Modulation of cell spreading and cell-substrate adhesion dynamics by dystroglycan

Recent advances of physiochemical cues on surfaces for directing cell fates

Surface modification plays an essential role in dictating cell behavior and fate, as it creates a microenvironment that profoundly influences cell attachment, migration, proliferation, and differentiation. This review aims to the intricate interplay of culture surface properties, including topography, stiffness, charge, and chemical modifications, demonstrating their profound impact on cell destiny. We explore the nuanced responses of cells to varying surface topographies, from nano- to microscale features, elucidating the influence of geometric patterns and roughness. We also investigate the impact of substrate stiffness, highlighting the way cells perceive and respond to mechanical cues mimicking their native environments. The role of surface charge is examined, revealing how electrostatic interactions influence cell adhesion, signaling, and cell fate decisions. Finally, we delve into the diverse effects of chemical modifications, including the presentation of bioactive molecules, growth factors, and extracellular matrix (ECM) components, demonstrating their ability to guide cell behavior and stimulate specific cellular responses. This review offers comprehensive insights into the important role of surface properties in shaping cell fate, offering promising avenues for developing sophisticated cell culture platforms for applications in drug discovery, regenerative medicine, and fundamental research.

Extracellular matrix: Dystroglycan interactions-Roles for the dystrophin-associated glycoprotein complex in skeletal tissue dynamics

Contributions made by the dystrophin-associated glycoprotein complex (DGC) to cell-cell and cell-extracellular matrix (ECM) interactions are vital in development, homeostasis and pathobiology. This review explores how DGC functions may extend to skeletal pathophysiology by appraising the known roles of its major ECM ligands, and likely associated DGC signalling pathways, in regulating cartilage and bone cell behaviour and emergent skeletal phenotypes. These considerations will be contextualised by highlighting the potential of studies into the role of the DGC in isolated chondrocytes, osteoblasts and osteoclasts, and by fuller deliberation of skeletal phenotypes that may emerge in very young mice lacking vital, yet diverse core elements of the DGC. Our review points to roles for individual DGC components-including the glycosylation of dystroglycan itself-beyond the establishment of membrane stability which clearly accounts for severe muscle phenotypes in muscular dystrophy. It implies that the short stature, low bone mineral density, poor bone health and greater fracture risk in these patients, which has been attributed due to primary deficiencies in muscle-evoked skeletal loading, may instead arise due to primary roles for the DGC in controlling skeletal tissue (re)modelling.

Single-cell analysis of osmoregulation reveals heterogeneity of aquaporin 4 functionality in human astrocytes

The water channel aquaporin 4 (AQP4) contributes to water flow and waste removal across the blood-brain barrier and its levels, organization and localization are perturbed in various neurological diseases, including Alzheimer's Disease. This renders AQP4 a potentially valuable therapeutic target. However, most functional assays aimed at identifying modulators of AQP4 function are performed with primary rodent cells and do not consider inter-cellular variations in AQP4 abundance and presentation. To address this, we have established and applied a robust live cell microscopy assay that captures the contribution of AQP4 in the osmotically driven (de-)quenching of the vital dye Calcein-AM with single-cell resolution. Using human astrocytoma cells, we found that performing measurements on cellular regions instead of whole fields of view yielded a more sensitive readout of the osmotic response, which correlated with AQP4 abundance. Stable co-expression of the two major AQP4 isoforms, but not of the individual isoforms, provoked a faster adaptation to osmotic changes, while siRNA-mediated knockdown of AQP4 had the opposite effect. Post-hoc correlation with the canonical membrane marker CD44 revealed that the speed of the osmotic response scaled with AQP4 membrane enrichment. Coating the substrate with laminin promoted AQP4 membrane enrichment, while cell confinement with fixed-size micropatterns further increased the speed of osmoregulation, underscoring the influence of extracellular factors. The osmotic response of primary fetal astrocytes and human iPSC-derived astrocyte models was comparable to AQP4-deficient astrocytoma cells, in line with their low AQP4 levels and indicative of their immature state. In conclusion, a correlative single-cell approach based on the quantification of Calcein-AM quenching capacity, AQP4 abundance and AQP4 membrane enrichment, allows resolving osmoregulation in a more sensitive manner and reveals heterogeneity between and within human astrocyte (-like) cultures, which could prove crucial for future screens aimed at identifying AQP4 modulators.

Bacopa monnieri phytochemicals regulate fibroblast cell migration via modulation of focal adhesions

The Bacopa monnieri plant contains phytochemicals that have been used extensively in traditional medicine to treat various diseases. More recently it has been shown to accelerate wound healing, though its mechanism of action is largely unknown. Here we investigated the cellular pathways activated by a methanol extract of Bacopa monnieri in human dermal fibroblasts, which play many critical roles in the wound healing program. Gene expression analysis revealed that the Bacopa monnieri extract can modulate multiple processes involved in the wound healing program such as migration, proliferation, and angiogenesis. We discovered that the extract can increase migration of fibroblasts via modulating the size and number of focal adhesions. Bacopa monnieri-mediated changes in focal adhesions are dependent on α5β1 integrin activation and subsequent phosphorylation of focal adhesion kinase (FAK). Altogether our results suggest that Bacopa monnieri extract could enhance the wound healing rate via modulating fibroblast migration into the wound bed.

Effect of Focal Adhesion Kinase and Vinculin Expression on Migration Parameters of Normal and Tumor Epitheliocytes

Focal adhesions (FAs) are mechanosensory structures that transform physical stimuli into chemical signals guiding cell migration. Comprehensive studies postulate correlation between the FA parameters and cell motility metrics for individual migrating cells. However, which properties of the FAs are critical for epithelial cell motility in a monolayer remains poorly elucidated. We used high-throughput microscopy to describe relationship between the FA parameters and cell migration in immortalized epithelial keratinocytes (HaCaT) and lung carcinoma cells (A549) with depleted or inhibited vinculin and focal adhesion kinase (FAK) FA proteins. To evaluate relationship between the FA morphology and cell migration, we used substrates with varying stiffness in the model of wound healing. Cells cultivated on fibronectin had the highest FA area values, migration rate, and upregulated expression of FAK and vinculin mRNAs, while the smallest FA area and slower migration rate to the wound were specific to cells cultivated on glass. Suppression of vinculin expression in both normal and tumor cells caused decrease of the FA size and fluorescence intensity but did not affect cell migration into the wound. In contrast, downregulation or inactivation of FAK did not affect the FA size but significantly slowed down the wound closure rate by both HaCaT and A549 cell lines. We also showed that the FAK knockdown results in the FA lifetime decrease for the cells cultivated both on glass and fibronectin. Our data indicate that the FA lifetime is the most important parameter defining migration of epithelial cells in a monolayer. The observed change in the cell migration rate in a monolayer caused by changes in expression/activation of FAK kinase makes FAK a promising target for anticancer therapy of lung carcinoma.

