The Structure of the Plakin Domain of Plectin Reveals an Extended Rod-like Shape

Homozygosity for a Rare Plec Variant Suggests a Contributory Role in Congenital Insensitivity to Pain

Congenital insensitivity to pain is a rare human condition in which affected individuals do not experience pain throughout their lives. This study aimed to identify the molecular etiology of congenital insensitivity to pain in two Thai patients. Clinical, radiographic, histopathologic, immunohistochemical, and molecular studies were performed. Patients were found to have congenital insensitivity to pain, self-mutilation, acro-osteolysis, cornea scars, reduced temperature sensation, tooth agenesis, root maldevelopment, and underdeveloped maxilla and mandible. The skin biopsies revealed fewer axons, decreased vimentin expression, and absent neurofilament expression, indicating lack of dermal nerves. Whole exome and Sanger sequencing identified a rare homozygous variant c.4039C>T; p.Arg1347Cys in the plakin domain of Plec, a cytolinker protein. This p.Arg1347Cys variant is in the spectrin repeat 9 region of the plakin domain, a region not previously found to harbor pathogenic missense variants in other plectinopathies. The substitution with a cysteine is expected to decrease the stability of the spectrin repeat 9 unit of the plakin domain. Whole mount in situ hybridization and an immunohistochemical study suggested that Plec is important for the development of maxilla and mandible, cornea, and distal phalanges. Additionally, the presence of dental anomalies in these patients further supports the potential involvement of Plec in tooth development. This is the first report showing the association between the Plec variant and congenital insensitivity to pain in humans.

Reconstitution of cytolinker-mediated crosstalk between actin and vimentin

Cell shape and motility are determined by the cytoskeleton, an interpenetrating network of actin filaments, microtubules, and intermediate filaments. The biophysical properties of each filament type individually have been studied extensively by cell-free reconstitution. By contrast, the interactions between the three cytoskeletal networks are relatively unexplored. They are coupled via crosslinkers of the plakin family such as plectin. These are challenging proteins for reconstitution because of their giant size and multidomain structure. Here we engineer a recombinant actin-vimentin crosslinker protein called 'ACTIF' that provides a minimal model system for plectin, recapitulating its modular design with actin-binding and intermediate filament-binding domains separated by a coiled-coil linker for dimerisation. We show by fluorescence and electron microscopy that ACTIF has a high binding affinity for vimentin and actin and creates mixed actin-vimentin bundles. Rheology measurements show that ACTIF-mediated crosslinking strongly stiffens actin-vimentin composites. Finally, we demonstrate the modularity of this approach by creating an ACTIF variant with the intermediate filament binding domain of Adenomatous Polyposis Coli. Our protein engineering approach provides a new cell-free system for the biophysical characterization of intermediate filament-binding crosslinkers and for understanding the mechanical synergy between actin and vimentin in mesenchymal cells.

METTL3-mediated m6A modification of EPPK1 to promote the development of esophageal cancer through regulating the PI3K/AKT pathway

Methyltransferase like 3 (METTL3) has been proved to be involved in the progression of various cancers. In this study, we explored the role of METTL3 and its underlying mechanism in esophageal cancer progression. The mRNA and protein levels of METTL3 and epiplakin1 (EPPK1) were determined using qRT-PCR and western blot. The proliferative ability was evaluated through 3-(4,5)-dimethylthiahiazo (-z-y1)-3,5-di- phenytetrazoliumromide (MTT), colony formation, and EdU assays. Transwell invasion assay and wound-healing assay were employed for detecting cell invasion and migration, respectively. Cell stemness was evaluated by sphere-formation assay. Xenograft tumor experiments and immunohistochemistry (IHC) were performed to explore the effects of METTL3 knockdown on tumor growth in vivo. The N6-methyladenosine (m6A) modification of EPPK1 was analyzed using MeRIP. RNA-protein immunoprecipitation (RIP) and dual-luciferase reporter assays were used to verify the relationship between EPPK1 and METTL3. METTL3 was upregulated in esophageal cancer tissues and cells, which was related to the poor prognosis of esophageal cancer patients. Knockdown of METTL3 overtly decreased the proliferative, invasive, migrated abilities, and cell stemness of esophageal cancer cells in vitro. Moreover, depletion of METTL3 also observably suppressed the growth of tumor in vivo. EPPK1 was a direct target of METTL3, and METTL3 could mediate the m6A modification of EPPK1. EPPK1 was downregulated in esophageal cancer tissues and cells, and EPPK1 depletion markedly repressed cell proliferation, invasion, migration, and stemness of esophageal cancer cells. The inhibition effects of METTL3 deficiency on these malignant behaviors were harbored by EPPK1 upregulation in esophageal cancer cells. In addition, METTL3 deficiency reduced EPPK1 expression to inactivate the PI3K/AKT pathway. Our results revealed that METTL3 deficiency regulated the m6A modification of EPPK1 to inhibit the PI3K/AKT pathway, thereby restraining the progression of esophageal cancer.

