Src kinase Hck association with the WASp and mDia1 cytoskeletal regulators promotes chemoattractant-induced Hck membrane targeting and activation in neutrophils

SHC4 orchestrates β-catenin pathway-mediated metastasis in triple-negative breast cancer by promoting Src kinase autophosphorylation

Triple-negative breast cancer (TNBC) is highly aggressive and metastatic, and has the poorest prognosis among all breast cancer subtypes. Activated β-catenin is enriched in TNBC and involved in Wnt signaling-independent metastasis. However, the underlying mechanisms of β-catenin activation in TNBC remain unknown. Here, we found that SHC4 was upregulated in TNBC and high SHC4 expression was significantly correlated with poor outcomes. Overexpression of SHC4 promoted TNBC aggressiveness in vitro and facilitated TNBC metastasis in vivo. Mechanistically, SHC4 interacted with Src and maintained its autophosphorylated activation, which activated β-catenin independent of Wnt signaling, and finally upregulated the transcription and expression of its downstream genes CD44 and MMP7. Furthermore, we determined that the PxPPxPxxxPxxP sequence on CH2 domain of SHC4 was critical for SHC4-Src binding and Src kinase activation. Overall, our results revealed the mechanism of β-catenin activation independent of Wnt signaling in TNBC, which was driven by SHC4-induced Src autophosphorylation, suggesting that SHC4 might be a potential prognostic marker and therapeutic target in TNBC.

Intelectin enhances the phagocytosis of macrophages via CDC42-WASF2-ARPC2 signaling axis in Megalobrama amblycephala

Intelectin has been identified in various vertebrates and plays an important role in the host immune system. In our previous studies, recombinant Megalobrama amblycephala intelectin (rMaINTL) protein with excellent bacterial binding and agglutination activities enhances the phagocytic and killing activities of macrophages in M. amblycephala; however, the underlying regulatory mechanisms remain unclear. The present study showed that treatment with Aeromonas hydrophila and LPS induced the expression of rMaINTL in macrophages, and its level and distribution in macrophages or kidney tissue markedly increased after incubation or injection with rMaINTL. The cellular structure of macrophages was significantly affected after incubation with rMaINTL, resulting in an increased surface area and pseudopodia extension, which might contribute to enhancing the phagocytic ability of macrophages. Then, digital gene expression profiling analysis of the kidneys from rMaINTL-treated juvenile M. amblycephala identified some phagocytosis-related signaling factors that were enriched in pathways involved in the regulation of the actin cytoskeleton. In addition, qRT-PCR and western blotting verified that rMaINTL upregulated the expression of CDC42, WASF2, and ARPC2 in vitro and in vivo; however, the expression of these proteins was inhibited by a CDC42 inhibitor in macrophages. Moreover, CDC42 mediated the promotion of rMaINTL on actin polymerization by increasing the F-actin/G-actin ratio, which led to the extension of pseudopodia and remodeling of the macrophage cytoskeleton. Furthermore, the enhancement of macrophage phagocytosis by rMaINTL was blocked by the CDC42 inhibitor. These results suggested that rMaINTL induced the expression of CDC42 as well as the downstream signaling molecules WASF2 and ARPC2, thereby facilitating actin polymerization to promote cytoskeletal remodeling and phagocytosis. Overall, MaINTL enhanced the phagocytosis activity of macrophages in M. amblycephala via activation of the CDC42-WASF2-ARPC2 signaling axis.

Reforming the Barrier: The Role of Formins in Wound Repair

The restoration of an intact epidermal barrier after wound injury is the culmination of a highly complex and exquisitely regulated physiological process involving multiple cells and tissues, overlapping dynamic events and protein synthesis and regulation. Central to this process is the cytoskeleton, a system of intracellular proteins that are instrumental in regulating important processes involved in wound repair including chemotaxis, cytokinesis, proliferation, migration, and phagocytosis. One highly conserved family of cytoskeletal proteins that are emerging as major regulators of actin and microtubule nucleation, polymerization, and stabilization are the formins. The formin family includes 15 different proteins categorized into seven subfamilies based on three formin homology domains (FH1, FH2, and FH3). The formins themselves are regulated in different ways including autoinhibition, activation, and localization by a range of proteins, including Rho GTPases. Herein, we describe the roles and effects of the formin family of cytoskeletal proteins on the fundamental process of wound healing and highlight recent advances relating to their important functions, mechanisms, and regulation at the molecular and cellular levels.