The Role of β-Dystroglycan in Nuclear Dynamics

Dystroglycan is a ubiquitously expressed heterodimeric cell-surface laminin receptor with roles in cell adhesion, signalling, and membrane stabilisation. More recently, the transmembrane β-subunit of dystroglycan has been shown to localise to both the nuclear envelope and the nucleoplasm. This has led to the hypothesis that dystroglycan may have a structural role at the nuclear envelope analogous to its role at the plasma membrane. The biochemical fraction of myoblast cells clearly supports the presence of dystroglycan in the nucleus. Deletion of the dystroglycan protein by disruption of the DAG1 locus using CRISPR/Cas9 leads to changes in nuclear size but not overall morphology; moreover, the Young's modulus of dystroglycan-deleted nuclei, as determined by atomic force microscopy, is unaltered. Dystroglycan-disrupted myoblasts are also no more susceptible to nuclear stresses including chemical and mechanical, than normal myoblasts. Re-expression of dystroglycan in DAG1-disrupted myoblasts restores nuclear size without affecting other nuclear parameters.

Reactive oxygen species downregulate dystroglycans in the megakaryocytes of rats with arterial hypertension

Hypertension is a multifactorial disease characterized by vascular and renal dysfunction, cardiovascular remodeling, inflammation, and fibrosis, all of which are associated with oxidative stress. We previously demonstrated cellular reactive oxygen species (ROS) imbalances may impact the structural and biochemical functions of blood cells and reported downregulation of β-dystroglycan (β-Dg) and overexpression of the epithelial sodium channel (ENaC) contribute to the pathophysiology of hypertension. In this study, we aimed to determine the expression of dystroglycans (Dg) and ENaC in platelet progenitors (megakaryocytes) and their surrounding niches. Thin sections of bone marrow from 5- and 28-week-old spontaneous hypertensive rats (SHR) were compared to age-matched normotensive rats (WKY). Cytometry and immunohistochemical assays demonstrated an oxidative environment in SHR bone marrow, characterized by high levels of myeloperoxidase and 3-nitrotyrosine and downregulation of peroxiredoxin II. In addition, transmission electron micrography and confocal microscopy revealed morphological changes in platelets and Mgks from SHR rats, including swollen mitochondria. Quantitative qRT-PCR assays confirmed downregulation of Dg mRNA and immunohistochemistry and western-blotting validated low expression of β-Dg, mainly in the phosphorylated form, in Mgks from 28-week-old SHR rats. Moreover, we observed a progressive increase in β-1 integrin expression in Mgks and extracellular matrix proteins in Mgk niches in SHR rats compared to WKY controls. These results indicate accumulation of ROS promotes oxidative stress within the bone marrow environment and detrimentally affects cellular homeostasis in hypertensive individuals.

Heterogeneity of nanomechanical properties of the human umbilical vein endothelial cell surface

Endothelial cells, due to heterogeneity in the cell structure, can potentially form an inhomogeneous on structural and mechanical properties of the inner layer of the capillaries. Using quantitative nanomechanical mapping mode of atomic force microscopy, the parameters of the structural, elastic, and adhesive properties of the cell surface for living and glutaraldehyde-fixed human umbilical vein endothelial cells were studied. A significant difference in the studied parameters for three cell surface zones (peripheral, perinuclear, and nuclear zones) was established. The perinuclear zone appeared to be the softest zone of the endothelial cell surface. The heterogeneity of the endothelial cell mechanical properties at the nanoscale level can be an important mechanism in regulating the endothelium functions in blood vessels.

Perlingeiro R, Cisneros B. Loss of Dystroglycan Drives Cellular Senescence via Defective Mitosis-Mediated Genomic Instability

Nuclear β-dystroglycan (β-DG) is involved in the maintenance of nuclear architecture and function. Nonetheless, its relevance in defined nuclear processes remains to be determined. In this study we generated a C2C12 cell-based DG-null model using CRISPR-Cas9 technology to provide insights into the role of β-DG on nuclear processes. Since DG-null cells exhibited decreased levels of lamin B1, we aimed to elucidate the contribution of DG to senescence, owing to the central role of lamin B1 in this pathway. Remarkably, the lack of DG enables C2C12 cells to acquire senescent features, including cell-cycle arrest, increased senescence-associated-β-galactosidase activity, heterochromatin loss, aberrant nuclear morphology and nucleolar disruption. We demonstrated that genomic instability is one driving cause of the senescent phenotype in DG-null cells via the activation of a DNA-damage response associated with mitotic failure, as shown by the presence of multipolar mitotic spindles, which in turn induced the formation of micronuclei and γH2AX foci (DNA-damage marker), telomere shortening and p53/p21 upregulation. Altogether, these events might ultimately lead to premature senescence, impeding the replication of the damaged genome. In summary, we present evidence supporting a role for DG in protecting against senescence, through the maintenance of proper lamin B1 expression/localization and proper mitotic spindle organization.

Sustained activation of P2X7 induces MMP-2-evoked cleavage and functional purinoceptor inhibition

P2X7 purinoceptor promotes survival or cytotoxicity depending on extracellular adenosine triphosphate (ATP) stimulus intensity controlling its ion channel or P2X7-dependent large pore (LP) functions. Mechanisms governing this operational divergence and functional idiosyncrasy are ill-understood. We have discovered a feedback loop where sustained activation of P2X7 triggers release of active matrix metalloproteinase 2 (MMP-2), which halts ion channel and LP responses via the MMP-2-dependent receptor cleavage. This mechanism operates in cells as diverse as macrophages, dystrophic myoblasts, P2X7-transfected HEK293, and human tumour cells. Given that serum-born MMP-2 activity also blocked receptor functions, P2X7 responses in vivo may decrease in organs with permeable capillaries. Therefore, this mechanism represents an important fine-tuning of P2X7 functions, reliant on both cell-autonomous and extraneous factors. Indeed, it allowed evasion from the ATP-induced cytotoxicity in macrophages and human cancer cells with high P2X7 expression levels. Finally, we demonstrate that P2X7 ablation eliminated gelatinase activity in inflamed dystrophic muscles in vivo. Thus, P2X7 antagonists could be used as an alternative to highly toxic MMP inhibitors in treatments of inflammatory diseases and cancers.

Sulfation degree not origin of chondroitin sulfate derivatives modulates keratinocyte response

Chondroitin sulfate (CS) sulfation-dependently binds transforming growth factor-β1 (TGF-β1) and chronic wounds often accompany with epidermal hyperproliferation due to downregulated TGF-β signaling. However, the impact of CS on keratinocytes is unknown. Especially biotechnological-chemical strategies are promising to replace animal-derived CS. Thus, this study aims to evaluate the effects of CS derivatives on the interaction with vascular endothelial growth factor-A (VEGF-A) and on keratinocyte response. Over-sulfated CS (sCS3) interacts stronger with VEGF-A than CS. Furthermore, collagen coatings with CS variants are prepared by in vitro fibrillogenesis. Stability analyses demonstrate that collagen is firmly integrated, while the fibril diameters decrease with increasing sulfation degree. CS variants sulfation-dependently decelerate keratinocyte (HaCaT) migration and proliferation in a scratch assay. HaCaT cultured on sCS3-containing coatings produced increased amounts of solute active TGF-β1 which could be translated into biomaterials able to decrease epidermal hyperproliferation in chronic wounds. Overall, semi-synthetic and natural CS yield to comparable responses.

