Recessive TMOD1 mutation causes childhood cardiomyopathy.

Familial cardiomyopathy in pediatric stages is a poorly understood presentation of heart disease in children that is attributed to pathogenic mutations. Through exome sequencing, we report a homozygous variant in tropomodulin 1 (TMOD1; c.565C>T, p.R189W) in three individuals from two unrelated families with childhood-onset dilated and restrictive cardiomyopathy. To decipher the mechanism of pathogenicity of the R189W mutation in TMOD1, we utilized a wide array of methods, including protein analyses, biochemistry and cultured cardiomyocytes. Structural modeling revealed potential defects in the local folding of TMOD1R189W and its affinity for actin. Cardiomyocytes expressing GFP-TMOD1R189W demonstrated longer thin filaments than GFP-TMOD1wt-expressing cells, resulting in compromised filament length regulation. Furthermore, TMOD1R189W showed weakened activity in capping actin filament pointed ends, providing direct evidence for the variant's effect on actin filament length regulation. Our data indicate that the p.R189W variant in TMOD1 has altered biochemical properties and reveals a unique mechanism for childhood-onset cardiomyopathy.

A nemaline myopathy-linked mutation inhibits the actin-regulatory functions of tropomodulin and leiomodin.

Actin is a highly expressed protein in eukaryotic cells and is essential for numerous cellular processes. In particular, efficient striated muscle contraction is dependent upon the precise regulation of actin-based thin filament structure and function. Alterations in the lengths of actin-thin filaments can lead to the development of myopathies. Leiomodins and tropomodulins are members of an actin-binding protein family that fine-tune thin filament lengths, and their dysfunction is implicated in muscle diseases. An Lmod3 mutation [G326R] was previously identified in patients with nemaline myopathy (NM), a severe skeletal muscle disorder; this residue is conserved among Lmod and Tmod isoforms and resides within their homologous leucine-rich repeat (LRR) domain. We mutated this glycine to arginine in Lmod and Tmod to determine the physiological function of this residue and domain. This G-to-R substitution disrupts Lmod and Tmod's LRR domain structure, altering their binding interface with actin and destroying their abilities to regulate thin filament lengths. Additionally, this mutation renders Lmod3 nonfunctional in vivo. We found that one single amino acid is essential for folding of Lmod and Tmod LRR domains, and thus is essential for the opposing actin-regulatory functions of Lmod (filament elongation) and Tmod (filament shortening), revealing a mechanism underlying the development of NM.

A human FLII gene variant alters sarcomeric actin thin filament length and predisposes to cardiomyopathy.

To better understand the genetic basis of heart disease, we identified a variant in the Flightless-I homolog (FLII) gene that generates a R1243H missense change and predisposes to cardiac remodeling across multiple previous human genome-wide association studies (GWAS). Since this gene is of unknown function in the mammalian heart we generated gain- and loss-of-function genetically altered mice, as well as knock-in mice with the syntenic R1245H amino acid substitution, which showed that Flii protein binds the sarcomeric actin thin filament and influences its length. Deletion of Flii from the heart, or mice with the R1245H amino acid substitution, show cardiomyopathy due to shortening of the actin thin filaments. Mechanistically, Flii is a known actin binding protein that we show associates with tropomodulin-1 (TMOD1) to regulate sarcomere thin filament length. Indeed, overexpression of leiomodin-2 in the heart, which lengthens the actin-containing thin filaments, partially rescued disease due to heart-specific deletion of Flii. Collectively, the identified FLII human variant likely increases cardiomyopathy risk through an alteration in sarcomere structure and associated contractile dynamics, like other sarcomere gene-based familial cardiomyopathies.

Drosophila Tropomodulin is required for multiple actin-dependent processes within developing myofibers.

