Non-muscle myosin IIA differentially regulates intestinal epithelial cell restitution and matrix invasion

Non-muscle myosin heavy chain IIA regulates cell morphology, stress fibre structure, and cell migration in FLO-1 oesophageal adenocarcinoma cells

The incidence of oesophageal adenocarcinoma (OAC) is increasing at a rapid rate in Western countries. Early oesophageal cancer is often asymptomatic and metastatic disease is common at presentation leading to poor prognosis and survival rates. Cell migration is tightly controlled in the healthy cell but can become dysregulated in diseases such as OAC where increased cell motility and migration can contribute to metastasis. We investigated the role of an actin-based molecular motor, non-muscle myosin heavy chain IIA (NMHCIIA) in the migratory capacity of oesophageal adenocarcinoma cells. Immunofluorescence microscopy and ratiometric imaging demonstrated that NMHCIIA co-localises with F-actin at the leading edge and retracting rear of migrating FLO-1 OAC cells. siRNA-mediated depletion of NMHCIIA from FLO-1 cells altered cell morphology, gave rise to an increased number of stress fibre like structures and reduced FLO-1 cell migration. These findings suggest that NMHCIIA influences FLO-1 cell migration by regulating F-actin dynamics and the actin cytoskeleton, providing insight into the mechanisms of migration employed by OAC cells and identifying NMHCIIA as a potential therapeutic target for this disease.

Exploring the nexus between MYH9 and tumors: novel insights and new therapeutic opportunities

The myosin heavy chain 9 (MYH9) gene, located on human chromosome 22, encodes non-muscle myosin heavy chain IIA (NM IIA). This protein is essential to various cellular events, such as generating intracellular chemomechanical force and facilitating the movement of the actin cytoskeleton. Mutations associated with thrombocytopenia in autosomal dominant diseases first highlighted the significance of the MYH9 gene. In recent years, numerous studies have demonstrated the pivotal roles of MYH9 in various cancers. However, its effects on cancer are intricate and not fully comprehended. Furthermore, the elevated expression of MYH9 in certain malignancies suggests its potential as a target for tumor therapy. Nonetheless, there is a paucity of literature summarizing MYH9's role in tumors and the therapeutic strategies centered on it, necessitating a systematic analysis. This paper comprehensively reviews and analyzes the pertinent literature in this domain, elucidating the fundamental structural characteristics, biological functions, and the nexus between MYH9 and tumors. The mechanisms through which MYH9 contributes to tumor development and its multifaceted roles in the tumorigenic process are also explored. Additionally, we discuss the relationship between MYH9-related diseases (MYH9-RD) and tumors and also summarize tumor therapeutic approaches targeting MYH9. The potential clinical applications of studying the MYH9 gene include improving early diagnosis, clinical staging, and prognosis of tumors. This paper is anticipated to provide novel insights for tumor therapy.

Coactosin-like protein 1 regulates integrity and repair of model intestinal epithelial barriers via actin binding dependent and independent mechanisms

The actin cytoskeleton regulates the integrity and repair of epithelial barriers by mediating the assembly of tight junctions (TJs), and adherens junctions (AJs), and driving epithelial wound healing. Actin filaments undergo a constant turnover guided by numerous actin-binding proteins, however, the roles of actin filament dynamics in regulating intestinal epithelial barrier integrity and repair remain poorly understood. Coactosin-like protein 1 (COTL1) is a member of the ADF/cofilin homology domain protein superfamily that binds and stabilizes actin filaments. COTL1 is essential for neuronal and cancer cell migration, however, its functions in epithelia remain unknown. The goal of this study is to investigate the roles of COTL1 in regulating the structure, permeability, and repair of the epithelial barrier in human intestinal epithelial cells (IEC). COTL1 was found to be enriched at apical junctions in polarized IEC monolayers in vitro. The knockdown of COTL1 in IEC significantly increased paracellular permeability, impaired the steady state TJ and AJ integrity, and attenuated junctional reassembly in a calcium-switch model. Consistently, downregulation of COTL1 expression in Drosophila melanogaster increased gut permeability. Loss of COTL1 attenuated collective IEC migration and decreased cell-matrix attachment. The observed junctional abnormalities in COTL1-depleted IEC were accompanied by the impaired assembly of the cortical actomyosin cytoskeleton. Overexpression of either wild-type COTL1 or its actin-binding deficient mutant tightened the paracellular barrier and activated junction-associated myosin II. Furthermore, the actin-uncoupled COTL1 mutant inhibited epithelial migration and matrix attachment. These findings highlight COTL1 as a novel regulator of the intestinal epithelial barrier integrity and repair.

MYH9: A key protein involved in tumor progression and virus-related diseases

The myosin heavy chain 9 (MYH9) gene encodes the heavy chain of non-muscle myosin IIA (NMIIA), which belongs to the myosin II subfamily of actin-based molecular motors. Previous studies have demonstrated that abnormal expression and mutations of MYH9 were correlated with MYH9-related diseases and tumors. Furthermore, earlier investigations identified MYH9 as a tumor suppressor. However, subsequent research revealed that MYH9 promoted tumorigenesis, progression and chemoradiotherapy resistance. Note-worthily, MYH9 has also been linked to viral infections, like severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), Epstein-Barr virus, and hepatitis B virus, as a receptor or co-receptor. In addition, MYH9 promotes the development of hepatocellular carcinoma by interacting with the hepatitis B virus-encoding X protein. Finally, various findings highlighted the role of MYH9 in the development of these illnesses, especially in tumors. This review summarizes the involvement of the MYH9-regulated signaling network in tumors and virus-related diseases and presents possible drug interventions on MYH9, providing insights for the use of MYH9 as a therapeutic target for tumors and virus-mediated diseases.

Regeneration in calcareous sponge relies on 'purse-string' mechanism and the rearrangements of actin cytoskeleton

The crucial step in any regeneration process is epithelization, i.e. the restoration of an epithelium structural and functional integrity. Epithelization requires cytoskeletal rearrangements, primarily of actin filaments and microtubules. Sponges (phylum Porifera) are early branching metazoans with pronounced regenerative abilities. Calcareous sponges have a unique step during regeneration: the formation of a temporary structure, called regenerative membrane which initially covers a wound. It forms due to the morphallactic rearrangements of exopinaco- and choanoderm epithelial-like layers. The current study quantitatively evaluates morphological changes and characterises underlying actin cytoskeleton rearrangements during regenerative membrane formation in asconoid calcareous sponge Leucosolenia variabilis through a combination of time-lapse imaging, immunocytochemistry, and confocal laser scanning microscopy. Regenerative membrane formation has non-linear stochastic dynamics with numerous fluctuations. The pinacocytes at the leading edge of regenerative membrane form a contractile actomyosin cable. Regenerative membrane formation either depends on its contraction or being coordinated through it. The cell morphology changes significantly during regenerative membrane formation. Exopinacocytes flatten, their area increases, while circularity decreases. Choanocytes transdifferentiate into endopinacocytes, losing microvillar collar and flagellum. Their area increases and circularity decreases. Subsequent redifferentiation of endopinacocytes into choanocytes is accompanied by inverse changes in cell morphology. All transformations rely on actin filament rearrangements similar to those characteristic of bilaterian animals. Altogether, we provide here a qualitative and quantitative description of cell transformations during reparative epithelial morphogenesis in a calcareous sponge.