Structure-function analysis of PorXFj, the PorX homolog from Flavobacterium johnsioniae, suggests a role of the CheY-like domain in type IX secretion motor activity

The type IX secretion system (T9SS) is a large multi-protein transenvelope complex distributed into the Bacteroidetes phylum and responsible for the secretion of proteins involved in pathogenesis, carbohydrate utilization or gliding motility. In Porphyromonas gingivalis, the two-component system PorY sensor and response regulator PorX participate to T9SS gene regulation. Here, we present the crystal structure of PorXFj, the Flavobacterium johnsoniae PorX homolog. As for PorX, the PorXFj structure is comprised of a CheY-like N-terminal domain and an alkaline phosphatase-like C-terminal domain separated by a three-helix bundle central domain. While not activated and monomeric in solution, PorXFj crystallized as a dimer identical to active PorX. The CheY-like domain of PorXFj is in an active-like conformation, and PorXFj possesses phosphodiesterase activity, in agreement with the observation that the active site of its phosphatase-like domain is highly conserved with PorX.

The cyto-linker and scaffolding protein "plectin" mis-localization leads to softening of cancer cells

Discovering tools to prevent cancer progression requires understanding the fundamental differences between normal and cancer cells. More than a decade ago, atomic force microscopy (AFM) revealed cancer cells' softer body compared to their healthy counterparts. Here, we investigated the mechanism underlying the softening of cancerous cells in comparison with their healthy counterparts based on AFM high resolution stiffness tomography and 3D confocal microscopy. We showed microtubules (MTs) network in invasive ductal carcinoma cell cytoskeleton is basally located and segmented for around 400 nm from the cell periphery. Additionally, the cytoskeleton scaffolding protein plectin exhibits a mis-localization from the cytoplasm to the surface of cells in the carcinoma which justifies the dissociation of the MT network from the cell's cortex. Furthermore, the assessment of MTs' persistence length using a worm-like-chain (WLC) model in high resolution AFM images showed lower persistence length of the single MTs in ductal carcinoma compared to that in the normal state. Overall, these tuned mechanics support the invasive cells to ascertain more flexibility under compressive forces in small deformations. These data provide new insights into the structural origins of cancer aids in progression.

Pathogen-specific structural features of Candida albicans Ras1 activation complex: uncovering new antifungal drug targets

An important feature associated with Candida albicans pathogenicity is its ability to switch between yeast and hyphal forms, a process in which CaRas1 plays a key role. CaRas1 is activated by the guanine nucleotide exchange factor (GEF) CaCdc25, triggering hyphal growth-related signaling pathways through its conserved GTP-binding (G)-domain. An important function in hyphal growth has also been proposed for the long hypervariable region downstream the G-domain, whose unusual content of polyglutamine stretches and Q/N repeats make CaRas1 unique within Ras proteins. Despite its biological importance, both the structure of CaRas1 and the molecular basis of its activation by CaCdc25 remain unexplored. Here, we show that CaRas1 has an elongated shape and limited conformational flexibility and that its hypervariable region contains helical structural elements, likely forming an intramolecular coiled-coil. Functional assays disclosed that CaRas1-activation by CaCdc25 is highly efficient, with activities up to 2,000-fold higher than reported for human GEFs. The crystal structure of the CaCdc25 catalytic region revealed an active conformation for the α-helical hairpin, critical for CaRas1-activation, unveiling a specific region exclusive to CTG-clade species. Structural studies on CaRas1/CaCdc25 complexes also revealed an interaction surface clearly distinct from that of homologous human complexes. Furthermore, we identified an inhibitory synthetic peptide, prompting the proposal of a key regulatory mechanism for CaCdc25. To our knowledge, this is the first report of specific inhibition of the CaRas1-activation via targeting its GEF. This, together with their unique pathogen-structural features, disclose a set of novel strategies to specifically block this important virulence-related mechanism. IMPORTANCE Candida albicans is the main causative agent of candidiasis, the commonest fungal infection in humans. The eukaryotic nature of C. albicans and the rapid emergence of antifungal resistance raise the challenge of identifying novel drug targets to battle this prevalent and life-threatening disease. CaRas1 and CaCdc25 are key players in the activation of signaling pathways triggering multiple virulence traits, including the yeast-to-hypha interconversion. The structural similarity of the conserved G-domain of CaRas1 to those of human homologs and the lack of structural information on CaCdc25 has impeded progress in targeting these proteins. The unique structural and functional features for CaRas1 and CaCdc25 presented here, together with the identification of a synthetic peptide capable of specifically inhibiting the GEF activity of CaCdc25, open new possibilities to uncover new antifungal drug targets against C. albicans virulence.