Control of nuclear β-dystroglycan content is crucial for the maintenance of nuclear envelope integrity and function

β-Dystroglycan (β-DG) is a plasma membrane protein that has ability to target to the nuclear envelope (NE) to maintain nuclear architecture. Nevertheless, mechanisms controlling β-DG nuclear localization and the physiological consequences of a failure of trafficking are largely unknown. We show that β-DG has a nuclear export pathway in myoblasts that depends on the recognition of a nuclear export signal located in its transmembrane domain, by CRM1. Remarkably, NES mutations forced β-DG nuclear accumulation resulting in mislocalization and decreased levels of emerin and lamin B1 and disruption of various nuclear processes in which emerin (centrosome-nucleus linkage and β-catenin transcriptional activity) and lamin B1 (cell cycle progression and nucleoli structure) are critically involved. In addition to nuclear export, the lifespan of nuclear β-DG is restricted by its nuclear proteasomal degradation. Collectively our data show that control of nuclear β-DG content by the combination of CRM1 nuclear export and nuclear proteasome pathways is physiologically relevant to preserve proper NE structure and activity.

Retrograde trafficking of β-dystroglycan from the plasma membrane to the nucleus

β-Dystroglycan (β-DG) is a transmembrane protein with critical roles in cell adhesion, cytoskeleton remodeling and nuclear architecture. This functional diversity is attributed to the ability of β-DG to target to, and conform specific protein assemblies at the plasma membrane (PM) and nuclear envelope (NE). Although a classical NLS and importin α/β mediated nuclear import pathway has already been described for β-DG, the intracellular trafficking route by which β-DG reaches the nucleus is unknown. In this study, we demonstrated that β-DG undergoes retrograde intracellular trafficking from the PM to the nucleus via the endosome-ER network. Furthermore, we provided evidence indicating that the translocon complex Sec61 mediates the release of β-DG from the ER membrane, making it accessible for importins and nuclear import. Finally, we show that phosphorylation of β-DG at Tyr⁸⁹⁰ is a key stimulus for β-DG nuclear translocation. Collectively our data describe the retrograde intracellular trafficking route that β-DG follows from PM to the nucleus. This dual role for a cell adhesion receptor permits the cell to functionally connect the PM with the nucleus and represents to our knowledge the first example of a cell adhesion receptor exhibiting retrograde nuclear trafficking and having dual roles in PM and NE.

Mesoporous Silica Nanoparticles as an Antitumoral-Angiogenesis Strategy

Tumors depend heavily on angiogenesis for nutrient derivation and their subsequent metastasis. Targeting tumor induced angiogenesis per se can address both tumor growth and progression simultaneously. Here, we show that we could elegantly restrict the endothelial cells angiogenic behavior through digital size control of mesoporous silica nanoparticle (MSN). This antiangiogenesis effect was derived from the particle size dependent uptake and production of intracellular reactive oxygen species (ROS) that directly interfered with p53 tumor suppressor pathway. The resulting signaling cascade wrestled back the tumoral control of endothelial cells' migration, invasion, and proliferation. Overall, a mere control over the size of a highly oxidative reactive surfaced nanoparticle could provide an alternative strategy to curb the tumor induced angiogenesis process in a conventional drug-free manner.

CD93 and dystroglycan cooperation in human endothelial cell adhesion and migration adhesion and migration

CD93 is a transmembrane glycoprotein predominantly expressed in endothelial cells. Although CD93 displays proangiogenic activity, its molecular function in angiogenesis still needs to be clarified. To get molecular insight into the biological role of CD93 in the endothelium, we performed proteomic analyses to examine changes in the protein profile of endothelial cells after CD93 silencing. Among differentially expressed proteins, we identified dystroglycan, a laminin-binding protein involved in angiogenesis, whose expression is increased in vascular endothelial cells within malignant tumors. Using immunofluorescence, FRET, and proximity ligation analyses, we observed a close interaction between CD93 and β-dystroglycan. Moreover, silencing experiments showed that CD93 and dystroglycan promoted endothelial cell migration and organization into capillary-like structures. CD93 proved to be phosphorylated on tyrosine 628 and 644 following cell adhesion on laminin through dystroglycan. This phosphorylation was shown to be necessary for a proper endothelial migratory phenotype. Moreover, we showed that during cell spreading phosphorylated CD93 recruited the signaling protein Cbl, which in turn was phosphorylated on tyrosine 774. Altogether, our results identify a new signaling pathway which is activated by the cooperation between CD93 and dystroglycan and involved in the control of endothelial cell function.

HECTD1 controls the protein level of IQGAP1 to regulate the dynamics of adhesive structures

Background

Cell migration including collective cell movement and individual cell migration are crucial factors in embryogenesis. During the spreading/migration of cells, several types of adhesive structures physically interacting with the extracellular matrix (ECM) or with another cell have been described and the formation and maturation of adhesion structures are coordinated, however the molecular pathways involved are still not fully understood.

Results

We generated a mouse embryonic fibroblast line (MEF) from homozygous mutant (Hectd1^R/R, Hectd1^Gt(RRC200)) mouse of the E3 ubiquitin ligase for inhibin B receptor (Hectd1). Detailed examination of cell motion on MEF cells demonstrated that loss of Hectd1 resulted in accelerated cell spreading and migration but impaired directionality of migration. In Hectd1^R/R cells paxillin and zyxin were largely mis-localized, whereas their expression levels were unchanged. In addition the formation of focal adhesions (FAs) was impaired and the focal complexes (FXs) were increased. We further identified HECTD1 as a key regulator of IQGAP1. IQGAP1 co-localized together with HECTD1 in the leading edge of cells. HECTD1 interacted with IQGAP1 and regulated its degradation through ubiquitination. Over-expression of IQGAP1 in control MEF phenocopied the spreading and migration defects of Hectd1^R/R cells. In contrast, siRNA-mediated knockdown of IQGAP1 rescued the defects in cellular movement of Hectd1^R/R cells.

Conclusions

The E3 ligase activity of Hectd1 regulates the protein level of IQGAP1 through ubiquitination and therefore mediates the dynamics of FXs including the recruitment of paxillin and actinin. IQGAP1 is one of the effectors of HECTD1.

Electronic supplementary material

The online version of this article (doi:10.1186/s12964-016-0156-8) contains supplementary material, which is available to authorized users.

Promoting differentiation of cultured myoblasts using biomimetic surfaces that present alpha-laminin-2 peptides

Traditionally, muscle cell lines are cultured on glass coverslips and differentiated to investigate myoblast fusion and differentiation. Efficient differentiation of myoblasts produces a dense network of myotubes with the correct organisation for contraction. Here we have tested the ability of artificially generated, precisely controlled peptide surfaces to enhance the efficiency of myoblast differentiation. We focused on specific short peptides from α-laminin-2 (IKVSV, VQLRNGFPYFSY and GLLFYMARINHA) as well as residues 15–155 from FGF1. We tested if these peptides in isolation, and/or in combination promoted muscle differentiation in culture, by promoting fusion and/or by improving sarcomere organisation. The majority of these peptides promoted fusion and differentiation in two different mouse myogenic cell lines and in primary human myoblasts. The additive effects of all four peptides gave the best results for both mouse cell lines tested, while primary human cell cultures differentiated equally well on most peptide surfaces tested. These data show that a mixture of short biomimetic peptides can reliably promote differentiation in mouse and human myoblasts.