Unique and redundant functions of cytoplasmic actins and nonmuscle myosin II isoforms at epithelial junctions

The integrity and functions of epithelial barriers depend on the formation of adherens junctions (AJs) and tight junctions (TJs). A characteristic feature of AJs and TJs is their association with the cortical cytoskeleton composed of actin filaments and nonmuscle myosin II (NM-II) motors. Mechanical forces generated by the actomyosin cytoskeleton are essential for junctional assembly, stability, and remodeling. Epithelial cells express two different actin proteins and three NM-II isoforms, all known to be associated with AJs and TJs. Despite their structural similarity, different actin and NM-II isoforms have distinct biochemical properties, cellular distribution, and functions. The diversity of epithelial actins and myosin motors could be essential for the regulation of different steps of junctional formation, maturation, and disassembly. This review focuses on the roles of actin and NM-II isoforms in controlling the integrity and barrier properties of various epithelia. We discuss the effects of the depletion of individual actin isoforms and NM-II motors on the assembly and barrier function of AJs and TJs in model epithelial monolayers in vitro. We also describe the functional consequences of either total or tissue-specific gene knockout of different actins and NM-II motors, with a focus on the development and integrity of different epithelia in vivo.

Myosins and membrane trafficking in intestinal brush border assembly

Myosins are a class of motors that participate in a wide variety of cellular functions including organelle transport, cell adhesion, endocytosis and exocytosis, movement of RNA, and cell motility. Among the emerging roles for myosins is regulation of the assembly, morphology, and function of actin protrusions such as microvilli. The intestine harbors an elaborate apical membrane composed of highly organized microvilli. Microvilli assembly and function are intricately tied to several myosins including Myosin 1a, non-muscle Myosin 2c, Myosin 5b, Myosin 6, and Myosin 7b. Here, we review the research progress made in our understanding of myosin mediated apical assembly.

A myosin chaperone, UNC-45A, is a novel regulator of intestinal epithelial barrier integrity and repair

The actomyosin cytoskeleton serves as a key regulator of the integrity and remodeling of epithelial barriers by controlling assembly and functions of intercellular junctions and cell-matrix adhesions. Although biochemical mechanisms that regulate the activity of non-muscle myosin II (NM-II) in epithelial cells have been extensively investigated, little is known about assembly of the contractile myosin structures at the epithelial adhesion sites. UNC-45A is a cytoskeletal chaperone that is essential for proper folding of NM-II heavy chains and myofilament assembly. We found abundant expression of UNC-45A in human intestinal epithelial cell (IEC) lines and in the epithelial layer of the normal human colon. Interestingly, protein level of UNC-45A was decreased in colonic epithelium of patients with ulcerative colitis. CRISPR/Cas9-mediated knock-out of UNC-45A in HT-29cf8 and SK-CO15 IEC disrupted epithelial barrier integrity, impaired assembly of epithelial adherence and tight junctions and attenuated cell migration. Consistently, decreased UNC-45 expression increased permeability of the Drosophila gut in vivo. The mechanisms underlying barrier disruptive and anti-migratory effects of UNC-45A depletion involved disorganization of the actomyosin bundles at epithelial junctions and the migrating cell edge. Loss of UNC-45A also decreased contractile forces at apical junctions and matrix adhesions. Expression of deletion mutants revealed roles for the myosin binding domain of UNC-45A in controlling IEC junctions and motility. Our findings uncover a novel mechanism that regulates integrity and restitution of the intestinal epithelial barrier, which may be impaired during mucosal inflammation.

P-Cadherin Regulates Intestinal Epithelial Cell Migration and Mucosal Repair, but Is Dispensable for Colitis Associated Colon Cancer

Recurrent chronic mucosal inflammation, a characteristic of inflammatory bowel diseases (IBD), perturbs the intestinal epithelial homeostasis resulting in formation of mucosal wounds and, in most severe cases, leads to colitis-associated colon cancer (CAC). The altered structure of epithelial cell-cell adhesions is a hallmark of intestinal inflammation contributing to epithelial injury, repair, and tumorigenesis. P-cadherin is an important adhesion protein, poorly expressed in normal intestinal epithelial cells (IEC) but upregulated in inflamed and injured mucosa. The goal of this study was to investigate the roles of P-cadherin in regulating intestinal inflammation and CAC. P-cadherin expression was markedly induced in the colonic epithelium of human IBD patients and CAC tissues. The roles of P-cadherin were investigated in P-cadherin null mice using dextran sulfate sodium (DSS)-induced colitis and an azoxymethane (AOM)/DSS induced CAC. Although P-cadherin knockout did not affect the severity of acute DSS colitis, P-cadherin null mice exhibited faster recovery after colitis. No significant differences in the number of colonic tumors were observed in P-cadherin null and control mice. Consistently, the CRISPR/Cas9-mediated knockout of P-cadherin in human IEC accelerated epithelial wound healing without affecting cell proliferation. The accelerated migration of P-cadherin depleted IEC was driven by activation of Src kinases, Rac1 GTPase and myosin II motors and was accompanied by transcriptional reprogramming of the cells. Our findings highlight P-cadherin as a negative regulator of IEC motility in vitro and mucosal repair in vivo. In contrast, this protein is dispensable for IEC proliferation and CAC development.

Cytoskeletal dynamics regulates stromal invasion behavior of distinct liver cancer subtypes

Drug treatment against liver cancer has limited efficacy due to heterogeneous response among liver cancer subtypes. In addition, the functional biophysical phenotypes which arise from this heterogeneity and contribute to aggressive invasive behavior remain poorly understood. This study interrogated how heterogeneity in liver cancer subtypes contributes to differences in invasive phenotypes and drug response. Utilizing histological analysis, quantitative 2D invasion metrics, reconstituted 3D hydrogels, and bioinformatics, our study linked cytoskeletal dynamics to differential invasion profiles and drug resistance in liver cancer subtypes. We investigated cytoskeletal regulation in 2D and 3D culture environments using two liver cancer cell lines, SNU-475 and HepG2, chosen for their distinct cytoskeletal features and invasion profiles. For SNU-475 cells, a model for aggressive liver cancer, many cytoskeletal inhibitors abrogated 2D migration but only some suppressed 3D migration. For HepG2 cells, cytoskeletal inhibition did not significantly affect 3D migration but did affect proliferative capabilities and spheroid core growth. This study highlights cytoskeleton driven phenotypic variation, their consequences and coexistence within the same tumor, as well as efficacy of targeting biophysical phenotypes that may be masked in traditional screens against tumor growth.

Myosin Motors: Novel Regulators and Therapeutic Targets in Colorectal Cancer

Colorectal cancer (CRC) remains the third most common cause of cancer and the second most common cause of cancer deaths worldwide. Clinicians are largely faced with advanced and metastatic disease for which few interventions are available. One poorly understood aspect of CRC involves altered organization of the actin cytoskeleton, especially at the metastatic stage of the disease. Myosin motors are crucial regulators of actin cytoskeletal architecture and remodeling. They act as mechanosensors of the tumor environments and control key cellular processes linked to oncogenesis, including cell division, extracellular matrix adhesion and tissue invasion. Different myosins play either oncogenic or tumor suppressor roles in breast, lung and prostate cancer; however, little is known about their functions in CRC. This review focuses on the functional roles of myosins in colon cancer development. We discuss the most studied class of myosins, class II (conventional) myosins, as well as several classes (I, V, VI, X and XVIII) of unconventional myosins that have been linked to CRC development. Altered expression and mutations of these motors in clinical tumor samples and their roles in CRC growth and metastasis are described. We also evaluate the potential of using small molecular modulators of myosin activity to develop novel anticancer therapies.