Proper muscle contraction requires the assembly and maintenance of sarcomeres and myofibrils. Although the protein components of myofibrils are generally known, less is known about the mechanisms by which they individually function and together synergize for myofibril assembly and maintenance. For example, it is unclear how the disruption of actin filament (F-actin) regulatory proteins leads to the muscle weakness observed in myopathies. Here, we show that knockdown of Drosophila Tropomodulin (Tmod), results in several myopathy-related phenotypes, including reduction of muscle cell (myofiber) size, increased sarcomere length, disorganization and misorientation of myofibrils, ectopic F-actin accumulation, loss of tension-mediating proteins at the myotendinous junction, and misshaped and internalized nuclei. Our findings support and extend the tension-driven self-organizing myofibrillogenesis model. We show that, like its mammalian counterpart, Drosophila Tmod caps F-actin pointed-ends, and we propose that this activity is crucial for cellular processes in different locations within the myofiber that directly and indirectly contribute to the maintenance of muscle function. Our findings provide significant insights to the role of Tmod in muscle development, maintenance and disease.

UBR2 targets myosin heavy chain IIb and IIx for degradation: Molecular mechanism essential for cancer-induced muscle wasting.

Cancer cachexia is a lethal metabolic syndrome featuring muscle wasting with preferential loss of fast-twitching muscle mass through an undefined mechanism. Here, we show that cancer induces muscle wasting by selectively degrading myosin heavy chain (MHC) subtypes IIb and IIx through E3 ligase UBR2-mediated ubiquitylation. Induction of MHC loss and atrophy in C2C12 myotubes and mouse tibialis anterior (TA) by murine cancer cells required UBR2 up-regulation by cancer. Genetic gain or loss of UBR2 function inversely altered MHC level and muscle mass in TA of tumor-free mice. UBR2 selectively interacted with and ubiquitylated MHC-IIb and MHC-IIx through its substrate recognition and catalytic domain, respectively, in C2C12 myotubes. Elevation of UBR2 in muscle of tumor-bearing or free mice caused loss of MHC-IIb and MHC-IIx but not MHC-I and MHC-IIa or other myofibrillar proteins, including α-actin, troponin, tropomyosin, and tropomodulin. Muscle-specific knockout of UBR2 spared KPC tumor-bearing mice from losing MHC-IIb and MHC-IIx, fast-twitching muscle mass, cross-sectional area, and contractile force. The rectus abdominis (RA) muscle of patients with cachexia-prone cancers displayed a selective reduction of MHC-IIx in correlation with higher UBR2 levels. These data suggest that UBR2 is a regulator of MHC-IIb/IIx essential for cancer-induced muscle wasting, and that therapeutic interventions can be designed by blocking UBR2 up-regulation by cancer.

Vibrio splendidus flagellin C binds tropomodulin to induce p38 MAPK-mediated p53-dependent coelomocyte apoptosis in Echinodermata.

As a typical pathogen-associated molecular pattern, bacterial flagellin can bind Toll-like receptor 5 and the intracellular NAIP5 receptor component of the NLRC4 inflammasome to induce immune responses in mammals. However, these flagellin receptors are generally poorly understood in lower animal species. In this study, we found that the isolated flagellum of Vibrio splendidus AJ01 destroyed the integrity of the tissue structure of coelomocytes and promoted apoptosis in the sea cucumber Apostichopus japonicus. To further investigate the molecular mechanism, the novel intracellular LRR domain-containing protein tropomodulin (AjTmod) was identified as a protein that interacts with flagellin C (FliC) with a dissociation constant (Kd) of 0.0086 ± 0.33 µM by microscale thermophoresis assay. We show that knockdown of AjTmod also depressed FliC-induced apoptosis of coelomocytes. Further functional analysis with different inhibitor treatments revealed that the interaction between AjTmod and FliC could specifically activate p38 MAPK, but not JNK or ERK MAP kinases. We demonstrate that the transcription factor p38 is then translocated into the nucleus, where it mediates the expression of p53 to induce coelomocyte apoptosis. Our findings provide the first evidence that intracellular AjTmod serves as a novel receptor of FliC and mediates p53-dependent coelomocyte apoptosis by activating the p38 MAPK signaling pathway in Echinodermata.

Cleavage of tropomodulin-3 by asparagine endopeptidase promotes cancer malignancy by actin remodeling and SND1/RhoA signaling.

