Obscurin depletion impairs organization of skeletal muscle in developing zebrafish embryos

Migration and differentiation of muscle stem cells are coupled by RhoA signalling during regeneration

Skeletal muscle is highly regenerative and is mediated by a population of migratory adult muscle stem cells (muSCs). Effective muscle regeneration requires a spatio-temporally regulated response of the muSC population to generate sufficient muscle progenitor cells that then differentiate at the appropriate time. The relationship between muSC migration and cell fate is poorly understood and it is not clear how forces experienced by migrating cells affect cell behaviour. We have used zebrafish to understand the relationship between muSC cell adhesion, behaviour and fate in vivo. Imaging of pax7-expressing muSCs as they respond to focal injuries in trunk muscle reveals that they migrate by protrusive-based means. By carefully characterizing their behaviour in response to injury we find that they employ an adhesion-dependent mode of migration that is regulated by the RhoA kinase ROCK. Impaired ROCK activity results in reduced expression of cell cycle genes and increased differentiation in regenerating muscle. This correlates with changes to focal adhesion dynamics and migration, revealing that ROCK inhibition alters the interaction of muSCs to their local environment. We propose that muSC migration and differentiation are coupled processes that respond to changes in force from the environment mediated by RhoA signalling.

The dominance of coinfecting parasites' indirect effects on host traits

Indirect genetic effects (IGEs) exist when there is heritable variation in one species' ability to alter a second species' traits. For example, parasites can evolve disparate strategies to manipulate host immune response, whether by evading detection or suppressing immunity. A complication arises during coinfection, when two or more parasite genotypes may try to impose distinct IGEs on the same host trait: which parasite's IGE will be dominant? Here, we apply the notion of dominance to IGEs during coinfection. Using a mathematical model we show that the dominance of IGEs can alter the evolutionary dynamics of parasites. We consider a resident parasite population receiving rare immigrants with a different immune manipulation trait. These immigrants' relative fitness depends on resident prevalence (e.g., the probability immigrants are alone in a host, or coinfecting with a native), and the dominance of the immigrant's IGE on host immunity. Next, we show experimentally that the cestode Schistocephalus solidus exerts an IGE on a host immune trait: parasite antigens from different populations produced different intensities of fibrosis. We then evaluated IGE dominance, finding evidence for overdominance (coinjected antigens induced an even stronger host immune response) which would be detrimental to immigrants when resident prevalence is high. This combination of experimental and modeling results shows that parasites do exhibit IGEs on host traits, and that the dominance of these IGEs during coinfection can substantially alter parasite evolution.

Loss-of-function variants in SAT1 cause X-linked childhood-onset systemic lupus erythematosus

OBJECTIVES

Families that contain multiple siblings affected with childhood onset of systemic lupus erythematosus (SLE) likely have strong genetic predispositions. We performed whole exome sequencing (WES) to identify familial rare risk variants and to assess their effects in lupus.

METHODS

Sanger sequencing validated the two ultra-rare, predicted pathogenic risk variants discovered by WES and identified additional variants in 562 additional patients with SLE. Effects of a splice site variant and a frameshift variant were assessed using a Minigene assay and CRISPR/Cas9-mediated knock-in (KI) mice, respectively.

RESULTS

The two familial ultra-rare, predicted loss-of-function (LOF) SAT1 variants exhibited X-linked recessive Mendelian inheritance in two unrelated African-American families. Each LOF variant was transmitted from the heterozygous unaffected mother to her two sons with childhood-onset SLE. The p.Asp40Tyr variant affected a splice donor site causing deleterious transcripts. The young hemizygous male and homozygous female Sat1 p.Glu92Leufs*6 KI mice spontaneously developed splenomegaly, enlarged glomeruli with leucocyte infiltration, proteinuria and elevated expression of type I interferon-inducible genes. SAT1 is highly expressed in neutrophils and encodes spermidine/spermine-N1-acetyltransferase 1 (SSAT1), a rate-limiting enzyme in polyamine catabolism. Young male KI mice exhibited neutrophil defects and decreased proportions of Foxp3 +CD4+ T-cell subsets. Circulating neutrophil counts and proportions of Foxp3 +CD4+ T cells correlated with decreased plasma levels of spermine in treatment-naive, incipient SLE patients.

CONCLUSIONS

We identified two novel SAT1 LOF variants, showed the ability of the frameshift variant to confer murine lupus, highlighted the pathogenic role of dysregulated polyamine catabolism and identified SAT1 LOF variants as new monogenic causes for SLE.