A Novel Pharmacological Approach to Enhance the Integrity and Accelerate Restitution of the Intestinal Epithelial Barrier

BACKGROUND

Disruption of the gut barrier is an essential mechanism of inflammatory bowel diseases (IBDs) contributing to the development of mucosal inflammation. A hallmark of barrier disruption is the disassembly of epithelial adherens junctions (AJs) driven by decreased expression of a major AJ protein, E-cadherin. A group of isoxazole compounds, such as E-cadherin-upregulator (ECU) and ML327, were previously shown to stimulate E-cadherin expression in poorly differentiated human cancer cells. This study was designed to examine whether these isoxazole compounds can enhance and protect model intestinal epithelial barriers in vitro.

METHODS

The study was conducted using T84, SK-CO15, and HT-29 human colonic epithelial cell monolayers. Disruption of the epithelial barrier was induced by pro-inflammatory cytokines, tumor necrosis factor-α, and interferon-γ. Barrier integrity and epithelial junction assembly was examined using different permeability assays, immunofluorescence labeling, and confocal microscopy. Epithelial restitution was analyzed using a scratch wound healing assay.

RESULTS

E-cadherin-upregulator and ML327 treatment of intestinal epithelial cell monolayers resulted in several barrier-protective effects, including reduced steady-state epithelial permeability, inhibition of cytokine-induced barrier disruption and junction disassembly, and acceleration of epithelial wound healing. Surprisingly, these effects were not due to upregulation of E-cadherin expression but were mediated by multiple mechanisms including inhibition of junction protein endocytosis, attenuation of cytokine-induced apoptosis, and activation of promigratory Src and AKT signaling.

CONCLUSIONS

Our data highlight ECU and ML327 as promising compounds for developing new therapeutic strategies to protect the integrity and accelerate the restitution of the intestinal epithelial barrier in IBD and other inflammatory disorders.

DT-13 inhibits breast cancer cell migration via non-muscle myosin II-A regulation in tumor microenvironment synchronized adaptations

BACKGROUND

Tumor metastasis is a terrifying characteristic of cancer. Numerous studies have been conducted to overcome metastasis by targeting tumor microenvironment (TME). However, due to complexity of tumor microenvironment, it remained difficult for accurate targeting. Dwarf-lillytruf tuber monomer-13 (DT-13) possess good potential against TME.

OBJECTIVE

As TME is supportive for tumor metastasis, alternatively it is a challenging for therapeutic intervention. In our present study, we explored molecular mechanism through which TME induced cell migration and how DT-13 interferes in this mechanism.

METHODS

We used a novel model of co-culture system which is eventually developed in our lab. Tumor cells were co-cultured with hypoxia induced cancer-associated fibroblasts (CAF) or with chemically induced cancer-associated adipocytes (CAA). The effect of hypoxia in conditioned medium for CAF was assessed through expression of α-SMA and HIF by western blotting while oil red staining was done to assess the successful chemical induction for adipocytes (CAA), the effect of TME through conditioned medium on cell migration was analyzed by trans-well cell migration, and cell motility (wound healing) analyses. The expression changes in cellular proteins were assessed through western blotting and immunofluorescent studies.

RESULTS AND CONCLUSION

Our results showed that tumor microenvironment has a direct role in promoting breast cancer cell migration by stromal cells; moreover, we found that DT-13 restricts this TME regulated cell migration via targeting stromal cells in vitro. Additionally we also found that DT-13 targets NMII-A for its effect on breast cancer cell migration for the regulation of stromal cells in TME.

Assembly of myosin II filament arrays: Network Contraction versus Expansion

How cellular contractile systems assemble has fascinated scientists for generations. The major molecule responsible for cellular force generation is the molecular motor, non-muscle myosin II (NMII). NMII molecules are organized into single myosin filaments and larger arrays of filaments called NMII stacks, which are capable of generating increasing amounts of force. The textbook model of NMII stack assembly is the Network Contraction Model, where ensembles of distinct NMII filaments condense into a NMII stack by pulling on actin filaments. While this model has been widely accepted for ~20 years, it has been difficult to test inside cells due to the small size of NMII filaments. Recently, interest in how NMII stacks form has been reinvigorated by the advent of super-resolution microscopy techniques which have afforded unprecedented resolution of NMII filaments inside cells. A number of recent publications using these techniques have called into question key aspects of the Network Contraction Model, and our understanding of how NMII stacks assemble.

Evidence for calpains in cancer metastasis

Metastatic dissemination represents the final stage of tumor progression as well as the principal cause of cancer-associated deaths. Calpains are a conserved family of calcium-dependent cysteine proteinases with ubiquitous or tissue-specific expression. Accumulating evidence indicates a central role for calpains in tumor migration and invasion via participating in several key processes, including focal adhesion dynamics, cytoskeletal remodeling, epithelial-to-mesenchymal transition, and apoptosis. Activated after the increased intracellular calcium concentration ( [ Ca 2 + ] i ) induced by membrane channels and extracellular or intracellular stimuli, calpains induce the limited cleavage or functional modulation of various substrates that serve as metastatic mediators. This review covers established literature to summarize the mechanisms and underlying signaling pathways of calpains in cancer metastasis, making calpains attractive targets for aggressive tumor therapies.

Adducins inhibit lung cancer cell migration through mechanisms involving regulation of cell-matrix adhesion and cadherin-11 expression

Cell migration is a critical mechanism controlling tissue morphogenesis, epithelial wound healing and tumor metastasis. Migrating cells depend on orchestrated remodeling of the plasma membrane and the underlying actin cytoskeleton, which is regulated by the spectrin-adducin-based membrane skeleton. Expression of adducins is altered during tumorigenesis, however, their involvement in metastatic dissemination of tumor cells remains poorly characterized. This study investigated the roles of α-adducin (ADD1) and γ-adducin (ADD3) in regulating migration and invasion of non-small cell lung cancer (NSCLC) cells. ADD1 was mislocalized, whereas ADD3 was markedly downregulated in NSCLC cells with the invasive mesenchymal phenotype. CRISPR/Cas9-mediated knockout of ADD1 and ADD3 in epithelial-type NSCLC and normal bronchial epithelial cells promoted their Boyden chamber migration and Matrigel invasion. Furthermore, overexpression of ADD1, but not ADD3, in mesenchymal-type NSCLC cells decreased cell migration and invasion. ADD1-overexpressing NSCLC cells demonstrated increased adhesion to the extracellular matrix (ECM), accompanied by enhanced assembly of focal adhesions and hyperphosphorylation of Src and paxillin. The increased adhesiveness and decreased motility of ADD1-overexpressing cells were reversed by siRNA-mediated knockdown of Src. By contrast, the accelerated migration of ADD1 and ADD3-depleted NSCLC cells was ECM adhesion-independent and was driven by the upregulated expression of pro-motile cadherin-11. Overall, our findings reveal a novel function of adducins as negative regulators of NSCLC cell migration and invasion, which could be essential for limiting lung cancer progression and metastasis.