BACKGROUND: Abnormal proliferation and migration of cells are hallmarks of cancer initiation and malignancy. Asparagine endopeptidase (AEP) has specific substrate cleavage ability and plays a pro-cancer role in a variety of cancers. However, the underlying mechanism of AEP in cancer proliferation and migration still remains unclear. METHODS: Co-immunoprecipitation and following mass spectrometry were used to identify the substrate of AEP. Western blotting was applied to measure the expression of proteins. Single cell/nuclear-sequences were done to detect the heterogeneous expression of Tmod3 in tumor tissues. CCK-8 assay, flow cytometry assays, colony formation assay, Transwell assay and scratch wound-healing assay were performed as cellular functional experiments. Mouse intracranial xenograft tumors were studied in in vivo experiments. RESULTS: Here we showed that AEP cleaved a ubiquitous cytoskeleton regulatory protein, tropomodulin-3 (Tmod3) at asparagine 157 (N157) and produced two functional truncations (tTmod3-N and tTmod3-C). Truncated Tmod3 was detected in diverse tumors and was found to be associated with poor prognosis of high-grade glioma. Functional studies showed that tTmod3-N and tTmod3-C enhanced cancer cell migration and proliferation, respectively. Animal models further revealed the tumor-promoting effects of AEP truncated Tmod3 in vivo. Mechanistically, tTmod3-N was enriched in the cell cortex and competitively inhibited the pointed-end capping effect of wild-type Tmod3 on filamentous actin (F-actin), leading to actin remodeling. tTmod3-C translocated to the nucleus, where it interacted with Staphylococcal Nuclease And Tudor Domain Containing 1 (SND1), facilitating the transcription of Ras Homolog Family Member A/Cyclin Dependent Kinases (RhoA/CDKs). CONCLUSION: The newly identified AEP-Tmod3 protease signaling axis is a novel "dual-regulation" mechanism of tumor cell proliferation and migration. Our work provides new clues to the underlying mechanisms of cancer proliferation and invasive progression and evidence for targeting AEP or Tmod3 for therapy.

Genetic dissection of novel myopathy models reveals a role of CapZα and Leiomodin 3 during myofibril elongation.

Myofibrils within skeletal muscle are composed of sarcomeres that generate force by contraction when their myosin-rich thick filaments slide past actin-based thin filaments. Although mutations in components of the sarcomere are a major cause of human disease, the highly complex process of sarcomere assembly is not fully understood. Current models of thin filament assembly highlight a central role for filament capping proteins, which can be divided into three protein families, each ascribed with separate roles in thin filament assembly. CapZ proteins have been shown to bind the Z-disc protein α-actinin to form an anchoring complex for thin filaments and actin polymerisation. Subsequent thin filaments extension dynamics are thought to be facilitated by Leiomodins (Lmods) and thin filament assembly is concluded by Tropomodulins (Tmods) that specifically cap the pointed end of thin filaments. To study thin filament assembly in vivo, single and compound loss-of-function zebrafish mutants within distinct classes of capping proteins were analysed. The generated lmod3- and capza1b-deficient zebrafish exhibited aspects of the pathology caused by variations in their human orthologs. Although loss of the analysed main capping proteins of the skeletal muscle, capza1b, capza1a, lmod3 and tmod4, resulted in sarcomere defects, residual organised sarcomeres were formed within the assessed mutants, indicating that these proteins are not essential for the initial myofibril assembly. Furthermore, detected similarity and location of myofibril defects, apparent at the peripheral ends of myofibres of both Lmod3- and CapZα-deficient mutants, suggest a function in longitudinal myofibril growth for both proteins, which is molecularly distinct to the function of Tmod4.

Erythroid differentiation in mouse erythroleukemia cells depends on Tmod3-mediated regulation of actin filament assembly into the erythroblast membrane skeleton.

