Myoblast migration is regulated by calpain through its involvement in cell attachment and cytoskeletal organization

Calpain Promotes LPS-induced Lung Endothelial Barrier Dysfunction via Cleavage of Talin

Acute lung injury (ALI) is characterized by lung vascular endothelial cell (EC) barrier compromise resulting in increased endothelial permeability and pulmonary edema. The infection of gram-negative bacteria that produce toxins like LPS is one of the major causes of ALI. LPS activates Toll-like receptor 4, leading to cytoskeleton reorganization, resulting in lung endothelial barrier disruption and pulmonary edema in ALI. However, the signaling pathways that lead to the cytoskeleton reorganization and lung microvascular EC barrier disruption remain largely unexplored. Here we show that LPS induces calpain activation and talin cleavage into head and rod domains and that inhibition of calpain attenuates talin cleavage, RhoA activation, and pulmonary EC barrier disruption in LPS-treated human lung microvascular ECs in vitro and lung EC barrier disruption and pulmonary edema induced by LPS in ALI in vivo. Moreover, overexpression of calpain causes talin cleavage and RhoA activation, myosin light chain (MLC) phosphorylation, and increases in actin stress fiber formation. Furthermore, knockdown of talin attenuates LPS-induced RhoA activation and MLC phosphorylation and increased stress fiber formation and mitigates LPS-induced lung microvascular endothelial barrier disruption. Additionally, overexpression of talin head and rod domains increases RhoA activation, MLC phosphorylation, and stress fiber formation and enhances lung endothelial barrier disruption. Finally, overexpression of cleavage-resistant talin mutant reduces LPS-induced increases in MLC phosphorylation in human lung microvascular ECs and attenuates LPS-induced lung microvascular endothelial barrier disruption. These results provide the first evidence that calpain mediates LPS-induced lung microvascular endothelial barrier disruption in ALI via cleavage of talin.

Rare variants in CAPN2 increase risk for isolated hypoplastic left heart syndrome

Hypoplastic left heart syndrome (HLHS) is a severe congenital heart defect (CHD) characterized by hypoplasia of the left ventricle and aorta along with stenosis or atresia of the aortic and mitral valves. HLHS represents only ∼4%-8% of all CHDs but accounts for ∼25% of deaths. HLHS is an isolated defect (i.e., iHLHS) in 70% of families, the vast majority of which are simplex. Despite intense investigation, the genetic basis of iHLHS remains largely unknown. We performed exome sequencing on 331 families with iHLHS aggregated from four independent cohorts. A Mendelian-model-based analysis demonstrated that iHLHS was not due to single, large-effect alleles in genes previously reported to underlie iHLHS or CHD in >90% of families in this cohort. Gene-based association testing identified increased risk for iHLHS associated with variation in CAPN2 (p = 1.8 × 10-5), encoding a protein involved in functional adhesion. Functional validation studies in a vertebrate animal model (Xenopus laevis) confirmed CAPN2 is essential for cardiac ventricle morphogenesis and that in vivo loss of calpain function causes hypoplastic ventricle phenotypes and suggest that human CAPN2707C>T and CAPN21112C>T variants, each found in multiple individuals with iHLHS, are hypomorphic alleles. Collectively, our findings show that iHLHS is typically not a Mendelian condition, demonstrate that CAPN2 variants increase risk of iHLHS, and identify a novel pathway involved in HLHS pathogenesis.

Biological activities of a new crotamine-like peptide from Crotalus oreganus helleri on C2C12 and CHO cell lines, and ultrastructural changes on motor endplate and striated muscle

Crotamine and crotamine-like peptides are non-enzymatic polypeptides, belonging to the family of myotoxins, which are found in high concentration in the venom of the Crotalus genus. Helleramine was isolated and purified from the venom of the Southern Pacific rattlesnake, Crotalus oreganus helleri. This peptide had a similar, but unique, identity to crotamine and crotamine-like proteins isolated from other rattlesnakes species. The variability of crotamine-like protein amino acid sequences may allow different toxic effects on biological targets or optimize the action against the same target of different prey. Helleramine was capable of increasing intracellular Ca2+ in Chinese Hamster Ovary (CHO) cell line. It inhibited cell migration as well as cell viability (IC50 = 11.44 μM) of C2C12, immortalized skeletal myoblasts, in a concentration dependent manner, and promoted early apoptosis and cell death under our experimental conditions. Skeletal muscle harvested from mice 24 h after helleramine injection showed contracted myofibrils and profound vacuolization that enlarged the subsarcolemmal space, along with loss of plasmatic and basal membrane integrity. The effects of helleramine provide further insights and evidence of myotoxic activities of crotamine-like peptides and their possible role in crotalid envenomings.

Theaflavin Promotes Myogenic Differentiation by Regulating the Cell Cycle and Surface Mechanical Properties of C2C12 Cells

Aging and muscle diseases often lead to a decline in the differentiation capacity of myoblasts, which in turn results in the deterioration of skeletal muscle (SkM) function and impairment of regeneration ability after injury. Theaflavins, the "gold molecules" found in black tea, have been reported to possess various biological activities and have a positive effect on maintaining human health. In this study, we found that among the four theaflavins (theaflavin (TF1), theaflavin-3-gallate (TF2A), theaflavin-3'-gallate (TF2B), and theaflavin-3,3'-digallate (TF3) monomers), TF1 (20 μM) significantly promoted the fusion index of myoblasts, number of mature myotubes, and degree of myotube development. By combining transcriptomics, bioinformatics, and molecular biology experiments, we showed that TF1 may promote myoblast differentiation by (1) regulating the withdrawal of myoblasts from the cell cycle, inducing the release of myogenic factors (MyoD, MyoG, and MyHC) and accelerating myogenic differentiation and (2) regulating the adhesion force of myoblasts and mechanical properties of mature myotubes and promoting the migration, fusion, and development of myoblasts. In conclusion, our study outcomes show that TF1 can promote myoblast differentiation and regulate myotube mechanical properties. It is a potential dietary supplement for the elderly. Our findings provide a new scientific basis for the relationship between tea drinking and aging.

Natural flavonoid silibinin promotes the migration and myogenic differentiation of murine C2C12 myoblasts via modulation of ROS generation and down-regulation of estrogen receptor α expression

Skeletal muscle regeneration is a complex process, involving the proliferation, migration, and differentiation of myoblasts. Recent studies suggest that some natural flavanones stimulate myogenesis. However, the effect of plant estrogen, silibinin, on the regulation of myoblast behaviors is unclarified. In this study, we investigated the effects of silibinin on immortalized murine myoblast C2C12 in the aspects of proliferation, migration, differentiation along with underlying mechanisms. The results show that silibinin at concentrations below 50 μM enhanced the migration and differentiation of C2C12 cells, but had no effect on cell proliferation. Silibinin significantly promoted the production of ROS, which appeared to play important roles in the migration and differentiation of the myoblasts. Interestingly, among ROS, the superoxide anion and hydroxyl radical were associated with the migration, whereas hydrogen peroxide contributed to the myogenic differentiation. We used ER agonist and antagonist to explore whether estrogen receptors (ERs), which are affected by silibinin treatment in the silibinin-enhanced C2C12 migration and differentiation. Migration was independent of ERs, whereas the differentiation was associated with decreased ERα activity. In summary, silibinin treatment increases ROS levels, leading to the promotion of migration and myogenic differentiation. Negative regulation ERα of differentiation but not of migration may suggest that ERα represses hydrogen peroxide generation. The effect of silibinin on myoblast migration and differentiation suggests that silibinin may have therapeutic benefits for muscle regeneration.