Novel biallelic variants in the PLEC gene are associated with severe hearing loss

Pediatric auditory neuropathy spectrum disorder is a particular type of hearing loss caused by abnormal sound transmission from the cochlea to the brain. It is due to defective peripheral synaptic function or improper neuronal conduction. Using trio whole-exome sequencing, we have identified novel biallelic variants in the PLEC gene in three individuals with profound deafness from two unrelated families. Among them, one pediatric patient diagnosed with auditory neuropathy spectrum disorder had a good cochlear implantation outcome. The other two adult patients were diagnosed with non-syndromic hearing loss. Studies in mice and zebrafish confirmed that plectin is developmentally expressed in the inner ear. Moreover, plectin's knockdown resulted in a reduction of synaptic mitochondrial potential and loss of ribbon synapses, reinforcing the idea of a role for plectin in neuronal transmission. Altogether, the results presented here, point to a new unconventional role for plectin in the inner ear. Contrary to the well-characterized association of plectin to skin and muscle diseases, we found that specific plectin mutations can result in hearing loss with no other clinical manifestations. This is important because 1) it provides evidence of plectin's involvement in inner ear function and 2) it will help clinicians at the time of diagnosis and treatment.

Junctional epithelium and hemidesmosomes: Tape and rivets for solving the "percutaneous device dilemma" in dental and other permanent implants

The percutaneous device dilemma describes etiological factors, centered around the disrupted epithelial tissue surrounding non-remodelable devices, that contribute to rampant percutaneous device infection. Natural percutaneous organs, in particular their extracellular matrix mediating the "device"/epithelium interface, serve as exquisite examples to inspire longer lasting long-term percutaneous device design. For example, the tooth's imperviousness to infection is mediated by the epithelium directly surrounding it, the junctional epithelium (JE). The hallmark feature of JE is formation of hemidesmosomes, cell/matrix adhesive structures that attach surrounding oral gingiva to the tooth's enamel through a basement membrane. Here, the authors survey the multifaceted functions of the JE, emphasizing the role of the matrix, with a particular focus on hemidesmosomes and their five main components. The authors highlight the known (and unknown) effects dental implant - as a model percutaneous device - placement has on JE regeneration and synthesize this information for application to other percutaneous devices. The authors conclude with a summary of bioengineering strategies aimed at solving the percutaneous device dilemma and invigorating greater collaboration between clinicians, bioengineers, and matrix biologists.

Structural/functional studies of Trio provide insights into its configuration and show that conserved linker elements enhance its activity for Rac1

Trio is a large and highly conserved metazoan signaling scaffold that contains two Dbl family guanine nucleotide exchange factor (GEF) modules, TrioN and TrioC, selective for Rac and RhoA GTPases, respectively. The GEF activities of TrioN and TrioC are implicated in several cancers, especially uveal melanoma. However, little is known about how these modules operate in the context of larger fragments of Trio. Here we show via negative stain electron microscopy that the N-terminal region of Trio is extended and could thus serve as a rigid spacer between the N-terminal putative lipid-binding domain and TrioN, whereas the C-terminal half of Trio seems globular. We found that regions C-terminal to TrioN enhance its Rac1 GEF activity and thus could play a regulatory role. We went on to characterize a minimal, well-behaved Trio fragment with enhanced activity, Trio1284-1959, in complex with Rac1 using cryo-electron microscopy and hydrogen-deuterium exchange mass spectrometry and found that the region conferring enhanced activity is disordered. Deletion of two different strongly conserved motifs in this region eliminated this enhancement, suggesting that they form transient intramolecular interactions that promote GEF activity. Because Dbl family RhoGEF modules have been challenging to directly target with small molecules, characterization of accessory Trio domains such as these may provide alternate routes for the development of therapeutics that inhibit Trio activity in human cancer.

