DAP kinase mediates the phosphorylation of tropomyosin-1 downstream of the ERK pathway, which regulates the formation of stress fibers in response to oxidative stress

ALPK2 prevents cardiac diastolic dysfunction in heart failure with preserved ejection fraction

Protein phosphorylation, controlled by protein kinases, is central to regulating various pathophysiological processes, including cardiac systolic function. The dysregulation of protein kinase activity plays a significant role in the pathogenesis of cardiac systolic dysfunction. While cardiac contraction mechanisms are well documented, the mechanisms underlying cardiac diastole remain elusive. This gap persists owing to the historical focus on systolic dysfunction in heart failure research. Recently, heart failure with preserved ejection fraction (HFpEF), an age-related disease characterized by cardiac diastolic dysfunction, has emerged as a major public health concern. However, its underlying mechanism remains unclear. In this study, we investigated cardiac protein kinases by analyzing the gene expression of 518 protein kinases in human tissues. We identified alpha-kinase 2 (ALPK2) as a novel cardiac-specific atypical kinase and generated tamoxifen-inducible, cardiomyocyte-specific Alpk2-knockout mice and Alpk2-overexpressing mice. Alpk2 deficiency did not affect cardiac systolic dysfunction in the myocardial infarction model or the pressure-overload-induced heart failure model. Notably, cardiomyocyte-specific Alpk2 deficiency exacerbated cardiac diastolic dysfunction induced by aging and in the HFpEF model. Conversely, Alpk2 overexpression increased the phosphorylation of tropomyosin 1, a major regulator that binds myosin to actin, and mitigated cardiac stiffness in HFpEF. This study provides novel evidence that ALPK2 represents a potential therapeutic target for cardiac diastolic dysfunction in HFpEF and age-related cardiac impairments.

Comparative proteomic and phosphoproteomic analysis reveals differential heat response mechanism in two congeneric oyster species

High-temperature stress caused by global climate change poses a significant threat to marine ectotherms. This study investigated the role of protein phosphorylation modifications in the molecular regulation network under heat stress in oysters, which are representative intertidal organisms that experience considerable temperature changes. Firstly, the study compared the extent of thermal damage between two congeneric oyster species, the relative heat-tolerant Crassostrea angulata (C. angulata) and heat-sensitive Crassostrea gigas (C. gigas), under sublethal temperature (37 °C) for 12 h, using various physiological and biochemical methods. Subsequently, the comparative proteomic and phosphoproteomic analyses revealed that high-temperature considerably regulated signal transduction, energy metabolism, protein synthesis, cell survival and apoptosis, and cytoskeleton remodeling through phosphorylation modifications of related receptors and kinases. Furthermore, the protein kinase A, mitogen-activated protein kinase 1, tyrosine-protein kinase Src, and serine/threonine kinase AKT, exhibiting differential phosphorylation modification patterns, were identified as hub regulators that may enhance glycolysis and TCA cycle to increase the energy supply, distribute protein synthesis, inhibit Caspase-dependent apoptosis activated by endogenous mitochondrial cytochrome release and maintain cytoskeletal stability, ultimately shaping the higher thermal resistance of C. angulata. This study represents the first investigation of protein phosphorylation dynamics in marine invertebrates under heat stress, reveals the molecular mechanisms underlying the differential thermal responses between two Crassostrea oysters at the phosphorylation level, and provides new insights into understanding phosphorylation-mediated molecular responses in marine organisms during environmental changes and predicting the adaptive potential in the context of global warming.

Tumor Suppressor DAPK1 Catalyzes Adhesion Assembly on Rigid but Anoikis on Soft Matrices

Cancer cells normally grow on soft surfaces due to impaired mechanosensing of the extracellular matrix rigidity. Upon restoration of proper mechanosensing, cancer cells undergo apoptosis on soft surfaces (anoikis) like most normal cells. However, the link between mechanosensing and activation of anoikis is not clear. Here we show that death associated protein kinase 1 (DAPK1), a tumor suppressor that activates cell death, is directly linked to anoikis activation through rigidity sensing. We find that when rigidity sensing is decreased through inhibition of DAPK1 activity, cells are transformed for growth on soft matrices. Further, DAPK1 catalyzes matrix adhesion assembly and is part of adhesions on rigid surfaces. This pathway involves DAPK1 phosphorylation of tropomyosin1.1, the talin1 head domain, and tyrosine phosphorylation of DAPK1 by Src. On soft surfaces, DAPK1 rapidly dissociates from the adhesion complexes and activates apoptosis as catalyzed by PTPN12 activity and talin1 head. Thus, DAPK1 is important for adhesion assembly on rigid surfaces and the activation of anoikis on soft surfaces through its binding to rigidity-sensing modules.

Investigations on the Wound Healing Potential of Tilapia Piscidin (TP)2-5 and TP2-6

Wound healing is a highly orchestrated process involving many cell types, such as keratinocytes, fibroblasts and endothelial cells. This study aimed to evaluate the potential application of synthetic peptides derived from tilapia piscidin (TP)2, TP2-5 and TP2-6 in skin wound healing. The treatment of HaCaT keratinocytes with TP2-5 and TP2-6 did not cause cytotoxicity, but did enhance cell proliferation and migration, which could be attributed to the activation of epidermal growth factor receptor signaling. In CCD-966SK fibroblasts, although TP2-5 (31.25 μg/mL) and TP2-6 (125 μg/mL) showed cytotoxic effects, we observed the significant promotion of cell proliferation and migration at low concentrations. In addition, collagen I, collagen III, and keratinocyte growth factor were upregulated by the peptides. We further found that TP2-5 and TP2-6 showed pro-angiogenic properties, including the enhancement of human umbilical vein endothelial cell (HUVEC) migration and the promotion of neovascularization. In a murine model, wounds treated topically with TP2-5 and TP2-6 were reduced by day 2 post-injury and healed significantly faster than untreated wounds. Taken together, these findings demonstrate that both TP2-5 and TP2-6 have multifaceted effects when used as topical agents for accelerating wound healing.

A structurally conserved RNA element within SARS-CoV-2 ORF1a RNA and S mRNA regulates translation in response to viral S protein-induced signaling in human lung cells

The positive-sense, single-stranded RNA genome SARS-CoV-2 harbors functionally important cis-acting elements governing critical aspects of viral gene expression. However, insights on how these elements sense various signals from the host cell and regulate viral protein synthesis are lacking. Here, we identified two novel cis-regulatory elements in SARS-CoV-2 ORF1a and S RNAs and describe their role in translational control of SARS-CoV-2. These elements are sequence-unrelated but form conserved hairpin structures (validated by NMR) resembling Gamma Activated Inhibitor of Translation (GAIT) elements that are found in a cohort of human mRNAs directing translational suppression in myeloid cells in response to IFN-γ. Our studies show that treatment of human lung cells with receptor-binding S1 subunit, S protein pseudotyped lentivirus, and S protein-containing virus-like particles triggers a signaling pathway involving DAP-kinase1 that leads to phosphorylation and release of the ribosomal protein L13a from the large ribosomal subunit. Released L13a forms a Virus Activated Inhibitor of Translation (VAIT) complex that binds to ORF1a and S VAIT elements, causing translational silencing. Translational silencing requires extracellular S protein (and its interaction with host ACE2 receptor), but not its intracellular synthesis. RNA-protein interaction analyses and in vitro translation experiments showed that GAIT and VAIT elements do not compete with each other, highlighting differences between the two pathways. Sequence alignments of SARS-CoV-2 genomes showed a high level of conservation of VAIT elements, suggesting their functional importance. This VAIT-mediated translational control mechanism of SARS-CoV-2 may provide novel targets for small molecule intervention and/or facilitate development of more effective mRNA vaccines. Importance Specific RNA elements in the genomes of RNA viruses play important roles in host-virus interaction. For SARS-CoV-2, the mechanistic insights on how these RNA elements could sense the signals from the host cell are lacking. Here we report a novel relationship between the GAIT-like SARS-CoV-2 RNA element (called VAITs) and the signal generated from the host cell. We show that for SARS-CoV-2, the interaction of spike protein with ACE2 not only serves the purpose for viral entry into the host cell, but also transduces signals that culminate into the phosphorylation and the release of L13a from the large ribosomal subunit. We also show that this event leads to the translational arrest of ORF1a and S mRNAs in a manner dependent on the structure of the RNA elements. Translational control of viral mRNA by a host-cell generated signal triggered by viral protein is a new paradigm in the host-virus relationship.