TEM8 Tri-specific Killer Engager binds both tumor and tumor stroma to specifically engage natural killer cell anti-tumor activity

BACKGROUND

The tumor microenvironment contains stromal cells, including endothelial cells and fibroblasts, that aid tumor growth and impair immune cell function. Many solid tumors remain difficult to cure because of tumor-promoting stromal cells, but current therapies targeting tumor stromal cells are constrained by modest efficacy and toxicities. TEM8 is a surface antigen selectively upregulated on tumor and tumor stromal cells, endothelial cells and fibroblasts that may be targeted with specific natural killer (NK) cell engagement.

METHODS

A Tri-specific Killer Engager (TriKE) against TEM8-'cam1615TEM8'-was generated using a mammalian expression system. Its function on NK cells was assessed by evaluation of degranulation, inflammatory cytokine production, and killing against tumor and stroma cell lines in standard co-culture and spheroid assays. cam1615TEM8-mediated proliferation and STAT5 phosphorylation in NK cells was tested and compared with T cells by flow cytometry. NK cell proliferation, tumor infiltration, and tumor and tumor-endothelium killing by cam1615TEM8 and interleukin-15 (IL-15) were assessed in NOD scid gamma (NSG) mice.

RESULTS

cam1615TEM8 selectively stimulates NK cell degranulation and inflammatory cytokine production against TEM8-expressing tumor and stromal cell lines. The increased activation translated to superior NK cell killing of TEM8-expressing tumor spheroids. cam1615TEM8 selectively stimulated NK cell but not T cell proliferation in vitro and enhanced NK cell proliferation, survival, and tumor infiltration in vivo. Finally, cam1615TEM8 stimulated NK cell killing of tumor and tumor endothelial cells in vivo.

CONCLUSIONS

Our findings indicate that the cam1615TEM8 TriKE is a novel anti-tumor, anti-stroma, and anti-angiogenic cancer therapy for patients with solid tumors. This multifunctional molecule works by selectively targeting and activating NK cells by costimulation with IL-15, and then targeting that activity to TEM8+ tumor cells and TEM8+ tumor stroma.

IBD therapeutics: what is in the pipeline?

Inflammatory bowel disease (IBD) is an idiopathic long-term relapsing and remitting disorder including ulcerative colitis and Crohn's disease. The aim of therapy is to induce and maintain remission. Anti-TNF therapies dramatically improved clinical outcomes but primary failure or secondary loss is a common problem as well as potential side effects potentially limiting efficacy and long-term use. The advent of new targeted agents with the potential for greater safety is welcomed in IBD and offers the potential for different agents as the disease becomes refractory or even combination therapies to maximise effectiveness without compromising safety in the future. More data are required to understand the best positioning in pathways and longer-term safety effects.

Obscurin: A multitasking giant in the fight against cancer

Giant obscurins (720-870 kDa), encoded by OBSCN, were originally discovered in striated muscles as cytoskeletal proteins with scaffolding and regulatory roles. Recently though, they have risen to the spotlight as key players in cancer development and progression. Herein, we provide a timely prudent synopsis of the expanse of OBSCN mutations across 16 cancer types. Given the extensive work on OBSCN's role in breast epithelium, we summarize functional studies implicating obscurins as potent tumor suppressors in breast cancer and delve into an in silico analysis of its mutational profile and epigenetic (de)regulation using different dataset platforms and sophisticated computational tools. Lastly, we formally describe the OBSCN-Antisense-RNA-1 gene, which belongs to the long non-coding RNA family and discuss its potential role in modulating OBSCN expression in breast cancer. Collectively, we highlight the escalating involvement of obscurins in cancer biology and outline novel potential mechanisms of OBSCN (de)regulation that warrant further investigation.

Sex differences in type and occurrence of adverse reactions to opioid analgesics: a retrospective cohort study

OBJECTIVES

Sex as a biological variable affects response to opioids. However, few reports describe the prevalence of specific adverse reactions to commonly prescribed opioids in men and women separately. A large cohort was used to investigate sex differences in type and occurrence of adverse reactions associated with use of codeine, tramadol, oxycodone and hydrocodone.

DESIGN

Retrospective cohort study.

SETTING

Participants in the Right Drug, Right Dose, Right Time (RIGHT) Study.

PARTICIPANTS

The medical records of 8457 participants in the RIGHT Study who received an opioid prescription between 1 January 2004 and 31 December 2017 were reviewed 61% women, 94% white, median age (Q1-Q3)=58 (47-66).

PRIMARY AND SECONDARY OUTCOME MEASURES

Adverse reactions including gastrointestinal, skin, psychiatric and nervous system issues were collected from the allergy section of each patient's medical record. Sex differences in the risk of adverse reactions due to prescribed opioids were modelled using logistic regression adjusted for age, body mass index, race and ethnicity.

