Vasodilator-stimulated phosphoprotein (VASP) regulates actin polymerization and contraction in airway smooth muscle by a vinculin-dependent mechanism

A-Kinase-Anchoring Protein Subtypes Differentially Regulate GPCR Signaling and Function in Human Airway Smooth Muscle

AKAPs (A-kinase-anchoring proteins) act as scaffold proteins that anchor the regulatory subunits of the cAMP-dependent PKA (protein kinase A) to coordinate and compartmentalize signaling elements and signals downstream of Gs-coupled GPCRs (G protein-coupled receptors). The β2AR (β-2-adrenoceptor), as well as the Gs-coupled EP2 and EP4 (E-prostanoid) receptor subtypes of the EP receptor subfamily, are effective regulators of multiple airway smooth muscle (ASM) cell functions whose dysregulation contributes to asthma pathobiology. Here, we identify specific roles of the AKAPs Ezrin and Gravin in differentially regulating PKA substrates downstream of the β2AR, EP2R (EP2 receptor) and EP4R. Knockdown of Ezrin, Gravin, or both in primary human ASM cells caused differential phosphorylation of the PKA substrates VASP (vasodilator-stimulated phosphoprotein) and HSP20 (heat shock protein 20). Ezrin knockdown, as well as combined Ezrin and Gravin knockdown, significantly reduced the induction of phospho-VASP and phospho-HSP20 by β2AR, EP2R, and EP4R agonists. Gravin knockdown inhibited the induction of phospho-HSP20 by β2AR, EP2R, and EP4R agonists. Knockdown of Ezrin, Gravin, or both also attenuated histamine-induced phosphorylation of MLC20. Moreover, knockdown of Ezrin, Gravin, or both suppressed the inhibitory effects of Gs-coupled receptor agonists on cell migration in ASM cells. These findings demonstrate the role of AKAPs in regulating Gs-coupled GPCR signaling and function in ASM and suggest the therapeutic utility of targeting specific AKAP family members in the management of asthma.

Targeting cytoskeletal biomechanics to modulate airway smooth muscle contraction in asthma

To contract, to deform, and remodel, the airway smooth muscle cell relies on dynamic changes in the structure of its mechanical force-bearing cytoskeleton. These alternate between a "fluid-like" (relaxed) state characterized by weak contractile protein-protein interactions within the cytoskeletal apparatus and a "solid-like" (contractile) state promoted by strong and highly organized molecular interactions. In this review, we discuss the roles for actin, myosin, factors promoting actin polymerization and depolymerization, adhesome complexes, and cell-cell junctions in these dynamic processes. We describe the relationship between these cytoskeletal factors, extracellular matrix components of bronchial tissue, and mechanical stretch and other changes within the airway wall in the context of the physical mechanisms of cytoskeletal fluidization-resolidification. We also highlight studies that emphasize the distinct processes of cell shortening and force transmission in airway smooth muscle and previously unrecognized roles for actin in cytoskeletal dynamics. Finally, we discuss the implications of these discoveries for understanding and treating airway obstruction in asthma.

Aberrant expression of VASP serves as a potential prognostic biomarker and therapeutic target for oral squamous cell carcinoma

OBJECTIVE

To address the molecular markers linked to the development and progression of oral squamous cell carcinoma (OSCC), we sought to analyze the expression of vasodilator-stimulated phosphoproteins (VASP) in OSCC samples.

STUDY DESIGN

This study used 51 OSCC patients and The Cancer Genome Atlas-Head and Neck Squamous Cell Carcinoma (TCGA-HNSC) dataset to analyze VASP expression. The association between VASP mRNA expression and HNSCC clinicopathological features, tumor infiltration, functional roles, and gene co-expression of VASP also were evaluated.

RESULTS

Our study observed increased VASP mRNA expression in OSCC tumor tissues compared to normal tissues, supported by TCGA-HNSC dataset analysis. Elevated VASP levels correlated with advanced tumor stage, higher grade, nodal metastasis, and poor survival, indicating its potential as a prognostic marker. Protein analysis and immunohistochemistry confirmed these findings, and in silico analysis revealed VASP involvement in key cancer-related processes and its correlation with IL8, RAP1A expression, and tumor infiltration levels.

CONCLUSIONS

In conclusion, VASP emerges as a promising diagnostic and prognostic marker for OSCC within HNSCC, emphasizing the importance of exploring its regulatory mechanisms and therapeutic applications. The revealed pathways present avenues for targeted treatment in OSCC. Despite limitations, this study provides valuable insights with potential implications for improving patient outcomes.

Yiqi Kaimi prescription regulates protein phosphorylation to promote intestinal motility in slow transit constipation

ETHNOPHARMACOLOGICAL RELEVANCE

The clinical efficacy of the Yiqi Kaimi prescription has been confirmed in slow transit constipation. However, the effects and biological mechanism of Yiqi Kaimi prescription are still unclear.

AIMS OF THE STUDY

To identify the effects of Yiqi Kaimi prescription on intestinal motility; To reveal the potential key targets and pathways of Yiqi Kaimi prescription for the treatment of slow transit constipation.

