes is relevant to understanding normal physiology and cancer. In this review, we will discuss the contribution of the Arf GAP family members to the regulation of integrin adhesion complexes, examining the diverse mechanisms by which they control integrin adhesion complex formation, maturation and dissolution. GIT1 and ARAP2 serve as GAPs for Arf6, regulating Rac1 and other effectors by mechanisms still being defined. In contrast, GIT2 regulates Rac1 independent of Arf6. AGAP2 binds to and regulates focal adhesion kinase (FAK). ARAP2 and ACAP1, both Arf6 GAPs, regulate membrane trafficking of integrins through different endocytic pathways, exerting opposite effects on focal adhesions. ASAP1 not only regulates actin cytoskeleton remodeling through its interaction with nonmuscle myosin 2A, but is also important in integrin recycling. These examples illustrate the diversity and versatility of Arf GAPs as regulators of integrin adhesion complex structure and function.

Focal adhesion kinase signaling in unexpected places

Focal adhesion kinase (FAK) is a cytoplasmic protein-tyrosine kinase first identified at extracellular matrix and integrin receptor cell adhesion sites and is a key regulator of cell movement. FAK is activated by a variety of stimuli. Herein, we discuss advances in conformational-associated FAK activation and dimerization mechanisms. Additionally, new roles have emerged for FAK signaling at cell adhesions, adherens junctions, endosomes, and the nucleus. In light of these new findings, we review how FAK activation at these sites is connected to the regulation of integrin recycling-activation, vascular permeability, cell survival, and transcriptional regulation, respectively. Studies uncovering FAK signaling connections in unexpected places within cells have yielded important new regulatory insights in cell biology.

Crosstalk between CLCb/Dyn1-Mediated Adaptive Clathrin-Mediated Endocytosis and Epidermal Growth Factor Receptor Signaling Increases Metastasis

Signaling receptors are internalized and regulated by clathrin-mediated endocytosis (CME). Two clathrin light chain isoforms, CLCa and CLCb, are integral components of the endocytic machinery whose differential functions remain unknown. We report that CLCb is specifically upregulated in non-small-cell lung cancer (NSCLC) cells and is associated with poor patient prognosis. Engineered single CLCb-expressing NSCLC cells, as well as "switched" cells that predominantly express CLCb, exhibit increased rates of CME and altered clathrin-coated pit dynamics. This "adaptive CME" resulted from upregulation of dynamin-1 (Dyn1) and its activation through a positive feedback loop involving enhanced epidermal growth factor (EGF)-dependent Akt/GSK3β phosphorylation. CLCb/Dyn1-dependent adaptive CME selectively altered EGF receptor trafficking, enhanced cell migration in vitro, and increased the metastatic efficiency of NSCLC cells in vivo. We define molecular mechanisms for adaptive CME in cancer cells and a role for the reciprocal crosstalk between signaling and CME in cancer progression.

[Research progression of the relationship between integrin α2β1 and drug-induced gingival overgrowth]

Drug-induced gingival overgrowth (DIGO) is characterized by fibrous gingival hyperplasia and increased gingival volume. DIGO is histologically associated with proliferation of cells and deposition of extracellular matrices, particularly collagen. Integrin α2β1 is related to collagen phagocytosis and involved in the occurrence and progression of DIGO. This paper reviews the progress of research on the relationship between integrin α2β1 and DIGO.

Annexin A6-A multifunctional scaffold in cell motility

Annexin A6 (AnxA6) belongs to a highly conserved protein family characterized by their calcium (Ca²⁺)-dependent binding to phospholipids. Over the years, immunohistochemistry, subcellular fractionations, and live cell microscopy established that AnxA6 is predominantly found at the plasma membrane and endosomal compartments. In these locations, AnxA6 acts as a multifunctional scaffold protein, recruiting signaling proteins, modulating cholesterol and membrane transport and influencing actin dynamics. These activities enable AnxA6 to contribute to the formation of multifactorial protein complexes and membrane domains relevant in signal transduction, cholesterol homeostasis and endo-/exocytic membrane transport. Hence, AnxA6 has been implicated in many biological processes, including cell proliferation, survival, differentiation, inflammation, but also membrane repair and viral infection. More recently, we and others identified roles for AnxA6 in cancer cell migration and invasion. This review will discuss how the multiple scaffold functions may enable AnxA6 to modulate migratory cell behavior in health and disease.