Calpainopathy: Description of a Novel Mutation and Clinical Presentation with Early Severe Contractures

Presented here are five members of a family that was ascertained from an isolated, consanguineous, indigenous Amerindian community in Colombia that was affected with calpain 3-related, limb-girdle muscular dystrophy type R1. These patients are homozygous for a unique and novel deletion of four bases (TGCC) in exon 3 of the calpain 3 gene (CAPN3) (NM_000070.2; NP_000061.1) (g.409_412del). The mutation site occurs at the CysPc protein domain, triggering a modified truncated protein structure and affecting motifs within the calpain-like thiol protease family (peptidase family C2) region. The patients reported here developed a very severe phenotype with primary contractures, spinal rigidity in the early stages of the disease, and bilateral talipes equinovarus (clubfoot) in the most affected patients who had the selective involvement of their extremities’ distal muscles in a way that resembled Emery–Dreifuss syndrome. We recommend mandatory screening for calpainopathy in all patients with an Emery–Dreifuss-like syndrome or those presenting a non-congenital illness with primary contractures and who, because of other data, are suspected of having muscular dystrophy.

Association of CAST gene polymorphism with carcass value and meat quality in two synthetic lines of sheep

The aim of study was to estimate genotype frequencies of the polymorphism in the intron 12 of CAST gene of growing lambs, and to evaluate associations between the CAST genotype and carcass and meat traits. A total number of 317 rams representing the synthetic BCP (163) and SCP (154) meaty lines were genotyped by the RFLP/MspI/NcoI/Hin6I. Three genotypes including "aa", "ae" and "ac" with most frequencies of 0.48, 0.27 and 0.19, were observed in whole population. Lambs with the "aa" CAST genotype showed the highest muscle percentage and the lowest fat percentage in the hind legs. On the other hand, the loins of rams with "ac" genotype had the highest intramuscular fat content, indicative of beneficial health-related properties and technological usefulness. However, differences between CAST genotype stated for the sensory properties, texture and thawing and cooking losses of the meat were insignificant. Breeding efforts aimed at the improvement of lamb meat quality should prioritize the selection of the "ac" genotype.

Comprehensive assessment of candidate genes associated with fattening performance in Holstein-Friesian bulls

The objective of this study was to determine the association of single nucleotide polymorphisms (SNPs) in selected candidate genes with fattening performance traits in a commercial cattle herd. Fifteen SNPs in 12 candidate genes (LEP, FABP4, DGAT1, TG, IGF1, IGF1R, MYF5, LGB, CAPN1, CAST, GHR, and OLR1) were evaluated in 296 purebred Holstein-Friesian bulls using PCR-RFLP (polymerase chain reaction - restriction fragment length polymorphism). Associations between each segregating SNP and genetic merit for fattening performance were quantified using linear mixed models. Traits included in the study were fattening period, final weight, dry matter intake, feed conversion rate, and average daily weight gain. Apart from the general determination of the above-mentioned traits, each trait was evaluated based on the fattening periods between five selected target body weights (W1  =  100 kg, W2  =  200 kg, W3  =  300 kg, W4  =  400 kg, W5  =  450 kg). All markers with the exception of CAPN1 530, IGF1R, TG, and DGAT1 were associated with at least one of the traits. Furthermore, novel associations were observed for LEP  ×  GHR, IGF1  ×  LEP, FABP4 3691  ×  FABP4 2834, and FAP4 3533  ×  LEP interactions. The results of this study confirm some previously reported associations. Moreover, novel associations have been identified, which may be incorporated into breeding programs to improve fattening performance.

Quantitative characterization of single-cell adhesion properties by atomic force microscopy using protein-functionalized microbeads

A method was developed to characterize the adhesion properties of single cells by using protein-functionalized atomic force microscopy (AFM) probes. The quantification by force spectroscopy of the mean detachment force between cells and a gelatin-functionalized colloidal tip reveals differences in cell adhesion properties that are not within reach of a traditional bulk technique, the washing assay. In this latter method, experiments yield semiquantitative and average adhesion properties of a large population of cells. They are also limited to stringent conditions and cannot highlight disparities in adhesion in the subset of adherent cells. In contrast, this AFM-based method allows for a reproducible and quantitative investigation of the adhesive properties of individual cells in common cell culture conditions and allows for the detection of adhesive subpopulations of cells. These characteristics meet the critical requirements of many fields, such as the study of cancer cell migratory abilities.

MYC leads the way

Members of the MYC family of proto-oncogenes are the most commonly deregulated genes in all human cancers. MYC proteins drive an increase in cellular proliferation and facilitate multiple aspects of tumor initiation and progression, thereby controlling all hallmarks of cancer. MYC's ability to drive metabolic reprogramming of tumor cells leading to biomass accumulation and cellular proliferation is the most studied function of these oncogenes. MYC also regulates tumor progression and is often implicated in resistance to chemotherapy and in metastasis. While most oncogenic functions of MYC are attributed to its role as a transcription factor, more recently, new roles of MYC as a pro-survival factor in the cytoplasm suggest a previously unappreciated diversity in MYC's roles in cancer progression. This review will focus on the role of MYC in invasion and will discuss the canonical functions of MYC in Epithelial to Mesenchymal Transition and the cytoplasmic functions of MYC-nick in collective migration.

The MARCKS protein amount is differently regulated by calpain during toxic effects of methylmercury between SH-SY5Y and EA.hy926 cells

Methylmercury (MeHg) is an environmental pollutant that shows severe toxicity to humans and animals. However, the molecular mechanisms mediating MeHg toxicity are not completely understood. We have previously reported that the MARCKS protein is involved in the MeHg toxicity to SH-SY5Y neuroblastoma and EA.hy926 vascular endothelial cell lines. In addition, calpain, a Ca²⁺-dependent protease, is suggested to be associated with the MeHg toxicity. Because MARCKS is known as a substrate of calpain, we studied the relation between calpain activation and cleavage of MARCKS and its role in MeHg toxicity. In SH-SY5Y cells, MeHg decreased cell viability along with increased calcium mobilization, calpain activation and a decrease in MARCKS amounts. However, pretreatment with calpain inhibitors attenuated the decrease in cell viability and MARCKS amount induced only by 1 µM but not by 3 µM MeHg. In cells with a MARCKS knockdown, calpain inhibitors failed to attenuate the decrease in cell viability caused by MeHg. In EA.hy926 cells, although MeHg caused calcium mobilization and a decrease in MARCKS levels, calpain activation was not observed. These results indicate that the participation of calpain in the regulation of MARCKS amounts is dependent on the cell type and concentration of MeHg. In SH-SY5Y cells, calpain-mediated proteolysis of MARCKS is involved in cytotoxicity induced by a low concentration of MeHg.

Focal Adhesion Kinase Activation Is Necessary for Stretch-Induced Alignment and Enhanced Differentiation of Myogenic Precursor Cells

Myogenic precursors sense and dynamically respond to mechanical stimulation through complex integrin-mediated mechanotransduction, in which focal adhesion kinase (FAK) is a fundamental intracellular signaling mediator. When skeletal myoblasts are exposed to uniaxial cyclic tensile strain (UCTS), they display uniform alignment and an enhanced rate of differentiation. In this work, we explored the role of FAK activation by using C2C12 myoblasts that were grown on flexible culture plates and exposed to UCTS during the early differentiation phase. After 24 h, the cells oriented perpendicularly to the direction of strain and exhibited an enhanced differentiation profile. Next, the cells were exposed to a strain field that was either kept in the same direction or rotated 90°, in the presence or not of an FAK phosphorylation inhibitor. On reorientation of the strain field by 90°, the cells reassembled their focal adhesions and actin cytoskeleton to regain the perpendicular position with respect to the engaging stress. After blocking the FAK, however, the cells failed to respond to the reoriented strain field and their differentiation was abrogated. Interestingly, when the strain field remained in the same direction, the FAK inhibitor compromised the differentiation, even though there was no evident change in cell orientation. Our data indicate that during exposure to UCTS, the activation of FAK is necessary for the myoblasts to undergo alignment and enhanced differentiation.