MATERIALS AND METHODS

The effects of Yiqi Kaimi prescription on slow transit constipation were investigated in a mouse model. The terminal ink propulsion experiment and fecal indocyanine green imaging was used to measure the intestinal transit time. Protein phosphorylation changes in colon tissues treated with Yiqi Kaimi prescription were detected using a Phospho Explorer antibody microarray. Bioinformatic analyses were performed using the Database for Annotation Visualization and Integrated Discovery (DAVID) and the Search Tool for the Retrieval of Interacting Genes (STRING). Western blot analysis and immunohistochemistry confirmed the observed changes in phosphorylation.

RESULT

s: Yiqi Kaimi prescription significantly increased the intestinal transit rate (P < 0.05 vs. model) and reduced the time to first discharge of feces containing fecal indocyanine green imaging in mice (P < 0.05 vs. model). The administration of Yiqi Kaimi prescription induced phosphorylation changes in 41 proteins, with 9 upregulated proteins and 32 downregulated proteins. Functional classification of the phosphorylated proteins with DAVID revealed that the critical biological processes included tyrosine protein kinases, positive regulation of calcium-mediated signaling and response to muscle stretch. The phosphorylation of the spleen tyrosine kinase (SYK) at Tyr348 increased 2.19-fold, which was the most significant change. The phosphorylation level of the transcription factor p65 (RELA) at Thr505 was decreased 0.57-fold. SYK was a hub protein in the protein-protein interaction network and SYK and RELA formed the core of the secondary subnetwork. The key protein phosphorylation after treatment with Yiqi Kaimi prescription were verified by Western blot analysis and immunohistochemistry.

CONCLUSION

Yiqi Kaimi prescription significantly enhanced intestinal motility. This effect was attributed to alterations in the phosphorylation levels of various target proteins. The observed changes in protein phosphorylation, including SYK and RELA, may serve as crucial factors in the treatment of slow transit constipation.

Rho-Kinase Inhibition of Active Force and Passive Tension in Airway Smooth Muscle: A Strategy for Treating Airway Hyperresponsiveness in Asthma

Rho-kinase inhibitors have been identified as a class of potential drugs for treating asthma because of their ability to reduce airway inflammation and active force in airway smooth muscle (ASM). Past research has revealed that, besides the effect on the ASM's force generation, rho-kinase (ROCK) also regulates actin filament formation and filament network architecture and integrity, thus affecting ASM's cytoskeletal stiffness. The present review is not a comprehensive examination of the roles played by ROCK in regulating ASM function but is specifically focused on passive tension, which is partially determined by the cytoskeletal stiffness of ASM. Understanding the molecular basis for maintaining active force and passive tension in ASM by ROCK will allow us to determine the suitability of ROCK inhibitors and its downstream enzymes as a class of drugs in treating airway hyperresponsiveness seen in asthma. Because clinical trials using ROCK inhibitors in the treatment of asthma have yet to be conducted, the present review focuses on the in vitro effects of ROCK inhibitors on ASM's mechanical properties which include active force generation, relaxation, and passive stiffness. The review provides justification for future clinical trials in the treatment of asthma using ROCK inhibitors alone and in combination with other pharmacological and mechanical interventions.

Membrane adhesion junctions regulate airway smooth muscle phenotype and function

The local environment surrounding airway smooth muscle (ASM) cells has profound effects on the physiological and phenotypic properties of ASM tissues. ASM is continually subjected to the mechanical forces generated during breathing and to the constituents of its surrounding extracellular milieu. The smooth muscle cells within the airways continually modulate their properties to adapt to these changing environmental influences. Smooth muscle cells connect to the extracellular cell matrix (ECM) at membrane adhesion junctions that provide mechanical coupling between smooth muscle cells within the tissue. Membrane adhesion junctions also sense local environmental signals and transduce them to cytoplasmic and nuclear signaling pathways in the ASM cell. Adhesion junctions are composed of clusters of transmembrane integrin proteins that bind to ECM proteins outside the cell and to large multiprotein complexes in the submembranous cytoplasm. Physiological conditions and stimuli from the surrounding ECM are sensed by integrin proteins and transduced by submembranous adhesion complexes to signaling pathways to the cytoskeleton and nucleus. The transmission of information between the local environment of the cells and intracellular processes enables ASM cells to rapidly adapt their physiological properties to modulating influences in their extracellular environment: mechanical and physical forces that impinge on the cell, ECM constituents, local mediators, and metabolites. The structure and molecular organization of adhesion junction complexes and the actin cytoskeleton are dynamic and constantly changing in response to environmental influences. The ability of ASM to rapidly accommodate to the ever-changing conditions and fluctuating physical forces within its local environment is essential for its normal physiological function.