Annexin A8 promotes VEGF-A driven endothelial cell sprouting

The physiological and pathological process of angiogenesis relies on orchestrated endothelial cell (EC) adhesion, migration and formation of new vessels. Here we report that human umbilical vein endothelial cells (HUVECs) deficient in Annexin A8 (AnxA8), a member of the annexin family of Ca²⁺- and membrane binding proteins, are strongly deficient in their ability to sprout in response to vascular endothelial growth factor (VEGF)-A, and are strongly impaired in their ability to migrate and adhere to β1 integrin-binding extracellular matrix (ECM) proteins. We find that these cells are defective in the formation of complexes containing the tetraspanin CD63, the main VEGF-A receptor VEGFR2, and the β1 integrin subunit, on the cell surface. We observe that upon VEGF-A activation of AnxA8-depleted HUVECs, VEGFR2 internalization is reduced, phosphorylation of VEGFR2 is increased, and the spatial distribution of Tyr577-phosphorylated focal adhesion kinase (pFAK577) is altered. We conclude that AnxA8 affects CD63/VEGFR2/β1 integrin complex formation, leading to hyperactivation of the VEGF-A signal transduction pathway, and severely disturbed VEGF-A-driven angiogenic sprouting.

Microtubules in 3D cell motility

Three-dimensional (3D) cell motility underlies essential processes, such as embryonic development, tissue repair and immune surveillance, and is involved in cancer progression. Although the cytoskeleton is a well-studied regulator of cell migration, most of what we know about its functions originates from studies conducted in two-dimensional (2D) cultures. This research established that the microtubule network mediates polarized trafficking and signaling that are crucial for cell shape and movement in 2D. In parallel, developments in light microscopy and 3D cell culture systems progressively allowed to investigate cytoskeletal functions in more physiologically relevant settings. Interestingly, several studies have demonstrated that microtubule involvement in cell morphogenesis and motility can differ in 2D and 3D environments. In this Commentary, we discuss these differences and their relevance for the understanding the role of microtubules in cell migration in vivo. We also provide an overview of microtubule functions that were shown to control cell shape and motility in 3D matrices and discuss how they can be investigated further by using physiologically relevant models.

L-type calcium channels regulate filopodia stability and cancer cell invasion downstream of integrin signalling

Mounting in vitro, in vivo and clinical evidence suggest an important role for filopodia in driving cancer cell invasion. Using a high-throughput microscopic-based drug screen, we identify FDA-approved calcium channel blockers (CCBs) as potent inhibitors of filopodia formation in cancer cells. Unexpectedly, we discover that L-type calcium channels are functional and frequently expressed in cancer cells suggesting a previously unappreciated role for these channels during tumorigenesis. We further demonstrate that, at filopodia, L-type calcium channels are activated by integrin inside-out signalling, integrin activation and Src. Moreover, L-type calcium channels promote filopodia stability and maturation into talin-rich adhesions through the spatially restricted regulation of calcium entry and subsequent activation of the protease calpain-1. Altogether we uncover a novel and clinically relevant signalling pathway that regulates filopodia formation in cancer cells and propose that cycles of filopodia stabilization, followed by maturation into focal adhesions, directs cancer cell migration and invasion.

Filopodia have a prominent role in driving cancer cell invasion. Here, the authors show that L-type calcium channels are a druggable target regulating filopodia stability and maturation into focal adhesions in metastatic breast cancer cells.

Amyloid β-induced astrogliosis is mediated by β1-integrin via NADPH oxidase 2 in Alzheimer's disease