Genome-Wide Association Study for Identifying Loci that Affect Fillet Yield, Carcass, and Body Weight Traits in Rainbow Trout (Oncorhynchus mykiss)

Fillet yield (FY, %) is an economically-important trait in rainbow trout aquaculture that affects production efficiency. Despite that, FY has received little attention in breeding programs because it is difficult to measure on a large number of fish and cannot be directly measured on breeding candidates. The recent development of a high-density SNP array for rainbow trout has provided the needed tool for studying the underlying genetic architecture of this trait. A genome-wide association study (GWAS) was conducted for FY, body weight at 10 (BW10) and 13 (BW13) months post-hatching, head-off carcass weight (CAR), and fillet weight (FW) in a pedigreed rainbow trout population selectively bred for improved growth performance. The GWAS analysis was performed using the weighted single-step GBLUP method (wssGWAS). Phenotypic records of 1447 fish (1.5 kg at harvest) from 299 full-sib families in three successive generations, of which 875 fish from 196 full-sib families were genotyped, were used in the GWAS analysis. A total of 38,107 polymorphic SNPs were analyzed in a univariate model with hatch year and harvest group as fixed effects, harvest weight as a continuous covariate, and animal and common environment as random effects. A new linkage map was developed to create windows of 20 adjacent SNPs for use in the GWAS. The two windows with largest effect for FY and FW were located on chromosome Omy9 and explained only 1.0-1.5% of genetic variance, thus suggesting a polygenic architecture affected by multiple loci with small effects in this population. One window on Omy5 explained 1.4 and 1.0% of the genetic variance for BW10 and BW13, respectively. Three windows located on Omy27, Omy17, and Omy9 (same window detected for FY) explained 1.7, 1.7, and 1.0%, respectively, of genetic variance for CAR. Among the detected 100 SNPs, 55% were located directly in genes (intron and exons). Nucleotide sequences of intragenic SNPs were blasted to the Mus musculus genome to create a putative gene network. The network suggests that differences in the ability to maintain a proliferative and renewable population of myogenic precursor cells may affect variation in growth and fillet yield in rainbow trout.

Analysis of the effect of LRP-1 silencing on the invasive potential of cancer cells by nanomechanical probing and adhesion force measurements using atomic force microscopy

Low-density lipoprotein receptor-related protein 1 (LRP-1) can internalize proteases involved in cancer progression and is thus considered a promising therapeutic target. However, it has been demonstrated that LRP-1 is also able to regulate the endocytosis of membrane-anchored proteins. Thus, strategies that target LRP-1 to modulate proteolysis could also affect adhesion and cytoskeleton dynamics. Here, we investigated the effect of LRP-1 silencing on parameters reflecting cancer cells' invasiveness by atomic force microscopy (AFM). The results show that LRP-1 silencing induces changes in the cells' adhesion behavior, particularly the dynamics of cell attachment. Clear alterations in morphology, such as more pronounced stress fibers and increased spreading, leading to increased area and circularity, were also observed. The determination of the cells' mechanical properties by AFM showed that these differences are correlated with an increase in Young's modulus. Moreover, the measurements show an overall decrease in cell motility and modifications of directional persistence. An overall increase in the adhesion force between the LRP-1-silenced cells and a gelatin-coated bead was also observed. Ultimately, our AFM-based force spectroscopy data, recorded using an antibody directed against the β1 integrin subunit, provide evidence that LRP-1 silencing modifies the rupture force distribution. Together, our results show that techniques traditionally used for the investigation of cancer cells can be coupled with AFM to gain access to complementary phenotypic parameters that can help discriminate between specific phenotypes associated with different degrees of invasiveness.

Retinoids and glucocorticoids have opposite effects on actin cytoskeleton rearrangement in hippocampal HT22 cells

A chronic excess of glucocorticoids elicits deleterious effects in the hippocampus. Conversely, retinoic acid plays a major role in aging brain plasticity. As synaptic plasticity depends on mechanisms related to cell morphology, we investigated the involvement of retinoic acid and glucocorticoids in the remodelling of the HT22 neurons actin cytoskeleton. Cells exhibited a significantly more elongated shape with retinoic acid and a rounder shape with dexamethasone; retinoic acid reversed the effects of dexamethasone. Actin expression and abundance were unchanged by retinoic acid or dexamethasone but F-actin organization was dramatically modified. Indeed, retinoic acid and dexamethasone increased (70 ± 7% and 176 ± 5%) cortical actin while retinoic acid suppressed the effect of dexamethasone (90 ± 6%). Retinoic acid decreased (-22 ± 9%) and dexamethasone increased (134 ± 16%) actin stress fibres. Retinoic acid also suppressed the effect of dexamethasone (-21 ± 7%). Spectrin is a key protein in the actin network remodelling. Its abundance was decreased by retinoic acid and increased by dexamethasone (-21 ± 11% and 52 ± 10%). However, retinoic acid did not modify the effect of dexamethasone (48 ± 7%). Calpain activity on spectrin was increased by retinoic acid and decreased by dexamethasone (26 ± 14% and -57 ± 5%); retinoic acid mildly but significantly modified the effect of dexamethasone (-44 ± 7%). The calpain inhibitor calpeptin suppressed the effects of retinoic acid and dexamethasone on cell shape and actin stress fibres remodelling but did not modify the effects on cortical actin. Retinoic acid and dexamethasone have a dramatic but mainly opposite effect on actin cytoskeleton remodelling. These effects originate, at least partly, from calpain activity.

Toxoplasma gondii-skeletal muscle cells interaction increases lipid droplet biogenesis and positively modulates the production of IL-12, IFN-g and PGE2

Background

The interest in the mechanisms involved in Toxoplasma gondii lipid acquisition has steadily increased during the past few decades, but it remains not completely understood. Here, we investigated the biogenesis and the fate of lipid droplets (LD) of skeletal muscle cells (SkMC) during their interaction with T. gondii by confocal and electron microscopy. We also evaluated whether infected SkMC modulates the production of prostaglandin E₂ (PGE₂), cytokines interleukin-12 (IL-12) and interferon-gamma (INF-g), and also the cyclooxygenase-2 (COX-2) gene induction.

Methods

Primary culture of skeletal muscle cells were infected with tachyzoites of T. gondii and analysed by confocal microscopy for observation of LD. Ultrastructural cytochemistry was also used for lipid and sarcoplasmatic reticulum (SR) detection. Dosage of cytokines (IL-12 and INF-g) by ELISA technique and enzyme-linked immunoassay (EIA) for PGE₂ measurement were employed. The COX-2 gene expression analysis was performed by real time reverse transcriptase polymerase chain reaction (qRT-PCR).

Results

We demonstrated that T. gondii infection of SkMC leads to increase in LD number and area in a time course dependent manner. Moreover, the ultrastructural analysis demonstrated that SR and LD are in direct contact with parasitophorous vacuole membrane (PVM), within the vacuolar matrix, around it and interacting directly with the membrane of parasite, indicating that LD are recruited and deliver their content inside the parasitophorous vacuole (PV) in T. gondii-infected SkMC. We also observed a positive modulation of the production of IL-12 and IFN-g, increase of COX-2 mRNA levels in the first hour of T. gondii-SkMC interaction and an increase of prostaglandin E₂ (PGE₂) synthesis from 6 h up to 48 h of infection.