Transgenic Rescue of the LARGEmyd Mouse: A LARGE Therapeutic Window?

LARGE is a glycosyltransferase involved in glycosylation of α-dystroglycan (α-DG). Absence of this protein in the LARGE_myd mouse results in α-DG hypoglycosylation, and is associated with central nervous system abnormalities and progressive muscular dystrophy. Up-regulation of LARGE has previously been proposed as a therapy for the secondary dystroglycanopathies: overexpression in cells compensates for defects in multiple dystroglycanopathy genes. Counterintuitively, LARGE overexpression in an FKRP-deficient mouse exacerbates pathology, suggesting that modulation of α-DG glycosylation requires further investigation. Here we demonstrate that transgenic expression of human LARGE (LARGE-LV5) in the LARGE_myd mouse restores α-DG glycosylation (with marked hyperglycosylation in muscle) and that this corrects both the muscle pathology and brain architecture. By quantitative analyses of LARGE transcripts we also here show that levels of transgenic and endogenous LARGE in the brains of transgenic animals are comparable, but that the transgene is markedly overexpressed in heart and particularly skeletal muscle (20–100 fold over endogenous). Our data suggest LARGE overexpression may only be deleterious under a forced regenerative context, such as that resulting from a reduction in FKRP: in the absence of such a defect we show that systemic expression of LARGE can indeed act therapeutically, and that even dramatic LARGE overexpression is well-tolerated in heart and skeletal muscle. Moreover, correction of LARGE_myd brain pathology with only moderate, near-physiological LARGE expression suggests a generous therapeutic window.

Alterations in plasma membrane promote overexpression and increase of sodium influx through epithelial sodium channel in hypertensive platelets

Platelets are small, anucleated cell fragments that activate in response to a wide variety of stimuli, triggering a complex series of intracellular pathways leading to a hemostatic thrombus formation at vascular injury sites. However, in essential hypertension, platelet activation contributes to causing myocardial infarction and ischemic stroke. Reported abnormalities in platelet functions, such as platelet hyperactivity and hyperaggregability to several agonists, contribute to the pathogenesis and complications of thrombotic events associated with hypertension. Platelet membrane lipid composition and fluidity are determining for protein site accessibility, structural arrangement of platelet surface, and response to appropriate stimuli. The present study aimed to demonstrate whether structural and biochemical abnormalities in lipid membrane composition and fluidity characteristic of platelets from hypertensive patients influence the expression of the Epithelial Sodium Channel (ENaC), fundamental for sodium influx during collagen activation. Wb, cytometry and quantitative Reverse Transcription-Polymerase Chain Reaction (qRT-PCR) assays demonstrated ENaC overexpression in platelets from hypertensive subjects and in relation to control subjects. Additionally, our results strongly suggest a key role of β-dystroglycan as a scaffold for the organization of ENaC and associated proteins. Understanding of the mechanisms of platelet alterations in hypertension should provide valuable information for the pathophysiology of hypertension.

γ-Secretase Dependent Nuclear Targeting of Dystroglycan

Dystroglycan is frequently lost in adenocarcinoma. α‐dystroglycan is known to become hypoglycosylated due to transcriptional silencing of LARGE, whereas β‐dystroglycan is proteolytically cleaved and degraded. The mechanism and proteases involved in the cleavage events affecting β‐dystroglycan are poorly understood. Using LNCaP prostate cancer cells as a model system, we have investigated proteases and tyrosine phosphorylation affecting β‐dystroglycan proteolysis and nuclear targeting. Cell density or phorbol ester treatment increases dystroglycan proteolysis, whereas furin or γ‐secretase inhibitors decreased dystroglycan proteolysis. Using resveratrol treatment of LNCaP cells cultured at low cell density in order to up‐regulate notch and activate proteolysis, we identified significant increases in the levels of a 26 kDa β‐dystroglycan fragment. These data, therefore, support a cell density‐dependent γ‐secretase and furin mediated proteolysis of β‐dystroglycan, which could be notch stimulated, leading to nuclear targeting and subsequent degradation. 117: 2149–2157, 2016. © 2016 The Authors. Journal of Cellular Biochemistry Published by Wiley Periodicals, Inc.

Dystroglycan Depletion Impairs Actin-Dependent Functions of Differentiated Kasumi-1 Cells

Background

Dystroglycan has recently been characterised in blood tissue cells, as part of the dystrophin glycoprotein complex involved in the differentiation process of neutrophils.

Purpose

In the present study we have investigated the role of dystroglycan in the human promyelocytic leukemic cell line Kasumi-1 differentiated to macrophage-like cells.

Methods

We characterised the pattern expression and subcellular distribution of dystroglycans in non-differentiated and differentiated Kasumi-1 cells.

Results

Our results demonstrated by WB and flow cytometer assays that during the differentiation process to macrophages, dystroglycans were down-regulated; these results were confirmed with qRT-PCR assays. Additionally, depletion of dystroglycan by RNAi resulted in altered morphology and reduced properties of differentiated Kasumi-1 cells, including morphology, migration and phagocytic activities although secretion of IL-1β and expression of markers of differentiation are not altered.

Conclusion

Our findings strongly implicate dystroglycan as a key membrane adhesion protein involved in actin-based structures during the differentiation process in Kasumi-1 cells.

Regulation of Endothelial Cell Adherence and Elastic Modulus by Substrate Stiffness

Although substrate stiffness has been previously reported to affect various cellular aspects, such as morphology, migration, viability, growth, and cytoskeletal structure, its influence on cell adherence has not been well examined. Here, we prepared three soft, medium, and hard polyacrylamide (PAAM) substrates and utilized AFM to study substrate elasticity and also the adhesion and mechanical properties of endothelial cells in response to changing substrate stiffness. Maximum detachment force and cell stiffness were increased with increasing substrate stiffness. Maximum detachment force values were 0.28 ± 0.14, 0.94 ± 0.27, and 1.99 ± 0.59 nN while Young's moduli of cells were 218.85 ± 38.73, 385.58 ± 131.67, and 933.20 ± 428.92 Pa for soft, medium, and hard substrates, respectively. Human umbilical vein endothelial cells (HUVECs) showed round to more spread shapes on soft to hard substrates, with the most organized and elongated actin structure on the hard hydrogel. Our results confirm the importance of substrate stiffness in regulating cell mechanics and adhesion for a successful cell therapy.