Astrogliosis is a hallmark of Alzheimer's disease (AD) and may constitute a primary pathogenic component of that disorder. Elucidation of signaling cascades inducing astrogliosis should help characterizing the function of astrocytes and identifying novel molecular targets to modulate AD progression. Here, we describe a novel mechanism by which soluble amyloid-β modulates β1-integrin activity and triggers NADPH oxidase (NOX)-dependent astrogliosis in vitro and in vivo. Amyloid-β oligomers activate a PI3K/classical PKC/Rac1/NOX pathway which is initiated by β1-integrin in cultured astrocytes. This mechanism promotes β1-integrin maturation, upregulation of NOX2 and of the glial fibrillary acidic protein (GFAP) in astrocytes in vitro and in hippocampal astrocytes in vivo. Notably, immunochemical analysis of the hippocampi of a triple-transgenic AD mouse model shows increased levels of GFAP, NOX2, and β1-integrin in reactive astrocytes which correlates with the amyloid β-oligomer load. Finally, analysis of these proteins in postmortem frontal cortex from different stages of AD (II to V/VI) and matched controls confirmed elevated expression of NOX2 and β1-integrin in that cortical region and specifically in reactive astrocytes, which was most prominent at advanced AD stages. Importantly, protein levels of NOX2 and β1-integrin were significantly associated with increased amyloid-β load in human samples. These data strongly suggest that astrogliosis in AD is caused by direct interaction of amyloid β oligomers with β1-integrin which in turn leads to enhancing β1-integrin and NOX2 activity via NOX-dependent mechanisms. These observations may be relevant to AD pathophysiology.

Direct effect of dasatinib on signal transduction pathways associated with a rapid mobilization of cytotoxic lymphocytes

It has been shown that an increase in cytotoxic lymphocyte counts in the peripheral blood occurs rapidly after taking dasatinib, but the underlying mechanism is not yet elucidated. To investigate the influence of dasatinib on signal transduction pathways, we investigated the changes in JAK-STAT, mitogen-activated protein kinase (MAPK), and AKT in cytotoxic lymphocytes, including natural killer (NK) cells and cytotoxic T lymphocytes (CTLs), before and after dasatinib treatment in chronic myeloid leukemia patients. Among a total of 30 patients, 18 were treated with dasatinib, nine with imatinib, and three with nilotinib. At constitutive levels, the expression of phosphorylated proteins, pSTAT1, pSTAT3, and pERK in NK cells and pSTAT3 in CTLs, was significantly higher in dasatinib-treated patients. Among the patients evaluated, only dasatinib-treated patients showed inhibition of multiple signaling pathways after taking a tyrosine kinase inhibitor. The magnitude of pERK and pAKT inhibition was closely associated with an increase in NK cells and CTLs, respectively, after taking a tyrosine kinase inhibitor. Those responses were more evident in patients with cytomegalovirus IgG positivity. In this study, we demonstrated for the first time, the influence of dasatinib on cell events in cytotoxic lymphocytes in vivo and explained the possible underlying mechanism that results in lymphocyte mobilization after dasatinib treatment.

Transcriptional Control of Developmental Cell Behaviors

Tissue-specific transcription regulators emerged as key developmental control genes, which operate in the context of complex gene regulatory networks (GRNs) to coordinate progressive cell fate specification and tissue morphogenesis. We discuss how GRNs control the individual cell behaviors underlying complex morphogenetic events. Cell behaviors classically range from mesenchymal cell motility to cell shape changes in epithelial sheets. These behaviors emerge from the tissue-specific, multiscale integration of the local activities of universal and pleiotropic effectors, which underlie modular subcellular processes including cytoskeletal dynamics, cell-cell and cell-matrix adhesion, signaling, polarity, and vesicle trafficking. Extrinsic cues and intrinsic cell competence determine the subcellular spatiotemporal patterns of effector activities. GRNs influence most subcellular activities by controlling only a fraction of the effector-coding genes, which we argue is enriched in effectors involved in reading and processing the extrinsic cues to contextualize intrinsic subcellular processes and canalize developmental cell behaviors. The properties of the transcription-cell behavior interface have profound implications for evolution and disease.

Autophagy in adhesion and migration

Autophagy, a pathway for lysosomal-mediated cellular degradation, has recently been described as a regulator of cell migration. Although the molecular mechanisms underlying autophagy-dependent motility are only beginning to emerge, new work demonstrates that selective autophagy mediated by the autophagy cargo receptor, NBR1, specifically promotes the dynamic turnover of integrin-based focal adhesion sites during motility. Here, we discuss the detailed mechanisms through which NBR1-dependent selective autophagy supports focal adhesion remodeling, and we describe the interconnections between this pathway and other established regulators of focal adhesion turnover, such as microtubules. We also highlight studies that examine the contribution of autophagy to selective degradation of proteins that mediate cellular tension and to integrin trafficking; these findings hint at further roles for autophagy in supporting adhesion and migration. Given the recently appreciated importance of selective autophagy in diverse cellular processes, we propose that further investigation into autophagy-mediated focal adhesion turnover will not only shed light onto how focal adhesions are regulated but will also unveil new mechanisms regulating selective autophagy.