Diaphanous-related formin mDia2 regulates beta2 integrins to control hematopoietic stem and progenitor cell engraftment

Bone marrow engraftment of the hematopoietic stem and progenitor cells (HSPCs) involves homing to the vasculatures and lodgment to their niches. How HSPCs transmigrate from the vasculature to the niches is unclear. Here, we show that loss of diaphanous-related formin mDia2 leads to impaired engraftment of long-term hematopoietic stem cells and loss of competitive HSPC repopulation. These defects are likely due to the compromised trans-endothelial migration of HSPCs since their homing to the bone marrow vasculatures remained intact. Mechanistically, loss of mDia2 disrupts HSPC polarization and induced cytoplasmic accumulation of MAL, which deregulates the activity of serum response factor (SRF). We further reveal that beta2 integrins are transcriptional targets of SRF. Knockout of beta2 integrins in HSPCs phenocopies mDia2 deficient mice. Overexpression of SRF or beta2 integrins rescues HSPC engraftment defects associated with mDia2 deficiency. Our findings show that mDia2-SRF-beta2 integrin signaling is critical for HSPC lodgment to the niches.

Bone marrow engraftment of haematopoietic stem and progenitor cells (HSPCs) requires homing and lodgement to the niche. Here, the authors show that mDia2 is required for HSPC polarization, nuclear MAL, and SRF-induced beta2 integrin expression during transendothelial migration of HSPCs required for engraftment.

OLT1177, a β-sulfonyl nitrile compound, safe in humans, inhibits the NLRP3 inflammasome and reverses the metabolic cost of inflammation

The NLRP3 inflammasome is an intracellular oligomer regulating the activation of caspase-1 for the processing and secretion of IL-1β and IL-18. Although there is growing evidence to substantiate inflammasome inhibition as a therapeutic option for the treatment of inflammatory diseases, to date, there are no approved humans agents. OLT1177, a β-sulfonyl nitrile molecule, shown to be safe in humans, is a selective inhibitor of the NLRP3 inflammasome, with unique properties to reverse the metabolic costs of inflammation and to treat IL-1β– and IL-18–mediated diseases.

Activation of the NLRP3 inflammasome induces maturation of IL-1β and IL-18, both validated targets for treating acute and chronic inflammatory diseases. Here, we demonstrate that OLT1177, an orally active β-sulfonyl nitrile molecule, inhibits activation of the NLRP3 inflammasome. In vitro, nanomolar concentrations of OLT1177 reduced IL-1β and IL-18 release following canonical and noncanonical NLRP3 inflammasome activation. The molecule showed no effect on the NLRC4 and AIM2 inflammasomes, suggesting specificity for NLRP3. In LPS-stimulated human blood-derived macrophages, OLT1177 decreased IL-1β levels by 60% and IL-18 by 70% at concentrations 100-fold lower in vitro than plasma concentrations safely reached in humans. OLT1177 also reduced IL-1β release and caspase-1 activity in freshly obtained human blood neutrophils. In monocytes isolated from patients with cryopyrin-associated periodic syndrome (CAPS), OLT1177 inhibited LPS-induced IL-1β release by 84% and 36%. Immunoprecipitation and FRET analysis demonstrated that OLT1177 prevented NLRP3-ASC, as well as NLRP3-caspase-1 interaction, thus inhibiting NLRP3 inflammasome oligomerization. In a cell-free assay, OLT1177 reduced ATPase activity of recombinant NLRP3, suggesting direct targeting of NLRP3. Mechanistically, OLT1177 did not affect potassium efflux, gene expression, or synthesis of the IL-1β precursor. Steady-state levels of phosphorylated NF-κB and IkB kinase were significantly lowered in spleen cells from OLT1177-treated mice. We observed reduced IL-1β content in tissue homogenates, limited oxidative stress, and increased muscle oxidative metabolism in OLT1177-treated mice challenged with LPS. Healthy humans receiving 1,000 mg of OLT1177 daily for 8 d exhibited neither adverse effects nor biochemical or hematological changes.

