Interaction of α-catulin with dystrobrevin contributes to integrity of dystrophin complex in muscle

Catulin reporter marks a heterogeneous population of invasive breast cancer cells with some demonstrating plasticity and participating in vascular mimicry

Breast cancer is the most commonly diagnosed cancer in women worldwide. The activation of partial or more complete epithelial–mesenchymal transition in cancer cells enhances acquisition of invasive behaviors and expands their generation of cancer stem cells. Increased by EMT plasticity of tumor cells could promote vascular mimicry, a newly defined pattern of tumor microvascularization by which aggressive tumor cells can form vessel-like structures themselves. VM is strongly associated with a poor prognosis, but biological features of tumor cells that form VM remains unknown. Here we show that catulin is expressed in human BC samples and its expression correlates with the tumor progression. Ablation of catulin in hBC cell lines decreases their invasive potential in the 3D assays. Using a novel catulin promoter based reporter we tracked and characterized the small population of invasive BC cells in xenograft model. RNAseq analysis revealed enrichment in genes important for cellular movement, invasion and interestingly for tumor-vasculature interactions. Analysis of tumors unveiled that catulin reporter marks not only invasive cancer cells but also rare population of plastic, MCAM positive cancer cells that participate in vascular mimicry. Ablation of catulin in the xenograft model revealed deregulation of genes involved in cellular movement, and adhesive properties with striking decrease in CD44 which may impact stemness potential, and plasticity of breast cancer cells. These findings show directly that some plastic tumor cells can change the fate into endothelial-like, expressing MCAM and emphasize the importance of catulin in this process and breast cancer progression.

Caenorhabditis elegans as a Model System for Duchenne Muscular Dystrophy

The nematode worm Caenorhabditis elegans has been used extensively to enhance our understanding of the human neuromuscular disorder Duchenne Muscular Dystrophy (DMD). With new arising clinically relevant models, technologies and treatments, there is a need to reconcile the literature and collate the key findings associated with this model.

The Dystrophin Node as Integrator of Cytoskeletal Organization, Lateral Force Transmission, Fiber Stability and Cellular Signaling in Skeletal Muscle

The systematic bioanalytical characterization of the protein product of the DMD gene, which is defective in the pediatric disorder Duchenne muscular dystrophy, led to the discovery of the membrane cytoskeletal protein dystrophin. Its full-length muscle isoform Dp427-M is tightly linked to a sarcolemma-associated complex consisting of dystroglycans, sarcoglyans, sarcospan, dystrobrevins and syntrophins. Besides these core members of the dystrophin-glycoprotein complex, the wider dystrophin-associated network includes key proteins belonging to the intracellular cytoskeleton and microtubular assembly, the basal lamina and extracellular matrix, various plasma membrane proteins and cytosolic components. Here, we review the central role of the dystrophin complex as a master node in muscle fibers that integrates cytoskeletal organization and cellular signaling at the muscle periphery, as well as providing sarcolemmal stabilization and contractile force transmission to the extracellular region. The combination of optimized tissue extraction, subcellular fractionation, advanced protein co-purification strategies, immunoprecipitation, liquid chromatography and two-dimensional gel electrophoresis with modern mass spectrometry-based proteomics has confirmed the composition of the core dystrophin complex at the sarcolemma membrane. Importantly, these biochemical and mass spectrometric surveys have identified additional members of the wider dystrophin network including biglycan, cavin, synemin, desmoglein, tubulin, plakoglobin, cytokeratin and a variety of signaling proteins and ion channels.

Mutation in histone deacetylase HDA-3 leads to shortened locomotor healthspan in Caenorhabditis elegans

Some genes are essential for survival, while other genes play modulatory roles on health and survival. Genes that play modulatory roles may promote an organism’s survival and health by fine-tuning physiological processes. An unbiased search for genes that alter an organism’s ability to maintain aspects of health may uncover modulators of lifespan and healthspan. From an unbiased screen for Caenorhabditis elegans mutants that show a progressive decline in motility, we aimed to identify genes that play a modulatory role in maintenance of locomotor healthspan. Here we report the involvement of hda-3, encoding a class I histone deacetylase, as a genetic factor that contributes in the maintenance of general health and locomotion in C. elegans. We identified a missense mutation in HDA-3 as the causative mutation in one of the isolated strains that show a progressive decline in maximum velocity and travel distance. From transcriptome analysis, we found a cluster of genes on Chromosome II carrying BATH domains that were downregulated by hda-3. Furthermore, downregulation of individual bath genes leads to significant decline in motility. Our study identifies genetic factors that modulate the maintenance of locomotor healthspan and may reveal potential targets for delaying age-related locomotor decline.