Protective Effect of Crocin on Malathion-induced Cardiotoxicity in Rats: A Biochemical, Histopathological and Proteomics Study

In this study, the protective effect of crocin on malathion (MTN) induced cardiotoxicity in rats in subacute exposure was evaluated. Rats were divided into 6 groups; control (normal saline); MTN (100 mg/kg); MTN + crocin (10, 20 and 40 mg/kg) and MTN + vitamin E 200 IU/kg. Treatments were continued for two weeks. Creatine phosphokinase MB (CK-MB), malondialdehyde (MDA) and glutathione (GSH) levels were evaluated in heart tissue at the end of treatments. The effect of crocin and MTN on histopathological changes in rat cardiac tissue was also investigated. The alteration of protein profile in the heart of the animals exposed to MTN was evaluated by proteomic approach through two-dimensional gel electrophoresis followed by matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) software. MTN induced histopathological damages and elevated the level of cardiac marker CK-MB (P < 0.01). The level of MDA increased and the level of GSH reduced (P < 0.001). MDA levels were reduced in all crocin plus MTN groups (P < 0.001) and vitamin E plus MTN (P < 0.001) groups as compared to MTN groups. However, in the crocin (10 mg/kg) + MTN group, the content of GSH compared to MTN treated rats increased (P < 0.001). Protein abundance analysis identified proteins implicated in cardiac necrosis, tricarboxylic acid cycle, cellular energy homeostasis, arrhythmias, heart development, heart failure and cardiovascular homeostasis to be affected by MTN. In summary, MTN may induce damage in the heart tissue of rats following subacute exposure and crocin, as an antioxidant, showed protective effects against MTN cardiotoxicity.

Deletion of the Actin-Associated Tropomyosin Tpm3 Leads to Reduced Cell Complexity in Cultured Hippocampal Neurons-New Insights into the Role of the C-Terminal Region of Tpm3.1

Tropomyosins (Tpms) have been described as master regulators of actin, with Tpm3 products shown to be involved in early developmental processes, and the Tpm3 isoform Tpm3.1 controlling changes in the size of neuronal growth cones and neurite growth. Here, we used primary mouse hippocampal neurons of C57/Bl6 wild type and Bl6^Tpm3flox transgenic mice to carry out morphometric analyses in response to the absence of Tpm3 products, as well as to investigate the effect of C-terminal truncation on the ability of Tpm3.1 to modulate neuronal morphogenesis. We found that the knock-out of Tpm3 leads to decreased neurite length and complexity, and that the deletion of two amino acid residues at the C-terminus of Tpm3.1 leads to more detrimental changes in neurite morphology than the deletion of six amino acid residues. We also found that Tpm3.1 that lacks the 6 C-terminal amino acid residues does not associate with stress fibres, does not segregate to the tips of neurites, and does not impact the amount of the filamentous actin pool at the axonal growth cones, as opposed to Tpm3.1, which lacks the two C-terminal amino acid residues. Our study provides further insight into the role of both Tpm3 products and the C-terminus of Tpm3.1, and it forms the basis for future studies that aim to identify the molecular mechanisms underlying Tpm3.1 targeting to different subcellular compartments.

Further Investigation into the Biochemical Effects of Phosphorylation of Tropomyosin Tpm1.1(α). Serine-283 Is in Communication with the Midregion

The phosphorylated and unphosphorylated forms of tropomyosin Tpm1.1(α) are prepared from adult rabbit heart and compared biochemically. Electrophoresis confirms the high level of enrichment of the chromatography fractions and is consistent with a single site of phosphorylation. Covalently bound phosphate groups at position 283 of Tpm1.1(α) increase the rate of digestion at Leu-169, suggestive of a conformational rearrangement that extends to the midregion. Such a rearrangement, which is supported by ellipticity measurements between 25 and 42 °C, is consistent with a phosphorylation-mediated tightening of the interaction between various myofilament components. In a nonradioactive, co-sedimentation assay [30 mM KCl, 1 mM Mg(II), and 4 °C], phosphorylated Tpm1.1(α) displays a higher affinity for F-actin compared to that of the unphosphorylated control (K_d, 0.16 μM vs 0.26 μM). Phosphorylation decreases the concentration of thin filaments (pCa 4 plus ATP) required to attain a half-maximal rate of release of product from a pre-power stroke complex [myosin-S1-2-deoxy-3-O-(N-methylanthraniloyl)ADP-P_i], as investigated by double-mixing stopped-flow fluorescence, suggestive of a change in the proportion of active (turned on) and inactive (turned off) conformers, but similar maximum rates of product release are observed with either type of reconstituted thin filament. Phosphorylated thin filaments (pCa 4 and 8) display a higher affinity for myosin-S1(ADP) versus the control scenario without affecting isotherm steepness. Specific activities of ATP and Tpm1.1(α) are determined during an in vitro incubation of rat cardiac tissue [12 day-old, 50% phosphorylated Tpm1.1(α)] with [³²P]orthophosphate. The incorporation of an isotope into tropomyosin lags behind that of ATP by a factor of approximately 10, indicating that transfer is a comparatively slow process.

Inorganic Phosphate (Pi) Signaling in Endothelial Cells: A Molecular Basis for Generation of Endothelial Microvesicles in Uraemic Cardiovascular Disease

Hyperphosphataemia increases cardiovascular mortality in patients with kidney disease. Direct effects of high inorganic phosphate (Pi) concentrations have previously been demonstrated on endothelial cells (ECs), including generation of procoagulant endothelial microvesicles (MVs). However, no mechanism directly sensing elevated intracellular Pi has ever been described in mammalian cells. Here, we investigated the hypothesis that direct inhibition by Pi of the phosphoprotein phosphatase PP2A fulfils this sensing role in ECs, culminating in cytoskeleton disruption and MV generation. ECs were treated with control (1 mM [Pi]) vs. high (2.5 mM [Pi]), a condition that drives actin stress fibre depletion and MV generation demonstrated by confocal microscopy of F-actin and NanoSight Nanoparticle tracking, respectively. Immuno-blotting demonstrated that high Pi increased p-Src, p-PP2A-C and p-DAPK-1 and decreased p-TPM-3. Pi at 100 μM directly inhibited PP2A catalytic activity. Inhibition of PP2A enhanced inhibitory phosphorylation of DAPK-1, leading to hypophosphorylation of Tropomyosin-3 at S284 and MV generation. p-Src is known to perform inhibitory phosphorylation on DAPK-1 but also on PP2A-C. However, PP2A-C can itself dephosphorylate (and therefore inhibit) p-Src. The direct inhibition of PP2A-C by Pi is, therefore, amplified by the feedback loop between PP2A-C and p-Src, resulting in further PP2A-C inhibition. These data demonstrated that PP2A/Src acts as a potent sensor and amplifier of Pi signals which can further signal through DAPK-1/Tropomyosin-3 to generate cytoskeleton disruption and generation of potentially pathological MVs.

The MicroRNA MiR-29c Alleviates Renal Fibrosis via TPM1-Mediated Suppression of the Wnt/β-Catenin Pathway

Purpose

This study aimed to evaluate the mechanism by which miR-29c expression in fibroblasts regulates renal interstitial fibrosis.

Methods

We stimulated NRK-49F cells with TGF-β1 to mimic the effects of fibrosis in vitro, while unilateral ureteral obstruction (UUO) was performed to obstruct the mid-ureter in mice. MiR-29c mimic or miR-29c inhibitor was used to mediate genes expressions in vitro. The recombinant adeno associated virus (rAAV) vectors carrying a FSP1 promoter that encodes miR-29c precursor or miR-29c inhibitor was used to mediate genes expressions in vivo, and a flank incision was made to expose the left kidney of each animal.

Results

In the present study, TGF-β1 was demonstrated to regulate miR-29c expression through Wnt/β-catenin signaling. In contrast, miR-29c appears to inhibit the Wnt/β-catenin pathway by suppressing TPM1 expression. As suggested by this feedback mechanism, miR-29c may be a key fibrosis-related microRNA expressed by fibroblasts in TGF-β1/Wnt/β-catenin-driven renal fibrosis, and manipulation of miR-29c action may accordingly offer a potential therapeutic pathway for renal fibrosis treatment.

Conclusion

MiR-29c expression was downregulated in UUO mouse kidneys as well as TGF-β1-treated NRK-49F cells, which thus inhibits myofibroblast formation via targeting of TPM1. Additionally, the production of extracellular matrix (ECM) in renal fibroblasts appears to be controlled by the reciprocal regulation of miR-29c action and the Wnt/β-catenin pathway.