Liprin-α1 and ERC1 control cell edge dynamics by promoting focal adhesion turnover

Liprin-α1 and ERC1 are interacting scaffold proteins regulating the motility of normal and tumor cells. They act as part of plasma membrane-associated platforms at the edge of motile cells to promote protrusion by largely unknown mechanisms. Here we identify an amino-terminal region of the liprin-α1 protein (liprin-N) that is sufficient and necessary for the interaction with other liprin-α1 molecules. Similar to liprin-α1 or ERC1 silencing, expression of the liprin-N negatively affects tumor cell motility and extracellular matrix invasion, acting as a dominant negative by interacting with endogenous liprin-α1 and causing the displacement of the endogenous ERC1 protein from the cell edge. Interfering with the localization of ERC1 at the cell edge inhibits the disassembly of focal adhesions, impairing protrusion. Liprin-α1 and ERC1 proteins colocalize with active integrin β1 clusters distinct from those colocalizing with cytoplasmic focal adhesion proteins, and influence the localization of peripheral Rab7-positive endosomes. We propose that liprin-α1 and ERC1 promote protrusion by displacing cytoplasmic adhesion components to favour active integrin internalization into Rab7-positive endosomes.

The functional interplay of Rab11, FIP3 and Rho proteins on the endosomal recycling pathway controls cell shape and symmetry

Several families of small GTPases regulate a variety of fundamental cellular processes, encompassing growth factor signal transduction, vesicular trafficking and control of the cytoskeleton. Frequently, their action is hierarchical and complementary, but much of the detail of their functional interactions remains to be clarified. It is well established that Rab family members regulate a variety of intracellular vesicle trafficking pathways. Moreover, Rho family GTPases are pivotal for the control of the actin and microtubule cytoskeleton. However, the interplay between these 2 types of GTPases has been rarely reported. We discuss here our recent findings showing that Rab11, a key regulator of endosomal recycling, and Rac1, a central actin cytoskeleton regulator involved in lamellipodium formation and cell migration, interplay on endosomes through the Rab11 effector FIP3. In the context of the rapidly reactive T lymphocytes, Rab11-Rac1 endosomal functional interplay is important to control cell shape changes and cell symmetry during lymphocyte spreading and immunological synapse formation and ultimately modulate T cell activation.

Arf proteins in cancer cell migration

Members of the ADP-ribosylation factor (Arf) family of small GTP-binding (G) proteins regulate several aspects of membrane trafficking, such as vesicle budding, tethering and cytoskeleton organization. Arf family members, including Arf-like (Arl) proteins have been implicated in several essential cellular functions, like cell spreading and migration. These functions are used by cancer cells to disseminate and invade the tissues surrounding the primary tumor, leading to the formation of metastases. Indeed, Arf and Arl proteins, as well as their guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs) have been found to be abnormally expressed in different cancer cell types and human cancers. Here, we review the current evidence supporting the involvement of Arf family proteins and their GEFs and GAPs in cancer progression, focusing on 3 different mechanisms: cell-cell adhesion, integrin internalization and recycling, and actin cytoskeleton remodeling.

MenaINV mediates synergistic cross-talk between signaling pathways driving chemotaxis and haptotaxis

Directed cell migration, a key process in metastasis, arises from the combined influence of multiple processes, including chemotaxis-the directional movement of cells to soluble cues-and haptotaxis-the migration of cells on gradients of substrate-bound factors. However, it is unclear how chemotactic and haptotactic pathways integrate with each other to drive overall cell behavior. Mena^INV has been implicated in metastasis by driving chemotaxis via dysregulation of phosphatase PTP1B and more recently in haptotaxis via interaction with integrin α5β1. Here we find that Mena^INV-driven haptotaxis on fibronectin (FN) gradients requires intact signaling between α5β1 integrin and the epidermal growth factor receptor (EGFR), which is influenced by PTP1B. Furthermore, we show that Mena^INV-driven haptotaxis and ECM reorganization both require the Rab-coupling protein RCP, which mediates α5β1 and EGFR recycling. Finally, Mena^INV promotes synergistic migratory response to combined EGF and FN in vitro and in vivo, leading to hyperinvasive phenotypes. Together our data demonstrate that Mena^INV is a shared component of multiple prometastatic pathways that amplifies their combined effects, promoting synergistic cross-talk between RTKs and integrins.