Carcinoma associated fibroblasts (CAFs) promote breast cancer motility by suppressing mammalian Diaphanous-related formin-2 (mDia2)

The tumor microenvironment (TME) promotes tumor cell invasion and metastasis. An important step in the shift to a pro-cancerous microenvironment is the transformation of normal stromal fibroblasts to carcinoma-associated fibroblasts (CAFs). CAFs are present in a majority of solid tumors and can directly promote tumor cell motility via cytokine, chemokine and growth factor secretion into the TME. The exact effects that the TME has upon cytoskeletal regulation in motile tumor cells remain enigmatic. The conserved formin family of cytoskeleton regulating proteins plays an essential role in the assembly and/or bundling of unbranched actin filaments. Mammalian Diaphanous-related formin 2 (mDia2/DIAPH3/Drf3/Dia) assembles a dynamic F-actin cytoskeleton that underlies tumor cell migration and invasion. We therefore sought to understand whether CAF-derived chemokines impact breast tumor cell motility through modification of the formin-assembled F-actin cytoskeleton. In MDA-MB-231 cells, conditioned media (CM) from WS19T CAFs, a human breast tumor-adjacent CAF line, significantly and robustly increased wound closure and invasion relative to normal human mammary fibroblast (HMF)-CM. WS19T-CM also promoted proteasome-mediated mDia2 degradation in MDA-MB-231 cells relative to control HMF-CM and WS21T CAF-CM, a breast CAF cell line that failed to promote robust MDA-MB-231 migration. Cytokine array analysis of CM identified up-regulated secreted factors in WS19T relative to control WS21T CM. We identified CXCL12 as a CM factor influencing loss of mDia2 protein while increasing MDA-MB-231 cell migration. Our data suggest a mechanism whereby CAFs promote tumor cell migration and invasion through CXCL12 secretion to regulate the mDia2-directed cytoskeleton in breast tumor cells.

Mechanisms for fast cell migration in complex environments

Cell migration depends on a combination of the cell's intrinsic capacity to move and the proper interpretation of external cues. This multistep process enables leukocytes to travel long distances in organs in just a few hours. This fast migration is partly due to the leukocytes' high level of plasticity, which helps them to adapt to a changing environment. Here, we review recent progress in understanding the mechanisms used by leukocytes to move rapidly and efficiently in intricate anatomical landscapes. We shall focus on specific cytoskeletal rearrangements used by neutrophils and dendritic cells to migrate within confined environments. Lastly, we will describe the properties that facilitate the rapid migration of leukocyte in complex tissue geometries.

WASP and SCAR are evolutionarily conserved in actin-filled pseudopod-based motility

Eukaryotic cells use diverse cellular mechanisms to crawl through complex environments. Fritz-Laylin et al. define α-motility as a mode of migration associated with dynamic, actin-filled pseudopods and show that WASP and SCAR constitute an evolutionarily conserved genetic signature of α-motility.