RESULTS

From 8457 participants (of which 449 (5.3%) reported adverse reactions), more women (6.5%) than men (3.4%) reported adverse reactions to at least one opioid (OR (95% CI)=2.3 (1.8 to 2.8), p<0.001). Women were more likely to report adverse reactions to tramadol (OR (95% CI)=2.8 (1.8 to 4.4), p<0.001) and oxycodone (OR (95% CI)=2.2 (1.7 to 2.9), p<0.001). Women were more likely to report gastrointestinal (OR (95% CI)=3.1 (2.3 to 4.3), p<0.001), skin (OR (95% CI)=2.1 (1.4 to 3.3), p=0.001) and nervous system issues (OR (95% CI)=2.3 (1.3 to 4.2), p=0.004).

CONCLUSIONS

These findings support the importance of sex as a biological variable to be factored into pain management studies.

Telomerase gene variants and telomere shortening in patients with silicosis or asbestosis

OBJECTIVES

Telomerase gene variants that lead to accelerated telomere shortening are linked to progressive-fibrosing interstitial lung diseases. However, little is known about their relationships with pneumoconiosis. This study aimed to identify TERT/TERC variants and leucocyte telomere lengths (LTL) in patients with silicosis or asbestosis.

METHODS

In the present study, Sanger sequencing of TERT/TERC variants was performed in 193 Chinese Han patients with pneumoconiosis, including 109 with silicosis and 84 with asbestosis. Quantitative PCR was used to measure LTL in peripheral blood of the patients and 200 age and sex-matched healthy controls.

RESULTS

In total, 7.3% patients with pneumoconiosis had 17 TERT/TERC variants. Among which 8.3% of patients with silicosis and 3.6% of patients with asbestosis had TERT variants, respectively. No TERC variants were detected in silicosis, whereas 3.6% of patients with asbestosis had TERC variants. Telomeres were significantly shorter in the patients with pneumoconiosis compared with healthy controls (p<0.001). No significant differences in LTL were found between TERT/TERC variant carriers and non-carriers. Exposure to silica dust was associated with the severity of pneumoconiosis after adjusting for covariates (OR 4.92, p=0.002). However, TERT/TERC variants and short telomeres were not associated with the severity of pneumoconiosis.

CONCLUSION

Telomerase gene variants and short telomeres may be identified in the patients with silicosis and asbestosis in response to the exposure to silica or asbestos dust but are not related to disease severity.

Antibody profiling of patients with prostate cancer reveals differences in antibody signatures among disease stages

BACKGROUND

Previous studies of prostate cancer autoantibodies have largely focused on diagnostic applications. So far, there have been no reports attempting to more comprehensively profile the landscape of prostate cancer-associated antibodies. Specifically, it is unknown whether the quantity of antibodies or the types of proteins recognized change with disease progression.

METHODS

A peptide microarray spanning the amino acid sequences of the gene products of 1611 prostate cancer-associated genes was synthesized. Serum samples from healthy male volunteers (n=15) and patients with prostate cancer (n=85) were used to probe the array. These samples included patients with various clinical stages of disease: newly diagnosed localized prostate cancer (n=15), castration-sensitive non-metastatic prostate cancer (nmCSPC, n=40), castration-resistant non-metastatic prostate cancer (n=15) and castration-resistant metastatic disease (n=15). The patients with nmCSPC received treatment with either standard androgen deprivation therapy (ADT) or an antitumor DNA vaccine encoding prostatic acid phosphatase. Serial sera samples from these individuals were also used to probe the array, to secondarily determine whether this approach could be used to detect treatment-related changes.

RESULTS

We demonstrated that this peptide array yielded highly reproducible measurements of serum IgG levels. We found that the overall number of antibody responses did not increase with disease burden. However, the composition of recognized proteins shifted with clinical stage of disease. Our analysis revealed that the largest difference was between patients with castration-sensitive and castration-resistant disease. Patients with castration-resistant disease recognized more proteins associated with nucleic acid binding and gene regulation compared with men in other groups. Our longitudinal data showed that treatments can elicit antibodies detectable by this array, and notably vaccine-treated patients developed increased responses to more proteins over the course of treatment than did ADT-treated patients.

CONCLUSIONS

This study represents the largest survey of prostate cancer-associated antibodies to date. We have been able to characterize the classes of proteins recognized by patients and determine how they change with disease burden. Our findings further demonstrate the potential of this platform for measuring antigen spread and studying responses to immunomodulatory therapies.