Erythroid differentiation (ED) is a complex cellular process entailing morphologically distinct maturation stages of erythroblasts during terminal differentiation. Studies of actin filament (F-actin) assembly and organization during terminal ED have revealed essential roles for the F-actin pointed-end capping proteins, tropomodulins (Tmod1 and Tmod3). Tmods bind tropomyosins (Tpms), which enhance Tmod capping and F-actin stabilization. Tmods can also nucleate F-actin assembly, independent of Tpms. Tmod1 is present in the red blood cell (RBC) membrane skeleton, and deletion of Tmod1 in mice leads to a mild compensated anemia due to mis-regulated F-actin lengths and membrane instability. Tmod3 is not present in RBCs, and global deletion of Tmod3 leads to embryonic lethality in mice with impaired ED. To further decipher Tmod3's function during ED, we generated a Tmod3 knockout in a mouse erythroleukemia cell line (Mel ds19). Tmod3 knockout cells appeared normal prior to ED, but showed defects during progression of ED, characterized by a marked failure to reduce cell and nuclear size, reduced viability, and increased apoptosis. Tmod3 does not assemble with Tmod1 and Tpms into the Triton X-100 insoluble membrane skeleton during ED, and loss of Tmod3 had no effect on α1,ß1-spectrin and protein 4.1R assembly into the membrane skeleton. However, F-actin, Tmod1 and Tpms failed to assemble into the membrane skeleton during ED in absence of Tmod3. We propose that Tmod3 nucleation of F-actin assembly promotes incorporation of Tmod1 and Tpms into membrane skeleton F-actin, and that this is integral to morphological maturation and cell survival during erythroid terminal differentiation.

The role of leiomodin in actin dynamics: a new road or a secret gate.

Leiomodin is an important emerging regulator of thin filaments. As novel molecular, cellular, animal model, and human data accumulate, the mechanisms of its action become clearer. Structural studies played a significant part in understanding the functional significance of leiomodin's interacting partners and functional domains. In this review, we present the current state of knowledge on the structural and cellular properties of leiomodin which has led to two proposed mechanisms of its function. Although it is known that leiomodin is essential for life, numerous domains within leiomodin remain unstudied and as such, we outline future directions for investigations that we predict will provide evidence that leiomodin is a multifunctional protein.

Heterozygous Tropomodulin 3 mice have improved lung vascularization after chronic hypoxia.

The molecular mechanisms leading to high-altitude pulmonary hypertension (HAPH) remains poorly understood. We previously analyzed the whole genome sequence of Kyrgyz highland population and identified eight genomic intervals having a potential role in HAPH. Tropomodulin 3 gene (TMOD3), which encodes a protein that binds and caps the pointed ends of actin filaments and inhibits cell migration, was one of the top candidates. Here we systematically sought additional evidence to validate the functional role of TMOD3. In-silico analysis reveals that some of the SNPs in HAPH associated genomic intervals were positioned in a regulatory region that could result in alternative splicing of TMOD3. In order to functionally validate the role of TMOD3 in HAPH, we exposed Tmod3-/+ mice to 4 weeks of constant hypoxia, i.e. 10% O2 and analyzed both functional (hemodynamic measurements) and structural (angiography) parameters related to HAPH. The hemodynamic measurements, such as right ventricular systolic pressure, a surrogate measure for pulmonary arterial systolic pressure, and right ventricular contractility (RV- ± dP/dt), increases with hypoxia did not separate between Tmod3-/+ and control mice. Remarkably, there was a significant increase in the number of lung vascular branches and total length of pulmonary vascular branches (P < 0.001) in Tmod3-/+ after 4 weeks of constant hypoxia as compared with controls. Notably, the Tmod3-/+ endothelial cells migration was also significantly higher than that from the wild-type littermates. Our results indicate that, under chronic hypoxia, lower levels of Tmod3 play an important role in the maintenance or neo-vascularization of pulmonary arteries.

Tmod3 Phosphorylation Mediates AMPK-Dependent GLUT4 Plasma Membrane Insertion in Myoblasts.

Insulin and muscle contractions mediate glucose transporter 4 (GLUT4) translocation and insertion into the plasma membrane (PM) for glucose uptake in skeletal muscles. Muscle contraction results in AMPK activation, which promotes GLUT4 translocation and PM insertion. However, little is known regarding AMPK effectors that directly regulate GLUT4 translocation. We aim to identify novel AMPK effectors in the regulation of GLUT4 translocation. We performed biochemical, molecular biology and fluorescent microscopy imaging experiments using gain- and loss-of-function mutants of tropomodulin 3 (Tmod3). Here we report Tmod3, an actin filament capping protein, as a novel AMPK substrate and an essential mediator of AMPK-dependent GLUT4 translocation and glucose uptake in myoblasts. Furthermore, Tmod3 plays a key role in AMPK-induced F-actin remodeling and GLUT4 insertion into the PM. Our study defines Tmod3 as a key AMPK effector in the regulation of GLUT4 insertion into the PM and glucose uptake in muscle cells, and offers new mechanistic insights into the regulation of glucose homeostasis.