Myosins as fundamental components during tumorigenesis: diverse and indispensable

Myosin is a kind of actin-based motor protein. As the crucial functions of myosin during tumorigenesis have become increasingly apparent, the profile of myosin in the field of cancer research has also been growing. Eighteen distinct classes of myosins have been discovered in the past twenty years and constitute a diverse superfamily. Various myosins share similar structures. They all convert energy from ATP hydrolysis to exert mechanical stress upon interactions with microfilaments. Ongoing research is increasingly suggesting that at least seven kinds of myosins participate in the formation and development of cancer. Myosins play essential roles in cytokinesis failure, chromosomal and centrosomal amplification, multipolar spindle formation and DNA microsatellite instability. These are all prerequisites of tumor formation. Subsequently, myosins activate various processes of tumor invasion and metastasis development including cell migration, adhesion, protrusion formation, loss of cell polarity and suppression of apoptosis. In this review, we summarize the current understanding of the roles of myosins during tumorigenesis and discuss the factors and mechanisms which may regulate myosins in tumor progression. Furthermore, we put forward a completely new concept of “chromomyosin” to demonstrate the pivotal functions of myosins during karyokinesis and how this acts to optimize the functions of the members of the myosin superfamily.

Mutations of MYH14 are associated to anorectal malformations with recto-perineal fistulas in a small subset of Chinese population

BACKGROUND

Anorectal malformations (ARMs) are among the most commonly congenital abnormalities of distal hindgut development, ranging from anal stenosis to anal atresia with or without fistulas and persistent cloaca. The etiology remains elusive for most ARM cases and the majority of genetic studies on ARMs were based on a candidate gene approach.

MATERIALS AND METHODS

In all eight family members of a non-consanguineous Chinese family, we performed whole-exome sequencing. Subsequently, exome sequencing of MYH14 in 72 unrelated probands with ARMs was performed. The accurate distribution of non-muscle myosin II heavy chain (NMHC II) was investigated by immunohistochemistry in serial sagittal sections of E11.5-13.5 mouse cloacal regions.

RESULTS

A homozygous mutation in MYH14 was identified in the two siblings of family 1. Compound heterozygous MYH14 changes were identified in an unrelated individual. Immunohistochemical analysis suggest stronger NMHC IIC localization in the epithelium of the murine embryonic cloaca, urorectal septum and hindgut compared with another two NMHC II isoforms.

CONCLUSION

This is the first identification of mutations in MYH14 as a cause of ARMs. The stronger localization of NMHC IIC in E11.5-13.5 mouse cloacal regions further supports the role of MYH14 in anorectal development.

Rho GTPases and actomyosin: Partners in regulating epithelial cell-cell junction structure and function

Epithelial tissues are defined by polarized epithelial cells that are integrated into tissues and exhibit barrier function in order to regulate what is allowed to pass between cells. Cell-cell junctions must be stable enough to promote barrier function and tissue integrity, yet plastic enough to remodel when necessary. This remarkable ability to dynamically sense and respond to changes in cell shape and tissue tension allows cell-cell junctions to remain functional during events that disrupt epithelial homeostasis including morphogenesis, wound healing, and cell division. In order to achieve this plasticity, both tight junctions and adherens junctions are coupled to the underlying actomyosin cytoskeleton. Here, we discuss the importance of the junctional linkage to actomyosin and how a localized zone of active RhoA along with other Rho GTPases work together to orchestrate junctional actomyosin dynamics. We focus on how scaffold proteins help coordinate Rho GTPases, their upstream regulators, and their downstream effectors for efficient, localized Rho GTPase signaling output. Additionally, we highlight important roles junctional actin-binding proteins play in addition to their traditional roles in organizing actin. Together, Rho GTPases, their regulators, and effectors form compartmentalized signaling modules that regulate actomyosin structure and contractility to achieve proper cell-cell adhesion and tissue barriers.

Myosin IIA Heavy Chain Phosphorylation Mediates Adhesion Maturation and Protrusion in Three Dimensions

Non-muscle myosin II (NMII) is a conserved force-producing cytoskeletal enzyme with important but poorly understood roles in cell migration. To investigate myosin heavy chain (MHC) phosphorylation roles in 3D migration, we expressed GFP-tagged NMIIA wild-type or mutant constructs in cells depleted of endogenous NMIIA protein. We find that individual mutation or double mutation of Ser-1916 or Ser-1943 to alanine potently blocks recruitment of GFP-NM-IIA filaments to leading edge protrusions in 2D, and this in turn blocks maturation of anterior focal adhesions. When placed in 3D collagen gels, cells expressing wild-type GFP MHC-IIA behave like parental cells, displaying robust and active formation and retraction of protrusions. However, cells depleted of NMIIA or cells expressing the mutant GFP MHC-IIA display severe defects in invasion and in stabilizing protrusions in 3D. These studies reveal an NMIIA-specific role in 3D invasion that requires competence for NMIIA phosphorylation at Ser-1916 and Ser-1943. In sum, these results demonstrate a critical and previously unrecognized role for NMIIA phosphorylation in 3D invasion.

Coronin 1B supports RhoA signaling at cell-cell junctions through Myosin II

Non-muscle myosin II (NMII) motor proteins are responsible for generating contractile forces inside eukaryotic cells. There is also a growing interest in the capacity for these motor proteins to influence cell signaling through scaffolding, especially in the context of RhoA GTPase signaling. We previously showed that NMIIA accumulation and stability within specific regions of the cell cortex, such as the zonula adherens (ZA), allows the formation of a stable RhoA signaling zone. Now we demonstrate a key role for Coronin 1B in maintaining this junctional pool of NMIIA, as depletion of Coronin 1B significantly compromised myosin accumulation and stability at junctions. The loss of junctional NMIIA, upon Coronin 1B knockdown, perturbed RhoA signaling due to enhanced junctional recruitment of the RhoA antagonist, p190B Rho GAP. This effect was blocked by the expression of phosphomimetic MRLC-DD, thus reinforcing the central role of NMII in regulating RhoA signaling.

Coronin 1B Reorganizes the Architecture of F-Actin Networks for Contractility at Steady-State and Apoptotic Adherens Junctions

In this study we sought to identify how contractility at adherens junctions influences apoptotic cell extrusion. We first found that the generation of effective contractility at steady-state junctions entails a process of architectural reorganization whereby filaments that are initially generated as poorly organized networks of short bundles are then converted into co-aligned perijunctional bundles. Reorganization requires coronin 1B, which is recruited to junctions by E-cadherin adhesion and is necessary to establish contractile tension at the zonula adherens. When cells undergo apoptosis within an epithelial monolayer, coronin 1B is also recruited to the junctional cortex at the apoptotic/neighbor cell interface in an E-cadherin-dependent fashion to support actin architectural reorganization, contractility, and extrusion. We propose that contractile stress transmitted from the apoptotic cell through E-cadherin adhesions elicits a mechanosensitive response in neighbor cells that is necessary for the morphogenetic event of apoptotic extrusion to occur.

Nonmuscle Myosin IIA Regulates Intestinal Epithelial Barrier in vivo and Plays a Protective Role During Experimental Colitis

The actin cytoskeleton is a critical regulator of intestinal mucosal barrier permeability, and the integrity of epithelial adherens junctions (AJ) and tight junctions (TJ). Non muscle myosin II (NM II) is a key cytoskeletal motor that controls actin filament architecture and dynamics. While NM II has been implicated in the regulation of epithelial junctions in vitro, little is known about its roles in the intestinal mucosa in vivo. In this study, we generated a mouse model with an intestinal epithelial-specific knockout of NM IIA heavy chain (NM IIA cKO) and examined the structure and function of normal gut barrier, and the development of experimental colitis in these animals. Unchallenged NM IIA cKO mice showed increased intestinal permeability and altered expression/localization of several AJ/TJ proteins. They did not develop spontaneous colitis, but demonstrated signs of a low-scale mucosal inflammation manifested by prolapses, lymphoid aggregates, increased cytokine expression, and neutrophil infiltration in the gut. NM IIA cKO animals were characterized by a more severe disruption of the gut barrier and exaggerated mucosal injury during experimentally-induced colitis. Our study provides the first evidence that NM IIA plays important roles in establishing normal intestinal barrier, and protection from mucosal inflammation in vivo.