Conclusions

Taken together, the close association between SR and LD with PV could represent a source of lipids as well as other nutrients for the parasite survival, and together with the increased levels of IL-12, INF-g and inflammatory indicators PGE₂ and COX-2 might contribute to the establishment and maintenance of chronic phase of the T. gondii infection in muscle cell.

skNAC depletion stimulates myoblast migration and perturbs sarcomerogenesis by enhancing calpain 1 and 3 activity

skNAC (skeletal and heart muscle specific variant of nascent polypeptide-associated complex α) is a skeletal and heart muscle-specific protein known to be involved in the regulation of sarcomerogenesis. The respective mechanism, however, is largely unknown. In the present paper, we demonstrate that skNAC regulates calpain activity. Specifically, we show that inhibition of skNAC gene expression leads to enhanced, and overexpression of the skNAC gene to repressed, activity of calpain 1 and, to a lesser extent, calpain 3 in myoblasts. In skNAC siRNA-treated cells, enhanced calpain activity is associated with increased migration rates, as well as with perturbed sarcomere architecture. Treatment of skNAC-knockdown cells with the calpain inhibitor ALLN (N-acetyl-leucyl-leucyl-norleucinal) reverts both the positive effect on myoblast migration and the negative effect on sarcomere architecture. Taken together, our data suggest that skNAC controls myoblast migration and sarcomere architecture in a calpain-dependent manner.

Significant role of μ-calpain (CANP1) in proliferation/survival of bovine skeletal muscle satellite cells

Calpains are a family of Ca²⁺-dependent intracellular cysteine proteases, including the ubiquitously expressed μ-calpain (CANP1) and m-calpain (CANP2). The CANP1 has been found to play a central role in postmortem proteolysis and meat tenderization. However, the physiological roles of CANP1 in cattle skeletal satellite cells remain unclear. In this study, three small interference RNA sequences (siRNAs) targeting CANP1 gene were designed and ligated into pSilencer plasmid vector to construct shRNA expression constructs. Suppression of CANP1 in satellite cells was evaluated using these shRNA expressing constructs. Our results revealed that all three siRNAs could downregulate the expression of CANP1. Suppression of CANP1 significantly reduced cell viability in cell proliferation when compared with control cells. We found a crosstalk between CANP1 and caspase systems, particularly suppression of CANP1 resulted in an increase in the expressions of apoptotic caspases such as caspase-3, caspase-6, caspase-7, caspase-8, and caspase-9, as well as heat-shock protein (HSP) systems. Additionally, suppression of CANP1 led to the upregulation of other apoptosis and DNA damage-regulating genes whilst at the same time downregulating proliferation, migration, and differentiation-regulating genes. The results of our findings report for the first time that suppression of CANP1 resulted in the activation of caspase and HSP systems which might in turn regulate apoptosis through the caspase-dependent cell death pathway. This clearly demonstrates the key roles of CANP1 in regulation of cell proliferation and survival.

The effects of Capn1 gene inactivation on skeletal muscle growth, development, and atrophy, and the compensatory role of other proteolytic systems

Myofibrillar protein turnover is a key component of muscle growth and degeneration, requiring proteolytic enzymes to degrade the skeletal muscle proteins. The objective of this study was to investigate the role of the calpain proteolytic system in muscle growth development using μ-calpain knockout (KO) mice in comparison with control wild-type (WT) mice, and evaluate the subsequent effects of silencing this gene on other proteolytic systems. No differences in muscle development between genotypes were observed during the early stages of growth due to the up regulation of other proteolytic systems. The KO mice showed significantly greater m-calpain protein abundance (P < 0.01) and activity (P < 0.001), and greater caspase 3/7 activity (P < 0.05). At 30 wk of age, KO mice showed increased protein:DNA (P < 0.05) and RNA:DNA ratios (P < 0.01), greater protein content (P < 0.01) at the expense of lipid deposition (P < 0.05), and an increase in size and number of fast-twitch glycolytic muscle fibers (P < 0.05), suggesting that KO mice exhibit an increased capacity to accumulate and maintain protein in their skeletal muscle. Also, expression of proteins associated with muscle regeneration (neural cell adhesion molecule and myoD) were both reduced in the mature KO mice (P < 0.05 and P < 0.01, respectively), indicating less muscle regeneration and, therefore, less muscle damage. These findings indicate the concerted action of proteolytic systems to ensure muscle protein homeostasis in vivo. Furthermore, these data contribute to the existing evidence of the importance of the calpain system's involvement in muscle growth, development, and atrophy. Collectively, these data suggest that there are opportunities to target the calpain system to promote the growth and/or restoration of skeletal muscle mass.

Fibroblast Migration Is Regulated by Myristoylated Alanine-Rich C-Kinase Substrate (MARCKS) Protein

Myristoylated alanine-rich C-kinase substrate (MARCKS) is a ubiquitously expressed substrate of protein kinase C (PKC) that is involved in reorganization of the actin cytoskeleton. We hypothesized that MARCKS is involved in regulation of fibroblast migration and addressed this hypothesis by utilizing a unique reagent developed in this laboratory, the MANS peptide. The MANS peptide is a myristoylated cell permeable peptide corresponding to the first 24-amino acids of MARCKS that inhibits MARCKS function. Treatment of NIH-3T3 fibroblasts with the MANS peptide attenuated cell migration in scratch wounding assays, while a myristoylated, missense control peptide (RNS) had no effect. Neither MANS nor RNS peptide treatment altered NIH-3T3 cell proliferation within the parameters of the scratch assay. MANS peptide treatment also resulted in inhibited NIH-3T3 chemotaxis towards the chemoattractant platelet-derived growth factor-BB (PDGF-BB), with no effect observed with RNS treatment. Live cell imaging of PDGF-BB induced chemotaxis demonstrated that MANS peptide treatment resulted in weak chemotactic fidelity compared to RNS treated cells. MANS and RNS peptides did not affect PDGF-BB induced phosphorylation of MARCKS or phosphoinositide 3-kinase (PI3K) signaling, as measured by Akt phosphorylation. Further, no difference in cell migration was observed in NIH-3T3 fibroblasts that were transfected with MARCKS siRNAs with or without MANS peptide treatment. Genetic structure-function analysis revealed that MANS peptide-mediated attenuation of NIH-3T3 cell migration does not require the presence of the myristic acid moiety on the amino-terminus. Expression of either MANS or unmyristoylated MANS (UMANS) C-terminal EGFP fusion proteins resulted in similar levels of attenuated cell migration as observed with MANS peptide treatment. These data demonstrate that MARCKS regulates cell migration and suggests that MARCKS-mediated regulation of fibroblast migration involves the MARCKS amino-terminus. Further, this data demonstrates that MANS peptide treatment inhibits MARCKS function during fibroblast migration and that MANS mediated inhibition occurs independent of myristoylation.

ELF-MF transiently increases skeletal myoblast migration: possible role of calpain system

PURPOSE

Cell migration is crucial for myogenesis since it is required for the alignment and fusion of myoblast. Ca(2+) signals are involved in regulating myoblast migration and an extremely low frequency (ELF) magnetic field (MF) increases intracellular calcium levels in C2C12 myoblast. This study was aimed at investigating whether ELF-MF could affect myoblast migration. As calpains contribute to the regulation of myoblast motility, the effect of ELF-MF on μ- and m-calpain was also investigated.