Cardiovascular Functions of Ena/VASP Proteins: Past, Present and Beyond

Actin binding proteins are of crucial importance for the spatiotemporal regulation of actin cytoskeletal dynamics, thereby mediating a tremendous range of cellular processes. Since their initial discovery more than 30 years ago, the enabled/vasodilator-stimulated phosphoprotein (Ena/VASP) family has evolved as one of the most fascinating and versatile family of actin regulating proteins. The proteins directly enhance actin filament assembly, but they also organize higher order actin networks and link kinase signaling pathways to actin filament assembly. Thereby, Ena/VASP proteins regulate dynamic cellular processes ranging from membrane protrusions and trafficking, and cell-cell and cell-matrix adhesions, to the generation of mechanical tension and contractile force. Important insights have been gained into the physiological functions of Ena/VASP proteins in platelets, leukocytes, endothelial cells, smooth muscle cells and cardiomyocytes. In this review, we summarize the unique and redundant functions of Ena/VASP proteins in cardiovascular cells and discuss the underlying molecular mechanisms.

Vascular mechanotransduction

This review aims to survey the current state of mechanotransduction in vascular smooth muscle cells (VSMCs) and endothelial cells (ECs), including their sensing of mechanical stimuli and transduction of mechanical signals that result in the acute functional modulation and longer-term transcriptomic and epigenetic regulation of blood vessels. The mechanosensors discussed include ion channels, plasma membrane-associated structures and receptors, and junction proteins. The mechanosignaling pathways presented include the cytoskeleton, integrins, extracellular matrix, and intracellular signaling molecules. These are followed by discussions on mechanical regulation of transcriptome and epigenetics, relevance of mechanotransduction to health and disease, and interactions between VSMCs and ECs. Throughout this review, we offer suggestions for specific topics that require further understanding. In the closing section on conclusions and perspectives, we summarize what is known and point out the need to treat the vasculature as a system, including not only VSMCs and ECs but also the extracellular matrix and other types of cells such as resident macrophages and pericytes, so that we can fully understand the physiology and pathophysiology of the blood vessel as a whole, thus enhancing the comprehension, diagnosis, treatment, and prevention of vascular diseases.

Single-cell transcriptomic heterogeneity between conduit and resistance mesenteric arteries in rats

The endothelium contains morphologically similar cells throughout the vasculature, but individual cells along the length of a single vascular tree or in different regional circulations function dissimilarly. When observations made in large arteries are extrapolated to explain the function of endothelial cells (ECs) in the resistance vasculature, only a fraction of these observations are consistent between artery sizes. To what extent endothelial (EC) and vascular smooth muscle cells (VSMCs) from different arteriolar segments of the same tissue differ phenotypically at the single-cell level remains unknown. Therefore, single-cell RNA-seq (10x Genomics) was performed using a 10X Genomics Chromium system. Cells were enzymatically digested from large (>300 µm) and small (<150 µm) mesenteric arteries from nine adult male Sprague-Dawley rats, pooled to create six samples (3 rats/sample, 3 samples/group). After normalized integration, the dataset was scaled before unsupervised cell clustering and cluster visualization using UMAP plots. Differential gene expression analysis allowed us to infer the biological identity of different clusters. Our analysis revealed 630 and 641 differentially expressed genes (DEGs) between conduit and resistance arteries for ECs and VSMCs, respectively. Gene ontology analysis (GO-Biological Processes, GOBP) of scRNA-seq data discovered 562 and 270 pathways for ECs and VSMCs, respectively, that differed between large and small arteries. We identified eight and seven unique ECs and VSMCs subpopulations, respectively, with DEGs and pathways identified for each cluster. These results and this dataset allow the discovery and support of novel hypotheses needed to identify mechanisms that determine the phenotypic heterogeneity between conduit and resistance arteries.

Structural, biochemical, and functional properties of the Rap1-Interacting Adaptor Molecule (RIAM)

Leukocytes, the leading players of immune system, are involved in innate and adaptive immune responses. Leukocyte adhesion to endothelial cells during transmigration or to antigen presenting cells during T cell activation, requires integrin activation through a process termed inside-out integrin signaling. In hematopoietic cells, Rap1 and its downstream effector RIAM (Rap1-interacting adaptor molecule) form a cornerstone for inside-out integrin activation. The Rap1/RIAM pathway is involved in signal integration for activation, actin remodeling and cytoskeletal reorganization in T cells, as well as in myeloid cell differentiation and function. RIAM is instrumental for phagocytosis, a process requiring particle recognition, cytoskeletal remodeling and membrane protrusion for engulfment and digestion. In the present review, we discuss the structural and molecular properties of RIAM and the recent discoveries regarding the functional role of the Rap1/RIAM module in hematopoietic cells.