A Role for Caveolin-3 in the Pathogenesis of Muscular Dystrophies

Caveolae are the cholesterol-rich small invaginations of the plasma membrane present in many cell types including adipocytes, endothelial cells, epithelial cells, fibroblasts, smooth muscles, skeletal muscles and cardiac muscles. They serve as specialized platforms for many signaling molecules and regulate important cellular processes like energy metabolism, lipid metabolism, mitochondria homeostasis, and mechano-transduction. Caveolae can be internalized together with associated cargo. The caveolae-dependent endocytic pathway plays a role in the withdrawal of many plasma membrane components that can be sent for degradation or recycled back to the cell surface. Caveolae are formed by oligomerization of caveolin proteins. Caveolin-3 is a muscle-specific isoform, whose malfunction is associated with several diseases including diabetes, cancer, atherosclerosis, and cardiovascular diseases. Mutations in Caveolin-3 are known to cause muscular dystrophies that are collectively called caveolinopathies. Altered expression of Caveolin-3 is also observed in Duchenne’s muscular dystrophy, which is likely a part of the pathological process leading to muscle weakness. This review summarizes the major functions of Caveolin-3 in skeletal muscles and discusses its involvement in the pathology of muscular dystrophies.

Arhgef5 Binds α-Dystrobrevin 1 and Regulates Neuromuscular Junction Integrity

The neuromuscular junctions (NMJs) connect muscle fibers with motor neurons and enable the coordinated contraction of skeletal muscles. The dystrophin-associated glycoprotein complex (DGC) is an essential component of the postsynaptic machinery of the NMJ and is important for the maintenance of NMJ structural integrity. To identify novel proteins that are important for NMJ organization, we performed a mass spectrometry-based screen for interactors of α-dystrobrevin 1 (aDB1), one of the components of the DGC. The guanidine nucleotide exchange factor (GEF) Arhgef5 was found to be one of the aDB1 binding partners that is recruited to Tyr-713 in a phospho-dependent manner. We show here that Arhgef5 localizes to the NMJ and that its genetic depletion in the muscle causes the fragmentation of the synapses in conditional knockout mice. Arhgef5 loss in vivo is associated with a reduction in the levels of active GTP-bound RhoA and Cdc42 GTPases, highlighting the importance of actin dynamics regulation for the maintenance of NMJ integrity.

BK channel clustering is required for normal behavioral alcohol sensitivity in C. elegans

The large conductance, calcium- and voltage-activated potassium channel, known as the BK channel, is one of the central proteins that mediate alcohol intoxication and tolerance across species. Although ethanol targets BK channels through direct interaction, how ethanol-mediated BK channel activation causes behavioral intoxication is poorly understood. In. C. elegans, loss of function in SLO-1, the BK channel ortholog, confers profound ethanol resistance in movement and egg-laying behaviors. Here, we show that depletion of SLO-1 channels clustered at the active zones with no change in the overall channel expression level results in locomotory resistance to the intoxicating effect of ethanol, equivalent to that of slo-1 loss-of-function mutants. Likewise, depletion of clustered SLO-1 channels in the sarcolemma and neurons leads to ethanol-resistant egg-laying behavior. By contrast, reduction in the overall SLO-1 channel level by over 70% causes only moderate ethanol resistance in movement, and minimal, if any, resistance in egg laying. Our findings strongly suggest that behavioral ethanol sensitivity is conferred by local, but not global, depression of excitability via clustered BK channels. Given that clustered BK channels are functionally coupled to, and localize near, calcium channels, ethanol may mediate its behavioral effects by targeting BK channels and their coupled calcium channels.

Liprin-α-1 is a novel component of the murine neuromuscular junction and is involved in the organization of the postsynaptic machinery

Neuromuscular junctions (NMJs) are specialized synapses that connect motor neurons to skeletal muscle fibers and orchestrate proper signal transmission from the nervous system to muscles. The efficient formation and maintenance of the postsynaptic machinery that contains acetylcholine receptors (AChR) are indispensable for proper NMJ function. Abnormalities in the organization of synaptic components often cause severe neuromuscular disorders, such as muscular dystrophy. The dystrophin-associated glycoprotein complex (DGC) was shown to play an important role in NMJ development. We recently identified liprin-α-1 as a novel binding partner for one of the cytoplasmic DGC components, α-dystrobrevin-1. In the present study, we performed a detailed analysis of localization and function of liprin-α-1 at the murine NMJ. We showed that liprin-α-1 localizes to both pre- and postsynaptic compartments at the NMJ, and its synaptic enrichment depends on the presence of the nerve. Using cultured muscle cells, we found that liprin-α-1 plays an important role in AChR clustering and the organization of cortical microtubules. Our studies provide novel insights into the function of liprin-α-1 at vertebrate neuromuscular synapses.