Nuclear import of β-dystroglycan is facilitated by ezrin-mediated cytoskeleton reorganization

The β-dystroglycan (β-DG) protein has the ability to target to multiple sites in eukaryotic cells, being a member of diverse protein assemblies including the transmembranal dystrophin-associated complex, and a nuclear envelope-localised complex that contains emerin and lamins A/C and B1. We noted that the importin α2/β1-recognised nuclear localization signal (NLS) of β-DG is also a binding site for the cytoskeletal-interacting protein ezrin, and set out to determine whether ezrin binding might modulate β-DG nuclear translocation for the first time. Unexpectedly, we found that ezrin enhances rather than inhibits β-DG nuclear translocation in C2C12 myoblasts. Both overexpression of a phosphomimetic activated ezrin variant (Ez-T567D) and activation of endogenous ezrin through stimulation of the Rho pathway resulted in both formation of actin-rich surface protrusions and significantly increased nuclear translocation of β-DG as shown by quantitative microscopy and subcellular fractionation/Western analysis. In contrast, overexpression of a nonphosphorylatable inactive ezrin variant (Ez-T567A) or inhibition of Rho signaling, decreased nuclear translocation of β-DG concomitant with a lack of cell surface protrusions. Further, a role for the actin cytoskeleton in ezrin enhancement of β-DG nuclear translocation was implicated by the observation that an ezrin variant lacking its actin-binding domain failed to enhance nuclear translocation of β-DG, while disruption of the actin cytoskeleton led to a reduction in β-DG nuclear localization. Finally, we show that ezrin-mediated cytoskeletal reorganization enhances nuclear translocation of the cytoplasmic but not the transmembranal fraction of β-DG. This is the first study showing that cytoskeleton reorganization can modulate nuclear translocation of β-DG, with the implication that β-DG can respond to cytoskeleton-driven changes in cell morphology by translocating from the cytoplasm to the nucleus to orchestrate nuclear processes in response to the functional requirements of the cell.

Vinculin-p130Cas interaction is critical for focal adhesion dynamics and mechano-transduction

Adherent cells, when mechanically stressed, show a wide range of responses including large-scale changes in their mechanical behaviour and gene expression pattern. This is in part facilitated by activating the focal adhesion (FA) protein p130Cas through force-induced conformational changes that lead to the phosphorylation by src family kinases. Janostiak et al. [Janostiak et al. Cell Mol Life Sci (2013) DOI 10.1007/s00018-013-1450-x] have reported that the phosphorylation site Y12 on the SH3 domain of p130Cas modulates the binding with vinculin, a prominent mechano-coupling protein in FAs. Tension changes in FAs (due to the anchorage of the SH3 domain and C-terminal) bring about an extension of the substrate domain of p130Cas by unmasking the phosphorylation sites. These observations demonstrate that vinculin is an important modulator of the p130Cas-mediated mechano-transduction pathway in cells. The central aim should be now to test that vinculin is critical for p130Cas incorporation into the focal adhesion complex and for transmitting forces to the p130Cas molecule.

Nuclear targeting of dystroglycan promotes the expression of androgen regulated transcription factors in prostate cancer

Dystroglycan is frequently lost in adenocarcinoma, but the mechanisms and consequences are poorly understood. We report an analysis of β-dystroglycan in prostate cancer in human tissue samples and in LNCaP cells in vitro. There is progressive loss of β-dystroglycan immunoreactivity from basal and lateral surfaces of prostate epithelia which correlates significantly with increasing Gleason grade. In about half of matched bone metastases there is significant dystroglycan re-expression. In tumour tissue and in LNCaP cells there is also a tyrosine phosphorylation-dependent translocation of β-dystroglycan to the nucleus. Analysis of gene expression data by microarray, reveals that nuclear targeting of β-dystroglycan in LNCaP cells alters the transcription of relatively few genes, the most unregulated being the transcription factor ETV1. These data suggest that proteolysis, tyrosine phosphorylation and translocation of dystroglycan to the nucleus resulting in altered gene transcription could be important mechanisms in the progression of prostate cancer.

Modulation of dorsal root ganglion development by ErbB signaling and the scaffold protein Sorbs3

The multipotent cells of the vertebrate neural crest (NC) arise at the dorsal aspect of the neural tube, then migrate throughout the developing embryo and differentiate into diverse cell types, including the sensory neurons and glia of the dorsal root ganglia (DRG). As multiple cell types are derived from this lineage, it is ideal for examining mechanisms of fate restriction during development. We have isolated a mutant, ouchless, that specifically fails to develop DRG neurons, although other NC derivatives develop normally. This mutation affects the expression of Sorbs3, a scaffold protein known to interact with proteins involved in focal adhesions and several signaling pathways. ouchless mutants share some phenotypic similarities with mutants in ErbB receptors, EGFR homologs that are implicated in diverse developmental processes and associated with several cancers; and ouchless interacts genetically with an allele of erbb3 in DRG neurogenesis. However, the defect in ouchless DRG neurogenesis is distinct from ErbB loss of function in that it is not associated with a loss of glia. Both ouchless and neurogenin1 heterozygous fish are sensitized to the effects of ErbB chemical inhibitors, which block the development of DRG in a dose-dependent manner. Inhibitors of MEK show similar effects on DRG neurogenesis. We propose a model in which Sorbs3 helps to integrate ErbB signals to promote DRG neurogenesis through the activation of MAPK and upregulation of neurogenin1.

Dystroglycan function is a novel determinant of tumor growth and behavior in prostate cancer

BACKGROUND

Dystroglycan is a ubiquitously expressed cell adhesion molecule frequently found to be altered or reduced in adenocarcinomas, however the mechanisms or consequences of dystroglycan loss have not been studied extensively.

METHODS

We examined the consequence of overexpression or RNAi depletion of dystroglycan on properties of in vitro growth migration and invasion of LNCaP, PC3, and DU145 prostate cancer cell lines.

RESULTS

Using LNCaP cells we observed cell density-dependent changes in β-dystroglycan with the appearance of several lower molecular weight species ranging in size from 43 to 26 kDa. The bands of 31 and 26 kDa were attributed to proteolysis, whereas bands between 43 and 38 kDa were a consequence of mis-glycosylation. The localization of β-dystroglycan in LNCaP colonies in culture also varied, cells with a mesenchymal appearance at the periphery of the colony had more pronounced membrane localization of dystroglycan. Whereas some cells demonstrated nuclear dystroglycan. Increased dystroglycan levels were inhibitory to growth in soft agar but promoted Matrigel invasion, whereas reduced dystroglycan levels promoted growth in soft agar but inhibited invasion. Similar results were also obtained for PC3 and DU145 cells.

CONCLUSIONS

This study suggests that changes in β-dystroglycan distribution within the cell and/or the loss of dystroglycan during tumorigenesis, through a combination of proteolysis and altered glycosylation, leads to an increased ability to grow in an anchorage independent manner, however dystroglycan may need to be re-expressed for cell invasion and metastasis to occur.

A role for β-dystroglycan in the organization and structure of the nucleus in myoblasts

We recently characterized a nuclear import pathway for β-dystroglycan; however, its nuclear role remains unknown. In this study, we demonstrate for the first time, the interaction of β-dystroglycan with distinct proteins from different nuclear compartments, including the nuclear envelope (NE) (emerin and lamins A/C and B1), splicing speckles (SC35), Cajal bodies (p80-coilin), and nucleoli (Nopp140). Electron microscopy analysis revealed that β-dystroglycan localized in the inner nuclear membrane, nucleoplasm, and nucleoli. Interestingly, downregulation of β-dystroglycan resulted in both mislocalization and decreased expression of emerin and lamin B1, but not lamin A/C, as well in disorganization of nucleoli, Cajal bodies, and splicing speckles with the concomitant decrease in the levels of Nopp140, and p80-coilin, but not SC35. Quantitative reverse transcription PCR and cycloheximide-mediated protein arrest assays revealed that β-dystroglycan deficiency did not change mRNA expression of NE proteins emerin and lamin B1 bud did alter their stability, accelerating protein turnover. Furthermore, knockdown of β-dystroglycan disrupted NE-mediated processes including nuclear morphology and centrosome-nucleus linkage, which provides evidence that β-dystroglycan association with NE proteins is biologically relevant. Unexpectedly, β-dystroglycan-depleted cells exhibited multiple centrosomes, a characteristic of cancerous cells. Overall, these findings imply that β-dystroglycan is a nuclear scaffolding protein involved in nuclear organization and NE structure and function, and that might be a contributor to the biogenesis of nuclear envelopathies.