Diverse eukaryotic cells crawl through complex environments using distinct modes of migration. To understand the underlying mechanisms and their evolutionary relationships, we must define each mode and identify its phenotypic and molecular markers. In this study, we focus on a widely dispersed migration mode characterized by dynamic actin-filled pseudopods that we call “α-motility.” Mining genomic data reveals a clear trend: only organisms with both WASP and SCAR/WAVE—activators of branched actin assembly—make actin-filled pseudopods. Although SCAR has been shown to drive pseudopod formation, WASP’s role in this process is controversial. We hypothesize that these genes collectively represent a genetic signature of α-motility because both are used for pseudopod formation. WASP depletion from human neutrophils confirms that both proteins are involved in explosive actin polymerization, pseudopod formation, and cell migration. WASP and WAVE also colocalize to dynamic signaling structures. Moreover, retention of WASP together with SCAR correctly predicts α-motility in disease-causing chytrid fungi, which we show crawl at >30 µm/min with actin-filled pseudopods. By focusing on one migration mode in many eukaryotes, we identify a genetic marker of pseudopod formation, the morphological feature of α-motility, providing evidence for a widely distributed mode of cell crawling with a single evolutionary origin.

Hijacking Host Cell Highways: Manipulation of the Host Actin Cytoskeleton by Obligate Intracellular Bacterial Pathogens

Intracellular bacterial pathogens replicate within eukaryotic cells and display unique adaptations that support key infection events including invasion, replication, immune evasion, and dissemination. From invasion to dissemination, all stages of the intracellular bacterial life cycle share the same three-dimensional cytosolic space containing the host cytoskeleton. For successful infection and replication, many pathogens hijack the cytoskeleton using effector proteins introduced into the host cytosol by specialized secretion systems. A subset of effectors contains eukaryotic-like motifs that mimic host proteins to exploit signaling and modify specific cytoskeletal components such as actin and microtubules. Cytoskeletal rearrangement promotes numerous events that are beneficial to the pathogen, including internalization of bacteria, structural support for bacteria-containing vacuoles, altered vesicular trafficking, actin-dependent bacterial movement, and pathogen dissemination. This review highlights a diverse group of obligate intracellular bacterial pathogens that manipulate the host cytoskeleton to thrive within eukaryotic cells and discusses underlying molecular mechanisms that promote these dynamic host-pathogen interactions.

An mDia2/ROCK signaling axis regulates invasive egress from epithelial ovarian cancer spheroids

Multi-cellular spheroids are enriched in ascites of epithelial ovarian cancer (OvCa) patients. They represent an invasive and chemoresistant cellular population fundamental to metastatic dissemination. The molecular mechanisms triggering single cell invasive egress from spheroids remain enigmatic. mDia formins are Rho GTPase effectors that are key regulators of F-actin cytoskeletal dynamics. We hypothesized that mDia2-driven F-actin dynamics promote single cell invasive transitions in clinically relevant three-dimensional (3D) OvCa spheroids. The current study is a dissection of the contribution of the F-actin assembly factor mDia2 formin in invasive transitions and using a clinically relevant ovarian cancer spheroid model. We show that RhoA-directed mDia2 activity is required for tight spheroid organization, and enrichment of mDia2 in the invasive cellular protrusions of collagen-embedded OVCA429 spheroids. Depleting mDia2 in ES-2 spheroids enhanced invasive dissemination of single amoeboid-shaped cells. This contrasts with spheroids treated with control siRNA, where a mesenchymal invasion program predominated. Inhibition of another RhoA effector, ROCK, had no impact on ES-2 spheroid formation but dramatically inhibited spheroid invasion through induction of a highly elongated morphology. Concurrent inhibition of ROCK and mDia2 blocked single cell invasion from ES-2 spheroids more effectively than inhibition of either protein alone, indicating that invasive egress of amoeboid cells from mDia2-depleted spheroids is ROCK-dependent. Our findings indicate that multiple GTPase effectors must be suppressed in order to fully block invasive egress from ovarian cancer spheroids. Furthermore, tightly regulated interplay between ROCK and mDia2 signaling pathways dictates the invasive capacities and the type of invasion program utilized by motile spheroid-derived ovarian cancer cells. As loss of the gene encoding mDia2, DRF3, has been linked to cancer progression and metastasis, our results set the stage for understanding molecular mechanisms involved in mDia2-dependent egress of invasive cells from primary epithelial tumors.