Acetylation of Abelson interactor 1 at K416 regulates actin cytoskeleton and smooth muscle contraction

Actin cytoskeletal reorganization plays an important role in regulating smooth muscle contraction, which is essential for the modulation of various physiological functions including airway tone. The adapter protein Abi1 (Abelson interactor 1) participates in the control of smooth muscle contraction. The mechanisms by which Abi1 coordinates smooth muscle function are not fully understood. Here, we found that contractile stimulation elicited Abi1 acetylation in human airway smooth muscle (HASM) cells. Mutagenesis analysis identified lysine‐416 (K416) as a major acetylation site. Replacement of K416 with Q (glutamine) enhanced the interaction of Abi1 with neuronal Wiskott‐Aldrich syndrome protein (N‐WASP), an important actin‐regulatory protein. Moreover, the expression of K416Q Abi1 promoted actin polymerization and smooth muscle contraction without affecting myosin light chain phosphorylation at Ser‐19 and vimentin phosphorylation at Ser‐56. Furthermore, p300 is a lysine acetyltransferase that catalyzes acetylation of histone and non‐histone proteins in various cell types. Here, we discovered that a portion of p300 was localized in the cytoplasm of HASM cells. Knockdown of p300 reduced the agonist‐induced Abi1 acetylation in HASM cells and in mouse airway smooth muscle tissues. Smooth muscle conditional knockout of p300 inhibited actin polymerization and the contraction of airway smooth muscle tissues without affecting myosin light chain phosphorylation and vimentin phosphorylation. Together, our results suggest that contractile stimulation induces Abi1 acetylation via p300 in smooth muscle. Acetylation at K416 promotes the coupling of Abi1 with N‐WASP, which facilitates actin polymerization and smooth muscle contraction. This is a novel acetylation‐dependent regulation of the actin cytoskeleton in smooth muscle.

Vasorelaxing cell permeant phosphopeptide mimetics for subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) due to rupture of an intracranial aneurysm leads to vasospasm resulting in delayed cerebral ischemia. Therapeutic options are currently limited to hemodynamic optimization and nimodipine, which have marginal clinical efficacy. Nitric oxide (NO) modulates cerebral blood flow through activation of the cGMP-Protein Kinase G (PKG) pathway. Our hypothesis is that SAH results in downregulation of signaling components in the NO-PKG pathway which could explain why treatments for vasospasm targeting this pathway lack efficacy and that treatment with a cell permeant phosphopeptide mimetic of downstream effector prevents delayed vasospasm after SAH. Using a rat endovascular perforation model, reduced levels of NO-PKG pathway molecules were confirmed. Additionally, it was determined that expression and phosphorylation of a PKG substrate: Vasodilator-stimulated phosphoprotein (VASP) was downregulated. A family of cell permeant phosphomimetic of VASP (VP) was wasdesigned and shown to have vasorelaxing property that is synergistic with nimodipine in intact vascular tissuesex vivo. Hence, treatment targeting the downstream effector of the NO signaling pathway, VASP, may bypass receptors and signaling elements leading to vasorelaxation and that treatment with VP can be explored as a therapeutic strategy for SAH induced vasospasm and ameliorate neurological deficits.

RIAM-VASP Module Relays Integrin Complement Receptors in Outside-In Signaling Driving Particle Engulfment

The phagocytic integrins and complement receptors α_Mβ₂/CR3 and α_Xβ₂/CR4 are classically associated with the phagocytosis of iC3b-opsonized particles. The activation of this receptor is dependent on signals derived from other receptors (inside-out signaling) with the crucial involvement of the Rap1-RIAM-Talin-1 pathway. Here, we analyze the implication of RIAM and its binding partner VASP in the signaling events occurring downstream of β₂ integrins (outside-in) during complement-mediated phagocytosis. To this end, we used HL-60 promyelocytic cell lines deficient in RIAM or VASP or overexpressing EGFP-tagged VASP to determine VASP dynamics at phagocytic cups. Our results indicate that RIAM-deficient HL-60 cells presented impaired particle internalization and altered integrin downstream signaling during complement-dependent phagocytosis. Similarly, VASP deficiency completely blocked phagocytosis, while VASP overexpression increased the random movement of phagocytic particles at the cell surface, with reduced internalization. Moreover, the recruitment of VASP to particle contact sites, amount of pSer157-VASP and formation of actin-rich phagocytic cups were dependent on RIAM expression. Our results suggested that RIAM worked as a relay for integrin complement receptors in outside-in signaling, coordinating integrin activation and cytoskeletal rearrangements via its interaction with VASP.

Ste20-like Kinase-mediated Control of Actin Polymerization Is a New Mechanism for Thin Filament-associated Regulation of Airway Smooth Muscle Contraction

It has been reported that actin polymerization is regulated by protein tyrosine phosphorylation in smooth muscle on contractile stimulation. The role of protein serine/threonine phosphorylation in modulating actin dynamics is underinvestigated. SLK (Ste20-like kinase) is a serine/threonine protein kinase that plays a role in apoptosis, cell cycle, proliferation, and migration. The function of SLK in smooth muscle is mostly unknown. Here, SLK knockdown (KD) inhibited acetylcholine (ACh)-induced actin polymerization and contraction without affecting myosin light chain phosphorylation at Ser-19 in human airway smooth muscle. Stimulation with ACh induced paxillin phosphorylation at Ser-272, which was reduced in SLK KD cells. However, SLK did not catalyze paxillin Ser-272 phosphorylation in vitro. But, SLK KD attenuated Plk1 (polo-like kinase 1) phosphorylation at Thr-210. Plk1 mediated paxillin phosphorylation at Ser-272 in vitro. Expression of the nonphosphorylatable paxillin mutant S272A (substitution of alanine at Ser-272) attenuated the agonist-enhanced F-actin/G-actin ratios without affecting myosin light chain phosphorylation. Because N-WASP (neuronal Wiskott-Aldrich Syndrome Protein) phosphorylation at Tyr-256 (an indication of its activation) promotes actin polymerization, we also assessed the role of paxillin phosphorylation in N-WASP activation. S272A paxillin inhibited the ACh-enhanced N-WASP phosphorylation at Tyr-256. Together, these results suggest that SLK regulates paxillin phosphorylation at Ser-272 via Plk1, which modulates N-WASP activation and actin polymerization in smooth muscle. SLK-mediated actin cytoskeletal reorganization may facilitate force transmission between the contractile units and the extracellular matrix.