Ancient Origins of Cytoskeletal Crosstalk: Spectraplakin-like Proteins Precede the Emergence of Cortical Microtubule Stabilization Complexes as Crosslinkers

Adhesion between cells and the extracellular matrix (ECM) is one of the prerequisites for multicellularity, motility, and tissue specialization. Focal adhesions (FAs) are defined as protein complexes that mediate signals from the ECM to major components of the cytoskeleton (microtubules, actin, and intermediate filaments), and their mutual communication determines a variety of cellular processes. In this study, human cytoskeletal crosstalk proteins were identified by comparing datasets with experimentally determined cytoskeletal proteins. The spectraplakin dystonin was the only protein found in all datasets. Other proteins (FAK, RAC1, septin 9, MISP, and ezrin) were detected at the intersections of FAs, microtubules, and actin cytoskeleton. Homology searches for human crosstalk proteins as queries were performed against a predefined dataset of proteomes. This analysis highlighted the importance of FA communication with the actin and microtubule cytoskeleton, as these crosstalk proteins exhibit the highest degree of evolutionary conservation. Finally, phylogenetic analyses elucidated the early evolutionary history of spectraplakins and cortical microtubule stabilization complexes (CMSCs) as model representatives of the human cytoskeletal crosstalk. While spectraplakins probably arose at the onset of opisthokont evolution, the crosstalk between FAs and microtubules is associated with the emergence of metazoans. The multiprotein complexes contributing to cytoskeletal crosstalk in animals gradually gained in complexity from the onset of metazoan evolution.

Epiplakin1 promotes the progression of esophageal squamous cell carcinoma by activating the PI3K-AKT signaling pathway

BACKGROUND

Epiplakin1 (EPPK1) has been associated with disease progression and unfavorable prognosis of many cancers, but its functional involvement in esophageal squamous cell carcinoma (ESCC) remains to be uncovered.

METHODS

The Quantitative Real-time PCR (qPCR) assay was employed to determine the expression of EPPK1 in ESCC tissues and cells. CCK-8 assay, colony forming assay, wound healing assay, and transwell invasion assay were utilized to evaluate the effects of EPPK1 on cell proliferation, migration, and invasion capacity in ESCC cells using small interfering ribonucleic acids. Flow cytometry was performed to estimate the cell apoptotic rate caused by silencing of EPPK1. The proteins related to epithelial-to-mesenchymal transition (EMT), apoptosis, and activation of the phosphatidylinositol 3-kinase/serine threonine protein kinase 1 (PI3K/AKT) signaling pathway were measured by western blot.

RESULTS

The expression of EPPK1 was dramatically increased in ESCC tissues and cells compared to that in relative controls. Additionally, silencing of EPPK1 suppressed ESCC cell growth, colony formation, migration, invasion, and EMT, while promoting ESCC cell apoptosis. Furthermore, EPPK1 induced ESCC cell progression via mediating the PI3K/AKT signaling pathway.

CONCLUSION

EPPK1 promotes ESCC progression by modulating the PI3K/AKT signaling pathway and could serve as a potential target for ESCC treatment.

A novel peptidomimetic therapeutic for selective suppression of lung cancer stem cells over non-stem cancer cells

Cancers are highly heterogeneous and typically contain a small subset of drug-resisting cells called tumor initiating cells or cancer stem cells (CSCs). CSCs can self-renew, divide asymmetrically, and often cause tumor invasion and metastasis. Therefore, treatments specifically targeting CSCs are critical to improve patient survival. Recently, we identified a highly specific peptidomimetic (peptoid - PCS2) that selectively binds to the CSC subpopulation of lung cancer over the remaining cancer cells (non-CSCs). Subsequently, we identified plectin as the target of PCS2. Plectin is an intracellular structural protein, which is involved in tumor invasion and metastasis when it appears on cell surface. While PCS2 monomer did not display any anti-cancer activity, we designed a series of homo-dimeric versions of PCS2, and identified PCS2D1.2 optimized homo-dimer that displayed highly specific cytotoxicity towards CSCs over non-CSCs. PCS2D1.2 effectively blocked the in vitro colony formation and cell migration, hallmarks of CSCs. Furthermore, PCS2D1.2 reduced the in vivo tumor formation. In both in vitro and in vivo studies, PCS2D1.2 effectively reduced plectin expression and/or plectin-rich CSCs, but had no effect on non-CSCs. Therefore, PCS2D1.2 has the potential to be developed as a highly CSC specific drug candidate, which can be used in combination with current anti-cancer drugs.

Identifying Plectin Isoform Functions through Animal Models

Plectin, a high-molecular-weight cytoskeletal linker protein, binds with high affinity to intermediate filaments of all types and connects them to junctional complexes, organelles, and inner membrane systems. In addition, it interacts with actomyosin structures and microtubules. As a multifunctional protein, plectin has been implicated in several multisystemic diseases, the most common of which is epidermolysis bullosa simplex with muscular dystrophy (EBS-MD). A great part of our knowledge about plectin’s functional diversity has been gained through the analysis of a unique collection of transgenic mice that includes a full (null) knockout (KO), several tissue-restricted and isoform-specific KOs, three double KOs, and two knock-in lines. The key molecular features and pathological phenotypes of these mice will be discussed in this review. In summary, the analysis of the different genetic models indicated that a functional plectin is required for the proper function of striated and simple epithelia, cardiac and skeletal muscle, the neuromuscular junction, and the vascular endothelium, recapitulating the symptoms of humans carrying plectin mutations. The plectin-null line showed severe skin and muscle phenotypes reflecting the importance of plectin for hemidesmosome and sarcomere integrity; whereas the ablation of individual isoforms caused a specific phenotype in myofibers, basal keratinocytes, or neurons. Tissue-restricted ablation of plectin rendered the targeted cells less resilient to mechanical stress. Studies based on animal models other than the mouse, such as zebrafish and C. elegans, will be discussed as well.