Identification and characterization of self-association domains on small ankyrin 1 isoforms

In striated muscles, the large scaffolding protein obscurin and a small SR-integral membrane protein sAnk1.5 control the retention of longitudinal SR across the sarcomere. How a complex of these proteins facilitates localization of longitudinal SR has yet to be resolved, but we hypothesize that obscurin interacts with a complex of sAnk1.5 proteins. To begin to address this hypothesis, we demonstrate that sAnk1.5 interacts with itself and identify two domains mediating self-association. Specifically, we show by co-precipitation and FLIM-FRET analysis that sAnk1.5 and another small AnkR isoform (sAnk1.6) interact with themselves and each other. We demonstrate that obscurin interacts with a complex of sAnk1.5 proteins and that this complex formation is enhanced by obscurin-binding. Using FLIM-FRET analysis, we show that obscurin interacts with sAnk1.5 alone and with sAnk1.6 in the presence of sAnk1.5. We find that sAnk1.5 self-association is disrupted by mutagenesis of residues Arg64-Arg69, residues previously associated with obscurin-binding. Molecular modeling of two interacting sAnk1.5 monomers facilitated the identification of Gly31-Val36 as an additional site of interaction, which was subsequently corroborated by co-precipitation and FLIM-FRET analysis. In closing, these results support a model in which sAnk1.5 forms large oligomers that interact with obscurin to facilitate the retention of longitudinal SR throughout skeletal and cardiac myocytes.

A follow-up study of occupational styrene exposure and risk of autoimmune rheumatic diseases

Objectives

Increased risk has been suggested for autoimmune rheumatic diseases following solvent exposure. The evidence for specific solvents is limited, and little is known about exposure–response relations. Styrene is an aromatic, organic solvent and the objective of this study was to analyse the association between occupational styrene exposure and autoimmune rheumatic diseases in men and women.

Methods

We followed 72 212 styrene-exposed workers of the Danish reinforced plastics industry from 1979 to 2012. We modelled full work history of styrene exposure from employment history, survey data and historical styrene exposure measurements. We identified cases in the national patient registry and investigated gender-specific exposure–response relations by cumulative styrene exposure for different exposure time windows adjusting for age, calendar year and educational level.

Results

During 1 515 126 person-years of follow-up, we identified 718 cases of an autoimmune rheumatic disease, of which 73% were rheumatoid arthritis. When adjusting for potential confounders and comparing the highest with the lowest styrene exposure tertile, we observed a statistically non-significantly increased risk of systemic sclerosis among women (incidence rate ratio (IRR)=2.50; 95% CI 0.50 to 12.50) and men (IRR=1.86; 95 % CI 0.50 to 7.00), based on 9 and 22 cases, respectively. Results were inconsistent for the other autoimmune rheumatic diseases examined.

Conclusion

This study suggests an association between occupational styrene exposure and systemic sclerosis in men as well as in women but based on few cases. This is a new finding and has to be replicated before conclusions can be drawn.

Somatic deletion of KDM1A/LSD1 gene is associated to advanced colorectal cancer stages

Aims

KDM1A/LSD1 and ZNF217 are involved in a protein complex that participates in transcriptional regulation. ZNF217 has been analysed in numerous cancers and its amplification has been associated with advanced stages of disease; however, a similar role for KDM1A/LSD1 has not been uncovered. In this study, we estimated the number of KDM1A/LSD1 and ZNF217 gene copies in tissue samples from patients diagnosed with colorectal cancer (CRC), as well as its association with clinicopathological features in patients with CRC.

Methods

Paraffin-embedded tumour samples from 50 patients with CRC with a histopathological diagnosis of CRC were included. The number of copies of KDM1A/LSD1 and ZNF217 genes was determined by fluorescence in situ hybridisation (FISH). We also analysed the association between copy numbers of selected genes and clinicopathological data based on multivariate analysis.

Results

Deletion of the KDM1A/LSD1 gene occurred in 19 samples (38%), whereas ZNF217 gene amplification was identified in 11 samples (22%). We found a significant association between lymph node metastasis or advanced tumour stage and KDM1A/LSD1 gene deletion (p value=0.0003 and p value=0.011, respectively).

Conclusions

KDM1A/LSD1 gene deletion could be considered a novel prognostic biomarker of late-stage CRC.

Murine obscurin and Obsl1 have functionally redundant roles in sarcolemmal integrity, sarcoplasmic reticulum organization, and muscle metabolism

Biological roles of obscurin and its close homolog Obsl1 (obscurin-like 1) have been enigmatic. While obscurin is highly expressed in striated muscles, Obsl1 is found ubiquitously. Accordingly, obscurin mutations have been linked to myopathies, whereas mutations in Obsl1 result in 3M-growth syndrome. To further study unique and redundant functions of these closely related proteins, we generated and characterized Obsl1 knockouts. Global Obsl1 knockouts are embryonically lethal. In contrast, skeletal muscle-specific Obsl1 knockouts show a benign phenotype similar to obscurin knockouts. Only deletion of both proteins and removal of their functional redundancy revealed their roles for sarcolemmal stability and sarcoplasmic reticulum organization. To gain unbiased insights into changes to the muscle proteome, we analyzed tibialis anterior and soleus muscles by mass spectrometry, uncovering additional changes to the muscle metabolism. Our analyses suggest that all obscurin protein family members play functions for muscle membrane systems.