Down-regulated in renal cell carcinoma 1 (DRR1) regulates axon outgrowth during hippocampal neuron development.

Down-regulated in renal cell carcinoma 1 (DRR1), a unique stress-induced protein, is highly expressed in the nervous system. This study investigated the roles of DRR1 in the brain by examining its expression pattern at different developmental stages of a rat brain and in cultured primary hippocampal neurons. High expression of DRR1 was observed in all developmental stages of a rat brain and cultured primary hippocampal neurons. We then focused on the role of DRR1 in promoting neurite outgrowth during the early stage of hippocampal neuron development. Results showed that down-regulation of DRR1 suppressed axon outgrowth. Mass spectrometry analysis revealed that tropomodulin-2 (Tmod2) is a novel binding partner of DRR1. Our results showed that both DRR1 and Tmod2 mediate axon formation during the early stage of hippocampal neuron development. Suppression of TMOD2 expression rescued the abnormal axon outgrowth induced by DRR1 knockdown during the early stage of hippocampal neuron development.

Cofilin Loss in Drosophila Muscles Contributes to Muscle Weakness through Defective Sarcomerogenesis during Muscle Growth.

Sarcomeres, the fundamental contractile units of muscles, are conserved structures composed of actin thin filaments and myosin thick filaments. How sarcomeres are formed and maintained is not well understood. Here, we show that knockdown of Drosophila cofilin (DmCFL), an actin depolymerizing factor, disrupts both sarcomere structure and muscle function. The loss of DmCFL also results in the formation of sarcomeric protein aggregates and impairs sarcomere addition during growth. The activation of the proteasome delays muscle deterioration in our model. Furthermore, we investigate how a point mutation in CFL2 that causes nemaline myopathy (NM) in humans affects CFL function and leads to the muscle phenotypes observed in vivo. Our data provide significant insights to the role of CFLs during sarcomere formation, as well as mechanistic implications for disease progression in NM patients.

Branched-Chain Amino Acid Catabolism Promotes Thrombosis Risk by Enhancing Tropomodulin-3 Propionylation in Platelets.

BACKGROUND: Branched-chain amino acids (BCAAs), essential nutrients including leucine, isoleucine, and valine, serve as a resource for energy production and the regulator of important nutrient and metabolic signals. Recent studies have suggested that dysfunction of BCAA catabolism is associated with the risk of cardiovascular disease. Platelets play an important role in cardiovascular disease, but the functions of BCAA catabolism in platelets remain unknown. METHODS: The activity of human platelets from healthy subjects before and after ingestion of BCAAs was measured. Protein phosphatase 2Cm specifically dephosphorylates branched-chain α-keto acid dehydrogenase and thereby activates BCAA catabolism. Protein phosphatase 2Cm-deficient mice were used to elucidate the impacts of BCAA catabolism on platelet activation and thrombus formation. RESULTS: We found that ingestion of BCAAs significantly promoted human platelet activity (n=5; P<0.001) and arterial thrombosis formation in mice (n=9; P<0.05). We also found that the valine catabolite α-ketoisovaleric acid and the ultimate oxidation product propionyl-coenzyme A showed the strongest promotion effects on platelet activation, suggesting that the valine/α-ketoisovaleric acid catabolic pathway plays a major role in BCAA-facilitated platelet activation. Protein phosphatase 2Cm deficiency significantly suppresses the activity of platelets in response to agonists (n=5; P<0.05). Our results also suggested that BCAA metabolic pathways may be involved in the integrin αIIbß3-mediated bidirectional signaling pathway that regulates platelet activation. Mass spectrometry identification and immunoblotting revealed that BCAAs enhanced propionylation of tropomodulin-3 at K255 in platelets or Chinese hamster ovary cells expressing integrin αIIbß3. The tropomodulin-3 K255A mutation abolished propionylation and attenuated the promotion effects of BCAAs on integrin-mediated cell spreading, suggesting that K255 propionylation of tropomodulin-3 is an important mechanism underlying integrin αIIbß3-mediated BCAA-facilitated platelet activation and thrombosis formation. In addition, the increased levels of BCAAs and the expression of positive regulators of BCAA catabolism in platelets from patients with type 2 diabetes mellitus are significantly correlated with platelet hyperreactivity. Lowering dietary BCAA intake significantly reduced platelet activity in ob/ob mice (n=4; P<0.05). CONCLUSIONS: BCAA catabolism is an important regulator of platelet activation and is associated with arterial thrombosis risk. Targeting the BCAA catabolism pathway or lowering dietary BCAA intake may serve as a novel therapeutic strategy for metabolic syndrome-associated thrombophilia.