Extracellular regulation of airway smooth muscle contraction

The molecular mechanisms governing the contraction of airway smooth muscle have always been at the forefront of asthma research. New extracellular molecules affecting the contraction of airway smooth muscle are steadily being discovered. Although interesting, this is disconcerting for researchers trying to find a mend for the significant part of asthma symptoms caused by contraction. Additional efforts are being deployed to understand the intracellular signaling pathways leading to contraction. The goal being to find common pathways that are essential to convey the contractile signal emanating from any single or combination of extracellular molecules. Not only these pathways exist and their details are being slowly unveiled, but some carry the signal inside-out to interact back with extracellular molecules. These latter represent targets with promising therapeutic potential, not only because they are molecules downstream of pathways essential for contraction but also because their extracellular location makes them readily accessible by inhaled drugs.

Alterations in VASP phosphorylation and profilin1 and cofilin1 expression in hyperoxic lung injury and BPD

BACKGROUND

Hyperoxia is a frequently employed therapy for prematurely born infants, induces lung injury and contributes to development of bronchopulmonary dysplasia (BPD). BPD is characterized by decreased cellular proliferation, cellular migration, and failure of injury repair systems. Actin binding proteins (ABPs) such as VASP, cofilin1, and profilin1 regulate cell proliferation and migration via modulation of actin dynamics. Lung mesenchymal stem cells (L-MSCs) initiate repair processes by proliferating, migrating, and localizing to sites of injury. These processes have not been extensively explored in hyperoxia induced lung injury and repair.

METHODS

ABPs and CD146+ L-MSCs were analyzed by immunofluorescence in human lung autopsy tissues from infants with and without BPD and by western blot in lung tissue homogenates obtained from our murine model of newborn hyperoxic lung injury.

RESULTS

Decreased F-actin content, ratio of VASPpS157/VASPpS239, and profilin 1 expression were observed in human lung tissues but this same pattern was not observed in lungs from hyperoxia-exposed newborn mice. Increases in cofilin1 expression were observed in both human and mouse tissues at 7d indicating a dysregulation in actin dynamics which may be related to altered growth. CD146 levels were elevated in human and newborn mice tissues (7d).

CONCLUSION

Altered phosphorylation of VASP and expression of profilin 1 and cofilin 1 in human tissues indicate that the pathophysiology of BPD involves dysregulation of actin binding proteins. Lack of similar changes in a mouse model of hyperoxia exposure imply that disruption in actin binding protein expression may be linked to interventions or morbidities other than hyperoxia alone.

VASP Regulates NK Cell Lytic Granule Convergence

NK cells eliminate viral-infected and malignant cells through a highly orchestrated series of cytoskeletal rearrangements, resulting in the release of cytolytic granule contents toward the target cell. Central to this process is the convergence of cytolytic granules to a common point, the microtubule-organizing center (MTOC), before delivery to the synapse. In this study, we show that vasodialator-stimulated phosphoprotein (VASP), an actin regulatory protein, localizes to the cytolytic synapse, but surprisingly, shows no impact on conjugate formation or synaptic actin accumulation despite being required for human NK cell-mediated killing. Interestingly, we also find that a pool of VASP copurifies with lytic granules and localizes with lytic granules at the MTOC. Significantly, depletion of VASP decreased lytic granule convergence without impacting MTOC polarization. Using the KHYG-1 cell line in which lytic granules are in a constitutively converged state, we find that either VASP depletion or F-actin destabilization promoted spreading of formerly converged granules. Our results demonstrate a novel requirement for VASP and actin polymerization in maintaining lytic granule convergence during NK cell-mediated killing.

Hypoxia-induced up-regulation of VASP promotes invasiveness and metastasis of hepatocellular carcinoma