Unraveling obscurins in heart disease

Obscurins, expressed from the single OBSCN gene, are a family of giant, modular, cytoskeletal proteins that play key structural and regulatory roles in striated muscles. They were first implicated in the development of heart disease in 2007 when two missense mutations were found in a patient diagnosed with hypertrophic cardiomyopathy (HCM). Since then, the discovery of over a dozen missense, frameshift, and splicing mutations that are linked to various forms of cardiomyopathy, including HCM, dilated cardiomyopathy (DCM), and left ventricular non-compaction (LVNC), has highlighted OBSCN as a potential disease-causing gene. At this time, the functional consequences of the identified mutations remain largely elusive, and much work has yet to be done to characterize the disease mechanisms of pathological OBSCN variants. Herein, we describe the OBSCN mutations known to date, discuss their potential impact on disease development, and provide future directions in order to better understand the involvement of obscurins in heart disease.

Upregulated immune checkpoint HHLA2 in clear cell renal cell carcinoma: a novel prognostic biomarker and potential therapeutic target

BACKGROUND

Clear cell renal cell carcinoma (ccRCC) is a malignant urogenital cancer with high mortality; however, current progress in understanding its molecular mechanism and predicting clinical treatment outcome is limited. Therefore, this study is to evaluate the clinical significance of immune inhibitory molecular human endogenous retrovirus-H long terminal repeat-associating protein 2 (HHLA2) in ccRCC prognosis and transcriptional regulatory network.

METHODS

Expression of HHLA2 in ccRCC was examined by an online database platform ONCOMINE. The ONCOMINE result was independently validated by qRT-PCR and immunohistochemistry. Kaplan-Meier survival was generated using IBM SPSS Statistics V.22. ccRCC tissues cells with high HHLA2 were sorted and subjected to microarray transcriptional profiling and analysis.

RESULTS

It was shown that expression of HHLA2 was statistically significantly increased in ccRCC tissues compared with normal renal tissues at both transcriptional and protein level. Moreover, the expression of HHLA2 was closely correlated with multiple clinicopathological features including tumour size, clinical stage and histological grade. High HHLA2 expression was associated with poor overall survival and clinical outcome. Comprehensive microarray analysis further identified thousands of HHLA2 targets including mRNA, long non-coding RNA and circular RNA that might function in various biological processes, especially, immune response.

CONCLUSION

Increased HHLA2 expression was observed in ccRCC tumour tissue, which leads to a remarkable shorter overall survival and poorer prognosis. Together with other molecular evidence, we have demonstrated that HHLA2 could be a potential prognostic biomarker for ccRCC.

Expansion of T follicular helper-T helper 1 like cells through epigenetic regulation by signal transducer and activator of transcription factors

OBJECTIVES

T follicular helper (Tfh) cells are critical in the development and progression of systemic lupus erythematosus (SLE). To assess the characteristics and mechanisms of differentiation of Tfh cells, we investigated the phenotype of T helper cells in patients with SLE and underlying epigenetic modifications by cytokine-induced signal transducer and activators of transcription (STAT) family factors.

METHODS

Peripheral blood mononuclear cells from patients and healthy donors were analysed by flow cytometry. CD4⁺ T cells were isolated and cultured under various stimulations. Expression of characteristic markers and phosphorylation of STATs were analysed by flow cytometry and quantitative PCR. Histone modifications were analysed by chromatin immunoprecipitation (ChIP)-PCR.

RESULTS

Differentiation of CD4⁺CXCR5⁺CXCR3⁺Bcl-6⁺T-bet⁺IL-21⁺IFN-γ⁺Tfh-Th1-like cells was induced by interleukin (IL)-12-induced activation of STAT1 and STAT4 simultaneously. The loci of Bcl-6 and T-bet at STAT binding sites were marked by bivalent histone modifications. After IL-12 stimulation, both STAT1 and STAT4 directly bound on BCL6 and TBX21 gene loci accompanied by suppression of repressive histone mark trimethylated histone 3 lysine 27. Levels of serum IL-12 and interferon (IFN)-γ, expression of IL-12 receptors and proportion of CXCR5⁺CXCR3⁺ activated Tfh-Th1-like cells were increased in patients with SLE. Furthermore, the level of pSTAT1, pSTAT4 and T-bet were higher in activated Tfh-Th1-like cells than non-Tfh-Th1 cells.