Tyrosine phosphorylation of Wiskott-Aldrich syndrome protein (WASP) by Hck regulates macrophage function

We have shown previously that tyrosine phosphorylation of Wiskott-Aldrich syndrome protein (WASP) is important for diverse macrophage functions including phagocytosis, chemotaxis, podosome dynamics, and matrix degradation. However, the specific tyrosine kinase mediating WASP phosphorylation is still unclear. Here, we provide evidence that Hck, which is predominantly expressed in leukocytes, can tyrosine phosphorylate WASP and regulates WASP-mediated macrophage functions. We demonstrate that tyrosine phosphorylation of WASP in response to stimulation with CX3CL1 or via Fcγ receptor ligation were severely reduced in Hck(-/-) bone marrow-derived macrophages (BMMs) or in RAW/LR5 macrophages in which Hck expression was silenced using RNA-mediated interference (Hck shRNA). Consistent with reduced WASP tyrosine phosphorylation, phagocytosis, chemotaxis, and matrix degradation are reduced in Hck(-/-) BMMs or Hck shRNA cells. In particular, WASP phosphorylation was primarily mediated by the p61 isoform of Hck. Our studies also show that Hck and WASP are required for passage through a dense three-dimensional matrix and transendothelial migration, suggesting that tyrosine phosphorylation of WASP by Hck may play a role in tissue infiltration of macrophages. Consistent with a role for this pathway in invasion, WASP(-/-) BMMs do not invade into tumor spheroids with the same efficiency as WT BMMs and cells expressing phospho-deficient WASP have reduced ability to promote carcinoma cell invasion. Altogether, our results indicate that tyrosine phosphorylation of WASP by Hck is required for proper macrophage functions.

Wiskott-Aldrich Syndrome causing mutation, Pro373Ser restricts conformational changes essential for WASP activity in T-cells

Wiskott-Aldrich Syndrome (WAS) is caused by mutations in Wiskott-Aldrich Syndrome Protein (WASP) and majority of the mutations are found in the WASP Homology 1 (WH1) domain which mediates interaction with WIP (WASP Interacting Protein), a WASP chaperone. Two point mutations together in the proline rich region (PRR) domain of WASP (S339Y/P373S) have been reported to cause WAS however the molecular defect has not been characterized. Expression of these mutants separately (WASPR(S339Y), WASPR(P373S)) or together (WASPR(SP/YS)) did not rescue the chemotaxis defect or membrane projection defect of Jurkat(WKD) T-cells (WASP knockdown). This is not due to the inability of WASP-PRR mutants to form functional WASP-WIP complex in growth rescue experiments in las17Δ yeast strain. Expression of WASPR(S339Y) but not WASPR(P373S) or WASPR(SP/YS) rescued the IL-2 expression defect of Jurkat(WKD) T-cells, suggesting that Pro373Ser mutation alone is sufficient to inhibit WASP functions in T-cell activation. The diffused localization of WASP-PRR mutants in activated Jurkat T-cells suggests that Ser339 and Pro373 are critical for WASP localization. WASP-PRR mutations either together or individually did not abolish interaction of WASP with sixteen WASP binding proteins including Hck, however they caused reduction in Hck mediated tyrosine phosphorylation of WASP which is critical for WASP activity. The auto-inhibitory conformation of WASP(P373S) mutant was not relieved by the binding of Toca-1 or Nck1. Thus, our results suggest that Pro373Ser mutation reduces Tyr291 phosphorylation and prevents conformational changes required for WASP activity in chemotaxis and T-cell activation. Thus Pro3373Ser is probably responsible for all the defects associated with WAS in the patients.

Formin' cellular structures: Physiological roles of Diaphanous (Dia) in actin dynamics

Members of the Diaphanous (Dia) protein family are key regulators of fundamental actin driven cellular processes, which are conserved from yeast to humans. Researchers have uncovered diverse physiological roles in cell morphology, cell motility, cell polarity, and cell division, which are involved in shaping cells into tissues and organs. The identification of numerous binding partners led to substantial progress in our understanding of the differential functions of Dia proteins. Genetic approaches and new microscopy techniques allow important new insights into their localization, activity, and molecular principles of regulation.