Rational: Patients with hepatocellular carcinoma (HCC) have a poor prognosis mostly due to intrahepatic as well as distal metastasis. Vasodilator-stimulated phosphoprotein (VASP), a regulator of actin cytoskeleton and cell migration, is overexpressed in HCC and correlated with its malignant features and poor prognosis. Very little is known about its function in HCC. Methods: qRT-PCR, Western blot and IHC were used to detect the VASP expression in tissues and cells. Transwell and wound healing assays were used to measure the migration and invasion of HCC cells. Immunoblotting and immunofluorescence were used for detection of epithelial-to-mesenchymal transition (EMT) progression in HCC cells. A lung metastasis mouse model was used to evaluate metastasis of HCC in vivo. The putative targets of miR-204 were disclosed by public databases and a dual-luciferase reporter assay. IP was used to show the interaction between VASP and CRKL. ChIP was used to analyze the binding of HIF-1α to VASP promoter region. Results: Our data involving both gain- and loss-of-function studies revealed that VASP activated AKT and ERK signaling and promoted HCC migration and invasion in vitro and in vivo by altering the EMT phenotype and expression of MMPs. We investigated the positive correlation between VASP and an adapter protein, CRKL. VASP dynamically co-localized at the SH3N domain of CRKL and mediated its function. Mechanistically, VASP overexpression at the transcriptional level was mediated by HIF-1α through direct binding to two hypoxia response elements (HRE) in the VASP promoter region. Furthermore, we identified hypoxia-induced down-regulation of miR-204, which functioned as the regulator of VASP overexpression at the post-transcriptional level. Also, hypoxia-activated p-Smad3 dependent TGF-β signaling indirectly promoted VASP expression. Conclusion: A variety of hypoxia-induced molecular mechanisms contributed to the upregulation of VASP at transcriptional and post-transcriptional levels. These mechanisms involved CRKL, HIF-1α, miR-204, and TGF-β activating the AKT and ERK signaling to promote EMT and expression of MMPs. Taken together, our results defined VASP as an oncogene of HCC pathogenesis and metastasis with the potential to serve as a prognostic biomarker.

Vasodilator-Stimulated Phosphoprotein: Regulators of Adipokines Resistin and Phenotype Conversion of Epicardial Adipocytes

Background

Endothelial dysfunction plays a central part in the pathogenesis of coronary atherosclerosis. The adipokine resistin is one of the key players in endothelial cell dysfunction. In addition, the role of epicardial fat in coronary artery endothelial dysfunction is also emphasized.

We investigated whether vasodilator-stimulated phosphoprotein (VASP) is involved in resistin-related endothelial dysfunction and the phenotype conversion of epicardial adipocytes.

Material/Methods

Cell proliferation and migration were evaluated by MTT and Transwell chamber assay, respectively. Next, we took epicardial fat samples from patients with valvular heart disease and non-coronary artery disease. Gene expression was determined by reverse transcription-quantitative polymerase chain reaction and relative abundance of the protein by Western blotting.

Results

Resistin induced endothelial proliferation and migration in a dose-dependent manner. Both resistin-induced cell proliferation and migration were effectively blocked by ablation of VASP. The brown adipose tissue-specific genes for uncoupling protein 1 (UCP-1) and PR-domain-missing16 (PRDM16) decreased, but the white adipose tissue-specific genes for resistin and RIP140 increased in VASP-deficient adipocytes compared with the LV-sicntr group. However, disruption of the Ras homolog gene family member A (RhoA) /Rho-associated kinase (ROCK) in VASP-deficient adipocytes with specific inhibitors inverted the adipocyte phenotype existing in VASP-deficient adipocytes. Furthermore, the expressions of proinflammatory cytokines interleukin-6 (IL-6), interleukin-8 (IL-8), and monocyte chemoattractantprotein-1 (MCP-1) in VASP-deficient adipocytes were markedly upregulated compared with the LV-sicntr group.

Conclusions

These results suggest a physiological role for VASP in coronary atherosclerosis through regulating adipokine resistin and phenotype conversion of epicardial adipose tissue.

Label-Free Quantitative Phosphoproteomics Reveals Regulation of Vasodilator-Stimulated Phosphoprotein upon Stathmin-1 Silencing in a Pair of Isogenic Colorectal Cancer Cell Lines

In this communication, we present the phosphoproteome changes in an isogenic pair of colorectal cancer cell lines, viz., the poorly metastatic HCT-116 and the highly metastatic derivative E1, upon stathmin-1 (STMN1) knockdown. The aim was to better understand how the alterations of the phosphoproteins in these cells are involved in cancer metastasis. After the phosphopeptides were enriched using the TiO₂ HAMMOC approach, comparative proteomics analysis was carried out using sequential window acquisition of all theoretical mass spectra-MS. Following bioinformatics analysis using MarkerView and OneOmics platforms, we identified a list of regulated phosphoproteins that may play a potential role in signaling, maintenance of cytoskeletal structure, and focal adhesion. Among these phosphoproteins, was the actin cytoskeleton regulator protein, vasodilator-stimulated phosphoprotein (VASP), where its change in phosphorylation status was found to be concomitant with STMN1-associated roles in metastasis. We further showed that silencing of stathmin-1 altered the expression, subcellular localization and phosphorylation status of VASP, which suggested that it might be associated with remodeling of the cell cytoskeleton in colorectal cancer metastasis.