CONCLUSION

Our findings suggest that IL-12-mediated co-activation of STAT1 and STAT4 alters histone modification, resulting in differentiation of Tfh-Th1-like cells that are characteristically expanded in patients with SLE. This could be one of the underlying mechanisms responsible for expansion of Tfh-Th1-like cells and potentially helpful towards development of cell-specific treatment for SLE.

The Use of Whole Body Cooling in the Treatment of Hypoxic-Ischemic Encephalopathy

Hypoxic-ischemic encephalopathy (HIE) is a major cause of morbidity and mortality in neonates. Hypoxic-ischemic encephalopathy occurs as a result of a perinatal hypoxic-ischemic event just prior to or during delivery. Therapeutic hypothermia using whole body cooling is the current treatment of choice to reduce brain injury and improve long-term neurodevelopmental outcomes for neonates with HIE. All English language articles published since 2005 in PubMed and the Cumulative Index to Nursing and Allied Health Literature (CINAHL) were analyzed for existing evidence-based methods for whole body cooling. Whole body cooling is effective in the treatment of HIE in term and near-term neonates. Further research is needed to investigate the use of adjunctive therapies in conjunction with whole body cooling for improved neuroprotection.

Loss of giant obscurins alters breast epithelial cell mechanosensing of matrix stiffness

Obscurins are a family of RhoGEF-containing proteins with tumor and metastasis suppressing roles in breast epithelium. Downregulation of giant obscurins in normal breast epithelial cells leads to reduced levels of active RhoA and of its downstream effectors. Herein, we elucidate how depletion of giant obscurins affects the response of breast epithelial cells to changes in the mechanical properties of the microenvironment. We find that knockdown of obscurins increases cell morphodynamics, migration speed, and diffusivity on polyacrylamide gels of ≥ 1 kPa, presumably by decreasing focal adhesion area and density as well as cell traction forces. Depletion of obscurins also increases cell mechanosensitivity on soft (0.4-4 kPa) surfaces. Similar to downregulation of obscurins, pharmacological inhibition of Rho kinase in breast epithelial cells increases migration and morphodynamics, suggesting that suppression of Rho kinase activity following obscurin knockdown can account for alterations in morphodynamics and migration. In contrast, inhibition of myosin light chain kinase reduces morphodynamics and migration, suggesting that temporal changes in cell shape are required for efficient migration. Collectively, downregulation of giant obscurins facilitates cell migration through heterogeneous microenvironments of varying stiffness by altering cell mechanobiology.

Binding of Myomesin to Obscurin-Like-1 at the Muscle M-Band Provides a Strategy for Isoform-Specific Mechanical Protection

The sarcomeric cytoskeleton is a network of modular proteins that integrate mechanical and signaling roles. Obscurin, or its homolog obscurin-like-1, bridges the giant ruler titin and the myosin crosslinker myomesin at the M-band. Yet, the molecular mechanisms underlying the physical obscurin(-like-1):myomesin connection, important for mechanical integrity of the M-band, remained elusive. Here, using a combination of structural, cellular, and single-molecule force spectroscopy techniques, we decode the architectural and functional determinants defining the obscurin(-like-1):myomesin complex. The crystal structure reveals a trans-complementation mechanism whereby an incomplete immunoglobulin-like domain assimilates an isoform-specific myomesin interdomain sequence. Crucially, this unconventional architecture provides mechanical stability up to forces of ∼135 pN. A cellular competition assay in neonatal rat cardiomyocytes validates the complex and provides the rationale for the isoform specificity of the interaction. Altogether, our results reveal a novel binding strategy in sarcomere assembly, which might have implications on muscle nanomechanics and overall M-band organization.

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The structure of the human obscurin-like-1:myomesin complex has been determined

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A myomesin sequence complements an immunoglobulin fold of obscurin-like-1

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This binding mechanism provides mechanical stability up to forces of ∼135 pN

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Possible implications on muscle nanomechanics and M-band organization are discussed

Loss of the obscurin-RhoGEF downregulates RhoA signaling and increases microtentacle formation and attachment of breast epithelial cells

Obscurins are RhoGEF-containing proteins whose downregulation has been implicated in the development and progression of breast cancer. Herein, we aim to elucidate the mechanism for increased motility of obscurin-deficient cells. We show that shRNA-mediated obscurin downregulation in MCF10A cells leads to >50% reduction in RhoA activity relative to scramble control (shCtrl), as well as decreased phosphorylation of RhoA effectors, including myosin light chain phosphatase, myosin light chain, lim kinase, and cofilin, in both attached and suspended cells. These alterations result in decreased actomyosin contractility, allowing suspended cells to escape detachment-induced apoptosis. Moreover, ~40% of shObsc-expressing cells, but only ~10% of shCtrl-expressing cells, extend microtentacles, tubulin-based projections that mediate the attachment of circulating tumor cells to endothelium. Indeed, we show that MCF10A cells expressing shObsc attach in vitro more readily than shCtrl cells, an advantage that persists following taxane exposure. Overall, our data suggest that loss of obscurins may represent a substantial selective advantage for breast epithelial cells during metastasis, and that treatment with paclitaxel may exacerbate this advantage by preferentially allowing obscurin-deficient, stem-like cells to attach to the endothelium of distant sites, a first step towards colonizing metastatic tumors.