Regulation of hemidesmosome dynamics and cell signaling by integrin α6β4

Hemidesmosomes (HDs) are specialized multiprotein complexes that connect the keratin cytoskeleton of epithelial cells to the extracellular matrix (ECM). In the skin, these complexes provide stable adhesion of basal keratinocytes to the underlying basement membrane. Integrin α6β4 is a receptor for laminins and plays a vital role in mediating cell adhesion by initiating the assembly of HDs. In addition, α6β4 has been implicated in signal transduction events that regulate diverse cellular processes, including proliferation and survival. In this Review, we detail the role of α6β4 in HD assembly and beyond, and we discuss the molecular mechanisms that regulate its function.

KLF5-mediated Eppk1 expression promotes cell proliferation in cervical cancer via the p38 signaling pathway

BACKGROUND

Epiplakin1 (Eppk1) is part of epidermal growth factor (EGF) signal and takes part in reorganization of cytoskeleton and cell proliferation. However, the role of Eppk1 in cervical cancer (CC) remains unknown.

METHODS

To express Eppk1 and KLF5 and their correlation, we used RNA-sequence, RT-qPCR, TCGA database and immunofluorescence staining in vitro and in different pathological cervical tissues. In CC cell lines, we tested adenovirus-mediated over expression or knockdown of KLF5 and siRNA-mediated knockdown of Eppk1 and a suiting assessment of cell proliferation and cell signaling by western blot and CCK8 tests. We studied the mechanism by which KLF5 regulates Eppk1 expression by reporter gene test and chromatin immunoprecipitation test.

RESULTS

Eppk1 expression promoted in CC tissues and cell lines compared with increased KLF5 expression. The results of immunofluorescence staining further showed the increased co-expression of Eppk1 and KLF5 correlated substantially with tumorigenesis in cervical tissues. Overexpression of KLF5 significantly increased Eppk1 expression at transcription and translation levels. Conversely, the knockdown of KLF5 by siRNA against KLF5 decreased Eppk1 expression. Mechanically, KLF5 activated Eppk1 transcription by direct binding to the Eppk1 promoter. Gain- and loss-of-function experiments reported that KLF5 promoted cell proliferation in Hela partly dependent on Eppk1 upregulation. Besides, KLF5-mediated activation of p38 signaling significantly decreased after Eppk1 knockdown compared with decline of proliferation, suggesting that Eppk1 lies upstream of p38 signaling affecting cell proliferation. Finally, Eppk1 expression is positively correlated with tumor size in clinicopathological features of CC.

CONCLUSIONS

Eppk1 may be an effective therapeutic target for affecting p38 signaling pathway and cell proliferation in cervical cancer.

IM30 IDPs form a membrane-protective carpet upon super-complex disassembly

Members of the phage shock protein A (PspA) family, including the inner membrane-associated protein of 30 kDa (IM30), are suggested to stabilize stressed cellular membranes. Furthermore, IM30 is essential in thylakoid membrane-containing chloroplasts and cyanobacteria, where it is involved in membrane biogenesis and/or remodeling. While it is well known that PspA and IM30 bind to membranes, the mechanism of membrane stabilization is still enigmatic. Here we report that ring-shaped IM30 super-complexes disassemble on membranes, resulting in formation of a membrane-protecting protein carpet. Upon ring dissociation, the C-terminal domain of IM30 unfolds, and the protomers self-assemble on membranes. IM30 assemblies at membranes have been observed before in vivo and were associated with stress response in cyanobacteria and chloroplasts. These assemblies likely correspond to the here identified carpet structures. Our study defines the thus far enigmatic structural basis for the physiological function of IM30 and related proteins, including PspA, and highlights a hitherto unrecognized concept of membrane stabilization by intrinsically disordered proteins.