Role and regulation of Abelson tyrosine kinase in Crk-associated substrate/profilin-1 interaction and airway smooth muscle contraction

BACKGROUND

Airway smooth muscle contraction is critical for maintenance of appropriate airway tone, and has been implicated in asthma pathogenesis. Smooth muscle contraction requires an "engine" (myosin activation) and a "transmission system" (actin cytoskeletal remodeling). However, the mechanisms that control actin remodeling in smooth muscle are not fully elucidated. The adapter protein Crk-associated substrate (CAS) regulates actin dynamics and the contraction in smooth muscle. In addition, profilin-1 (Pfn-1) and Abelson tyrosine kinase (c-Abl) are also involved in smooth muscle contraction. The interplays among CAS, Pfn-1 and c-Abl in smooth muscle have not been previously investigated.

METHODS

The association of CAS with Pfn-1 in mouse tracheal rings was evaluated by co-immunoprecipitation. Tracheal rings from c-Abl conditional knockout mice were used to assess the roles of c-Abl in the protein-protein interaction and smooth muscle contraction. Decoy peptides were utilized to evaluate the importance of CAS/Pfn-1 coupling in smooth muscle contraction.

RESULTS

Stimulation with acetylcholine (ACh) increased the interaction of CAS with Pfn-1 in smooth muscle, which was regulated by CAS tyrosine phosphorylation and c-Abl. The CAS/Pfn-1 coupling was also modified by the phosphorylation of cortactin (a protein implicated in Pfn-1 activation). In addition, ACh activation promoted the spatial redistribution of CAS and Pfn-1 in smooth muscle cells, which was reduced by c-Abl knockdown. Inhibition of CAS/Pfn-1 interaction by a decoy peptide attenuated the ACh-induced actin polymerization and contraction without affecting myosin light chain phosphorylation. Furthermore, treatment with the Src inhibitor PP2 and the actin polymerization inhibitor latrunculin A attenuated the ACh-induced c-Abl tyrosine phosphorylation (an indication of c-Abl activation).

CONCLUSIONS

Our results suggest a novel activation loop in airway smooth muscle: c-Abl promotes the CAS/Pfn-1 coupling and actin polymerization, which conversely facilitates c-Abl activation. The positive feedback may render c-Abl in active state after contractile stimulation.

Reciprocal role of SIRT6 and Hexokinase 2 in the regulation of autophagy driven monocyte differentiation

Emerging evidences suggest the impact of autophagy on differentiation but the underlying molecular links between metabolic restructuring and autophagy during monocyte differentiation remain elusive. An increase in PPARγ, HK2 and SIRT6 expression was observed upon PMA induced monocyte differentiation. While PPARγ positively regulated HK2 and SIRT6 expression, the latter served as a negative regulator of HK2. Changes in expression of these metabolic modelers were accompanied by decreased glucose uptake and increase in Chibby, a potent antagonist of β-catenin/Wnt pathway. Knockdown of Chibby abrogated PMA induced differentiation. While inhibition of HK2 either by Lonidamine or siRNA further elevated PMA induced Chibby, mitochondrial ROS, TIGAR and LC3II levels; siRNA mediated knock-down of SIRT6 exhibited contradictory effects as compared to HK2. Notably, inhibition of autophagy increased HK2, diminished Chibby level and CD33 expression. In addition, PMA induced expression of cytoskeletal architectural proteins, CXCR4, phagocytosis, acquisition of macrophage phenotypes and release of pro-inflammatory mediators was found to be HK2 dependent. Collectively, our findings highlight the previously unknown reciprocal influence of SIRT6 and HK2 in regulating autophagy driven monocyte differentiation.

The Dynamic Actin Cytoskeleton in Smooth Muscle

Smooth muscle contraction requires both myosin activation and actin cytoskeletal remodeling. Actin cytoskeletal reorganization facilitates smooth muscle contraction by promoting force transmission between the contractile unit and the extracellular matrix (ECM), and by enhancing intercellular mechanical transduction. Myosin may be viewed to serve as an "engine" for smooth muscle contraction whereas the actin cytoskeleton may function as a "transmission system" in smooth muscle. The actin cytoskeleton in smooth muscle also undergoes restructuring upon activation with growth factors or the ECM, which controls smooth muscle cell proliferation and migration. Abnormal smooth muscle contraction, cell proliferation, and motility contribute to the development of vascular and pulmonary diseases. A number of actin-regulatory proteins including protein kinases have been discovered to orchestrate actin dynamics in smooth muscle. In particular, Abelson tyrosine kinase (c-Abl) is an important molecule that controls actin dynamics, contraction, growth, and motility in smooth muscle. Moreover, c-Abl coordinates the regulation of blood pressure and contributes to the pathogenesis of airway hyperresponsiveness and vascular/airway remodeling in vivo. Thus, c-Abl may be a novel pharmacological target for the development of new therapy to treat smooth muscle diseases such as hypertension and asthma.