TM4SF5 suppression disturbs integrin α5-related signalling and muscle development in zebrafish

TM4SF5 suppression in zebrafish causes abnormal trunk morphology with aberrant translocation and organization of muscle cells, via altered fibronectin/integrin α5/FAK/vinculin/actin signalling. TM4SF5 controls muscle differentiation via alteration in integrin α5-related signalling.

Obscurins: Goliaths and Davids take over non-muscle tissues

Obscurins comprise a family of proteins originally identified in striated muscles, where they play essential roles in myofibrillogenesis, cytoskeletal organization, and Ca²⁺ homeostasis. They are encoded by the single OBSCN gene, and are composed of tandem adhesion domains and signaling motifs. To date, two giant obscurin isoforms have been described in detail that differ only at the extreme COOH-terminus; while obscurin-A (∼720 kDa) contains a non-modular COOH-terminus that harbors binding sites for the adaptor proteins ankyrins, obscurin-B (∼870 kDa) contains two COOH-terminal serine-threonine kinase domains preceded by adhesion motifs. Besides the two known giant obscurins, a thorough search of transcript databases suggests that complex alternative splicing of the obscurin transcript results in the generation of additional giant as well as small isoforms with molecular masses ranging between ∼50–970 kDa. These novel isoforms share common domains with the characterized isoforms, but also contain unique regions. Using a panel of highly specific antibodies directed against epitopes spanning the entire length of giant obscurins, we employed western blotting and immunohistochemistry to perform a systematic and comprehensive characterization of the expression profile of obscurins in muscle and non-muscle tissues. Our studies demonstrate for the first time that obscurins are not restricted to striated muscles, but are abundantly expressed in several tissues and organs including brain, skin, kidney, liver, spleen, and lung. While some obscurin isoforms are ubiquitously expressed, others are preferentially present in specific tissues and organs. Moreover, obscurins are present in select structures and cell types where they assume nuclear, cytosolic, and membrane distributions. Given the ubiquitous expression of some obscurins, along with the preferential expression of others, it becomes apparent that obscurins may play common and unique roles, respectively, in the regulation and maintenance of cell homeostasis in various tissues and organs throughout the body.

Propranolol inhibits glucose metabolism and 18F-FDG uptake of breast cancer through posttranscriptional downregulation of hexokinase-2

The advancement of breast cancer therapy is limited by the biologic behaviors of cancer cells, such as metastasis and recurrence. β-adrenoceptors (ADRB) are reported to be associated with the biologic behaviors of breast cancer and may influence glucose metabolism. Here, we sought to investigate the relationship between the activation of ADRB and the expression of glucose transporter (GLUT)-1 and hexokinase (HK)-2 and to clarify the impact of ADRB on (18)F-FDG PET imaging in breast cancer.

METHODS

ADRB1/2 expression in 4T1, MDA-MB-231, and MCF-7 breast cancer cell lines was detected by Western blotting and immunofluorescence. ADRB-dependent regulation of GLUT-1 and HK-2 was determined by in vitro pharmacologic intervention. 4T1 breast cancer cells were treated with phosphate-buffered saline, isoproterenol, or propranolol, and the transcription and expression of GLUT-1 and HK-2 were measured by quantitative real-time polymerase chain reaction (RT-PCR) and Western blotting, respectively. ADRB1/2 was, respectively, blocked by small-interfering RNA to investigate the direct relationship between ADRB1/2 and HK-2. To evaluate the impact of ADRB on (18)F-FDG PET imaging, BALB/c mice bearing 4T1 tumors were injected with phosphate-buffered saline, isoproterenol, or propranolol, and (18)F-FDG PET imaging was performed. The tumor-to-nontumor (T/NT) values of tumors and brown adipose tissue were calculated by defining the liver as a reference. The in vivo expression of GLUT-1 and HK-2 was observed by immunohistochemical analysis and Western blotting.