A Tale of Two States: Normal and Transformed, With and Without Rigidity Sensing

For many years, major differences in morphology, motility, and mechanical characteristics have been observed between transformed cancer and normal cells. In this review, we consider these differences as linked to different states of normal and transformed cells that involve distinct mechanosensing and motility pathways. There is a strong correlation between repeated tissue healing and/or inflammation and the probability of cancer, both of which involve growth in adult tissues. Many factors are likely needed to enable growth, including the loss of rigidity sensing, but recent evidence indicates that microRNAs have important roles in causing the depletion of growth-suppressing proteins. One microRNA, miR-21, is overexpressed in many different tissues during both healing and cancer. Normal cells can become transformed by the depletion of cytoskeletal proteins that results in the loss of mechanosensing, particularly rigidity sensing. Conversely, the transformed state can be reversed by the expression of cytoskeletal proteins-without direct alteration of hormone receptor levels. In this review, we consider the different stereotypical forms of motility and mechanosensory systems. A major difference between normal and transformed cells involves a sensitivity of transformed cells to mechanical perturbations. Thus, understanding the different mechanical characteristics of transformed cells may enable new approaches to treating wound healing and cancer.

Analysis of fibrosis in control or pressure overloaded rat hearts after mechanical unloading by heterotopic heart transplantation

Mechanical unloading (MU) by implantation of left ventricular assist devices (LVAD) has become clinical routine. This procedure has been shown to reverse cardiac pathological remodeling, with the underlying molecular mechanisms incompletely understood. Most studies thus far were performed in non-standardized human specimens or MU of healthy animal hearts. Our study investigates cardiac remodeling processes in sham-operated healthy rat hearts and in hearts subjected to standardized pathological pressure overload by transverse aortic constriction (TAC) prior to MU by heterotopic heart transplantation (hHTx/MU). Rats underwent sham or TAC surgery. Disease progression was monitored by echocardiography prior to MU by hHTx/MU. Hearts after TAC or TAC combined with hHTx/MU were removed and analyzed by histology, western immunoblot and gene expression analysis. TAC surgery resulted in cardiac hypertrophy and impaired cardiac function. TAC hearts revealed significantly increased cardiac myocyte diameter and mild fibrosis. Expression of hypertrophy associated genes after TAC was higher compared to hearts after hHTx/MU. While cardiac myocyte cell diameter regressed to the level of sham-operated controls in all hearts subjected to hHTx/MU, fibrotic remodeling was significantly exacerbated. Transcription of pro-fibrotic and apoptosis-related genes was markedly augmented in all hearts after hHTx/MU. Sarcomeric proteins involved in excitation-contraction coupling displayed significantly lower phosphorylation levels after TAC and significantly reduced total protein levels after hHTx/MU. Development of myocardial fibrosis, cardiac myocyte atrophy and loss of sarcomeric proteins was observed in all hearts that underwent hHTX/MU regardless of the disease state. These results may help to explain the clinical experience with low rates of LVAD removal due to lack of myocardial recovery.

iTRAQ-based quantitative proteomics reveals the neuroprotection of rhubarb in experimental intracerebral hemorrhage

ETHNOPHARMACOLOGICAL RELEVANCE

Rhubarb is a traditional Chinese medicine(TCM), that possesses neuroprotective, anti-inflammatory, antibacterial, antioxidative, purgative and anticancer properties, and has been used to treat intracerebral hemorrhage (ICH) and many other diseases.

AIMS OF THE STUDY

This study aimed to investigate the changes of brain protein in ICH rats treated with rhubarb and to explore the multi-target mechanism of rhubarb in the treatment of ICH via bioinformatics analysis of differentially expressed proteins (DEPs).

MATERIALS AND METHODS

Rats were subjected to collagenase-induced ICH and then treated orally with 3 or 12 g/kg rhubarb daily for 2 days following ICH. After sacrifice, total protein of brain tissue was extracted, and isobaric tag for relative and absolute quantification (iTRAQ)-based liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis was employed to quantitatively identify of the DEPs in two treatment groups compared with the vehicle group. The DEPs were analyzed by Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) and STRING databases. Bioinformatics Analysis Tool for Molecular mechanism of TCM (BATMAN-TCM) was used to predict the target of rhubarb and western blotting was used for verification.

RESULTS

In total, 1356 proteins were identified with a 1% false discovery rate (FDR). Among them, 55 DEPs were significantly altered in the sham, vehicle, low dose rhubarb group (LDR, 3 g/kg), and high dose rhubarb group (HDR, 12 g/kg). Enrichment analysis of GO annotations indicated that rhubarb mainly regulated expression of some neuron projection proteins involved in the response to drug and nervous system development. The dopaminergic synapse pathway was found to be the most significant DEP in the combined analysis of the KEGG and BATMAN-TCM databases. Based on the results of the STRING analysis, oxidative stress (OS), calcium binding protein regulation, vascularization, and energy metabolism were important in the rhubarb therapeutic process.

CONCLUSION

Rhubarb achieves its effects mainly through the dopaminergic synapse pathway in ICH treatment. The ICH-treating mechanisms of rhubarb may also involve anti-OS, calcium binding protein regulation, angiogenic regulation, and energy metabolism improvement. This study adds new evidence to clinical applications of rhubarb for ICH.

Tropomyosin pseudo-phosphorylation results in dilated cardiomyopathy

Phosphorylation of cardiac sarcomeric proteins plays a major role in the regulation of the physiological performance of the heart. Phosphorylation of thin filament proteins, such as troponin I and T, dramatically affects calcium sensitivity of the myofiber and systolic and diastolic functions. Phosphorylation of the regulatory protein tropomyosin (Tpm) results in altered biochemical properties of contraction; however, little is known about the physiological effect of Tpm phosphorylation on cardiac function. To address the in vivo significance of Tpm phosphorylation, here we generated transgenic mouse lines having a phosphomimetic substitution in the phosphorylation site of α-Tpm (S283D). High expression of Tpm S283D variant in one transgenic mouse line resulted in an increased heart:body weight ratio, coupled with a severe dilated cardiomyopathic phenotype resulting in death within 1 month of birth. Moderate Tpm S283D mice expression in other lines caused mild myocyte hypertrophy and fibrosis, did not affect lifespan, and was coupled with decreased expression of extracellular signal-regulated kinase 1/2 kinase signaling. Physiological analysis revealed that the transgenic mice exhibit impaired diastolic function, without changes in systolic performance. Surprisingly, we observed no alterations in calcium sensitivity of the myofibers, cooperativity, or calcium-ATPase activity in the myofibers. Our experiments also disclosed that casein kinase 2 plays an integral role in Tpm phosphorylation. In summary, increased expression of pseudo-phosphorylated Tpm impairs diastolic function in the intact heart, without altering calcium sensitivity or cooperativity of myofibers. Our findings provide the first extensive in vivo assessment of Tpm phosphorylation in the heart and its functional role in cardiac performance.

ROCK inhibitor reduces Myc-induced apoptosis and mediates immortalization of human keratinocytes

The Myc/Max/Mad network plays a critical role in cell proliferation, differentiation and apoptosis and c-Myc is overexpressed in many cancers, including HPV-positive cervical cancer cell lines. Despite the tolerance of cervical cancer keratinocytes to high Myc expression, we found that the solitary transduction of the Myc gene into primary cervical and foreskin keratinocytes induced rapid cell death. These findings suggested that the anti-apoptotic activity of E7 in cervical cancer cells might be responsible for negating the apoptotic activity of over-expressed Myc. Indeed, our earlier in vitro studies demonstrated that Myc and E7 synergize in the immortalization of keratinocytes. Since we previously postulated that E7 and the ROCK inhibitor, Y-27632, were members of the same functional pathway in cell immortalization, we tested whether Y-27632 would inhibit apoptosis induced by the over-expression of Myc. Our findings indicate that Y-27632 rapidly inhibited Myc-induced membrane blebbing and cellular apoptosis and, more generally, functioned as an inhibitor of extrinsic and intrinsic pathways of cell death. Most important, Y-27632 cooperated with Myc to immortalize keratinocytes efficiently, indicating that apoptosis is a major barrier to Myc-induced immortalization of keratinocytes. The anti-apoptotic activity of Y-27632 correlated with a reduction in p53 serine 15 phosphorylation and the consequent reduction in the expression of downstream target genes p21 and DAPK1, two genes involved in the induction of cell death.