A Proteomic Analysis of the Body Wall, Digestive Tract, and Reproductive Tract of Brugia malayi

Filarial worms are parasitic nematodes that cause devastating diseases such as lymphatic filariasis (LF) and onchocerciasis. Filariae are nematodes with complex anatomy including fully developed digestive tracts and reproductive organs. To better understand the basic biology of filarial parasites and to provide insights into drug targets and vaccine design, we conducted a proteomic analysis of different anatomic fractions of Brugia malayi, a causative agent of LF. Approximately 500 adult female B. malayi worms were dissected, and three anatomical fractions (body wall, digestive tract, and reproductive tract) were obtained. Proteins from each anatomical fraction were extracted, desalted, trypsinized, and analyzed by microcapillary reverse-phase liquid chromatography-tandem-mass spectrometry. In total, we identified 4,785 B. malayi proteins. While 1,894 were identified in all three anatomic fractions, 396 were positively identified only within the digestive tract, 114 only within the body wall, and 1,011 only within the reproductive tract. Gene set enrichment analysis revealed a bias for transporters to be present within the digestive tract, suggesting that the intestine of adult filariae is functional and important for nutrient uptake or waste removal. As expected, the body wall exhibited increased frequencies of cytoskeletal proteins, and the reproductive tract had increased frequencies of proteins involved in nuclear regulation and transcription. In assessing for possible vaccine candidates, we focused on proteins sequestered within the digestive tract, as these could possibly represent “hidden antigens” with low risk of prior allergic sensitization. We identified 106 proteins that are enriched in the digestive tract and are predicted to localize to the surface of cells in the the digestive tract. It is possible that some of these proteins are on the luminal surface and may be accessible by antibodies ingested by the worm. A subset of 27 of these proteins appear especially promising vaccine candidates as they contain significant non-cytoplasmic domains, only 1–2 transmembrane domains, and a high degree of homology to W. bancrofti and/or O. volvulus.

Filarial worms are parasitic worms that can live for years within humans and cause diseases such as elephantiasis and river blindness. In this study, we identified the proteins that exist within the worm's digestive tract, reproductive tract, and body wall. In addition to increasing our understanding of the basic biology of these parasites, this information is valuable for predicting which proteins may be candidates for vaccine development and rational drug design. Specifically, by analyzing which intestinal proteins are likely expressed on the surface of cells contained within the parasite's digestive tract and have little similarity to human proteins, we identified 27 possible vaccine candidates that warrant further study.

Phosphorylation of Nonmuscle myosin II-A regulatory light chain resists Sendai virus fusion with host cells

Enveloped viruses enter host cells through membrane fusion and the cells in turn alter their shape to accommodate components of the virus. However, the role of nonmuscle myosin II of the actomyosin complex of host cells in membrane fusion is yet to be understood. Herein, we show that both (−) blebbistatin, a specific inhibitor of nonmuscle myosin II (NMII) and small interfering RNA markedly augment fusion of Sendai virus (SeV), with chinese hamster ovary cells and human hepatocarcinoma cells. Inhibition of RLC phosphorylation using inhibitors against ROCK, but not PKC and MRCK, or overexpression of phospho-dead mutant of RLC enhances membrane fusion. SeV infection increases cellular stiffness and myosin light chain phosphorylation at two hour post infection. Taken together, the present investigation strongly indicates that Rho-ROCK-NMII contractility signaling pathway may provide a physical barrier to host cells against viral fusion.

Alterations of the apical junctional complex and actin cytoskeleton and their role in colorectal cancer progression

Colorectal cancer represents the fourth highest mortality rate among cancer types worldwide. An understanding of the molecular mechanisms that regulate their progression can prevents or reduces mortality due to this disease. Epithelial cells present an apical junctional complex connected to the actin cytoskeleton, which maintains the dynamic properties of this complex, tissue architecture and cell homeostasis. Several studies have indicated that apical junctional complex alterations and actin cytoskeleton disorganization play a critical role in epithelial cancer progression. However, few studies have examined the existence of an interrelation between these 2 components, particularly in colorectal cancer. This review discusses the recent progress toward elucidating the role of alterations of apical junctional complex constituents and of modifications of actin cytoskeleton organization and discusses how these events are interlinked to modulate cellular responses related to colorectal cancer progression toward successful metastasis.

Quantitative proteomic analysis reveals heat stress-induced injury in rat small intestine via activation of the MAPK and NF-κB signaling pathways

We employed comparative proteomics to reveal a heat stress-induced injury mechanism in rat small intestine.

The interaction between Shroom3 and Rho-kinase is required for neural tube morphogenesis in mice

Shroom3 is an actin-associated regulator of cell morphology that is required for neural tube closure, formation of the lens placode, and gut morphogenesis in mice and has been linked to chronic kidney disease and directional heart looping in humans. Numerous studies have shown that Shroom3 likely regulates these developmental processes by directly binding to Rho-kinase and facilitating the assembly of apically positioned contractile actomyosin networks. We have characterized the molecular basis for the neural tube defects caused by an ENU-induced mutation that results in an arginine-to-cysteine amino acid substitution at position 1838 of mouse Shroom3. We show that this substitution has no effect on Shroom3 expression or localization but ablates Rock binding and renders Shroom3 non-functional for the ability to regulate cell morphology. Our results indicate that Rock is the major downstream effector of Shroom3 in the process of neural tube morphogenesis. Based on sequence conservation and biochemical analysis, we predict that the Shroom-Rock interaction is highly conserved across animal evolution and represents a signaling module that is utilized in a variety of biological processes.

N-ethylmaleimide-sensitive factor attachment protein α (αSNAP) regulates matrix adhesion and integrin processing in human epithelial cells

Integrin-based adhesion to the extracellular matrix (ECM) plays critical roles in controlling differentiation, survival, and motility of epithelial cells. Cells attach to the ECM via dynamic structures called focal adhesions (FA). FA undergo constant remodeling mediated by vesicle trafficking and fusion. A soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein α (αSNAP) is an essential mediator of membrane fusion; however, its roles in regulating ECM adhesion and cell motility remain unexplored. In this study, we found that siRNA-mediated knockdown of αSNAP induced detachment of intestinal epithelial cells, whereas overexpression of αSNAP increased ECM adhesion and inhibited cell invasion. Loss of αSNAP impaired Golgi-dependent glycosylation and trafficking of β1 integrin and decreased phosphorylation of focal adhesion kinase (FAK) and paxillin resulting in FA disassembly. These effects of αSNAP depletion on ECM adhesion were independent of apoptosis and NSF. In agreement with our previous reports that Golgi fragmentation mediates cellular effects of αSNAP knockdown, we found that either pharmacologic or genetic disruption of the Golgi recapitulated all the effects of αSNAP depletion on ECM adhesion. Furthermore, our data implicates β1 integrin, FAK, and paxillin in mediating the observed pro-adhesive effects of αSNAP. These results reveal novel roles for αSNAP in regulating ECM adhesion and motility of epithelial cells.