MATERIALS AND METHODS

The effect of ELF-MF (1 mT; 50 Hz) on C2C12 cell motility was observed by wound-healing assay. Protein expression of calpains, calpastatin, myristoylated alanine-rich C-kinase substrate (MARCKS) and vinculin were examined by Western blot analysis. Casein zymography and immunofluorescence analysis were carried out to evaluate, respectively, activity levels of calpains and intracellular distribution of calpains, calpastatin and actin.

RESULTS

Exposure to ELF-MF resulted in a transient but significant increase of myoblast migration. This stimulatory effect was associated with a marked increase of μ- and m-calpain activity followed by the concomitant variation in their subcellular localization. No significant changes in intracellular distribution and protein levels of calpastatin were detected. Finally, a significant decrease of MARCKS expression and modifications of actin dynamics were reported.

CONCLUSIONS

This study clearly outlines an involvement of calpains in ELF-MF-mediated myoblast migration.

Prognostic significance of Capn4 overexpression in intrahepatic cholangiocarcinoma

BACKGROUND

Calpain small subunit 1 (Capn4) has been shown to correlate with the metastasis/invasion of hepatocellular carcinoma. This study aimed to investigate the role of Capn4 in intrahepatic cholangiocarcinoma (ICC).

METHODS

Capn4 expression was measured in 33 ICC tissues by quantitative real-time polymerase chain reaction and western blot. The role of Capn4 in the migration, invasion and proliferation of ICC cells and matrix metalloproteinase 2 (MMP2) expression were assessed after Capn4 depletion by specific small interfering RNA. Capn4 expression was further examined by immunohistochemistry in a tissue microarray consisting of 140 ICC patients and 13 normal liver tissues, and the prognostic role of Capn4 in ICC was evaluated by Kaplan-Meier and Cox regression analyses.

RESULTS

Capn4 expression was significantly higher in the ICC tissues compared to the peritumor tissues. Capn4 down-regulation impaired the migration/invasion ability of HCCC-9810 and QBC939 cells in vitro and decreased MMP2 expression. Capn4 overexpression significantly correlated with the presence of lymphatic metastasis of ICC (p = 0.026) and the tumor-node-metastasis (TNM) stage (p = 0.009). The postoperative 2- and 5-year overall survivals in patients with Capn4(low) were higher than those in the Capn4(high) group. The cumulative recurrence rate in patients with Capn4(low) was much lower than in the Capn4(high) group. Multivariate analysis showed that Capn4 overexpression was an independent prognostic marker in ICC.

CONCLUSIONS

Capn4 overexpression was implicated in ICC metastasis/invasion, and Capn4 overexpression may be used as a molecular therapeutic target for ICC.

Calpain and MARCKS protein regulation of airway mucin secretion

Hypersecretion of mucin plays an important role in the pathophysiology of many inflammatory airway diseases, including asthma, chronic bronchitis, and cystic fibrosis. Myristoylated alanine-rich C-kinase substrate (MARCKS) protein has been shown to play an important role in regulation of airway mucin secretion, as peptides analogous to the amino (N)-terminus of MARCKS attenuate mucin secretion by airway epithelium in vitro and in vivo. Here, we investigated a potential role for the protease Calpain, a calcium-dependent cysteine protease that can cleave MARCKS, in the MARCKS-related secretory mechanism. We theorized that Calpain might cleave MARCKS near the N-terminus, thereby attenuating the ability of MARCKS to bind to membranes and/or creating a small N-terminal peptide that could act as a competitive intracellular inhibitor to remaining endogenous full-length MARCKS molecules. Primary normal human bronchial epithelial (NHBE) cells and the virally-transformed human bronchial epithelial HBE1 cell line were exposed to phorbol-12-myristate-13-acetate (PMA) to stimulate the Protein Kinase C (PKC) pathway, leading to enhanced mucin secretion, and Calpain activity within the cells was measured with a fluorescent cleavage assay. Calpain activity was increased by PMA, and pretreatment of the cells with Calpain inhibitors reduced both Calpain activity and mucin secretion in a concentration-dependent manner. Thus, as opposed to the original hypothesis, inactivating Calpain caused a decrease rather than an increase in secretion. HBE1 cells transfected with DNA constructs encoding a MARCKS-YFP fusion protein showed cleavage at a putative site near the N-terminus in response to PMA. Cleavage of MARCKS by Calpain may have an important role in regulation of the PKC/MARCKS pathway regulating airway mucin secretion.

Effects of lysophosphatidic acid on calpain-mediated proteolysis of focal adhesion kinase in human prostate cancer cells

BACKGROUND

Calcium-mediated proteolysis plays an important role in cell migration. Lysophosphatidic acid (LPA), a lipid mediator present in serum, enhances migration of carcinoma cells. The effects of LPA on calpain-mediated proteolysis were, therefore, examined in PC-3, a human prostate cancer cell line.

METHODS

Cultured PC-3 cells were used in studies utilizing pharmacologic interventions, immunoblotting, and confocal immunolocalization.

RESULTS

Focal adhesion kinase (FAK), a tyrosine kinase involved in cell adhesion, is rapidly proteolyzed in serum-starved PC-3 cells exposed to the calcium ionophore, ionomycin; Nck, p130CAS, PKCα, and Ras-GAP are also degraded. Thapsigargin, which causes more moderate increases in intracellular calcium, induces partial proteolysis of these proteins. Calpain inhibitors block the proteolytic responses to ionomycin and thapsigargin. Ionomycin does not induce proteolysis in cells maintained in serum, suggesting a protective role for growth factors contained in serum. LPA causes minor FAK proteolysis when added alone, but protects against ionomycin-induced proteolysis in a time-dependent manner. LPA also protects against the cell detachment that eventually follows ionomycin treatment. The response to LPA is blocked by an LPA receptor antagonist. A similar effect of LPA is observed in ionomycin-treated Rat-1 fibroblasts. In PC-3 cells, the protective effects of LPA and serum are correlated with phosphorylation and redistribution of paxillin, suggesting roles for phosphorylation-mediated protein-protein interactions.

CONCLUSIONS

The complex effects of LPA on calpain-mediated proteolysis of FAK and other adhesion proteins are likely to play a role in the ability of LPA to promote attachment, migration, and survival of prostate cancer cells.

N-terminal cleavage fragment of focal adhesion kinase is required to activate the survival signalling pathway in cultured myoblasts under oxidative stress

We have previously shown that the cultured L6 myoblasts are susceptible to menadione-induced oxidative stress. Damaged cells were detached from the culture dishes. In the present study, we focused on focal adhesion kinase (FAK), which plays pivotal roles in maintaining focal adhesion function and cell survival. FAK, normally localized at the focal adhesion regions of the myoblasts, was not observed at the regions under oxidative stress induced by menadione and H(2) O(2) . Two cleavage products, 80-kDa N-terminal FAK and 35-kDa C-terminal FAK fragments, as well as full-length FAK (125 kDa) were detected in myoblasts cultured under normal conditions by western blotting with anti-N-terminal FAK or anti-C-terminal FAK sera. Of interest was the finding that the cleavage products of FAK (but not full-length FAK) disappeared under oxidative stress. The cleavage of full-length FAK to N-terminal FAK and C-terminal FAK was inhibited by calpeptin, a specific calpain inhibitor. In addition, pre-incubation of cells with calpeptin resulted in a sharp decrease in survival signals, such as Akt phosphorylation and the ratio of Bcl-2/Bax, under stress conditions. By contrast, not only relative viability, but also Akt phosphorylation and the ratio of Bcl-2/Bax was significantly improved when cells were transfected with a DNA construct of N-terminal FAK-Myc. These results suggest that the N-terminal FAK positively regulates survival signalling in early phases of oxidative stress in the cultured myoblasts.