ERG-28 controls BK channel trafficking in the ER to regulate synaptic function and alcohol response in C. elegans

Voltage- and calcium-dependent BK channels regulate calcium-dependent cellular events such as neurotransmitter release by limiting calcium influx. Their plasma membrane abundance is an important factor in determining BK current and thus regulation of calcium-dependent events. In C. elegans, we show that ERG-28, an endoplasmic reticulum (ER) membrane protein, promotes the trafficking of SLO-1 BK channels from the ER to the plasma membrane by shielding them from premature degradation. In the absence of ERG-28, SLO-1 channels undergo aspartic protease DDI-1-dependent degradation, resulting in markedly reduced expression at presynaptic terminals. Loss of erg-28 suppressed phenotypic defects of slo-1 gain-of-function mutants in locomotion, neurotransmitter release, and calcium-mediated asymmetric differentiation of the AWC olfactory neuron pair, and conferred significant ethanol-resistant locomotory behavior, resembling slo-1 loss-of-function mutants, albeit to a lesser extent. Our study thus indicates that the control of BK channel trafficking is a critical regulatory mechanism for synaptic transmission and neural function.

Retinoid acid-induced microRNA-27b-3p impairs C2C12 myoblast proliferation and differentiation by suppressing α-dystrobrevin

We previously reported that excess retinoic acid (RA) resulted in hypoplastic and derangement of myofilaments in embryonic tongue by inhibiting myogenic proliferation and differentiation through CamKIID pathway. Our further studies revealed that the expression of a series of miRNAs was altered by RA administration in embryonic tongue as well as in C2C12 cells. Thus, if excess RA impairs myogenic proliferation and differentiation through miRNAs is taken into account. In present study, miR-27b-3p was found up-regulated in RA-treated C2C12 cells as in embryonic tongue, and predicted to target the 3'UTR of α-dystrobrevin (DTNA). Luciferase reporter assays confirmed the direct interaction between miR-27b-3p and the 3'UTR of DTNA. MiR-27b-3p mimics recapitulated the RA repression on DTNA expression, C2C12 proliferation and differentiation, while the miR-27b-3p inhibitor circumvented these defects resulting from excess RA. As expected, the effects of siDTNA on C2C12 were coincided with those by RA treatment or miR-27b-3p mimics. Therefore, these findings indicated that excess RA inhibited the myoblast proliferation and differentiation by up-regulating miR-27b-3p to target DTNA, which implied a new mechanism in myogenic hypoplasia.

Absence of Dystrophin Disrupts Skeletal Muscle Signaling: Roles of Ca2+, Reactive Oxygen Species, and Nitric Oxide in the Development of Muscular Dystrophy

Dystrophin is a long rod-shaped protein that connects the subsarcolemmal cytoskeleton to a complex of proteins in the surface membrane (dystrophin protein complex, DPC), with further connections via laminin to other extracellular matrix proteins. Initially considered a structural complex that protected the sarcolemma from mechanical damage, the DPC is now known to serve as a scaffold for numerous signaling proteins. Absence or reduced expression of dystrophin or many of the DPC components cause the muscular dystrophies, a group of inherited diseases in which repeated bouts of muscle damage lead to atrophy and fibrosis, and eventually muscle degeneration. The normal function of dystrophin is poorly defined. In its absence a complex series of changes occur with multiple muscle proteins showing reduced or increased expression or being modified in various ways. In this review, we will consider the various proteins whose expression and function is changed in muscular dystrophies, focusing on Ca(2+)-permeable channels, nitric oxide synthase, NADPH oxidase, and caveolins. Excessive Ca(2+) entry, increased membrane permeability, disordered caveolar function, and increased levels of reactive oxygen species are early changes in the disease, and the hypotheses for these phenomena will be critically considered. The aim of the review is to define the early damage pathways in muscular dystrophy which might be appropriate targets for therapy designed to minimize the muscle degeneration and slow the progression of the disease.