Dynamics and regulation of epithelial adherens junctions: recent discoveries and controversies

Adherens junctions (AJs) are evolutionarily conserved plasma-membrane structures that mediate cell-cell adhesions in multicellular organisms. They are organized by several types of adhesive integral membrane proteins, most notably cadherins and nectins that are clustered and stabilized by a number of cytoplasmic scaffolds. AJs are key regulators of tissue architecture and dynamics via control of cell proliferation, polarity, shape, motility, and survival. They are absolutely critical for normal tissue morphogenesis and their disruption results in pathological abnormalities in different tissues. Although the field of adherens-junction research dramatically progressed in recent years, a number of important questions remain controversial and poorly understood. This review outlines basic principles that regulate organization of AJs in mammalian epithelia and discusses recent advances and standing controversies in the field. A special attention is paid to the regulation of AJs by vesicle trafficking and the intracellular cytoskeleton as well as roles and mechanisms of adherens-junction disruption during tumor progression and tissue inflammation.

Structure and regulation of intestinal epithelial tight junctions: current concepts and unanswered questions

Intestinal epithelium serves as a key interface between internal body compartments and the gut lumen. The epithelial layer forms a physical barrier that protects the body from the harmful environment of the lumen and also mediates vectorial fluxes of fluids, nutrients and waste. Increased permeability of the epithelial barrier is a common manifestation of different gastrointestinal diseases that enhances body exposure to external pathogens thereby exaggerating mucosal inflammation. Barrier properties of the intestinal epithelium are regulated by specialized adhesive plasma membrane structures known as tight junctions (TJs). It is gengrally believed that disease-related increase in intestinal permeability is caused by defects in TJ structure and functions. This chapter describes the molecular composition of intestinal epithelial TJs, basic mechanisms that regulate TJ functions in healthy gut mucosa as well as molecular events that contribute to increased mucosal permeability during intestinal inflammation. The chapter outlines our current understanding of TJ structure and dynamics and highlights several unresolved questions regarding regulation of this junctional complex under normal conditions and in gastroenterological diseases.

Myosin IIA deficient cells migrate efficiently despite reduced traction forces at cell periphery

Cell motility is a cornerstone of embryogenesis, tissue remodeling and repair, and cancer cell invasion. It is generally thought that migrating cells grab and exert traction force onto the extracellular matrix in order to pull the cell body forward. While previous studies have shown that myosin II deficient cells migrate efficiently, whether these cells exert traction forces during cell migration in the absence of the major contractile machinery is currently unknown. Using an array of micron-sized pillars as a force sensor and shRNA specific to each myosin II isoform (A and B), we analyzed how myosin IIA and IIB individually regulate cell migration and traction force generation. Myosin IIA and IIB localized preferentially to the leading edge where traction force was greatest, and the trailing edge, respectively. When individual myosin II isoforms were depleted by shRNA, myosin IIA deficient cells lost actin stress fibers and focal adhesions, whereas myosin IIB deficient cells maintained similar actin organization and focal adhesions as wild-type cells. Interestingly, myosin IIA deficient cells migrated faster than wild-type or myosin IIB deficient cells on both a rigid surface and a pillar array, yet myosin IIA deficient cells exerted significantly less traction force at the leading edge than wild-type or myosin IIB deficient cells. These results suggest that, in the absence of myosin IIA mediated force-generating machinery, cells move with minimal traction forces at the cell periphery, thus demonstrating the remarkable ability of cells to adapt and migrate.

Clinicopathological significance of NMIIA overexpression in human gastric cancer

Altered expressions of nonmuscle myosin IIA (NMIIA) have been observed in certain types of cancers, but the impact of the alterations in gastric cancer (GC) remains unclear. The purpose of this study was to evaluate the expression of NMIIA at the mRNA and protein level in patients with GC and to assess its clinical significance. We investigated the expression of NMIIA in fresh, paired GC tissues by reverse transcriptase polymerase chain reaction (RT-PCR; n = 14) and Western blot analysis (n = 36). Simultaneously, we performed immunohistochemistry (IHC) on paraffin embedded specimens, including 96 GC specimens, 30 matched normal specimens and 30 paired metastatic lymph node samples. NMIIA is overexpressed in GC compared with the adjacent normal gastric epithelium (p < 0.001) and high-level NMIIA expression is significantly correlated with the depth of wall invasion, lymph node metastasis, distant metastasis and Tumor Node Metastasis (TNM) stage. Furthermore, elevated NMIIA expression is an independent prognostic factor in multivariate analysis using the Cox regression model (p = 0.021). These findings indicate that overexpression of NMIIA may contribute to the progression and poor prognosis of GC.

Nonmuscle myosin IIA is associated with poor prognosis of esophageal squamous cancer

Nonmuscle myosin IIA (myosin IIA) is a force-producing protein involved in the process of cell migration. Its expression has been considered as a bad prognostic indicator in stage I lung adenocarcinoma. However, the expression and clinical significance of myosin IIA in esophageal cancer has not been explored. In this study, we investigate the expression level of myosin IIA in 50 esophageal squamous cancer and 30 adjacent normal esophageal tissues by immunohistochemical staining and correlated its expression with clinicopathological features. Myosin IIA was expressed in all esophageal squamous cancer tissues (100%) and 8 of 30 adjacent normal tissues (26.7%, P = 0.000). In cancer tissues, elevated myosin IIA expression level was significantly correlated with increasing metastatic lymph nodes, poorer cancer differentiation, and advanced tumor stage. Further univariate analysis suggested that strong myosin IIA expression was associated with a significantly shorter overall survival (P = 0.021). In addition, MYH9 SiRNA was transfected into esophageal squamous cancer cell line (KYSE-510) to study the role of myosin IIA in cell migration. SiRNA-mediated depletion of myosin IIA in KYSE-510 cells significantly increased cell-matrix adhesion and attenuated cell migration ability (P = 0.000). In conclusion, these findings indicate that overexpression of myosin IIA may contribute to the progression and poor prognosis of esophageal squamous cancer, and this effect may be associated with increased cancer cell migration.

Clinical significance of myosin in colorectal cancer

Myosin has raised an interest in cancer research because of its role in tumor progression. The aim of this study was to investigate the expression and clinical relevance of myosin in colorectal cancer (CC). Myosin was detected in CC tumors with recurrence using matrix-assisted laser desorption/ionization time-of-flight analysis. An immunohistochemical study was performed using tissue arrays and specific antibodies against myosin heavy chain. Determinations on cancer specimens from 91 patients with resectable CCs were performed. The minimum follow-up period was of 12.5 years for these patients without tumor recurrence. Western blot and real-time polymerase chain reaction analysis were also performed. Samples of carcinomas with recurrence showed an increased expression of myosin. Tumors with high myosin expression by tumor cell were significantly associated with higher probability of metastasis. Our results suggest that myosin expression in CCs is associated with tumor progression and metastasis development. Therefore, myosin tumor expression may contribute to an improved prognostic evaluation in patients with CC.