Polarization and myelination in myelinating glia

Myelinating glia, oligodendrocytes in central nervous system and Schwann cells in peripheral nervous system, form myelin sheath, a multilayered membrane system around axons enabling salutatory nerve impulse conduction and maintaining axonal integrity. Myelin sheath is a polarized structure localized in the axonal side and therefore is supposed to be formed based on the preceding polarization of myelinating glia. Thus, myelination process is closely associated with polarization of myelinating glia. However, cell polarization has been less extensively studied in myelinating glia than other cell types such as epithelial cells. The ultimate goal of this paper is to provide insights for the field of myelination research by applying the information obtained in polarity study in other cell types, especially epithelial cells, to cell polarization of myelinating glia. Thus, in this paper, the main aspects of cell polarization study in general are summarized. Then, they will be compared with polarization in oligodendrocytes. Finally, the achievements obtained in polarization study for epithelial cells, oligodendrocytes, and other types of cells will be translated into polarization/myelination process by Schwann cells. Then, based on this model, the perspectives in the study of Schwann cell polarization/myelination will be discussed.

Focal adhesion size uniquely predicts cell migration

Focal adhesions are large protein complexes organized at the basal surface of cells, which physically connect the extracellular matrix to the cytoskeleton and have long been speculated to mediate cell migration. However, whether clustering of these molecular components into focal adhesions is actually required for these proteins to regulate cell motility is unclear. Here we use quantitative microscopy to characterize descriptors of focal adhesion and cell motility for mouse embryonic fibroblasts and human fibrosarcoma cells, across a wide range of matrix compliance and following genetic manipulations of focal adhesion proteins (vinculin, talin, zyxin, FAK, and paxilin). This analysis reveals a tight, biphasic gaussian relationship between mean size of focal adhesions (not their number, surface density, or shape) and cell speed. The predictive power of this relationship is comprehensively validated by disrupting nonfocal adhesion proteins (α-actinin, F-actin, and myosin II) and subcellular organelles (mitochondria, nuclear DNA, etc.) not known to affect either focal adhesions or cell migration. This study suggests that the mean size of focal adhesions robustly and precisely predicts cell speed independently of focal adhesion surface density and molecular composition.

Insertion of a myc-tag within α-dystroglycan domains improves its biochemical and microscopic detection

BACKGROUND

Epitope tags and fluorescent fusion proteins have become indispensable molecular tools for studies in the fields of biochemistry and cell biology. The knowledge collected on the subdomain organization of the two subunits of the adhesion complex dystroglycan (DG) enabled us to insert the 10 amino acids myc-tag at different locations along the α-subunit, in order to better visualize and investigate the DG complex in eukaryotic cells.

RESULTS

We have generated two forms of DG polypeptides via the insertion of the myc-tag 1) within a flexible loop (between a.a. 170 and 171) that separates two autonomous subdomains, and 2) within the C-terminal domain in position 500. Their analysis showed that double-tagging (the β-subunit is linked to GFP) does not significantly interfere with the correct processing of the DG precursor (pre-DG) and confirmed that the α-DG N-terminal domain is processed in the cell before α-DG reaches its plasma membrane localization. In addition, myc insertion in position 500, right before the second Ig-like domain of α-DG, proved to be an efficient tool for the detection and pulling-down of glycosylated α-DG molecules targeted at the membrane.

CONCLUSIONS

Further characterization of these and other myc-permissive site(s) will represent a valid support for the study of the maturation process of pre-DG and could result in the creation of a new class of intrinsic doubly-fluorescent DG molecules that would allow the monitoring of the two DG subunits, or of pre-DG, in cells without the need of antibodies.

Preventing phosphorylation of dystroglycan ameliorates the dystrophic phenotype in mdx mouse

Loss of dystrophin protein due to mutations in the DMD gene causes Duchenne muscular dystrophy. Dystrophin loss also leads to the loss of the dystrophin glycoprotein complex (DGC) from the sarcolemma which contributes to the dystrophic phenotype. Tyrosine phosphorylation of dystroglycan has been identified as a possible signal to promote the proteasomal degradation of the DGC. In order to test the role of tyrosine phosphorylation of dystroglycan in the aetiology of DMD, we generated a knock-in mouse with a phenylalanine substitution at a key tyrosine phosphorylation site in dystroglycan, Y890. Dystroglycan knock-in mice (Dag1(Y890F/Y890F)) had no overt phenotype. In order to examine the consequence of blocking dystroglycan phosphorylation on the aetiology of dystrophin-deficient muscular dystrophy, the Y890F mice were crossed with mdx mice an established model of muscular dystrophy. Dag1(Y890F/Y890F)/mdx mice showed a significant improvement in several parameters of muscle pathophysiology associated with muscular dystrophy, including a reduction in centrally nucleated fibres, less Evans blue dye infiltration and lower serum creatine kinase levels. With the exception of dystrophin, other DGC components were restored to the sarcolemma including α-sarcoglycan, α-/β-dystroglycan and sarcospan. Furthermore, Dag1(Y890F/Y890F)/mdx showed a significant resistance to muscle damage and force loss following repeated eccentric contractions when compared with mdx mice. While the Y890F substitution may prevent dystroglycan from proteasomal degradation, an increase in sarcolemmal plectin appeared to confer protection on Dag1(Y890F/Y890F)/mdx mouse muscle. This new model confirms dystroglycan phosphorylation as an important pathway in the aetiology of DMD and provides novel targets for therapeutic intervention.

The inside and out of dystroglycan post-translational modification

In neuromuscular systems dystroglycan provides a vital link between laminin in the extracellular matrix and dystrophin in the membrane cytoskeleton. The integrity of this link is maintained and regulated by post-translational modifications of dystroglycan that have effects both inside and outside the cell. Glycosylation of α-dystroglycan is crucial for its link to laminin and phosphorylation of β-dystroglycan on tyrosine regulates its association with intracellular binding partners. This short review focuses on some of the recent developments in our understanding of the role of these post-translational modification in regulating dystroglycan function, and how new knowledge of signalling through the laminin-dystroglycan axis is leading to hope for treatment for some neuromuscular diseases associated with this adhesion complex.