Unraveling the Mechanistic Complexity of the Glomerulocystic Phenotype in Dicer Conditional KO Mice by 2D Gel Electrophoresis Coupled Mass Spectrometry

PURPOSE

Dicer, an RNase III type endonuclease, is a key enzyme involved in miRNA biogenesis. It has been shown that this enzyme is essential for several aspects of postnatal kidney functions and homeostasis. In this study, we have examined conditional knockout (cKO) mice for Dicer in Pax8 (Paired-box gene 8) expressing cells to investigate the kidney protein profile. This specific model develops a glomerulocystic phenotype coupled with urinary concentration impairment, proteinuria, and severe renal failure.

EXPERIMENTAL DESIGN

Proteomic analysis was performed on kidney tissue extracts from cKO and control (Ctr) mice by 2D Gel Electrophoresis coupled with mass spectrometry.

RESULTS

The analysis highlighted 120 protein spots differentially expressed in Dicer cKO tissue compared with control; some of these proteins were validated by Western blotting. Ingenuity Pathway Analysis led to the identification of some interesting networks; among them, the one having ERK as a central hub may explain, through the modulation of the expression of a number of identified protein targets, the metabolic and structural alterations occurring during kidney cyst development in Dicer cKO mouse model.

CONCLUSIONS AND CLINICAL RELEVANCE

Our results contribute to gain new insights into molecular mechanisms through which Dicer endonuclease controls kidney development and physiological functions.

The p38 pathway, a major pleiotropic cascade that transduces stress and metastatic signals in endothelial cells

By gating the traffic of molecules and cells across the vessel wall, endothelial cells play a central role in regulating cardiovascular functions and systemic homeostasis and in modulating pathophysiological processes such as inflammation and immunity. Accordingly, the loss of endothelial cell integrity is associated with pathological disorders that include atherosclerosis and cancer. The p38 mitogen-activated protein kinase (MAPK) cascades are major signaling pathways that regulate several functions of endothelial cells in response to exogenous and endogenous stimuli including growth factors, stress and cytokines. The p38 MAPK family contains four isoforms p38α, p38β, p38γ and p38δ that are encoded by four different genes. They are all widely expressed although to different levels in almost all human tissues. p38α/MAPK14, that is ubiquitously expressed is the prototype member of the family and is referred here as p38. It regulates the production of inflammatory mediators, and controls cell proliferation, differentiation, migration and survival. Its activation in endothelial cells leads to actin remodeling, angiogenesis, DNA damage response and thereby has major impact on cardiovascular homeostasis, and on cancer progression. In this manuscript, we review the biology of p38 in regulating endothelial functions especially in response to oxidative stress and during the metastatic process.

Actin regulation by tropomodulin and tropomyosin in neuronal morphogenesis and function

Actin is a profoundly influential protein; it impacts, among other processes, membrane morphology, cellular motility, and vesicle transport. Actin can polymerize into long filaments that push on membranes and provide support for intracellular transport. Actin filaments have polar ends: the fast-growing (barbed) end and the slow-growing (pointed) end. Depolymerization from the pointed end supplies monomers for further polymerization at the barbed end. Tropomodulins (Tmods) cap pointed ends by binding onto actin and tropomyosins (Tpms). Tmods and Tpms have been shown to regulate many cellular processes; however, very few studies have investigated their joint role in the nervous system. Recent data directly indicate that they can modulate neuronal morphology. Additional studies suggest that Tmod and Tpm impact molecular processes influential in synaptic signaling. To facilitate future research regarding their joint role in actin regulation in the nervous system, we will comprehensively discuss Tpm and Tmod and their known functions within molecular systems that influence neuronal development.

Hypoxia and hyperoxia differentially control proliferation of rat neural crest stem cells via distinct regulatory pathways of the HIF1α-CXCR4 and TP53-TPM1 proteins

BACKGROUND

Neural crest stem cells (NCSCs) are a population of adult multipotent stem cells. We are interested in studying whether oxygen tensions affect the capability of NCSCs to self-renew and repair damaged tissues. NCSCs extracted from the hair follicle bulge region of the rat whisker pad were cultured in vitro under different oxygen tensions.

RESULTS

We found significantly increased and decreased rates of cell proliferation in rat NCSCs (rNCSCs) cultured, respectively, at 0.5% and 80% oxygen levels. At 0.5% oxygen, the expression of both hypoxia-inducible factor (HIF) 1α and CXCR4 was greatly enhanced in the rNCSC nuclei and was suppressed by incubation with the CXCR4-specific antagonist AMD3100. In addition, the rate of cell apoptosis in the rNCSCs cultured at 80% oxygen was dramatically increased, associated with increased nuclear expression of TP53, decreased cytoplasmic expression of TPM1 (tropomyosin-1), and increased nuclear-to-cytoplasmic translocation of S100A2. Incubation of rNCSCs with the antioxidant N-acetylcysteine (NAC) overcame the inhibitory effect of 80% oxygen on proliferation and survival of rNCSCs.

CONCLUSIONS

Our results show for the first time that extreme oxygen tensions directly control NCSC proliferation differentially via distinct regulatory pathways of proteins, with hypoxia via the HIF1α-CXCR4 pathway and hyperoxia via the TP53-TPM1 pathway. Developmental Dynamics 246:162-185, 2017. © 2016 Wiley Periodicals, Inc.

JunD/AP-1 Antagonizes the Induction of DAPK1 To Promote the Survival of v-Src-Transformed Cells

The increase in AP-1 activity is a hallmark of cell transformation by tyrosine kinases. Previously, we reported that blocking AP-1 using the c-Jun dominant negative mutant TAM67 induced senescence, adipogenesis, or apoptosis in v-Src-transformed chicken embryo fibroblasts (CEFs) whereas inhibition of JunD by short hairpin RNA (shRNA) specifically induced apoptosis. To investigate the role of AP-1 in Src-mediated transformation, we undertook a gene profiling study to characterize the transcriptomes of v-Src-transformed CEFs expressing either TAM67 or the JunD shRNA. Our study revealed a cluster of 18 probe sets upregulated exclusively in response to AP-1/JunD impairment and v-Src transformation. Four of these probe sets correspond to genes involved in the interferon pathway. One gene in particular, death-associated protein kinase 1 (DAPK1), is a C/EBPβ-regulated mediator of apoptosis in gamma interferon (IFN-γ)-induced cell death. Here, we show that inhibition of DAPK1 abrogates cell death in v-Src-transformed cells expressing the JunD shRNA. Chromatin immunoprecipitation data indicated that C/EBPβ was recruited to the DAPK1 promoter while the expression of a dominant negative mutant of C/EBPβ abrogated the induction of DAPK1 in response to the inhibition of AP-1. In contrast, as determined by chromatin immunoprecipitation (ChIP) assays, JunD was not detected on the DAPK1 promoter under any conditions, suggesting that JunD promotes survival by indirectly antagonizing the expression of DAPK1 in v-Src transformed cells.

IMPORTANCE

Transformation by the v-Src oncoprotein causes extensive changes in gene expression in primary cells such as chicken embryo fibroblasts. These changes, determining the properties of transformed cells, are controlled in part at the transcriptional level. Much attention has been devoted to transcription factors such as AP-1 and NF-κB and the control of genes associated with a more aggressive phenotype. In this report, we describe a novel mechanism of action determined by the JunD component of AP-1, a factor enhancing cell survival in v-Src-transformed cells. We show that the loss of JunD results in the aberrant activation of a genetic program leading to cell death. This program requires the activation of the tumor suppressor death-associated protein kinase 1 (DAPK1). Since DAPK1 is phosphorylated and inhibited by v-Src, these results highlight the importance of this kinase and the multiple mechanisms controlled by v-Src to antagonize the tumor suppressor function of DAPK1.

MicroRNAs-mediated epithelial-mesenchymal transition in fibrotic diseases

MicroRNAs (miRNAs), a large family of small and highly conserved non-coding RNAs, regulate gene expression through translational repression or mRNA degradation. Aberrant expression of miRNAs underlies a spectrum of diseases including organ fibrosis. Recent evidence suggests that miRNAs contribute to organ fibrosis through mediating epithelial-mesenchymal transition (EMT). Alleviation of EMT has been proposed as a promising strategy against fibrotic diseases given the key role of EMT in fibrosis. miRNAs impact the expression of specific ligands, receptors, and signaling pathways, thus modulating EMT and consequently influencing fibrosis. This review summarizes the current knowledge concerning how miRNAs regulate EMT and highlights the specific roles that miRNAs-regulated EMT plays in fibrotic diseases as diverse as pulmonary fibrosis, hepatic fibrosis, renal fibrosis and cardiac fibrosis. It is desirable that a more comprehensive understanding of the functions of miRNAs-regulated EMT will facilitate the development of novel diagnostic and therapeutic strategies for various debilitating organ fibrosis.