Increased expression of nonmuscle myosin IIs is associated with 3MC-induced mouse tumor

Administration of the chemical carcinogen, 3-methylcholanthrene (3MC), in the hind leg induces the progressive formation of tumors in mice within 110 days. Previous reports suggest that transformation of muscle cells to atypical cells is one of the causes of tumor formation. Molecular events that lead to transformation of normal cells to atypical cells are not well understood. Here, we investigate the effect of 3MC on the expression of nonmuscle myosin IIs (NM IIs) which are known to be involved in cell migration, division and adhesion. Mass spectroscopy analysis reveals that tumor tissue contains 64.5% NM II-A, 34% II-B and only 1.5% II-C of total NM IIs, whereas these three isoforms of NM IIs are undetectable by mass spectroscopy in normal tissue associated with the tumor (NTAT) from the hind leg. Quantification of heavy chain mRNAs of NM II suggests that tumor tissue contains 25.7-fold and 19.03-fold more of NM II-A and II-B, respectively, compared with NTAT. Unlike NM II-B, which is detected only after tumor formation, II-A is detectable as early as day 7 after a second dose of 3MC. Immunofluorescence confocal microscopy reveals that fibroblast cells which are sparsely distributed in normal tissue are densely populated but of atypical shape in the tumor. These findings suggest that transformation of fibroblasts or non-fibroblast cells to atypical, cancerous cells is associated with increased levels of NM II-A and NM II-B expression in the 3MC-induced tumor mouse model. 3MC-induced transformation is further demonstrated in C2C12 myotubes.

Myosin II activity is required for functional leading-edge cells and closure of epidermal sheets in fish skin ex vivo

Re-epithelialization in skin wound healing is a process in which epidermal sheets grow and close the wound. Although the actin-myosin system is thought to have a pivotal role in re-epithelialization, its role is not clear. In fish skin, re-epithelialization occurs around 500 μm/h and is 50 times faster than in mammalian skin. We had previously reported that leading-edge cells of the epidermal outgrowth have both polarized large lamellipodia and "purse string"-like actin filament cables in the scale-skin culture system of medaka fish, Oryzias latipes (Cell Tissue Res, 2007). The actin purse-string (APS) is a supracellular contractile machinery in which adherens junctions (AJs) link intracellular myosin II-including actin cables between neighboring cells. In this study, we developed a modified "face-to-face" scale-skin culture system as an ex vivo model to study epidermal wound healing, and examined the role of the actin-myosin system in the rapid re-epithelialization using a myosin II ATPase inhibitor, blebbistatin. A low level of blebbistatin suppressed the formation of APS and induced the dissociation of keratocytes from the leading edge without attenuating the growth of the epidermal sheet or the migration rate of solitary keratocytes. AJs in the superficial layer showed no obvious changes elicited by blebbistatin. However, two epidermal sheets without APSs did not make a closure with each other, which was confirmed by inhibiting the connecting AJs between the superficial layers. These results suggest that myosin II activity is required for functional leading-edge cells and for epidermal closure.

New approaches to targeting the actin cytoskeleton for chemotherapy

The actin cytoskeleton is indispensable for normal cellular function. In particular, several actin-based structures coordinate cellular motility, a process hijacked by tumor cells in order to facilitate their propagation to distant sites. The actin cytoskeleton, therefore, represents a point for chemotherapeutic intervention. The challenge in disrupting the actin cytoskeleton is in preserving actin-driven contraction of cardiac and skeletal muscle. By targeting actin-binding proteins with altered expression in malignancy, it may be possible to achieve tumor-specific toxicity. A number of actin-binding proteins act cooperatively and synergistically to regulate actin structures required for motility. The actin cytoskeleton is characterized by a significant degree of plasticity. Targeting specific actin-binding proteins for chemotherapy will only be successful if no other compensatory mechanisms exist.

Aberrant expression of the polarity complex atypical PKC and non-muscle myosin IIA in active and inactive inflammatory bowel disease

Epithelial barrier function is contingent on appropriate polarization of key protein components. Work in intestinal epithelial cell cultures and animal models of bowel inflammation suggested that atypical PKC (aPKC), the kinase component of the Par3–Par6 polarity complex, is downregulated by pro-inflammatory signaling. Data from other laboratories showed the participation of myosin light chain kinase in intestinal inflammation, but there is paucity of evidence for assembly of its major target, non-muscle myosin II, in inflammatory bowel disease (IBD). In addition, we showed before that non-muscle myosin IIA (nmMyoIIA) is upregulated in intestinal inflammation in mice and TNFα-treated Caco-2 cells. Thus far, it is unknown if a similar phenomena occur in patients with IBD. Moreover, it is unclear whether aPKC downregulation is directly correlated with local mucosal inflammation or occurs in uninvolved areas. Frozen sections from colonoscopy material were stained for immunofluorescence with extensively validated specific antibodies against phosphorylated aPKC turn motif (active form) and nmMyoIIA. Inflammation was scored for the local area from where the material was obtained. We found a significant negative correlation between the expression of active aPKC and local inflammation, and a significant increase in the apical expression of nmMyoIIA in surface colon epithelia in inflamed areas, but not in non-inflamed mucosa even in the same patients. Changes in aPKC and nmMyoIIA expression are likely to participate in the pathogenesis of epithelial barrier function in response to local pro-inflammatory signals. These results provide a rationale for pursuing mechanistic studies on the regulation of these proteins.

Wound healing of intestinal epithelial cells

The intestinal epithelial cells (IECs) form a selective permeability barrier separating luminal content from underlying tissues. Upon injury, the intestinal epithelium undergoes a wound healing process. Intestinal wound healing is dependent on the balance of three cellular events; restitution, proliferation, and differentiation of epithelial cells adjacent to the wounded area. Previous studies have shown that various regulatory peptides, including growth factors and cytokines, modulate intestinal epithelial wound healing. Recent studies have revealed that novel factors, which include toll-like receptors (TLRs), regulatory peptides, particular dietary factors, and some gastroprotective agents, also modulate intestinal epithelial wound repair. Among these factors, the activation of TLRs by commensal bacteria is suggested to play an essential role in the maintenance of gut homeostasis. Recent studies suggest that mutations and dysregulation of TLRs could be major contributing factors in the predisposition and perpetuation of inflammatory bowel disease. Additionally, studies have shown that specific signaling pathways are involved in IEC wound repair. In this review, we summarize the function of IECs, the process of intestinal epithelial wound healing, and the functions and mechanisms of the various factors that contribute to gut homeostasis and intestinal epithelial wound healing.

Detecting epistatic SNPs associated with complex diseases via a Bayesian classification tree search method

Complex phenotypes are known to be associated with interactions among genetic factors. A growing body of evidence suggests that gene-gene interactions contribute to many common human diseases. Identifying potential interactions of multiple polymorphisms thus may be important to understand the biology and biochemical processes of the disease etiology. However, despite the great success of genome-wide association studies that mostly focus on single locus analysis, it is challenging to detect these interactions, especially when the marginal effects of the susceptible loci are weak and/or they involve several genetic factors. Here we describe a Bayesian classification tree model to detect such interactions in case-control association studies. We show that this method has the potential to uncover interactions involving polymorphisms showing weak to moderate marginal effects as well as multi-factorial interactions involving more than two loci.

Nonmuscle myosin IIA is required for lamellipodia formation through binding to WAVE2 and phosphatidylinositol 3,4,5-triphosphate

Investigation of the mechanism underlying cell membrane-targeted WAVE2 capture by phosphatidylinositol 3,4,5-triphosphate (PIP(3)) through IRSp53 revealed an unidentified 250-kDa protein (p250) bound to PIP(3). We identified p250 as nonmuscle myosin IIA heavy chain (MYH9) by mass spectrometry and immunoblot analysis using anti-MYH9 antibody. After stimulation with insulin-like growth factor I (IGF-I), MYH9 colocalized with PIP(3) in lamellipodia at the leading edge of cells. Depletion of MYH9 expression by small interfering RNA (siRNA) and inhibition of myosin II activity by blebbistatin abrogated the formation of actin filament (F-actin) arcs and lamellipodia induced by IGF-I. MYH9 was constitutively associated with WAVE2, which was dependent on myosin II activity, and the MYH9-WAVE2 complex colocalized to PIP(3) at the leading edge after IGF-I stimulation. These results indicate that MYH9 is required for lamellipodia formation since it provides contractile forces and tension for the F-actin network to form convex arcs at the leading edge through constitutive binding to WAVE2 and colocalization with PIP(3) in response to IGF-I.