Proteomic study of calpeptin-induced differentiation on calpain-interacting proteins of C2C12 myoblast

Studies on skeletal muscle cell specification and development have demonstrated in the past that calpains interact with various transcriptional factors in regulating the cellular function. It has therefore, been assumed that transcriptional factors like myogenin, MyoD, Myf5, and MRF4 that are active during the myogenic differentiation might be affected and degraded by calpains. Therefore, to examine the biochemical adaptations of myoblasts during myocyte formation and muscle development comprehensively, the current study was designed to identify the effect of calpeptin (calpain inhibitors) on protein expression during differentiation of C2C12 mouse myoblast. Cells were proliferated to near 80% confluence under Dulbecco's modified eagle medium and differentiated further in 2% HS with 50 μM calpeptin. Incubated cells were collected at 0, 12, and 72 h and later the cell proteins were focused onto pH 4-7 IEF strip, followed by 12.5% SDS-PAGE. Obtained spots on the gels were compared and matched using commercial 2-DE analysis software and matched spots were identified by MALDI-ToF and/or Q-Tof systems. Conclusively, cell differentiation was observed to be active from 12 to 72 h however, calpeptin affected the differentiation process and cut down the rate of fusion by approximately 50%. Out of 41 proteins identified, 12 proteins were found to be upregulated where as 29 proteins were downregulated.

Two myristoylated alanine-rich C-kinase substrate (MARCKS) paralogs are required for normal development in zebrafish

Myristoylated alanine-rich C-kinase substrate (MARCKS) is an actin binding protein substrate of protein kinase C (PKC) and critical for mouse and Xenopus development. Herein two MARCKS paralogs, marcksa and marcksb, are identified in zebrafish and the role of these genes in zebrafish development is evaluated. Morpholino-based targeting of either MARCKS protein resulted in increased mortality and a range of gross phenotypic abnormalities. Phenotypic abnormalities were classified as mild, moderate or severe, which is characterized by a slight curve of a full-length tail, a severe curve or twist of a full-length tail and a truncated tail, respectively. All three phenotypes displayed abnormal neural architecture. Histopathology of Marcks targeted embryos revealed abnormalities in retinal layering, gill formation and skeletal muscle morphology. These results demonstrate that Marcksa and Marcksb are required for normal zebrafish development and suggest that zebrafish are a suitable model to further study MARCKS function.

Toxoplasma gondii down modulates cadherin expression in skeletal muscle cells inhibiting myogenesis

Background

Toxoplasma gondii belongs to a large and diverse group of obligate intracellular parasitic protozoa. Primary culture of mice skeletal muscle cells (SkMC) was employed as a model for experimental toxoplasmosis studies. The myogenesis of SkMC was reproduced in vitro and the ability of T. gondii tachyzoite forms to infect myoblasts and myotubes and its influence on SkMC myogenesis were analyzed.

Results

In this study we show that, after 24 h of interaction, myoblasts (61%) were more infected with T. gondii than myotubes (38%) and inhibition of myogenesis was about 75%. The role of adhesion molecules such as cadherin in this event was investigated. First, we demonstrate that cadherin localization was restricted to the contact areas between myocytes/myocytes and myocytes/myotubes during the myogenesis process. Immunofluorescence and immunoblotting analysis of parasite-host cell interaction showed a 54% reduction in cadherin expression at 24 h of infection. Concomitantly, a reduction in M-cadherin mRNA levels was observed after 3 and 24 h of T. gondii-host cell interaction.

Conclusions

These data suggest that T. gondii is able to down regulate M-cadherin expression, leading to molecular modifications in the host cell surface that interfere with membrane fusion and consequently affect the myogenesis process.

Adult skeletal muscle stem cell migration is mediated by a blebbing/amoeboid mechanism

Adult skeletal muscle possesses a resident stem cell population called satellite cells, which are responsible for tissue repair following damage. Satellite cell migration is crucial in promoting rapid tissue regeneration, but it is a poorly understood process. Furthermore, the mechanisms facilitating satellite cell movement have yet to be elucidated. This study investigates the process of satellite cell migration, revealing that they undergo two distinct phases of movement, first under the basal lamina and then rapidly increasing their velocity when on the myofiber surface. Most significantly, we show that satellite cells move using a highly dynamic blebbing or amoeboid-based mechanism and not via lamellipodia-mediated propulsion. We show that nitric oxide and noncanonical Wnt signaling pathways are necessary for regulating the formation of blebs and the migration of satellite cells. In summary, we propose that the formation of blebs and their necessity for satellite cell migration has significant implications in the future development of therapeutic regimes aimed at promoting skeletal muscle regeneration.

Calpains as potential anti-cancer targets

INTRODUCTION

The intracellular signaling cysteine proteases, calpains (specifically the ubiquitous calpains 1 and 2), are involved in numerous physiological and pathological phenomena. Several works have highlighted the implication of calpains in processes crucial for cancer development and progression. For these reasons, calpains are considered by several authors as potential anti-cancer targets.

AREAS COVERED

How calpains are implicated in cancer formation and development, how these enzymes are deregulated in cancer cells and how these proteases could be targeted by anti-cancer drugs. Studies published in the last 10 years are focused on.

EXPERT OPINION

Targeting calpain activity with specific inhibitors could be a novel approach to limiting development of primary tumors and formation of metastases, by inhibiting tumor cell migration and invasion, which allows dissemination as well as tumor neovascularization, which in turn allows expansion. However, such drugs could interfere with anti-cancer treatments, as ubiquitous calpains play crucial roles in chemotherapy-induced apoptosis. For these reasons, drugs targeting calpains would have to be used selectively to avoid interference with other treatments and physiological processes. Further studies will be required concerning the other members of the calpain family and their potential implication in cancer development before considering treatments targeting their activity.

Post-translational control of Myc function during differentiation

Myc proteins are deeply involved in multiple biological processes including cell proliferation, growth, metabolism, apoptosis, differentiation, and tumorigenesis. Paradoxically, Myc proteins have been found to be capable of both inhibiting and facilitating differentiation depending on the biological context. Recently we identified a new mode of Myc regulation in differentiating muscle cells in which c-Myc protein is proteolytically cleaved by calcium-dependent calpains in the cytoplasm. This cleavage serves two purposes. First, it inactivates the transcriptional function of Myc by removing its C-terminus, a region responsible for the interaction of Myc with Max and DNA. Second, it alters cytoskeletal architecture and accelerates muscle differentiation through the activity of the remaining N-terminal cleavage product (termed Myc-nick). Here we discuss the roles and regulation of full-length Myc and Myc-nick in terminal differentiation and propose a model in which calpain-mediated cleavage of Myc operates as a functional switch.

Association between molecular markers for beef tenderness and growth traits in Argentinian angus cattle

Molecular markers for beef tenderness are classic examples of the contribution of genome technology to animal breeding through marker-assisted selection (MAS). Markers on the μ-calpain (CAPN1) and calpastatin (CAST) genes have been extensively evaluated for their association with tenderness. However, little is known about their potential effect on other economically important traits. In this work, the association of molecular markers for beef tenderness with growth traits was evaluated in Angus cattle of Argentina. Expected progeny differences were extracted from the 2008 Angus Sire Summary of Argentina. Information corresponding to 268 influential bulls that had been genotyped for two markers in CAPN1 and two markers in CAST was provided by the Argentine Angus Association. Genotype probabilities were assigned, by segregation analysis, to those bulls in the Sire Summary that had no marker information. Expected progeny differences of 1365 sires were regressed on the number of alleles favouring tenderness at each locus. There was a significant effect of markers on expected progeny differences of birth weight, weaning weight (direct), weight at 18 months and rib eye area. In general, there was a negative effect of alleles favouring tenderness on growth traits. These correlated responses should be taken into account when molecular markers are used in selection schemes that aim to improve beef tenderness.