Deregulation of focal adhesion formation and cytoskeletal tension due to loss of A-type lamins

The nuclear lamina mechanically integrates the nucleus with the cytoskeleton and extracellular environment and regulates gene expression. These functions are exerted through direct and indirect interactions with the lamina's major constituent proteins, the A-type lamins, which are encoded by the LMNA gene. Using quantitative stable isotope labeling-based shotgun proteomics we have analyzed the proteome of human dermal fibroblasts in which we have depleted A-type lamins by means of a sustained siRNA-mediated LMNA knockdown. Gene ontology analysis revealed that the largest fraction of differentially produced proteins was involved in actin cytoskeleton organization, in particular proteins involved in focal adhesion dynamics, such as actin-related protein 2 and 3 (ACTR2/3), subunits of the ARP2/3 complex, and fascin actin-bundling protein 1 (FSCN1). Functional validation using quantitative immunofluorescence showed a significant reduction in the size of focal adhesion points in A-type lamin depleted cells, which correlated with a reduction in early cell adhesion capacity and an increased cell motility. At the same time, loss of A-type lamins led to more pronounced stress fibers and higher traction forces. This phenotype could not be mimicked or reversed by experimental modulation of the STAT3-IL6 pathway, but it was partly recapitulated by chemical inhibition of the ARP2/3 complex. Thus, our data suggest that the loss of A-type lamins perturbs the balance between focal adhesions and cytoskeletal tension. This imbalance may contribute to mechanosensing defects observed in certain laminopathies.

Inhibition of death-associated protein kinase 1 attenuates the phosphorylation and amyloidogenic processing of amyloid precursor protein

Extracellular deposition of amyloid-beta (Aβ) peptide, a metabolite of sequential cleavage of amyloid precursor protein (APP), is a critical step in the pathogenesis of Alzheimer's disease (AD). While death-associated protein kinase 1 (DAPK1) is highly expressed in AD brains and its genetic variants are linked to AD risk, little is known about the impact of DAPK1 on APP metabolism and Aβ generation. In this study, we demonstrated a novel effect of DAPK1 in the regulation of APP processing using cell culture and mouse models. DAPK1, but not its kinase deficient mutant (K42A), significantly increased human Aβ secretion in neuronal cell culture models. Moreover, knockdown of DAPK1 expression or inhibition of DAPK1 catalytic activity significantly decreased Aβ secretion. Furthermore, DAPK1, but not K42A, triggered Thr668 phosphorylation of APP, which may initiate and facilitate amyloidogenic APP processing leading to the generation of Aβ. In Tg2576 APPswe-overexpressing mice, knockout of DAPK1 shifted APP processing toward non-amyloidogenic pathway and decreased Aβ generation. Finally, in AD brains, elevated DAPK1 levels showed co-relation with the increase of APP phosphorylation. Combined together, these results suggest that DAPK1 promotes the phosphorylation and amyloidogenic processing of APP, and that may serve a potential therapeutic target for AD.

Molecular determinants of acute kidney injury

Background:

Acute kidney injury (AKI) is a condition that leads to a rapid deterioration of renal function associated with impairment to maintain electrolyte and acid balance, and, if left untreated, ultimately irreversible kidney damage and renal necrosis. There are a number of causes that can trigger AKI, ranging from underlying conditions as well as trauma and surgery. Specifically, the global rise in surgical procedures led to a substantial increase of AKI incidence rates, which in turn impacts on mortality rates, quality of life and economic costs to the healthcare system. However, no effective therapy for AKI exists. Current approaches, such as pharmacological intervention, help in alleviating symptoms in slowing down the progression, but do not prevent or reverse AKI-induced organ damage.

Methods:

An in-depth understanding of the molecular machinery involved in and modulated by AKI induction and progression is necessary to specifically pharmacologically target key molecules. A major hurdle to devise a successful strategy is the multifactorial and complex nature of the disorder itself, whereby the activation of a number of seemingly independent molecular pathways in the kidney leads to apoptotic and necrotic events.

Results:

The renin-angiotensin-aldosterone-system (RAAS) axis appears to be a common element, leading to downstream events such as triggers of immune responses via the NFB pathway. Other pathways intricately linked with AKI-induction and progression are the tumor necrosis factor alpha (TNF α) and transforming growth factor beta (TGF β) signaling cascades, as well as a number of other modulators. Surprisingly, it has been shown that the involvement of the glutamatergic axis, believed to be mainly a component of the neurological system, is also a major contributor.

Conclusions:

Here we address the current understanding of the molecular pathways evoked in AKI, their interplay, and the potential to pharmacologically intervene in the effective prevention and/or progression of AKI.

Involvement of Membrane Blebbing in Immunological Disorders and Cancer

Cellular blebbing is a unique form of dynamic protrusion emanating from the plasma membrane which can be either apoptotic or nonapoptotic in nature. Blebs have been observed in a wide variety of cell types and in response to multiple mechanical and chemical stimuli. They have been linked to various physiological and pathological processes including tumor motility and invasion, as well as to various immunological disorders. They can form and retract extremely rapidly in seconds or minutes, or slowly over hours or days. This review focuses on recent evidence regarding the role of blebbing in cell locomotion with particular emphasis on its role in tumor metastasis, indicating the role of specific causative molecules. The phenomenon of blebbing has been observed in endocrine-resistant breast cancer cells in response to brief exposure to extracellular alkaline pH, which leads to enhanced invasive capacity. Genetic or pharmacological targeting of cellular blebs could serve as a potential therapeutic option to control tumor metastasis.

Identification of Novel Death-Associated Protein Kinase 2 Interaction Partners by Proteomic Screening Coupled with Bimolecular Fluorescence Complementation

Death-associated protein kinase 2 (DAPK2) is a Ca(2+)/calmodulin-dependent Ser/Thr kinase that possesses tumor-suppressive functions and regulates programmed cell death, autophagy, oxidative stress, hematopoiesis, and motility. As only few binding partners of DAPK2 have been determined, the molecular mechanisms governing these biological functions are largely unknown. We report the identification of 180 potential DAPK2 interaction partners by affinity purification-coupled mass spectrometry, 12 of which are known DAPK binding proteins. A small subset of established and potential binding proteins detected in this screen was further investigated by bimolecular fluorescence complementation (BiFC) assays, a method to visualize protein interactions in living cells. These experiments revealed that α-actinin-1 and 14-3-3-β are novel DAPK2 binding partners. The interaction of DAPK2 with α-actinin-1 was localized at the plasma membrane, resulting in massive membrane blebbing and reduced cellular motility, whereas the interaction of DAPK2 with 14-3-3-β was localized to the cytoplasm, with no impact on blebbing, motility, or viability. Our results therefore suggest that DAPK2 effector functions are influenced by the protein's subcellular localization and highlight the utility of combining mass spectrometry screening with bimolecular fluorescence complementation to identify and characterize novel protein-protein interactions.

Muscle weakness in TPM3-myopathy is due to reduced Ca2+-sensitivity and impaired acto-myosin cross-bridge cycling in slow fibres

Dominant mutations in TPM3, encoding α-tropomyosinslow, cause a congenital myopathy characterized by generalized muscle weakness. Here, we used a multidisciplinary approach to investigate the mechanism of muscle dysfunction in 12 TPM3-myopathy patients. We confirm that slow myofibre hypotrophy is a diagnostic hallmark of TPM3-myopathy, and is commonly accompanied by skewing of fibre-type ratios (either slow or fast fibre predominance). Patient muscle contained normal ratios of the three tropomyosin isoforms and normal fibre-type expression of myosins and troponins. Using 2D-PAGE, we demonstrate that mutant α-tropomyosinslow was expressed, suggesting muscle dysfunction is due to a dominant-negative effect of mutant protein on muscle contraction. Molecular modelling suggested mutant α-tropomyosinslow likely impacts actin-tropomyosin interactions and, indeed, co-sedimentation assays showed reduced binding of mutant α-tropomyosinslow (R168C) to filamentous actin. Single fibre contractility studies of patient myofibres revealed marked slow myofibre specific abnormalities. At saturating [Ca(2+)] (pCa 4.5), patient slow fibres produced only 63% of the contractile force produced in control slow fibres and had reduced acto-myosin cross-bridge cycling kinetics. Importantly, due to reduced Ca(2+)-sensitivity, at sub-saturating [Ca(2+)] (pCa 6, levels typically released during in vivo contraction) patient slow fibres produced only 26% of the force generated by control slow fibres. Thus, weakness in TPM3-myopathy patients can be directly attributed to reduced slow fibre force at physiological [Ca(2+)], and impaired acto-myosin cross-bridge cycling kinetics. Fast myofibres are spared; however, they appear to be unable to compensate for slow fibre dysfunction. Abnormal Ca(2+)-sensitivity in TPM3-myopathy patients suggests Ca(2+)-sensitizing drugs may represent a useful treatment for this condition.