Dia-interacting protein (DIP) imposes migratory plasticity in mDia2-dependent tumor cells in three-dimensional matrices

Tumor cells rely upon membrane pliancy to escape primary lesions and invade secondary metastatic sites. This process relies upon localized assembly and disassembly cycles of F-actin that support and underlie the plasma membrane. Dynamic actin generates both spear-like and bleb structures respectively characterizing mesenchymal and amoeboid motility programs utilized by metastatic cells in three-dimensional matrices. The molecular mechanism and physiological trigger(s) driving membrane plasticity are poorly understood. mDia formins are F-actin assembly factors directing membrane pliancy in motile cells. mDia2 is functionally coupled with its binding partner DIP, regulating cortical actin and inducing membrane blebbing in amoeboid cells. Here we show that mDia2 and DIP co-tether to nascent blebs and this linkage is required for bleb formation. DIP controls mesenchymal/amoeboid cell interconvertability, while CXCL12 induces assembly of mDia2:DIP complexes to bleb cortices in 3D matrices. These results demonstrate how DIP-directed mDia2-dependent F-actin dynamics regulate morphological plasticity in motile cancer cells.

mDia1 targets v-Src to the cell periphery and facilitates cell transformation, tumorigenesis, and invasion

The small GTPase Rho regulates cell morphogenesis through remodeling of the actin cytoskeleton. While Rho is overexpressed in many clinical cancers, the role of Rho signaling in oncogenesis remains unknown. mDia1 is a Rho effector producing straight actin filaments. Here we transduced mouse embryonic fibroblasts from mDia1-deficient mice with temperature-sensitive v-Src and examined the involvement and mechanism of the Rho-mDia1 pathway in Src-induced oncogenesis. We showed that in v-Src-transduced mDia1-deficient cells, formation of actin filaments is suppressed, and v-Src in the perinuclear region does not move to focal adhesions upon a temperature shift. Consequently, membrane translocation of v-Src, v-Src-induced morphological transformation, and podosome formation are all suppressed in mDia1-deficient cells with impaired tyrosine phosphorylation. mDia1-deficient cells show reduced transformation in vitro as examined by focus formation and colony formation in soft agar and exhibit suppressed tumorigenesis and invasion when implanted in nude mice in vivo. Given overexpression of c-Src in various cancers, these findings suggest that Rho-mDia1 signaling facilitates malignant transformation and invasion by manipulating the actin cytoskeleton and targeting Src to the cell periphery.

The role of formins in human disease

Formins are a conserved family of proteins that play key roles in cytoskeletal remodeling. They nucleate and processively elongate non-branched actin filaments and also modulate microtubule dynamics. Despite their significant contributions to cell biology and development, few studies have directly implicated formins in disease pathogenesis. This review highlights the roles of formins in cell division, migration, immunity, and microvesicle formation in the context of human disease. In addition, we discuss the importance of controlling formin activity and protein expression to maintain cell homeostasis.

Contributions of Wiskott-Aldrich syndrome family cytoskeletal regulatory adapters to immune regulation

Cytoskeletal structure and dynamic rearrangement are integrally involved in coupling external stimuli to the orchestrated network of molecular interactions and cellular responses required for T-cell effector function. Members of the Wiskott-Aldrich syndrome protein (WASp) family are now widely recognized as cytoskeletal scaffolding adapters that coordinate the transmission of stimulatory signals to downstream induction of actin remodeling and cytoskeletal-dependent T-cell responses. In this review, we discuss the structural and functional properties of the WASp family members, with an emphasis on the roles of these proteins in the molecular pathways underpinning T-cell activation. The contributions of WASp family proteins and the cytoskeletal reorganization they evoke to expression of specific T-cell effector functions and the implications of such activity to normal immune responses and to the immunologic deficits manifested by Wiskott-Aldrich syndrome patients are also described.