Tropomodulins Control the Balance between Protrusive and Contractile Structures by Stabilizing Actin-Tropomyosin Filaments.

Eukaryotic cells have diverse protrusive and contractile actin filament structures, which compete with one another for a limited pool of actin monomers. Numerous actin-binding proteins regulate the dynamics of actin structures, including tropomodulins (Tmods), which cap the pointed end of actin filaments. In striated muscles, Tmods prevent actin filaments from overgrowing, whereas in non-muscle cells, their function has remained elusive. Here, we identify two Tmod isoforms, Tmod1 and Tmod3, as key components of contractile stress fibers in non-muscle cells. Individually, Tmod1 and Tmod3 can compensate for one another, but their simultaneous depletion results in disassembly of actin-tropomyosin filaments, loss of force-generating stress fibers, and severe defects in cell morphology. Knockout-rescue experiments reveal that Tmod's interaction with tropomyosin is essential for its role in the stabilization of actin-tropomyosin filaments in cells. Thus, in contrast to their role in muscle myofibrils, in non-muscle cells, Tmods bind actin-tropomyosin filaments to protect them from depolymerizing, not elongating. Furthermore, loss of Tmods shifts the balance from linear actin-tropomyosin filaments to Arp2/3 complex-nucleated branched networks, and this phenotype can be partially rescued by inhibiting the Arp2/3 complex. Collectively, the data reveal that Tmods are essential for the maintenance of contractile actomyosin bundles and that Tmod-dependent capping of actin-tropomyosin filaments is critical for the regulation of actin homeostasis in non-muscle cells.

Tropomodulin1 Expression Increases Upon Maturation in Dendritic Cells and Promotes Their Maturation and Immune Functions.

Dendritic cells (DCs) are the most potent antigen-presenting cells. Upon maturation, DCs express costimulatory molecules and migrate to the lymph nodes to present antigens to T cells. The actin cytoskeleton plays key roles in multiple aspects of DC functions. However, little is known about the mechanisms and identities of actin-binding proteins that control DC maturation and maturation-associated functional changes. Tropomodulin1 (Tmod1), an actin-capping protein, controls actin depolymerization and nucleation. We found that Tmod1 was expressed in bone marrow-derived immature DCs and was significantly upregulated upon lipopolysaccharide (LPS)-induced DC maturation. By characterizing LPS-induced mature DCs (mDCs) from Tmod1 knockout mice, we found that compared with Tmod1+/+ mDCs, Tmod1-deficient mDCs exhibited lower surface expression of costimulatory molecules and chemokine receptors and reduced secretion of inflammatory cytokines, suggesting that Tmod1 deficiency retarded DC maturation. Tmod1-deficient mDCs also showed impaired random and chemotactic migration, deteriorated T-cell stimulatory ability, and reduced F-actin content and cell stiffness. Furthermore, Tmod1-deficient mDCs secreted high levels of IFN-ß and IL-10 and induced immune tolerance in an experimental autoimmune encephalomyelitis (EAE) mouse model. Mechanistically, Tmod1 deficiency affected TLR4 signaling transduction, resulting in the decreased activity of MyD88-dependent NFκB and MAPK pathways but the increased activity of the TRIF/IRF3 pathway. Rescue with exogenous Tmod1 reversed the effect of Tmod1 deficiency on TLR4 signaling. Therefore, Tmod1 is critical in regulating DC maturation and immune functions by regulating TLR4 signaling and the actin cytoskeleton. Tmod1 may be a potential target for modulating DC functions, a strategy that would be beneficial for immunotherapy for several diseases.