Α-Dystrobrevin-1 recruits Grb2 and α-catulin to organize neurotransmitter receptors at the neuromuscular junction

Neuromuscular junctions (NMJs), the synapses made by motor neurons on muscle fibers, form during embryonic development but undergo substantial remodeling postnatally. Several lines of evidence suggest that α-dystrobrevin, a component of the dystrophin-associated glycoprotein complex (DGC), is a crucial regulator of the remodeling process and that tyrosine phosphorylation of one isoform, α-dystrobrevin-1, is required for its function at synapses. We identified a functionally important phosphorylation site on α-dystrobrevin-1, generated phosphorylation-specific antibodies to it and used them to demonstrate dramatic increases in phosphorylation during the remodeling period, as well as in nerve-dependent regulation in adults. We then identified proteins that bind to this site in a phosphorylation-dependent manner and others that bind to α-dystrobrevin-1 in a phosphorylation-independent manner. They include multiple members of the DGC, as well as α-catulin, liprin-α1, Usp9x, PI3K, Arhgef5 and Grb2. Finally, we show that two interactors, α-catulin (phosphorylation independent) and Grb2 (phosphorylation dependent) are localized to NMJs in vivo, and that they are required for proper organization of neurotransmitter receptors on myotubes.

Alpha-Catulin Co-Localizes With Vimentin Intermediate Filaments and Functions in Pulmonary Vascular Endothelial Cell Migration via ROCK

The ubiquitous α-catulin acts as a scaffold for distinct signalosomes including RhoA/ROCK; however, its function is not well understood. While α-catulin has homology to the cytoskeletal linkers α-catenin and vinculin, it appears to be functionally divergent. Here we further investigated α-catulin function in pulmonary vascular endothelial cells (VEC) on the premise that α-catulin has a unique cytoskeletal role. Examination of endogenous α-catulin intracellular localization by immunofluorescence revealed a highly organized cytosolic filamentous network suggestive of a cytoskeletal system in a variety of cultured VEC. Double-immunofluorescence analyses of VEC showed endogenous α-catulin co-localization with vimentin intermediate filaments. Similar to vimentin, α-catulin was found to distribute into detergent-soluble and -insoluble fractions. Treatment of VEC with withaferinA, an agent that targets vimentin filaments, disrupted the α-catulin network distribution and altered α-catulin solubility. Vimentin participates in cell migration, and withaferinA was found to inhibit VEC migration in vitro; similarly, α-catulin knock-down reduced VEC migration. Based on previous reports showing that ROCK modulates vimentin, we found that ROCK depletion attenuated VEC migration; furthermore, α-catulin depletion was shown to reduce ROCK-induced signaling. These findings indicate that α-catulin has a unique function in co-localization with vimentin filaments that contributes to VEC migration via a pathway that may involve ROCK signaling. J. Cell. Physiol. 231: 934-943, 2016. © 2015 Wiley Periodicals, Inc.

Presynaptic BK channel localization is dependent on the hierarchical organization of alpha-catulin and dystrobrevin and fine-tuned by CaV2 calcium channels

Background

Large conductance, calcium-activated BK channels regulate many important physiological processes, including smooth muscle excitation, hormone release and synaptic transmission. The biological roles of these channels hinge on their unique ability to respond synergistically to both voltage and cytosolic calcium elevations. Because calcium influx is meticulously regulated both spatially and temporally, the localization of BK channels near calcium channels is critical for their proper function. However, the mechanism underlying BK channel localization near calcium channels is not fully understood.

Results

We show here that in C. elegans the localization of SLO-1/BK channels to presynaptic terminals, where UNC-2/CaV2 calcium channels regulate neurotransmitter release, is controlled by the hierarchical organization of CTN-1/α-catulin and DYB-1/dystrobrevin, two proteins that interact with cortical cytoskeletal proteins. CTN-1 organizes a macromolecular SLO-1 channel complex at presynaptic terminals by direct physical interaction. DYB-1 contributes to the maintenance or stabilization of the complex at presynaptic terminals by interacting with CTN-1. We also show that SLO-1 channels are functionally coupled with UNC-2 calcium channels, and that normal localization of SLO-1 to presynaptic terminals requires UNC-2. In the absence of UNC-2, SLO-1 clusters lose the localization specificity, thus accumulating inside and outside of presynaptic terminals. Moreover, CTN-1 is also similarly localized in unc-2 mutants, consistent with the direct interaction between CTN-1 and SLO-1. However, localization of UNC-2 at the presynaptic terminals is not dependent on either CTN-1 or SLO-1. Taken together, our data strongly suggest that the absence of UNC-2 indirectly influences SLO-1 localization via the reorganization of cytoskeletal proteins.

Conclusion

CTN-1 and DYB-1, which interact with cortical cytoskeletal proteins, are required for the presynaptic punctate localization of SLO-1 in a hierarchical manner. In addition, UNC-2 calcium channels indirectly control the fidelity of SLO-1 puncta localization at presynaptic terminals. We suggest that the absence of UNC-2 leads to the reorganization of the cytoskeletal structure that includes CTN-1, which in turn influences SLO-1 puncta localization.

Electronic supplementary material

The online version of this article (doi:10.1186/s12868-015-0166-2) contains supplementary material, which is available to authorized users.