The plakin domain of C. elegans VAB-10/plectin acts as a hub in a mechanotransduction pathway to promote morphogenesis

Mechanical forces can elicit a mechanotransduction response through junction-associated proteins. In contrast to the wealth of knowledge available for focal adhesions and adherens junctions, much less is known about mechanotransduction at hemidesmosomes. Here, we focus on the C. elegans plectin homolog VAB-10A, the only evolutionary conserved hemidesmosome component. In C. elegans, muscle contractions induce a mechanotransduction pathway in the epidermis through hemidesmosomes. We used CRISPR to precisely remove spectrin repeats (SRs) or a partially hidden Src homology 3 (SH3) domain within the VAB-10 plakin domain. Deleting the SH3 or SR8 domains in combination with mutations affecting mechanotransduction, or just the part of SR5 shielding the SH3 domain, induced embryonic elongation arrest because hemidesmosomes collapse. Notably, recruitment of GIT-1, the first mechanotransduction player, requires the SR5 domain and the hemidesmosome transmembrane receptor LET-805. Furthermore, molecular dynamics simulations confirmed that forces acting on VAB-10 could make the central SH3 domain, otherwise in contact with SR4, available for interaction. Collectively, our data strongly indicate that the plakin domain plays a central role in mechanotransduction and raise the possibility that VAB-10/plectin might act as a mechanosensor.

Non-immunogenic utrophin gene therapy for the treatment of muscular dystrophy animal models

The essential product of the Duchenne muscular dystrophy (DMD) gene is dystrophin¹, a rod-like protein² that protects striated myocytes from contraction-induced injury^3,4. Dystrophin-related protein (or utrophin) retains most of the structural and protein binding elements of dystrophin⁵. Importantly, normal thymic expression in DMD patients⁶ should protect utrophin by central immunologic tolerance. We designed a codon-optimized, synthetic transgene encoding a miniaturized utrophin (µUtro), deliverable by adeno-associated virus (AAV) vectors. Here, we show that µUtro is a highly functional, non-immunogenic substitute for dystrophin, preventing the most deleterious histological and physiological aspects of muscular dystrophy in small and large animal models. Following systemic administration of an AAV-µUtro to neonatal dystrophin-deficient mdx mice, histological and biochemical markers of myonecrosis and regeneration are completely suppressed throughout growth to adult weight. In the dystrophin-deficient golden retriever model, µUtro non-toxically prevented myonecrosis, even in the most powerful muscles. In a stringent test of immunogenicity, focal expression of µUtro in the deletional-null German shorthaired pointer model produced no evidence of cell-mediated immunity, in contrast to the robust T cell response against similarly constructed µDystrophin (µDystro). These findings support a model in which utrophin-derived therapies might be used to treat clinical dystrophin deficiency, with a favorable immunologic profile and preserved function in the face of extreme miniaturization.

[Research advances in limb-girdle muscular dystrophy type 2Q]

Limb-girdle muscular dystrophy (LGMD) is a group of muscular dystrophies with predominantly proximal muscular weakness, and some genes associated with this disease have been identified at present. LGMD type 2Q (LGMD2Q) is a subtype of LGMD and is associated with PLEC gene mutation. Major phenotypes of PLEC gene mutation include epidermolysis bullosa with late-onset muscular dystrophy and epidermolysis bullosa with other lesions. LGMD2Q without skin lesions is rarely reported. This article reviews the pathogenic gene PLEC and clinical manifestations of LGMD2Q, so as to deepen the understanding of the pathogenic gene and phenotype of LGMD2Q.

Empirical and Computational Comparison of Alternative Therapeutic Exon Skip Repairs for Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a common and devastating genetic disease primarily caused by exon deletions that create a genetic frameshift in dystrophin. Exon skipping therapy seeks to correct this by masking an exon during the mRNA maturation process, restoring dystrophin expression, but creating an edited protein missing both the original defect and the therapeutically skipped region. Crucially, it is possible to correct many defects in alternative ways, by skipping an exon either before or after the patient's defect. This results in alternatively edited, hybrid proteins that might have different properties and therapeutic consequences. We examined three such dystrophin exon-skipped edits, Δe45-53, Δe46-54, and Δe47-55, comprising two pairs of alternative repairs of Δe46-53 and Δe47-54 DMD defects. We found that in both cases, Δe46-54 was the more stable repair as determined by a variety of thermodynamic and biochemical measurements. We also examined the origin of these differences with molecular dynamics simulations, which showed that these stability differences were the result of different types of structural perturbations. For example, in one edit there was partial unfolding at the edit site that caused domain-localized perturbations while in another there was unfolding at the protein domain junctions distal to the edit site that increased molecular flexibility. These results demonstrate that alternative exon skip repairs of the same underlying defect can have very different consequences at the level of protein structure and stability and furthermore that these can arise by different mechanisms, either locally or by more subtle long-range perturbations.

Genetic regulation of methylation in human endometrium and blood and gene targets for reproductive diseases

Background

Major challenges in understanding the functional consequences of genetic risk factors for human disease are which tissues and cell types are affected and the limited availability of suitable tissue. The aim of this study was to evaluate tissue-specific genotype-epigenetic characteristics in DNA samples from both endometrium and blood collected from women at different stages of the menstrual cycle and relate results to genetic risk factors for reproductive traits and diseases.