Death-associated protein kinase: A molecule with functional antagonistic duality and a potential role in inflammatory bowel disease (Review)

The cytoskeleton-associated serine/threonine kinase death-associated protein kinase (DAPK) has been described as a cancer gene chameleon with functional antagonistic duality in a cell type and context specific manner. The broad range of interaction partners and substrates link DAPK to inflammatory processes especially in the gut. Herein we summarize our knowledge on the role of DAPK in different cell types that play a role under inflammatory conditions in the gut. Besides some promising experimental data suggesting DAPK as an interesting drug target in inflammatory bowel disease there are many open questions regarding direct evidence for a role of DAPK in intestinal inflammation.

Shear stress attenuates apoptosis due to TNFα, oxidative stress, and serum depletion via death-associated protein kinase (DAPK) expression

Background

Misdirected apoptosis in endothelial cells participates in the development of pathological conditions such as atherosclerosis. Tight regulation of apoptosis is necessary to ensure normal cell function. The rate of cell turnover is increased at sites prone to lesion development. Laminar shear stress is protective against atherosclerosis, and helps suppress apoptosis induced by cytokines, oxidative stress, and serum depletion. Current Studies have shown that the pro-apoptotic DAPK expression and function to be regulated in part by shear stress, and that shearing cells already treated with cytokine tumor necrosis factor (TNF) α significantly reduced apoptosis. We investigate further the suppression of endothelial apoptosis by shear stress with other apoptotic triggers, and the involvement of DAPK and caspase 3/7.

Results

We have shown that exposure to shear stress (12 dynes/cm² for 6 hrs) suppressed endothelial apoptosis triggered by cytokine (TNFα), oxidative stress (H₂O₂), and serum depletion, either before or after a long term (18 hr) induction. This is correlated with a parallel decrease of DAPK expression and caspase activity compared to non-sheared cells. We found similar modulation of DAPK and apoptosis by shear stress with other pro-apoptotic signals. Changes in DAPK and caspase 3/7 are directly correlated to changes in apoptosis. Interestingly, shear stress applied to cells prior to induction with apoptosis agents resulted in a higher suppression of apoptosis and DAPK and caspase activity, compared to applying shear stress post induction. This is correlated with a higher expression and activation of DAPK in cells sheared at the end of 24-hr experiment. Also, shear stress alone also induced higher apoptosis and DAPK expression, and the effect is sustained even after 18 hrs incubation in static condition, compared to non-sheared cells.

Conclusions

Overall, we show that laminar shear stress inhibits various apoptosis pathways by modulating DAPK activity, as well as caspase activation, in a time-dependent manner. Shear stress could target DAPK as a converging point to exert its effects of suppressing endothelial apoptosis. The temporal shear stress stimulation of DAPK and its role in different apoptosis pathways may help identify key mechanisms of the endothelial mechanotransduction pathway.

Hyperphosphatemia, Phosphoprotein Phosphatases, and Microparticle Release in Vascular Endothelial Cells

Hyperphosphatemia in patients with advanced CKD is thought to be an important contributor to cardiovascular risk, in part because of endothelial cell (EC) dysfunction induced by inorganic phosphate (Pi). Such patients also have an elevated circulating concentration of procoagulant endothelial microparticles (MPs), leading to a prothrombotic state, which may contribute to acute occlusive events. We hypothesized that hyperphosphatemia leads to MP formation from ECs through an elevation of intracellular Pi concentration, which directly inhibits phosphoprotein phosphatases, triggering a global increase in phosphorylation and cytoskeletal changes. In cultured human ECs (EAhy926), incubation with elevated extracellular Pi (2.5 mM) led to a rise in intracellular Pi concentration within 90 minutes. This was mediated by PiT1/slc20a1 Pi transporters and led to global accumulation of tyrosine- and serine/threonine-phosphorylated proteins, a marked increase in cellular Tropomyosin-3, plasma membrane blebbing, and release of 0.1- to 1-μm-diameter MPs. The effect of Pi was independent of oxidative stress or apoptosis. Similarly, global inhibition of phosphoprotein phosphatases with orthovanadate or fluoride yielded a global protein phosphorylation response and rapid release of MPs. The Pi-induced MPs expressed VE-cadherin and superficial phosphatidylserine, and in a thrombin generation assay, they displayed significantly more procoagulant activity than particles derived from cells incubated in medium with a physiologic level of Pi (1 mM). These data show a mechanism of Pi-induced cellular stress and signaling, which may be widely applicable in mammalian cells, and in ECs, it provides a novel pathologic link between hyperphosphatemia, generation of MPs, and thrombotic risk.

SPECHT - single-stage phosphopeptide enrichment and stable-isotope chemical tagging: quantitative phosphoproteomics of insulin action in muscle

The study of cellular signaling remains a significant challenge for translational and clinical research. In particular, robust and accurate methods for quantitative phosphoproteomics in tissues and tumors represent significant hurdles for such efforts. In the present work, we design, implement and validate a method for single-stage phosphopeptide enrichment and stable isotope chemical tagging, or SPECHT, that enables the use of iTRAQ, TMT and/or reductive dimethyl-labeling strategies to be applied to phosphoproteomics experiments performed on primary tissue. We develop and validate our approach using reductive dimethyl-labeling and HeLa cells in culture, and find these results indistinguishable from data generated from more traditional SILAC-labeled HeLa cells mixed at the cell level. We apply the SPECHT approach to the quantitative analysis of insulin signaling in a murine myotube cell line and muscle tissue, identify known as well as new phosphorylation events, and validate these phosphorylation sites using phospho-specific antibodies. Taken together, our work validates chemical tagging post-single-stage phosphoenrichment as a general strategy for studying cellular signaling in primary tissues.

BIOLOGICAL SIGNIFICANCE

Through the use of a quantitatively reproducible, proteome-wide phosphopeptide enrichment strategy, we demonstrated the feasibility of post-phosphopeptide purification chemical labeling and tagging as an enabling approach for quantitative phosphoproteomics of primary tissues. Using reductive dimethyl labeling as a generalized chemical tagging strategy, we compared the performance of post-phosphopeptide purification chemical tagging to the well established community standard, SILAC, in insulin-stimulated tissue culture cells. We then extended our method to the analysis of low-dose insulin signaling in murine muscle tissue, and report on the analytical and biological significance of our results.

DAPK and cytoskeleton-associated functions

Death-associated protein kinase (DAPK) undergoes activation in response to various death stimuli, and they have been associated with an increase in DAPK catalytic activity. One of the most prominent features of DAPK-induced cell death is the effect on the cytoskeleton, including loss of matrix attachment, and membrane blebbing. One known cytoskeletal-associated substrate of DAPK is the myosin-II light chain, phosphorylated by DAPK on Ser(19), thus stabilizing actin stress fibres. Moreover, paxillin, a component of focal adhesions, was found to be localized in close proximity to the tips of the DAPK-positive filaments, indicating that stress fibres containing DAPK extend to focal contacts. Forced expression of DAPK in multiple cell types results in morphological changes such as cell rounding, membrane blebbing, shrinking and detachment. During directed migration, DAPK functions as a potent inhibitor of cell polarization, as evidenced by its perturbation of the formation of static protrusion at the leading edge. Furthermore, DAPK inhibits random migration by suppressing directional persistence. One of the studies considered DAPK as an anoikis inducer. Others showed that DAP-kinase inhibits the activities of cell surface integrins by converting them into an inactive conformation. Biochemical experiments have established the DAPK binding to Syntaxin1 and its subsequent phosphorylation at Ser(188) in a Ca(2+) dependent manner. This phosphorylation event has been shown to decrease the binding of Syntaxin to MUNC18-1, a protein critically involved in synaptic vesicle docking. Here, we have investigated the structural interactions that modulate DAPK phosphorylation with Syntaxin and its functional role in binding to the MUNC18-1 to regulate vesicle docking. This review will summarize our current knowledge of the role of DAPK on cytoskeleton reorganization and report the mechanisms that regulate these changes.