Microcontact printing of fibronectin on a biodegradable polymeric surface for skeletal muscle cell orientation

BACKGROUND AND OBJECTIVES

Micropatterning and microfabrication techniques have been widely used to control cell adhesion and proliferation along a preferential direction according to contact guidance theory. One of these techniques is microcontact printing, a soft lithographic technique based on the transfer of a "molecular ink" from an elastomeric stamp to a surface. This method allows the useful attachment of biomolecules in a few seconds on a variety of surfaces with sub-micrometer resolution and control, without modifying the biomolecule properties. The aim of this study is to develop an easy and versatile technique for in vitro production of arrays of skeletal muscle myofibers using microcontact printing technique on biodegradable substrata.

METHODS

Microcontact printing of fibronectin stripes (10, 25, 50 μm in width) was performed onto biodegradable L-lactide/trimethylene carbonate copolymer (PLLA-TMC) films. C2C12, a murine myoblast cell line, was used for the production of parallel myofibers.

RESULTS

This approach proved to be simple, reliable and effective in obtaining a stable pattern of fibronectin on the PLLA-TMC surface as observed by fluorescence microscopy. C2C12 cells were well aligned along the pattern 24 hours after seeding, especially on fibronectin stripes 10 and 25 μm in width. Seven days after confluence cells fused and formed aligned multinucleated cells expressing a-actinin.

CONCLUSIONS

Fibronectin patterning seems to be a useful method to induce cell alignment and to improve myotube formation. Further studies will be focused on the possibility of applying external stimuli to these structures to obtain healthy myotubes and to induce myofiber development.

Identification of subtilase cytotoxin (SubAB) receptors whose signaling, in association with SubAB-induced BiP cleavage, is responsible for apoptosis in HeLa cells

Subtilase cytotoxin (SubAB), which is produced by certain strains of Shiga-toxigenic Escherichia coli (STEC), causes the 78-kDa glucose-regulated protein (GRP78/BiP) cleavage, followed by induction of endoplasmic reticulum (ER) stress, leading to caspase-dependent apoptosis via mitochondrial membrane damage by Bax/Bak activation. The purpose of the present study was to identify SubAB receptors responsible for HeLa cell death. Four proteins, NG2, α2β1 integrin (ITG), L1 cell adhesion molecule (L1CAM), and hepatocyte growth factor receptor (Met), were identified to be SubAB-binding proteins by immunoprecipitation and purification, followed by liquid chromatography-tandem mass spectrometry analysis. SubAB-induced Bax conformational change, Bax/Bak complex formation, caspase activation, and cell death were decreased in β1 ITG, NG2, and L1CAM small interfering RNA-transfected cells, but unexpectedly, BiP cleavage was still observed. Pretreatment of cells with a function-blocking β1 ITG antibody (monoclonal antibody [MAb] P5D2) enhanced SubAB-induced caspase activation; MAb P5D2 alone had no effect on caspase activation. Furthermore, we found that SubAB induced focal adhesion kinase fragmentation, which was mediated by a proteasome-dependent pathway, and caspase activation was suppressed in the presence of proteasome inhibitor. Thus, β1 ITG serves as a SubAB-binding protein and may interact with SubAB-signaling pathways, leading to cell death. Our results raise the possibility that although BiP cleavage is necessary for SubAB-induced apoptotic cell death, signaling pathways associated with functional SubAB receptors may be required for activation of SubAB-dependent apoptotic pathways.

Myc-nick: a cytoplasmic cleavage product of Myc that promotes alpha-tubulin acetylation and cell differentiation

The Myc oncoprotein family comprises transcription factors that control multiple cellular functions and are widely involved in oncogenesis. Here we report the identification of Myc-nick, a cytoplasmic form of Myc generated by calpain-dependent proteolysis at lysine 298 of full-length Myc. Myc-nick retains conserved Myc box regions but lacks nuclear localization signals and the bHLHZ domain essential for heterodimerization with Max and DNA binding. Myc-nick induces alpha-tubulin acetylation and altered cell morphology by recruiting histone acetyltransferase GCN5 to microtubules. During muscle differentiation, while the levels of full-length Myc diminish, Myc-nick and acetylated alpha-tubulin levels are increased. Ectopic expression of Myc-nick accelerates myoblast fusion, triggers the expression of myogenic markers, and permits Myc-deficient fibroblasts to transdifferentiate in response to MyoD. We propose that the cleavage of Myc by calpain abrogates the transcriptional inhibition of differentiation by full-length Myc and generates Myc-nick, a driver of cytoplasmic reorganization and differentiation.

Regulation of adhesion dynamics by calpain-mediated proteolysis of focal adhesion kinase (FAK)

The coordinated and dynamic regulation of adhesions is required for cell migration. We demonstrated previously that limited proteolysis of talin1 by the calcium-dependent protease calpain 2 plays a critical role in adhesion disassembly in fibroblasts (Franco, S. J., Rodgers, M. A., Perrin, B. J., Han, J., Bennin, D. A., Critchley, D. R., and Huttenlocher, A. (2004) Nat. Cell Biol. 6, 977-983). However, little is known about the contribution of other calpain substrates to the regulation of adhesion dynamics. We now provide evidence that calpain 2-mediated proteolysis of focal adhesion kinase (FAK) regulates adhesion dynamics in motile cells. We mapped the preferred calpain cleavage site between the two C-terminal proline-rich regions after Ser-745, resulting in a C-terminal fragment similar in size to the FAK-related non-kinase (FRNK). We generated mutant FAK with a point mutation (V744G) that renders FAK resistant to calpain proteolysis but retains other biochemical properties of FAK. Using time-lapse microscopy, we show that the dynamics of green fluorescent protein-talin1 are impaired in FAK-deficient cells. Expression of wild-type but not calpain-resistant FAK rescues talin dynamics in FAK-deficient cells. Taken together, our findings suggest a novel role for calpain proteolysis of FAK in regulating adhesion dynamics in motile cells.

Calpain inhibitor SNJ-1945 attenuates events prior to angiogenesis in cultured human retinal endothelial cells

PURPOSE

Vascular endothelial growth factor (VEGF) is an important regulator of angiogenesis and microvascular permeability. VEGF-induced cytoskeletal reorganization plays a crucial role in angiogenesis. Cytoskeletal organization in endothelial cells is regulated by calpain proteases (EC 3.4.22.17). Calpains are a family of 14 calcium-regulated, intracellular cysteine proteases, which modulate cellular functions by limited, specific proteolysis. Calpain 1 (mu-calpain) and calpain 2 (m-calpain) are the 2 major typical calpain isoforms and are responsible for most calpain activity in endothelial cells. The purpose of the present study was to determine if an orally available form of calpain inhibitor, SNJ-1945, prevented angiogenesis induced by VEGF in cultured retinal endothelial cells.

METHODS

Human retinal microvascular endothelial cells (HRMEC) were incubated with VEGF (60-100 ng/mL) for 24 h. Calcium uptake was measured with Fluo8. Total calpain activity was measured using fluorescent-labeled casein substrate, and separate activities for calpains 1 and 2 were assessed by casein zymography. Proteolysis of endogenous calpain substrate alpha-spectrin in situ was analyzed by immunoblotting. Angiogenesis in vitro was evaluated by measuring cell migration and tube formation into Matrigel.

RESULTS

Incubation of HRMEC with VEGF resulted in calcium uptake, increased activity of mainly calpain 2, and increased calpain proteolysis of alpha-spectrin. Treatment of endothelial cells with calpain inhibitor SNJ-1945 reversed VEGF-mediated tube formation and cell motility.