Focal contact formation of vascular smooth muscle cells on Langmuir-Blodgett and solvent-cast films of biodegradable poly(ester amide)s

The ability of biomaterials to support the adhesion of cells is a necessary condition for their use in scaffold-guided tissue engineering. Waveguide evanescent field fluorescence (WEFF) microscopy is a relatively new microscopic technique that allows the number of cell adhesions to a waveguide surface be measured by imaging the interfacial contact region between the cells and their substratum. In this work, the adhesion of human coronary artery smooth muscle cells (HCASMCs) to ultrathin films (20 nm) of poly(ester amide)s (PEAs) prepared by Langmuir-Blodgett (LB) technology on waveguides was investigated and compared with conventional vinculin immunostaining on solvent cast PEA films. Cell culture was conducted both in the presence and absence of serum to evaluate the effect of nonspecific protein adsorption that mediates cell adhesion. WEFF microscopy analyses revealed that the cationic PEA enhanced the number of attachment sites compared with the control waveguides regardless of the culture medium. Although differences in cell adhesions between different PEAs were suggested by the results, no statistically significant differences were found. Similar results were observed with presently and previously reported vinculin immunostaining studies, further validating the use of WEFF microscopy to quantify cell adhesions. Moreover, the focal adhesions of the HCASMCs to the PEA surfaces indicate these PEAs can promote integrin signaling, which is vital in cell survival, migration, and proliferation, and ultimately in scaffold-guided vascular tissue engineering.

Depletion of the actin bundling protein SM22/transgelin increases actin dynamics and enhances the tumourigenic phenotypes of cells

Background

SM22 has long been studied as an actin-associated protein. Interestingly, levels of SM22 are often reduced in tumour cell lines, while they are increased during senescence possibly indicating a role for SM22 in cell fate decisions via its interaction with actin. In this study we aimed to determine whether reducing levels of SM22 could actively contribute to a tumourigenic phenotype.

Results

We demonstrate that in REF52 fibroblasts, decreased levels of SM22 disrupt normal actin organization leading to changes in the motile behaviour of cells. Interestingly, SM22 depletion also led to an increase in the capacity of cells to spontaneously form podosomes with a concomitant increase in the ability to invade Matrigel. In PC3 prostate epithelial cancer cells by contrast, where SM22 is undetectable, re-expression of SM22 reduced the ability to invade Matrigel. Furthermore SM22 depleted cells also had reduced levels of reactive oxygen species when under serum starvation stress.

Conclusions

These findings suggest that depletion of SM22 could contribute to tumourigenic properties of cells. Reduction in SM22 levels would tend to promote cell survival when cells are under stress, such as in a hypoxic tumour environment, and may also contribute to increases in actin dynamics that favour metastatic potential.

Dystroglycan promotes filopodial formation and process branching in differentiating oligodendroglia

During central nervous system (CNS) development, individual oligodendrocytes myelinate multiple axons, thus requiring the outgrowth and extensive branching of oligodendroglial processes. Laminin (Lm)-deficient mice have a lower percentage of myelinated axons, which may indicate a defect in the ability to properly extend and branch processes. It remains unclear, however, to what extent extracellular matrix (ECM) receptors contribute to oligodendroglial process remodeling itself. In the current study, we report that the ECM receptor dystroglycan is necessary for Lm enhancement of filopodial formation, process outgrowth, and process branching in differentiating oligodendroglia. During early oligodendroglial differentiation, the disruption of dystroglycan-Lm interactions, via blocking antibodies or dystroglycan small interfering RNA (siRNA), resulted in decreased filopodial number and length, decreased process length, and decreased numbers of primary and secondary processes. Later in oligodendrocyte differentiation, dystroglycan-deficient cells developed fewer branches, thus producing less complex networks of processes as determined by Sholl analysis. In newly differentiating oligodendroglia, dystroglycan was localized in filopodial tips, whereas, in more mature oligodendrocytes, dystroglycan was enriched in focal adhesion kinase (FAK)-positive focal adhesion structures. These results suggest that dystroglycan-Lm interactions influence oligodendroglial process dynamics and therefore may regulate the myelination capacity of individual oligodendroglia.

SH3 domain-mediated recruitment of host cell amphiphysins by alphavirus nsP3 promotes viral RNA replication

Among the four non-structural proteins of alphaviruses the function of nsP3 is the least well understood. NsP3 is a component of the viral replication complex, and composed of a conserved aminoterminal macro domain implicated in viral RNA synthesis, and a poorly conserved carboxyterminal region. Despite the lack of overall homology we noted a carboxyterminal proline-rich sequence motif shared by many alphaviral nsP3 proteins, and found it to serve as a preferred target site for the Src-homology 3 (SH3) domains of amphiphysin-1 and -2. Nsp3 proteins of Semliki Forest (SFV), Sindbis (SINV), and Chikungunya viruses all showed avid and SH3-dependent binding to amphiphysins. Upon alphavirus infection the intracellular distribution of amphiphysin was dramatically altered and colocalized with nsP3. Mutations in nsP3 disrupting the amphiphysin SH3 binding motif as well as RNAi-mediated silencing of amphiphysin-2 expression resulted in impaired viral RNA replication in HeLa cells infected with SINV or SFV. Infection of Balb/c mice with SFV carrying an SH3 binding-defective nsP3 was associated with significantly decreased mortality. These data establish SH3 domain-mediated binding of nsP3 with amphiphysin as an important host cell interaction promoting alphavirus replication.

The genus Alphavirus contains 29 known species that are transmitted by arthropods and include many important pathogens, such as Chikungunya virus (CHKV), which during the past decade has re-emerged to cause massive epidemics of febrile arthralgia around the Indian Ocean. The role of the alphaviral non-structural protein 3 (nsP3) has been linked to RNA replication and disease pathogenesis, but its molecular functions have remained elusive. Here we show that the nsP3s of CHKV as well as Sindbis and Semliki Forest viruses use a conserved proline-rich motif to interact with the Src-homology-3 (SH3) domain of host cell amphiphysins Amph1 and BIN1/Amph2, two adaptor proteins prominently involved in cellular membrane dynamics. We observed a striking re-localization of amphiphysin to alphaviral replication complexes in infected cells, and found that disruption of the amphiphysin SH3 binding motif in nsP3 strongly suppressed virus replication in vitro and attenuated Semliki Forest virus in infected mice. Thus, we conclude that amphiphysins are novel and important host cell factors involved in supporting alphavirus replication.

MMP2-9 cleavage of dystroglycan alters the size and molecular composition of Schwann cell domains

Myelinating glial cells exhibit a spectacular cytoarchitecture, because they polarize on multiple axes and domains. How this occurs is essentially unknown. The dystroglycan-dystrophin complex is required for the function of myelin-forming Schwann cells. Similar to other tissues, the dystroglycan complex in Schwann cells localizes with different dystrophin family members in specific domains, thus promoting polarization. We show here that cleavage of dystroglycan by matrix metalloproteinases 2 and 9, an event that is considered pathological in most tissues, is finely and dynamically regulated in normal nerves and modulates dystroglycan complex composition and the size of Schwann cell compartments. In contrast, in nerves of Dy(2j/2j) mice, a model of laminin 211 deficiency, metalloproteinases 2 and 9 are increased, causing excessive dystroglycan cleavage and abnormal compartments. Pharmacological inhibition of cleavage rescues the cytoplasmic defects of Dy(2j/2j) Schwann cells. Thus, regulated cleavage may be a general mechanism to regulate protein complex composition in physiological conditions, whereas unregulated processing is pathogenic and a target for treatment in disease.