Results

We analysed DNA methylation (DNAm) data from endometrium and blood samples from 66 European women. Methylation profiles were compared between stages of the menstrual cycle, and changes in methylation overlaid with changes in transcription and genotypes. We observed large changes in methylation (27,262 DNAm probes) across the menstrual cycle in endometrium that were not observed in blood. Individual genotype data was tested for association with methylation at 443,016 and 443,101 DNAm probes in endometrium and blood respectively to identify methylation quantitative trait loci (mQTLs). A total of 4546 sentinel cis-mQTLs (P < 1.13 × 10⁻¹⁰) and 434 sentinel trans-mQTLs (P < 2.29 × 10⁻¹²) were detected in endometrium and 6615 sentinel cis-mQTLs (P < 1.13 × 10⁻¹⁰) and 590 sentinel trans-mQTLs (P < 2.29 × 10⁻¹²) were detected in blood. Following secondary analyses, conducted to test for overlap between mQTLs in the two tissues, we found that 62% of endometrial cis-mQTLs were also observed in blood and the genetic effects between tissues were highly correlated. A number of mQTL SNPs were associated with reproductive traits and diseases, including one mQTL located in a known risk region for endometriosis (near GREB1).

Conclusions

We report novel findings characterising genetic regulation of methylation in endometrium and the association of endometrial mQTLs with endometriosis risk and other reproductive traits and diseases. The high correlation of genetic effects between tissues highlights the potential to exploit the power of large mQTL datasets in endometrial research and identify target genes for functional studies. However, tissue-specific methylation profiles and genetic effects also highlight the importance of also using disease-relevant tissues when investigating molecular mechanisms of disease risk.

Electronic supplementary material

The online version of this article (10.1186/s13148-019-0648-7) contains supplementary material, which is available to authorized users.

The dynamic nature of the conserved tegument protein UL37 of herpesviruses

In all herpesviruses, the space between the capsid shell and the lipid envelope is occupied by the unique tegument layer composed of proteins that, in addition to structural roles, play many other roles in the viral replication. UL37 is a highly conserved tegument protein that has activities ranging from virion morphogenesis to directional capsid trafficking to manipulation of the host innate immune response and binds multiple partners. The N-terminal half of UL37 (UL37N) has a compact bean-shaped α-helical structure that contains a surface region essential for neuroinvasion. However, no biochemical or structural information is currently available for the C-terminal half of UL37 (UL37C) that mediates most of its interactions with multiple binding partners. Here, we show that the C-terminal half of UL37 from pseudorabies virus UL37C is a conformationally flexible monomer composed of an elongated folded core and an unstructured C-terminal tail. This elongated structure, along with that of its binding partner UL36, explains the nature of filamentous tegument structures bridging the capsid and the envelope. We propose that the dynamic nature of UL37 underlies its ability to perform diverse roles during viral replication.

No major role for rare plectin variants in arrhythmogenic right ventricular cardiomyopathy

Aims

Likely pathogenic/pathogenic variants in genes encoding desmosomal proteins play an important role in the pathophysiology of arrhythmogenic right ventricular cardiomyopathy (ARVC). However, for a substantial proportion of ARVC patients, the genetic substrate remains unknown. We hypothesized that plectin, a cytolinker protein encoded by the PLEC gene, could play a role in ARVC because it has been proposed to link the desmosomal protein desmoplakin to the cytoskeleton and therefore has a potential function in the desmosomal structure.

Methods

We screened PLEC in 359 ARVC patients and compared the frequency of rare coding PLEC variants (minor allele frequency [MAF] <0.001) between patients and controls. To assess the frequency of rare variants in the control population, we evaluated the rare coding variants (MAF <0.001) found in the European cohort of the Exome Aggregation Database. We further evaluated plectin localization by immunofluorescence in a subset of patients with and without a PLEC variant.

Results

Forty ARVC patients carried one or more rare PLEC variants (11%, 40/359). However, rare variants also seem to occur frequently in the control population (18%, 4754/26197 individuals). Nor did we find a difference in the prevalence of rare PLEC variants in ARVC patients with or without a desmosomal likely pathogenic/pathogenic variant (14% versus 8%, respectively). However, immunofluorescence analysis did show decreased plectin junctional localization in myocardial tissue from 5 ARVC patients with PLEC variants.

Conclusions

Although PLEC has been hypothesized as a promising candidate gene for ARVC, our current study did not show an enrichment of rare PLEC variants in ARVC patients compared to controls and therefore does not support a major role for PLEC in this disorder. Although rare PLEC variants were associated with abnormal localization in cardiac tissue, the confluence of data does not support a role for plectin abnormalities in ARVC development.