Basement membrane fragments in the context of the epithelial-to-mesenchymal transition

The epithelial-to-mesenchymal transition (EMT) enables cells of epithelial phenotype to become motile and change to a migratory mesenchymal phenotype. EMT is known to be a fundamental requisite for tissue morphogenesis, and EMT-related pathways have been described in cancer metastasis and tissue fibrosis. Epithelial structures are marked by the presence of a sheet-like extracellular matrix, the basement membrane, which is assembled from two major proteins, laminin and collagen type IV. This specialized matrix is essential for tissue function and integrity, and provides an important barrier to the potential pathogenic migration of cells. The profound phenotypic transition in EMT involves the epithelial cells disrupting the basement membrane. Matrix metalloproteinases (MMPs) are known to cleave components of basement membranes, but MMP-basement membrane crosstalk during EMT in vivo is poorly understood. However, MMPs have been reported to play a role in EMT-related processes and a variety of basement membrane fragments have been shown to be released by specific MMPs in vitro and in vivo exhibiting distinct biological activities. This review discusses general considerations regarding the basement membrane in the context of EMT, a possible role for specific MMPs in EMT and highlights biologically active basement membrane fragments liberated by MMPs.

In vivo regulation of integrin turnover by outside-in activation

The development of three-dimensional tissue architecture requires precise control over the attachment of cells to the extracellular matrix (ECM). Integrins, the main ECM-binding receptors in animals, are regulated in multiple ways to modulate cell-ECM adhesion. One example is the conformational activation of integrins by extracellular signals ('outside-in activation') or by intracellular signals ('inside-out activation'), whereas another is the modulation of integrin turnover. We demonstrate that outside-in activation regulates integrin turnover to stabilize tissue architecture in vivo Treating Drosophila embryos with Mg(2+) and Mn(2+), known to induce outside-in activation, resulted in decreased integrin turnover. Mathematical modeling combined with mutational analysis provides mechanistic insight into the stabilization of integrins at the membrane. We show that as tissues mature, outside-in activation is crucial for regulating the stabilization of integrin-mediated adhesions. This data identifies a new in vivo role for outside-in activation and sheds light on the key transition between tissue morphogenesis and maintenance.

Cellular recruitment in myocardial ischaemia/reperfusion injury

BACKGROUND

Myocardial infarction (MI) is strictly linked to atherosclerosis. Beyond the mechanical narrowing of coronary vessels lumen, during MI a great burden of inflammation is carried out. One of the crucial events is represented by the ischaemia/reperfusion injury, a complex event involving inflammatory cells (such as neutrophils, platelets, monocytes/macrophages, lymphocytes and mast cells) and key activating signals (such as cytokines, chemokines and growth factors). Cardiac repair following myocardial infarction is dependent on a finely regulated response involving a sequential recruitment and the clearance of different subsets of inflammatory cells.

MATERIALS AND METHODS

This narrative review was based on the works detected on PubMed and MEDLINE up to November 2015.

RESULTS

Infarct healing classically follows three overlapping phases: the inflammatory phase, in which the innate immune pathways are activated and inflammatory leucocytes are recruited in order to clear the wound from dead cells; the proliferative phase, characterized by the suppression of pro-inflammatory signalling and infiltration of 'repairing' cells secreting matrix proteins in the injured area; and the maturation phase, which is associated with the quiescence and the elimination of the reparative cells together with cross-linking of the matrix. All these phases are timely regulated by the production of soluble mediators, such as cytokines, chemokines and growth factors.

CONCLUSION

Targeting inflammatory cell recruitment early during reperfusion and healing might be promising to selectively inhibit injury and favour repair. This approach might substantially improve adverse postischaemic left ventricle remodelling, characterized by dilation, hypertrophy of viable segments and progressive dysfunction.