Role of intrinsic disorder in muscle sarcomeres.

The role and utility of intrinsically disordered regions (IDRs) is reviewed for two groups of sarcomeric proteins, such as members of tropomodulin/leiomodin (Tmod/Lmod) protein homology group and myosin binding protein C (MyBP-C). These two types of sarcomeric proteins represent very different but strongly interdependent functions, being responsible for maintaining structure and operation of the muscle sarcomere. The role of IDRs in the formation of complexes between thin filaments and Tmods/Lmods is discussed within the framework of current understanding of the thin filament length regulation. For MyBP-C, the function of IDRs is discussed in the context of MYBP-C-dependent sarcomere contraction and actomyosin activation.

Targeted regulation of miR-17-5p on TMOD1 promotes the development of cardia cancer.

OBJECTIVE: Cardia cancer is a common type of gastric cancer. Most clinical prevention and prognosis focus on surgical resection, but the efficacy is not satisfactory. Studying the molecular mechanism of pathogenesis of cardia cancer helps us intervene in prognosis and treatment. MATERIALS AND METHODS: a total of 134 normal cases related to cardia cancer and 62 cases of cardia cancer samples from the Gene Expression Omnibus (GEO) database were collected. A series of bioinformatics analyses, including differential gene analysis, co-expression analysis, enrichment analysis, regulator prediction, and (Protein-protein interaction) PPI analysis validation were performed. RESULTS: Differential analysis highlighted 10882 differential genes (p<0.05). Weighted gene co-expression network analysis indicated 6 functional disorder modules. TMOD1, JAM2, SPARC, ST18, NOS1 were key genes of each module. Enrichment analysis showed the dysfunctional module genes were mainly related to the proteinaceous extracellular matrix and neuroactive ligand-receptor interaction. Pivotal analysis of ncRNA demonstrated miR-17-5p significantly regulates modular genes including m1, m3, and m5. Target genes were backtracked according to the key regulators. Then, the Module_target gene_ncRNA interaction network diagram was constructed. The network shows m1 has the strongest regulation effect in the network. PPI showed that the core gene TMOD1 (Tropomodulin1) of m1 was at TOP10 in the algorithm. In other words, PPI indicated the importance of TMOD1 in the interaction network. CONCLUSIONS: We believe that targeted regulation of miR-17-5p on TMOD1 gene affects the neuroactive ligand-receptor interaction pathway, and it promotes proliferation and apoptosis of cardia cancer cells.

Tropomodulin 3 promotes liver cancer progression by activating the MAPK/ERK signaling pathway.

Tropomodulin 3 (TMOD3) is a member of the pointed­end capping protein family that contributes to invasion and metastasis in several types of malignancies. TMOD3 has been found to be crucial for membranous skeleton and embryonic development; however, little is known regarding the role of TMOD3 in liver cancer progression. In addition, to the best of our knowledge, no previous studies have investigated the mechanism underlying the TMOD3­regulated promotion of liver cancer. The aim of the present study was to determine whether TMOD3 is associated with liver cancer progression. TMOD3 expression was found to be elevated in liver cancer cells and tissues. In the in vitro experiments, liver cancer cell proliferation, invasion and migration were inhibited by TMOD3 knockdown and promoted by ectopic expression of TMOD3. Furthermore, mechanistic analysis indicated that TMOD3 overexpression activated mitogen­activated protein kinase (MAPK)/extracellular signal­regulated kinase (ERK) signaling and increased the levels of other targets of this pathway, including matrix metalloproteinase (MMP)2, MMP9 and cyclin D1. TMOD3 overexpression was associated with changes in liver cancer cell morphology and altered expression of epithelial and mesenchymal markers. High TMOD3 expression was hypothesized to promote epithelial­to­mesenchymal transition in liver cancer cells. In conclusion, TMOD3 was shown to promote liver cancer cell growth, invasion and migration through the MAPK/ERK signaling pathway, and it may serve as a candidate biomarker and therapeutic target in liver cancer.