The phosphorylation state of MRLC is polyamine dependent in intestinal epithelial cells

Cell migration is important to the integrity of the gastrointestinal tract for the normal movement of cells from crypt to villi and the healing of wounds. Polyamines are essential to cell migration, mucosal restitution, and, hence, healing. Polyamine depletion by α-difluoromethyl ornithine (DFMO) inhibited migration by decreasing lamellipodia and stress fiber formation and preventing the activation of Rho-GTPases. Polyamine depletion increased the association of the thick F-actin cortex with phosphorylated myosin regulatory light chain (pMRLC). In this study, we determined why MRLC is constitutively phosphorylated as part of the actin cortex. Inhibition of myosin light chain kinase (MLCK) decreased RhoA and Rac1 activities and significantly inhibited migration. Polyamine depletion increased phosphorylation of MRLC (Thr18/Ser19) and stabilized the actin cortex and focal adhesions. The Rho-kinase inhibitor Y27632 increased spreading and migration by decreasing the phosphorylation of MRLC, remodeling focal adhesions, and by activating Rho-GTPases. Thus phosphorylation of MRLC appears to be the rate-limiting step during the migration of IEC-6 cells. In addition, increased localization of RhoA with the actin cortex in polyamine-depleted cells appears to activate Rho-kinase. In the absence of polyamines, activated Rho-kinase phosphorylates myosin phosphatase targeting subunit 1 (MYPT1) at serine-668 leading to its inactivation and preventing the recruitment of phosphatase (protein phosphastase, PP1cδ) to the actomyosin cortex. In this condition, MRLC is constitutively phosphorylated and cycling does not occur. Thus activated myosin binds F-actin stress fibers and prevents focal adhesion turnover, Rho-GTPase activation, and the remodeling of the cytoskeleton required for migration.

Ablation of nonmuscle myosin II-B and II-C reveals a role for nonmuscle myosin II in cardiac myocyte karyokinesis

Ablation of nonmuscle myosin (NM) II-A or NM II-B results in mouse embryonic lethality. Here, we report the results of ablating NM II-C as well as NM II-C/II-B together in mice. NM II-C ablated mice survive to adulthood and show no obvious defects compared with wild-type littermates. However, ablation of NM II-C in mice expressing only 12% of wild-type amounts of NM II-B results in a marked increase in cardiac myocyte hypertrophy compared with the NM II-B hypomorphic mice alone. In addition, these hearts develop interstitial fibrosis associated with diffuse N-cadherin and β-catenin localization at the intercalated discs, where both NM II-B and II-C are normally concentrated. When both NM II-C and II-B are ablated the B-C-/B-C- cardiac myocytes show major defects in karyokinesis. More than 90% of B-C-/B-C- myocytes demonstrate defects in chromatid segregation and mitotic spindle formation accompanied by increased stability of microtubules and abnormal formation of multiple centrosomes. This requirement for NM II in karyokinesis is further demonstrated in the HL-1 cell line derived from mouse atrial myocytes, by using small interfering RNA knockdown of NM II or treatment with the myosin inhibitor blebbistatin. Our study shows that NM II is involved in regulating cardiac myocyte karyokinesis by affecting microtubule dynamics.

Cytoskeletal regulation of epithelial barrier function during inflammation

Increased epithelial permeability is a common and important consequence of mucosal inflammation that results in perturbed body homeostasis and enhanced exposure to external pathogens. The integrity and barrier properties of epithelial layers are regulated by specialized adhesive plasma membrane structures known as intercellular junctions. It is generally believed that inflammatory stimuli increase transepithelial permeability by inducing junctional disassembly. This review highlights molecular events that lead to disruption of epithelial junctions during inflammation. We specifically focus on key mechanisms of junctional regulation that are dependent on reorganization of the perijunctional F-actin cytoskeleton. We discuss critical roles of myosin-II-dependent contractility and actin filament turnover in remodeling of the F-actin cytoskeleton that drive disruption of epithelial barriers under different inflammatory conditions. Finally, we highlight signaling pathways induced by inflammatory mediators that regulate reorganization of actin filaments and junctional disassembly in mucosal epithelia.

Blebbistatin inhibits contraction and accelerates migration in mouse hepatic stellate cells

BACKGROUND AND PURPOSE

Blebbistatin, an inhibitor of myosin-II-specific ATPase, has been used to inhibit contraction of invertebrate and mammalian muscle preparations containing non-muscle myosin. Activated hepatic stellate cells have contractile properties and play an important role in the pathophysiology of liver fibrosis and portal hypertension. Therefore, hepatic stellate cells are considered as therapeutic target cells. In the present study, we studied the effect of blebbistatin during the transition of mouse hepatic stellate cells into contractile myofibroblasts.

EXPERIMENTAL APPROACH

Effects of blebbistatin on cell morphology were evaluated by phase contrast microscopy. Cell stress fibres and focal adhesions were investigated by dual immunofluorescence staining and visualized using fluorescence microscopy. Contractile force generation was examined by silicone wrinkle formation assays and collagen gel contraction assays. Intracellular Ca(2+) release in response to endothelin-1 was measured by using Fluo-4. Cell migration was measured by wound healing experiments.

KEY RESULTS

In culture-activated hepatic stellate cells, blebbistatin was found to change both cell morphology and function. In the presence of blebbistatin, stellate cells became smaller, acquired a dendritic morphology and had less myosin IIA-containing stress fibres and vinculin-containing focal adhesions. Moreover, blebbistatin impaired silicone wrinkle formation, reduced collagen gel contraction and blocked endothelin-1-induced intracellular Ca(2+) release. Finally, it promoted wound-induced cell migration.

CONCLUSIONS AND IMPLICATIONS

By inhibiting myosin II ATPase, blebbistatin has profound effects on the morphology and function of activated hepatic stellate cells. Our data suggest that myosin II could be a therapeutic target in the treatment of liver fibrosis and portal hypertension.

INSIGHTS INTO THE ROLES OF NON-MUSCLE MYOSIN IIA IN HUMAN KERATINOCYTE MIGRATION

Epidermal cell migration is a key factor in wound healing responses, regulated by the F-actin-myosin II systems. Previous reports have established the importance of non-muscle myosin II (NMII) in regulating cell migration. However, the role of NMII in primary human keratinocytes has not been investigated. In this study we used a microfabrication-based two-dimensional migration assay to examine the role of NMII in keratinocyte migration. We developed confluent cell islands of various sizes (0.025 - 0.25 mm(2)) and quantified migration as Fold Increase in island area over time. We report here that NMII was expressed and activated in migrating keratinocytes. Inhibition of NMIIA motor activity with blebbistatin increased migration significantly in all cell island sizes in six hours compared to control. Inhibition of Rho-kinase by Y-27632 did not alter migration while inhibition of myosin light chain kinase by ML-7 suppressed migration significantly in six hours. Both blebbistatin and Y-27632 induced formation of large membrane ruffles and elongated tails. In contrast, ML-7 blocked cell spreading, resulting in a rounded morphology. Taken together, these data suggest that NMIIA decreases migration in keratinocytes, but the mechanism may be differentially regulated by upstream kinases.