CONCLUSIONS

Inhibition of angiogenesis by specific calpain inhibitor in the presence of VEGF supported our hypothesis that calpains may be involved in VEGF-mediated angiogenesis in retinal endothelial cells. Therefore, manipulating calpain activity by calpain inhibitor SNJ-1945 might provide a promising therapy for management of pathological angiogenesis, such as that occurring in proliferative retinopathy and age-related macular degeneration with neovascularization.

Synergic stimulation of laminin and epidermal growth factor facilitates the myoblast growth through promoting migration

The dynamic behaviors of human skeletal muscle myoblasts were investigated in the culture on a laminin-coated surface in the presence of 100 ng/ml epidermal growth factor (EGF) in medium. The coexistence of laminin and EGF caused the enhancement of myoblast migration, giving an average migration rate of 62.0 microm/h, which was 2.7 times that on a plain surface. This encouraged migration could be a driving force to separate the dividing cells from each other, accompanied by shortened disjunction time of daughter cells to complete cytokinesis. In addition, the synergic effect of laminin and EGF led to the promotion of myoblast growth with keeping a relatively high fraction of proliferative cells during the culture for 150 h, which is considered to arise from the reduced frequency of cell-cell contacts during cytokinesis and thereby suppressing the process towards myotube formation after cell division.

Up-regulation of calcium-dependent proteolysis in human myoblasts under acute oxidative stress

The reduced regenerative potential of muscle fibres, most likely due to a decreased number and/or function of satellite cells, could play a significant role in the progression of muscle ageing. Accumulation of reactive oxygen species has been clearly correlated to sarcopenia and could contribute to the impairment of satellite cell function. In this work we have investigated the effect of oxidative stress generated by hydrogen peroxide in cultured human skeletal muscle satellite cells. We specifically focused on the activity and regulation of calpains. These calcium-dependent proteases are known to regulate many transduction pathways including apoptosis and play a critical role in satellite cell function. In our experimental conditions, which induce an increase in calcium concentration, protein oxidation and apoptotic cell death, a significant up-regulation of calpain expression and activity were observed and ATP synthase, a major component of the respiratory chain, was identified as a calpain target. Interestingly we were able to protect the cells from these H(2)O(2)-induced effects and prevent calpain up-regulation with a natural antioxidant extracted from pine bark (Oligopin). These data strongly suggest that oxidative stress could impair satellite cell functionality via calpain-dependent pathways and that an antioxidant such as Oligopin could prevent apoptosis and calpain activation.

Microtubule plus-end binding protein EB1 is necessary for muscle cell differentiation, elongation and fusion

During muscle differentiation, microtubule stability, nucleation and orientation all undergo profound changes, which are simultaneous with and possibly necessary for the elongation and fusion of muscle cells. We do not yet understand these events, but they present similarities with the polarized migration of fibroblasts, in which EB1 is necessary for microtubule stabilization. However, it was recently reported that EB3, not EB1, is involved in muscle cell elongation and fusion, and that neither of these two proteins influences microtubule stabilization. To re-examine the role of EB1, we have generated C2 cell lines permanently expressing EB1-targeted shRNAs. In these lines, EB1 is specifically knocked down by more than 90% before any differentiation-related changes can take place. We find that differentiation (assessed by myogenin expression), elongation and fusion are prevented. In addition, two early events that normally precede differentiation - microtubule stabilization and the accumulation of cadherin and beta-catenin on the plasma membrane - are inhibited. Re-expression of EB1 as EB1-GFP restores all aspects of normal differentiation, whereas overexpression of EB3-GFP restores elongation but not fusion. We conclude that EB1 is necessary for the early stages of muscle differentiation.

The E3 ubiquitin ligase specificity subunit ASB2beta is a novel regulator of muscle differentiation that targets filamin B to proteasomal degradation

Ubiquitin-mediated protein degradation is the main mechanism for controlled proteolysis, which is crucial for muscle development and maintenance. The ankyrin repeat-containing protein with a suppressor of cytokine signaling box 2 gene (ASB2) encodes the specificity subunit of an E3 ubiquitin ligase complex involved in differentiation of hematopoietic cells. Here, we provide the first evidence that a novel ASB2 isoform, ASB2beta, is important for muscle differentiation. ASB2beta is expressed in muscle cells during embryogenesis and in adult tissues. ASB2beta is part of an active E3 ubiquitin ligase complex and targets the actin-binding protein filamin B (FLNb) for proteasomal degradation. Thus, ASB2beta regulates FLNb functions by controlling its degradation. Knockdown of endogenous ASB2beta by shRNAs during induced differentiation of C2C12 cells delayed FLNb degradation as well as myoblast fusion and expression of muscle contractile proteins. Finally, knockdown of FLNb in ASB2beta knockdown cells restores myogenic differentiation. Altogether, our results suggest that ASB2beta is involved in muscle differentiation through the targeting of FLNb to destruction by the proteasome.

Calcium and cyclic nucleotides affect TNF-alpha-induced stem cell migration

The purpose of this study was to study the effect of calcium, cyclic AMP (cAMP) and cyclic GMP (cGMP) on embryonic stem cell (ESC) motility during TNF-alpha-induced chemotaxis. ESCs were monitored using a chemotaxis chamber, with different concentrations of calcium or cAMP or cGMP added to the medium. Changes in intracellular calcium ([Ca(2+)](i)) were measured with the fluorescent dye fura-2/AM. We combined migratory parameters in a mathematical model and described it as "mobility". After adding calcium, a dose-dependant increase in cell speed was found. Cyclic AMP increased mobility as well as the [Ca(2+)](i). In contrast, adding dbcGMP resulted in a significant decrease in the mobility of the ESCs. During migration ESCs showed an increase in [Ca(2+)](i). Furthermore, TNF-alpha dramatically increased the movement as well as the directionality of ESCs. These results demonstrate that ESCs are highly motile and respond to different concentrations of calcium in a dose-related manner.

TRPC1 regulates skeletal myoblast migration and differentiation

Myoblast migration is a key step in myogenesis and regeneration. It allows myoblast alignment and their fusion into myotubes. The process has been shown to involve m-calpain or mu-calpain, two Ca(2+)-dependent cysteine proteases. Here we measure calpain activity in cultured cells and show a peak of activity at the beginning of the differentiation process. We also observed a concomitant and transient increase of the influx of Ca(2+) and expression of TRPC1 protein. Calpains are specifically activated by a store-operated entry of Ca(2+) in adult skeletal muscle fibres. We therefore repressed the expression of TRPC1 in myoblasts and studied the effects on Ca(2+) fluxes and on differentiation. TRPC1-depleted myoblasts presented a largely reduced store-operated entry of Ca(2+) and a significantly diminished transient influx of Ca(2+) at the beginning of differentiation. The concomitant peak of calpain activity was abolished. TRPC1-knockdown myoblasts also accumulated myristoylated alanine-rich C-kinase substrate (MARCKS), an actin-binding protein and substrate of calpain. Their fusion into myotubes was significantly slowed down as a result of the reduced speed of cell migration. Accordingly, migration of control myoblasts was inhibited by 2-5 microM GsMTx4 toxin, an inhibitor of TRP channels or by 50 microM Z-Leu-Leu, an inhibitor of calpain. By contrast, stimulation of control myoblasts with IGF-1 increased the basal influx of Ca(2+), activated calpain and accelerated migration. These effects were not observed in TRPC1-knockdown cells. We therefore suggest that entry of Ca(2+) through TRPC1 channels induces a transient activation of calpain and subsequent proteolysis of MARCKS, which allows in turn, myoblast migration and fusion.