The DAP-kinase interactome

DAP-kinase (DAPK) is a Ca(2+)/calmodulin regulated Ser/Thr kinase that activates a diverse range of cellular activities. It is subject to multiple layers of regulation involving both intramolecular signaling, and interactions with additional proteins, including other kinases and phosphatases. Its protein stability is modulated by at least three distinct ubiquitin-dependent systems. Like many kinases, DAPK participates in several signaling cascades, by phosphorylating additional kinases such as ZIP-kinase and protein kinase D (PKD), or Pin1, a phospho-directed peptidyl-prolyl isomerase that regulates the function of many phosphorylated proteins. Other substrate targets have more direct cellular effects; for example, phosphorylation of the myosin II regulatory chain and tropomyosin mediate some of DAPK's cytoskeletal functions, including membrane blebbing during cell death and cell motility. DAPK induces distinct death pathways of apoptosis, autophagy and programmed necrosis. Among the substrates implicated in these processes, phosphorylation of PKD, Beclin 1, and the NMDA receptor has been reported. Interestingly, not all cellular effects are mediated by DAPK's catalytic activity. For example, by virtue of protein-protein interactions alone, DAPK activates pyruvate kinase isoform M2, the microtubule affinity regulating kinases and inflammasome protein NLRP3, to promote glycolysis, influence microtubule dynamics, and enhance interleukin-1β production, respectively. In addition, a number of other substrates and interacting proteins have been identified, the physiological significance of which has not yet been established. All of these substrates, effectors and regulators together comprise the DAPK interactome. By presenting the components of the interactome network, this review will clarify both the mechanisms by which DAPK function is regulated, and by which it mediates its various cellular effects.

Vitamin D-responsive SGPP2 variants associated with lung cell expression and lung function

Background

Vitamin D is associated with lung health in epidemiologic studies, but mechanisms mediating observed associations are poorly understood. This study explores mechanisms for an effect of vitamin D in lung through an in vivo gene expression study, an expression quantitative trait loci (eQTL) analysis in lung tissue, and a population-based cohort study of sequence variants.

Methods

Microarray analysis investigated the association of gene expression in small airway epithelial cells with serum 25(OH)D in adult non-smokers. Sequence variants in candidate genes identified by the microarray were investigated in a lung tissue eQTL database, and also in relation to cross-sectional pulmonary function in the Health, Aging, and Body Composition (Health ABC) study, stratified by race, with replication in the Framingham Heart Study (FHS).

Results

13 candidate genes had significant differences in expression by serum 25(OH)D (nominal p < 0.05), and a genome-wide significant eQTL association was detected for SGPP2. In Health ABC, SGPP2 SNPs were associated with FEV₁ in both European- and African-Americans, and the gene-level association was replicated in European-American FHS participants. SNPs in 5 additional candidate genes (DAPK1, FSTL1, KAL1, KCNS3, and RSAD2) were associated with FEV₁ in Health ABC participants.

Conclusions

SGPP2, a sphingosine-1-phosphate phosphatase, is a novel vitamin D-responsive gene associated with lung function. The identified associations will need to be followed up in further studies.

In-depth proteomic analysis of human tropomyosin by top-down mass spectrometry

Tropomyosins (Tms) are a family of highly conserved actin-binding proteins that play critical roles in a variety of processes, most notably, in the regulation of muscle contraction and relaxation. It is well known that different Tm isoforms have distinct functions and that altered expression of Tm isoforms could lead to changes in cardiac structure and function. To precisely define Tm isoform expression in the human heart, towards a better understanding of their functional roles, we have employed top-down mass spectrometry for in-depth proteomic characterization of Tm isoforms. Using a minimal amount of human heart tissue from rejected donor organs, we confirmed the presence of multiple Tm isoforms including α-Tm, β-Tm and κ-Tm in the human heart, with α-Tm being the predominant isoform, followed by minor isoforms of β-Tm and κ-Tm. Interestingly, our data revealed regional variations of Tm isoforms and post-translational modifications in the human heart. Specifically, the expression level of κ-Tm was highest in the left atrium but nearly undetectable in the left ventricle. The phosphorylation level of α-Tm (pα-Tm) was significantly higher in the atria than it was in the ventricles. The sequences of all Tm isoforms were characterized and the sites of post-translational modifications were localized. Clearly, top-down mass spectrometry is an attractive method for comprehensive characterization of Tm isoforms and post-translational modifications since it can universally detect and quantify all types of protein modifications without a priori knowledge and without the need for specific antibodies.

Dynamic and differential regulation in the microRNA expression in the developing and mature cataractous rat lens

Recent evidence supports a role for microRNAs (miRNAs) in regulating gene expression, and alterations in gene expression are known to affect cells involved in the development of ageing disorders. Using developing rat lens epithelial cells (LECs), we profiled the expression of miRNAs by a microarray-based approach. Few gene expression changes known to be involved in pathogenesis or cytoprotection were uniquely influenced by miRNA expression. Most miRNAs increased or decreased in abundance (let 7b, let 7c, miR29a, miR29c, miR126 and miR551b) in LECs/lenses during late embryonic and post-natal development and in cataract. Among them, miR29a, miR29c and miR126 were dramatically decreased in cataractous LECs from Shumiya Cataract Rats (SCRs). Specifically, the cytoskeleton remodelling genes tropomyosin (Tm) 1α and 2β, which have been implicated in the initiation of pathophysiology, were targets of miR29c and were over-stimulated as demonstrated by inhibitor experiments. In transfection experiments, increasing the level of miR29c caused a corresponding decrease in the expression of Tm1α and 2β, suggesting that miR29c may regulate the translation of Tm1α and 2β. 3′UTR luciferase activity of Tm1α, not 2β, was significantly decreased in miR29c-transfected mouse LECs. These findings demonstrate changes in miRNAs expression, and target molecules have potential as diagnostic indicators of ageing and as a foundation of miR-based therapeutics for age-related diseases.

miR-29c is downregulated in renal interstitial fibrosis in humans and rats and restored by HIF-α activation

Treatment with L-mimosine, which activates hypoxia-inducible factor-α (HIF-α), attenuates renal tubulointerstitial injury and improves renal function in a rat remnant kidney model. The miR-29 family of microRNAs directly targets a large number of extracellular matrix genes and reduces renal interstitial fibrosis. We analyzed microRNA expression profiles in rat remnant kidneys with or without treatment with L-mimosine. The expression of miR-29c was downregulated in rat remnant kidneys compared with sham control and significantly restored by the L-mimosine treatment. In cultured human kidney epithelial HK2 cells, cobalt chloride activated HIF-α and upregulated miR-29c expression. The upregulation of miR-29c expression was significantly attenuated by knockdown of HIF-1α or HIF-2α. Downregulation of miR-29c was associated with significant increases in interstitial fibrosis, collagen type II α1 (COL2A1) protein, and tropomyosin 1α (TPM1) protein in rat remnant kidneys and in kidneys from IgA nephropathy patients. The increases in rat remnant kidneys were attenuated by the L-mimosine treatment. COL2A1 and TPM1 were confirmed to be new, direct targets of miR-29c. In conclusion, miR-29c, an antifibrotic microRNA, is upregulated by HIF-α activation. MiR-29c is downregulated in renal interstitial fibrosis in humans and rats and restored by activation of HIF-α that attenuates fibrosis.

Biochemical and functional characterization of the ROC domain of DAPK establishes a new paradigm of GTP regulation in ROCO proteins

DAPK (death-associated protein kinase) is a newly recognized member of the mammalian family of ROCO proteins, characterized by common ROC (Ras of complex proteins) and COR (C-terminal of ROC) domains. In the present paper, we review our recent work showing that DAPK is functionally a ROCO protein; its ROC domain binds and hydrolyses GTP. Furthermore, GTP binding regulates DAPK catalytic activity in a novel manner by enhancing autophosphorylation on inhibitory Ser308, thereby promoting the kinase 'off' state. This is a novel mechanism for in cis regulation of kinase activity by the distal ROC domain. The functional similarities between DAPK and the Parkinson's disease-associated protein LRRK2 (leucine-rich repeat protein kinase 2), another member of the ROCO family, are also discussed.