RESULTS

MDA-MB-231, MCF-7, and 4T1 breast cancer cells were positive for ADRB1/2 expression. The protein expression and posttranscriptional level of HK-2 were significantly decreased by treatment with propranolol in vitro, whereas GLUT-1 expression was not significantly altered by pharmacologic intervention. The expression of HK-2 could be reduced in ADRB2-blocked 4T1 cells. Mice in the propranolol-treated group exhibited lower T/NT values for the tumors and brown adipose tissue than the control group. Immunohistochemical analysis and Western blotting revealed reduced HK-2 expression in the tumors of propranolol-treated mice.

CONCLUSION

The expression of HK-2 was regulated by the activation of ADRB2 in 4T1 breast cancer cells primarily at the posttranscriptional level. Additionally, propranolol prevented glucose metabolism and (18)F-FDG PET imaging of 4T1 breast cancer tumors.

Membrane-myofibril cross-talk in myofibrillogenesis and in muscular dystrophy pathogenesis: lessons from the zebrafish

Striated muscle has a highly ordered structure in which specialized domains of the cell membrane involved in force transmission (costameres) and excitation-contraction coupling (T tubules) as well as the internal membranes of the sarcoplasmic reticulum are organized over specific regions of the sarcomere. Optimal muscle function is dependent on this high level of organization but how it established and maintained is not well understood. Due to its ex utero development and transparency, the zebrafish embryo is an excellent vertebrate model for the study of dynamic relationships both within and between cells during development. Transgenic models have allowed the delineation of cellular migration and complex morphogenic rearrangements during the differentiation of skeletal myocytes and the assembly and organization of new myofibrils. Molecular targeting of genes and transcripts has allowed the identification of key requirements for myofibril assembly and organization. With the recent advances in gene editing approaches, the zebrafish will become an increasingly important model for the study of human myopathies and muscular dystrophies. Its high fecundity and small size make it well suited to high-throughput screenings to identify novel pharmacologic and molecular therapies for the treatment of a broad range of neuromuscular conditions. In this review, we examine the lessons learned from the zebrafish model regarding the complex interactions between the sarcomere and the sarcolemma that pattern the developing myocyte and discuss the potential for zebrafish as a model system to examine the pathophysiology of, and identify new treatments for, human myopathies and muscular dystrophies.

Structure of giant muscle proteins

Giant muscle proteins (e.g., titin, nebulin, and obscurin) play a seminal role in muscle elasticity, stretch response, and sarcomeric organization. Each giant protein consists of multiple tandem structural domains, usually arranged in a modular fashion spanning 500 kDa to 4 MDa. Although many of the domains are similar in structure, subtle differences create a unique function of each domain. Recent high and low resolution structural and dynamic studies now suggest more nuanced overall protein structures than previously realized. These findings show that atomic structure, interactions between tandem domains, and intrasarcomeric environment all influence the shape, motion, and therefore function of giant proteins. In this article we will review the current understanding of titin, obscurin, and nebulin structure, from the atomic level through the molecular level.

Obscurin is required for ankyrinB-dependent dystrophin localization and sarcolemma integrity

Obscurin contributes to the organization of subsarcolemma microtubules, localization of dystrophin at costameres, and maintenance of sarcolemmal integrity in skeletal muscle fibers.

Obscurin is a large myofibrillar protein that contains several interacting modules, one of which mediates binding to muscle-specific ankyrins. Interaction between obscurin and the muscle-specific ankyrin sAnk1.5 regulates the organization of the sarcoplasmic reticulum in striated muscles. Additional muscle-specific ankyrin isoforms, ankB and ankG, are localized at the subsarcolemma level, at which they contribute to the organization of dystrophin and β-dystroglycan at costameres. In this paper, we report that in mice deficient for obscurin, ankB was displaced from its localization at the M band, whereas localization of ankG at the Z disk was not affected. In obscurin KO mice, localization at costameres of dystrophin, but not of β-dystroglycan, was altered, and the subsarcolemma microtubule cytoskeleton was disrupted. In addition, these mutant mice displayed marked sarcolemmal fragility and reduced muscle exercise tolerance. Altogether, the results support a model in which obscurin, by targeting ankB at the M band, contributes to the organization of subsarcolemma microtubules, localization of dystrophin at costameres, and maintenance of sarcolemmal integrity.

Obscurins: unassuming giants enter the spotlight

Discovered about a decade ago, obscurin (~720 kDa) is a member of a family of giant proteins expressed in striated muscle that are essential for normal muscle function. Much of what we understand about obscurin stems from its functions in cardiac and skeletal muscle. However, recent evidence has indicated that variants of obscurin ("obscurins") are expressed in diverse cell types, where they contribute to distinct cellular processes. Dysfunction or abrogation of obscurins has also been implicated in the development of several pathological conditions, including cardiac hypertrophy and cancer. Herein, we present an overview of obscurins with an emphasis on novel findings that demonstrate their heretofore-unsuspected importance in cell signaling and disease progression.