Non-muscle (NM) myosin heavy chain phosphorylation regulates the formation of NM myosin filaments, adhesome assembly and smooth muscle contraction

KEY POINTS

Non-muscle (NM) and smooth muscle (SM) myosin II are both expressed in smooth muscle tissues, however the role of NM myosin in SM contraction is unknown. Contractile stimulation of tracheal smooth muscle tissues stimulates phosphorylation of the NM myosin heavy chain on Ser1943 and causes NM myosin filament assembly at the SM cell cortex. Expression of a non-phosphorylatable NM myosin mutant, NM myosin S1943A, in SM tissues inhibits ACh-induced NM myosin filament assembly and SM contraction, and also inhibits the assembly of membrane adhesome complexes during contractile stimulation. NM myosin regulatory light chain (RLC) phosphorylation but not SM myosin RLC phosphorylation is regulated by RhoA GTPase during ACh stimulation, and NM RLC phosphorylation is required for NM myosin filament assembly and SM contraction. NM myosin II plays a critical role in airway SM contraction that is independent and distinct from the function of SM myosin.

ABSTRACT

The molecular function of non-muscle (NM) isoforms of myosin II in smooth muscle (SM) tissues and their possible role in contraction are largely unknown. We evaluated the function of NM myosin during contractile stimulation of canine tracheal SM tissues. Stimulation with ACh caused NM myosin filament assembly, as assessed by a Triton solubility assay and a proximity ligation assay aiming to measure interactions between NM myosin monomers. ACh stimulated the phosphorylation of NM myosin heavy chain on Ser1943 in tracheal SM tissues, which can regulate NM myosin IIA filament assembly in vitro. Expression of the non-phosphorylatable mutant NM myosin S1943A in SM tissues inhibited ACh-induced endogenous NM myosin Ser1943 phosphorylation, NM myosin filament formation, the assembly of membrane adhesome complexes and tension development. The NM myosin cross-bridge cycling inhibitor blebbistatin suppressed adhesome complex assembly and SM contraction without inhibiting NM myosin Ser1943 phosphorylation or NM myosin filament assembly. RhoA inactivation selectively inhibited phosphorylation of the NM myosin regulatory light chain (RLC), NM myosin filament assembly and contraction, although it did not inhibit SM RLC phosphorylation. We conclude that the assembly and activation of NM myosin II is regulated during contractile stimulation of airway SM tissues by RhoA-mediated NM myosin RLC phosphorylation and by NM myosin heavy chain Ser1943 phosphorylation. NM myosin II actomyosin cross-bridge cycling regulates the assembly of membrane adhesome complexes that mediate the cytoskeletal processes required for tension generation. NM myosin II plays a critical role in airway SM contraction that is independent and distinct from the function of SM myosin.

Polo-like Kinase 1 Regulates Vimentin Phosphorylation at Ser-56 and Contraction in Smooth Muscle

Polo-like kinase 1 (Plk1) is a serine/threonine-protein kinase that has been implicated in mitosis, cytokinesis, and smooth muscle cell proliferation. The role of Plk1 in smooth muscle contraction has not been investigated. Here, stimulation with acetylcholine induced Plk1 phosphorylation at Thr-210 (an indication of Plk1 activation) in smooth muscle. Contractile stimulation also activated Plk1 in live smooth muscle cells as evidenced by changes in fluorescence resonance energy transfer signal of a Plk1 sensor. Moreover, knockdown of Plk1 in smooth muscle attenuated force development. Smooth muscle conditional knock-out of Plk1 also diminished contraction of mouse tracheal rings. Plk1 knockdown inhibited acetylcholine-induced vimentin phosphorylation at Ser-56 without affecting myosin light chain phosphorylation. Expression of T210A Plk1 inhibited the agonist-induced vimentin phosphorylation at Ser-56 and contraction in smooth muscle. However, myosin light chain phosphorylation was not affected by T210A Plk1. Ste20-like kinase (SLK) is a serine/threonine-protein kinase that has been implicated in spindle orientation and microtubule organization during mitosis. In this study knockdown of SLK inhibited Plk1 phosphorylation at Thr-210 and activation. Finally, asthma is characterized by airway hyperresponsiveness, which largely stems from airway smooth muscle hyperreactivity. Here, smooth muscle conditional knock-out of Plk1 attenuated airway resistance and airway smooth muscle hyperreactivity in a murine model of asthma. Taken together, these findings suggest that Plk1 regulates smooth muscle contraction by modulating vimentin phosphorylation at Ser-56. Plk1 activation is regulated by SLK during contractile activation. Plk1 contributes to the pathogenesis of asthma.

Critical role of actin-associated proteins in smooth muscle contraction, cell proliferation, airway hyperresponsiveness and airway remodeling

Asthma is characterized by airway hyperresponsiveness and airway remodeling, which are largely attributed to increased airway smooth muscle contractility and cell proliferation. It is known that both chemical and mechanical stimulation regulates smooth muscle contraction. Recent studies suggest that contractile activation and mechanical stretch induce actin cytoskeletal remodeling in smooth muscle. However, the mechanisms that control actin cytoskeletal reorganization are not completely elucidated. This review summarizes our current understanding regarding how actin-associated proteins may regulate remodeling of the actin cytoskeleton in airway smooth muscle. In particular, there is accumulating evidence to suggest that Abelson tyrosine kinase (Abl) plays a critical role in regulating airway smooth muscle contraction and cell proliferation in vitro, and airway hyperresponsiveness and remodeling in vivo. These studies indicate that Abl may be a novel target for the development of new therapy to treat asthma.