The mechano-sensing role of the unique SH3 insertion in plakin domains revealed by Molecular Dynamics simulations

The plakin family of proteins, important actors in cross-linking force-bearing structures in the cell, contain a curious SH3 domain insertion in their chain of spectrin repeats (SRs). While SH3 domains are known to mediate protein-protein interactions, here, its canonical binding site is autoinhibited by the preceding SR. Under force, however, this SH3 domain could be released, and possibly launch a signaling cascade. We performed large-scale force-probe molecular dynamics simulations, across two orders of magnitude of loading rates, to test this hypothesis, on two prominent members of the plakin family: desmoplakin and plectin, obligate proteins at desmosomes and hemidesmosomes, respectively. Our simulations show that force unravels the SRs and abolishes the autoinhibition of the SH3 domain, an event well separated from the unfolding of this domain. The SH3 domain is free and fully functional for a significant portion of the unfolding trajectories. The rupture forces required for the two proteins significantly decrease when the SH3 domain is removed, which implies that the SH3 domain also stabilizes this junction. Our results persist across all simulations, and support a force-sensing as well as a stabilizing role of the unique SH3 insertion, putting forward this protein family as a new class of mechano-sensors.

Crystal structure of Mdm12 and combinatorial reconstitution of Mdm12/Mmm1 ERMES complexes for structural studies

Membrane contact sites between organelles serve as molecular hubs for the exchange of metabolites and signals. In yeast, the Endoplasmic Reticulum - Mitochondrion Encounter Structure (ERMES) tethers these two organelles likely to facilitate the non-vesicular exchange of essential phospholipids. Present in Fungi and Amoebas but not in Metazoans, ERMES is composed of five distinct subunits; among those, Mdm12, Mmm1 and Mdm34 each contain an SMP domain functioning as a lipid transfer module. We previously showed that the SMP domains of Mdm12 and Mmm1 form a hetero-tetramer. Here we describe our strategy to diversify the number of Mdm12/Mmm1 complexes suited for structural studies. We use sequence analysis of orthologues combined to protein engineering of disordered regions to guide the design of protein constructs and expand the repertoire of Mdm12/Mmm1 complexes more likely to crystallize. Using this combinatorial approach we report crystals of Mdm12/Mmm1 ERMES complexes currently diffracting to 4.5 Å resolution and a new structure of Mdm12 solved at 4.1 Å resolution. Our structure reveals a monomeric form of Mdm12 with a conformationally dynamic N-terminal β-strand; it differs from a previously reported homodimeric structure where the N-terminal β strands where swapped to promote dimerization. Based on our electron microscopy data, we propose a refined pseudo-atomic model of the Mdm12/Mmm1 complex that agrees with our crystallographic and small-angle X-ray scattering (SAXS) solution data.

Desmosomes and Intermediate Filaments: Their Consequences for Tissue Mechanics

Adherens junctions (AJs) and desmosomes connect the actin and keratin filament networks of adjacent cells into a mechanical unit. Whereas AJs function in mechanosensing and in transducing mechanical forces between the plasma membrane and the actomyosin cytoskeleton, desmosomes and intermediate filaments (IFs) provide mechanical stability required to maintain tissue architecture and integrity when the tissues are exposed to mechanical stress. Desmosomes are essential for stable intercellular cohesion, whereas keratins determine cell mechanics but are not involved in generating tension. Here, we summarize the current knowledge of the role of IFs and desmosomes in tissue mechanics and discuss whether the desmosome-keratin scaffold might be actively involved in mechanosensing and in the conversion of chemical signals into mechanical strength.

The role of MACF1 in nervous system development and maintenance

Microtubule-actin crosslinking factor 1 (MACF1), also known as actin crosslinking factor 7 (ACF7), is essential for proper modulation of actin and microtubule cytoskeletal networks. Most MACF1 isoforms are expressed broadly in the body, but some are exclusively found in the nervous system. Consequentially, MACF1 is integrally involved in multiple neural processes during development and in adulthood, including neurite outgrowth and neuronal migration. Furthermore, MACF1 participates in several signaling pathways, including the Wnt/β-catenin and GSK-3 signaling pathways, which regulate key cellular processes, such as proliferation and cell migration. Genetic mutation or dysregulation of the MACF1 gene has been associated with neurodevelopmental and neurodegenerative diseases, specifically schizophrenia and Parkinson's disease. MACF1 may also play a part in neuromuscular disorders and have a neuroprotective role in the optic nerve. In this review, the authors seek to synthesize recent findings relating to the roles of MACF1 within the nervous system and explore potential novel functions of MACF1 not yet examined.