Non-redundant function of dystroglycan and β1 integrins in radial sorting of axons

Radial sorting allows the segregation of axons by a single Schwann cell (SC) and is a prerequisite for myelination during peripheral nerve development. Radial sorting is impaired in models of human diseases, congenital muscular dystrophy (MDC) 1A, MDC1D and Fukuyama, owing to loss-of-function mutations in the genes coding for laminin α2, Large or fukutin glycosyltransferases, respectively. It is not clear which receptor(s) are activated by laminin 211, or glycosylated by Large and fukutin during sorting. Candidates are αβ1 integrins, because their absence phenocopies laminin and glycosyltransferase deficiency, but the topography of the phenotypes is different and β1 integrins are not substrates for Large and fukutin. By contrast, deletion of the Large and fukutin substrate dystroglycan does not result in radial sorting defects. Here, we show that absence of dystroglycan in a specific genetic background causes sorting defects with topography identical to that of laminin 211 mutants, and recapitulating the MDC1A, MDC1D and Fukuyama phenotypes. By epistasis studies in mice lacking one or both receptors in SCs, we show that only absence of β1 integrins impairs proliferation and survival, and arrests radial sorting at early stages, that β1 integrins and dystroglycan activate different pathways, and that the absence of both molecules is synergistic. Thus, the function of dystroglycan and β1 integrins is not redundant, but is sequential. These data identify dystroglycan as a functional laminin 211 receptor during axonal sorting and the key substrate relevant to the pathogenesis of glycosyltransferase congenital muscular dystrophies.

The role of dystroglycan in PDGF-BB-dependent migration of activated hepatic stellate cells/myofibroblasts

Hepatic stellate cells are embedded in the loose connective tissue matrix within the space of Disse. This extracellular matrix contains several basement membrane components including laminin, but its composition changes during liver injury because of the production of extracellular matrix components found in scar tissue. These changes in extracellular matrix composition and in cell-extracellular matrix interactions may play a key role in hepatic stellate cell transdifferentiation. In this communication we used early passages of mouse hepatic stellate cells (activated HSC/myofibroblasts) to study the platelet-derived growth factor BB (PDGF-BB)-dependent expression and regulation of β-dystroglycan and its role in activated HSC/myofibroblast migration. We used Northern and Western analysis to study dystroglycan expression and confocal microscopy to investigate changes in subcellular distribution of the protein. Activated HSC migration was investigated using an in vitro wound-healing assay. PDGF-BB induced significant changes in dystroglycan regulation and subcellular distribution of the protein. Whereas steady-state levels of dystroglycan mRNA remained constant, PDGF-BB increased dystroglycan transcription but shortened the t(1/2) by 50%. Moreover, PDGF-BB changed dystroglycan and α5-integrin cellular distribution. Cell migration experiments revealed that PDGF-BB-dependent migration of activated HSC/myofibroblasts was completely blocked by neutralizing antibodies to fibronectin, α5-integrin, laminin, and β-dystroglycan. Overall, these findings suggest that both laminin and fibronectin and their receptors play a key role in PDGF-BB-induced activated HSC migration.

Distribution of dystrophin- and utrophin-associated protein complexes (DAPC/UAPC) in human hematopoietic stem/progenitor cells

Hematopoietic stem cells (HSC) are defined by their cardinal properties, such as sustained proliferation, multilineage differentiation, and self-renewal, which give rise to a hierarchy of progenitor populations with more restricted potential lineage, ultimately leading to the production of all types of mature blood cells. HSC are anchored by cell adhesion molecules to their specific microenvironment, thus regulating their cell cycle, while cell migration is essentially required for seeding the HSC of the fetal bone marrow (BM) during development as well as in adult BM homeostasis. The dystrophin-associated protein complex (DAPC) is a large group of membrane-associated proteins linking the cytoskeleton to the extracellular matrix and exhibiting scaffolding, adhesion, and signaling roles in muscle and non-muscle cells including mature blood cells. Because adhesion and migration are mechanisms that influence the fate of the HSC, we explored the presence and the feasible role of DAPC. In this study, we characterized the pattern expression by immunoblot technique and, by confocal microscopy analysis, the cellular distribution of dystrophin and utrophin gene products, and the dystrophin-associated proteins (α-, β-dystroglycan, α-syntrophin, α-dystrobrevin) in relation to actin filaments in freshly isolated CD34+ cells from umbilical cord blood. Immunoprecipitation assays demonstrated the presence of Dp71d/Dp71Δ110m ∼DAPC and Up400/Up140∼DAPC. The subcellular distribution of the two DAPC in actin-based structures suggests their dynamic participation in adhesion and cell migration. In addition, the particular protein pattern expression found in hematopoietic stem/progenitor cells might be indicative of their feasible participation during differentiation.

Systems microscopy approaches to understand cancer cell migration and metastasis

Cell migration is essential in a number of processes, including wound healing, angiogenesis and cancer metastasis. Especially, invasion of cancer cells in the surrounding tissue is a crucial step that requires increased cell motility. Cell migration is a well-orchestrated process that involves the continuous formation and disassembly of matrix adhesions. Those structural anchor points interact with the extra-cellular matrix and also participate in adhesion-dependent signalling. Although these processes are essential for cancer metastasis, little is known about the molecular mechanisms that regulate adhesion dynamics during tumour cell migration. In this review, we provide an overview of recent advanced imaging strategies together with quantitative image analysis that can be implemented to understand the dynamics of matrix adhesions and its molecular components in relation to tumour cell migration. This dynamic cell imaging together with multiparametric image analysis will help in understanding the molecular mechanisms that define cancer cell migration.

Dystroglycan versatility in cell adhesion: a tale of multiple motifs

Dystroglycan is a ubiquitously expressed heterodimeric adhesion receptor. The extracellular alpha-subunit makes connections with a number of laminin G domain ligands including laminins, agrin and perlecan in the extracellular matrix and the transmembrane beta-subunit makes connections to the actin filament network via cytoskeletal linkers including dystrophin, utrophin, ezrin and plectin, depending on context. Originally discovered as part of the dystrophin glycoprotein complex of skeletal muscle, dystroglycan is an important adhesion molecule and signalling scaffold in a multitude of cell types and tissues and is involved in several diseases. Dystroglycan has emerged as a multifunctional adhesion platform with many interacting partners associating with its short unstructured cytoplasmic domain. Two particular hotspots are the cytoplasmic juxtamembrane region and at the very carboxy terminus of dystroglycan. Regions which between them have several overlapping functions: in the juxtamembrane region; a nuclear localisation signal, ezrin/radixin/moesin protein, rapsyn and ERK MAP Kinase binding function, and at the C terminus a regulatory tyrosine governing WW, SH2 and SH3 domain interactions. We will discuss the binding partners for these motifs and how their interactions and regulation can modulate the involvement of dystroglycan in a range of different adhesion structures and functions depending on context. Thus dystroglycan presents as a multifunctional scaffold involved in adhesion and adhesion-mediated signalling with its functions under exquisite spatio-temporal regulation.