Top-down targeted proteomics for deep sequencing of tropomyosin isoforms

Tropomyosins (Tm) constitute a family of ubiquitous and highly conserved actin-binding proteins, playing essential roles in a variety of biological processes. Tm isoforms produced by multiple Tm encoding genes and alternatively expressed exons along with post-translational modifications (PTMs) regulate Tm function. Therefore, to gain a better understanding of the functional role of Tm, it is essential to fully characterize Tm isoforms. Herein, we developed a top-down high-resolution mass spectrometry (MS)-based targeted proteomics method for comprehensive characterization of Tm isoforms. α-Tm was identified to be the predominant isoform in swine cardiac muscle. We further characterized its sequence and localized the PTMs such as acetylation and phosphorylation as well as amino acid polymorphisms. Interestingly, we discovered a "novel" Tm isoform that does not match with any of the currently available swine Tm sequences. A deep sequencing of this isoform by top-down MS revealed an exact match with mouse β-Tm sequence, suggesting that this "novel" isoform is swine β-Tm which is 100% conserved between swine and mouse. Taken together, we demonstrated that top-down targeted proteomics provides a powerful tool for deep sequencing of Tm isoforms from genetic variations together with complete mapping of the PTM sites.

Regulation of endothelial permeability and transendothelial migration of cancer cells by tropomyosin-1 phosphorylation

BACKGROUND

Loss of endothelial cell integrity and selective permeability barrier is an early event in the sequence of oxidant-mediated injury and may result in atherosclerosis, hypertension and facilitation of transendothelial migration of cancer cells during metastasis. We already reported that endothelial cell integrity is tightly regulated by the balanced co-activation of p38 and ERK pathways. In particular, we showed that phosphorylation of tropomyosin-1 (tropomyosin alpha-1 chain = Tm1) at Ser283 by DAP kinase, downstream of the ERK pathway might be a key event required to maintain the integrity and normal functions of the endothelium in response to oxidative stress.

METHODS

Endothelial permeability was assayed by monitoring the passage of Dextran-FITC through a tight monolayer of HUVECs grown to confluence in Boyden chambers. Actin and Tm1 dynamics and distribution were evaluated by immunofluorescence. We modulated the expression of Tm1 by siRNA and lentiviral-mediated expression of wild type and mutated forms of Tm1 insensitive to the siRNA. Transendothelial migration of HT-29 colon cancer cells was monitored in Boyden chambers similarly as for permeability.

RESULTS

We provide evidence indicating that Tm1 phosphorylation at Ser283 is essential to regulate endothelial permeability under oxidative stress by modulating actin dynamics. Moreover, the transendothelial migration of colon cancer cells is also regulated by the phosphorylation of Tm1 at Ser283.

CONCLUSION

Our finding strongly support the role for the phosphorylation of endothelial Tm1 at Ser283 to prevent endothelial barrier dysfunction associated with oxidative stress injury.

Shear stress regulates expression of death-associated protein kinase in suppressing TNFα-induced endothelial apoptosis

Death associated protein kinase (DAPK) is a positive regulator in tumor necrosis factor α (TNFα)-induced apoptotic pathway, and DAPK expression is lost in cancer cells. In the vasculature, misdirected apoptosis in endothelial cells leads to pathological conditions such as inflammation and physiological shear stress is protective against apoptosis. Using bovine aortic endothelial cells, we found that DAPK expression increased, while the auto-inhibitory phosphorylation of serine 308 decreased with shear stress at 12 dynes/cm(2) for 6 h. Quantitative RT-PCR revealed a corresponding increase in DAPK mRNA [P < 0.01]. We found that after 18-h TNFα induction, shearing cells for another 6 h significantly reduced apoptosis based on TUNEL staining [P < 0.05], although cell necrosis was not affected. Under the same conditions, we observed significantly decreased overall DAPK, as well as phospho-serine 308 DAPK [P < 0.05] compared to TNFα treatment alone. Caspase-3 and -7 activities downstream of DAPK were also attenuated. Shearing cells alone resulted in enhanced apoptosis, likely due to increased DAPK activity. Our findings were further supported by DAPK siRNA, which yielded contrary results. We present conclusive evidence for the first time that shear stress of up to 6 h up-regulates DAPK expression and activation. However, in the presence of apoptotic stimuli such as TNFα, shear stress caused decrease in DAPK activity. In fact, long-term shear stress of 24 h significantly reduced overall DAPK expression. Our findings strongly support a novel role for DAPK in mediating effects of shear stress in suppressing cytokine-activated apoptosis.

Endothelial cell dysfunction and cytoskeletal changes associated with repression of p16(INK4a) during immortalization

The immortalization process is a fundamental step in the development of most (if not all) human cancers, including the aggressive endothelial cell (EC)-derived malignancy angiosarcoma. Inactivation of the tumor suppressor p16^INK4a and the development of multiple chromosomal abnormalities are features of angiosarcoma that are recapitulated during telomerase-mediated immortalization of human ECs in vitro. The present study used a panel of telomerase-immortalized bone marrow EC (BMEC) lines to define the consequences of inactivation of p16^INK4a on EC function and to identify molecular changes associated with repression of p16^INK4a. In a comparison of two immortalized BMEC mass cultures and six clones, the cell lines that repressed p16^INK4a showed a higher rate of proliferation and an impaired ability to undergo morphogenic differentiation and form vessel-like structures in vitro. Proteomic comparison of a p16^INK4a-negative and a p16^INK4a-positive BMEC mass culture at early- and late-passage time points following transduction with telomerase reverse transcriptase (hTERT) revealed altered expression of cytoskeletal proteins, including vimentin and α-tropomyosin (αTm), in the immortal cells. Immunoblot analyses of a panel of 11 immortal clones showed that cells that lacked p16^INK4a expression tended to accumulate more dramatic changes in these cytoskeletal proteins than cells that retained p16^INK4a expression. This corresponded with aberrant cytoskeletal architectures among p16^INK4a-negative clones, which featured thicker actin stress fibers and less fluid membrane ruffles than p16^INK4a-positive cells. A direct link between p16^INK4a repression and defective EC function was confirmed by analysis of normal cells transfected with small interfering RNA (siRNA) targeting p16^INK4a. siRNA-mediated repression of p16^INK4a significantly impaired random motility and vessel formation in vitro. This report is the first to demonstrate that ECs that repress the expression of p16^INK4a are prone to defects in motility, morphogenesis and cytoskeletal organization. These defects are likely to reflect alterations that occur during the development of EC-derived malignancies.

Characterization of the endothelial cell cytoskeleton following HLA class I ligation

BACKGROUND

Vascular endothelial cells (ECs) are a target of antibody-mediated allograft rejection. In vitro, when the HLA class I molecules on the surface of ECs are ligated by anti-HLA class I antibodies, cell proliferation and survival pathways are activated and this is thought to contribute to the development of antibody-mediated rejection. Crosslinking of HLA class I molecules by anti-HLA antibodies also triggers reorganization of the cytoskeleton, which induces the formation of F-actin stress fibers. HLA class I induced stress fiber formation is not well understood.

METHODOLOGY AND PRINCIPAL FINDINGS

The present study examines the protein composition of the cytoskeleton fraction of ECs treated with HLA class I antibodies and compares it to other agonists known to induce alterations of the cytoskeleton in endothelial cells. Analysis by tandem mass spectrometry revealed unique cytoskeleton proteomes for each treatment group. Using annotation tools a candidate list was created that revealed 12 proteins, which were unique to the HLA class I stimulated group. Eleven of the candidate proteins were phosphoproteins and exploration of their predicted kinases provided clues as to how these proteins may contribute to the understanding of HLA class I induced antibody-mediated rejection. Three of the candidates, eukaryotic initiation factor 4A1 (eIF4A1), Tropomyosin alpha 4-chain (TPM4) and DDX3X, were further characterized by Western blot and found to be associated with the cytoskeleton. Confocal microscopy analysis showed that class I ligation stimulated increased eIF4A1 co-localization with F-actin and paxillin.

CONCLUSIONS/SIGNIFICANCE

Colocalization of eIF4A1 with F-actin and paxillin following HLA class I ligation suggests that this candidate protein could be a target for understanding the mechanism(s) of class I mediated antibody-mediated rejection. This proteomic approach for analyzing the cytoskeleton of ECs can be applied to other agonists and various cells types as a method for uncovering novel regulators of cytoskeleton changes.

Functional diversity of actin cytoskeleton in neurons and its regulation by tropomyosin

Neurons comprise functionally, molecularly, and spatially distinct subcellular compartments which include the soma, dendrites, axon, branches, dendritic spines, and growth cones. In this chapter, we detail the remarkable ability of the neuronal cytoskeleton to exquisitely regulate all these cytoplasmic distinct partitions, with particular emphasis on the microfilament system and its plethora of associated proteins. Importance will be given to the family of actin-associated proteins, tropomyosin, in defining distinct actin filament populations. The ability of tropomyosin isoforms to regulate the access of actin-binding proteins to the filaments is believed to define the structural diversity and dynamics of actin filaments and ultimately be responsible for the functional outcome of these filaments.