Vinculin, VASP, and profilin are coordinately regulated during actin remodeling in epithelial cells, which requires de novo protein synthesis and protein kinase signal transduction pathways

The Role of Vasodilator-stimulated Phosphoproteins in the Development of Malignant Tumors

Vasodilator-stimulated phosphoprotein (VASP) is an actin-binding protein that includes three structural domains: Enabled/VASP homolog1 (EVH1), EVH2, and proline-rich (PRR). VASP plays an important role in various cellular behaviors related to cytoskeletal regulation. More importantly, VASP plays a key role in the progression of several malignant tumors and is associated with malignant cell proliferation, invasion, and metastasis. Here, we have summarized current studies on the impact of VASP on the development of several malignant tumors and their mechanisms. This study provides a new theoretical basis for clinical molecular diagnosis and molecular targeted therapy.

Differential Ser phosphorylation of vasodilator-stimulated phosphoprotein regulates colon tumor formation and growth

AIMS

Vasodilator-stimulated phosphoprotein (VASP) controls actin dynamics associated with the malignant phenotype of colorectal tumors. Oncogenic VASP function, in turn, is finely regulated by cyclic nucleotide-dependent phosphorylation of serine (Ser) residues 157 and 239, whose differential expression determines cell survival behavior in colon cancer. However, the role of differential VASP Ser phosphorylation in colorectal carcinogenesis remains unclear.

MAIN METHODS

Specific VASP phosphomutant constructs were employed to selectively silence Ser157 or Ser239 phosphorylation in human colon carcinoma cells. Cyclic nucleotide-dependent manipulation of VASP Ser phosphorylation was performed with 8-bromoadenosine 3',5'-cyclic adenosine monophosphate (8-Br-cAMP) or 8-chlorophenylthio 3',5'-cyclic guanosine monophosphate (8-CPT-cGMP). Tumorigenic and locomotory phenotypes were examined in vitro with clonogenic and wound healing assays, respectively. Finally, tumor formation and growth were investigated in vivo employing two distinct xenograft models of colorectal cancer.

KEY FINDINGS

Disruption of VASP Ser157 phosphorylation weakened the clonogenic and migratory abilities of human colon cancer cells, effects mimicked by 8-CPT-cGMP-dependent regulation of VASP Ser239. In contrast, inhibition of VASP Ser239 phosphorylation enhanced cell clonogenicity and migration and was phenocopied by 8-Br-cAMP-dependent regulation of VASP Ser157. Importantly, cancer cells bearing the phosphomutant construct targeting VASP Ser157 decreased, while those with the phosphomutation at Ser239 improved their abilities to establish productive tumor colonies and grow in the peritoneal cavity or subcutaneous tissues of nude mice.

SIGNIFICANCE

Together, present observations suggest differential VASP Ser phosphorylation is a relevant, targetable molecular event underlying tumor formation and progression in colon cancer.

Profilin: many facets of a small protein

Profilin is a ubiquitously expressed protein well known as a key regulator of actin polymerisation. The actin cytoskeleton is involved in almost all cellular processes including motility, endocytosis, metabolism, signal transduction and gene transcription. Hence, profilin's role in the cell goes beyond its direct and essential function in regulating actin dynamics. This review will focus on the interactions of Profilin 1 and its ligands at the plasma membrane, in the cytoplasm and the nucleus of the cells and the regulation of profilin activity within those cell compartments. We will discuss the interactions of profilin in cell signalling pathways and highlight the importance of the cell context in the multiple functions that this small essential protein has in conjunction with its role in cytoskeletal organisation and dynamics. We will review some of the mechanisms that control profilin expression and the implications of changed expression of profilin in the light of cancer biology and other pathologies.

Endometrial profilin 1: a key player in embryo-endometrial crosstalk

Objective

Despite extensive research on implantation failure, little is known about the molecular mechanisms underlying the crosstalk between the embryo and the maternal endometrium, which is critical for successful pregnancy. Profilin 1 (PFN1), which is expressed both in the embryo and in the endometrial epithelium, acts as a potent regulator of actin polymerization and the cytoskeletal network. In this study, we identified the specific role of endometrial PFN1 during embryo implantation.

Methods

Morphological alterations depending on the status of PFN1 expression were assessed in PFN1-depleted or control cells grown on Matrigel-coated cover glass. Day-5 mouse embryos were cocultured with Ishikawa cells. Comparisons of the rates of F-actin formation and embryo attachment were performed by measuring the stability of the attached embryo onto PFN1-depleted or control cells.

Results

Depletion of PFN1 in endometrial epithelial cells induced a significant reduction in cell-cell adhesion displaying less formation of colonies and a more circular cell shape. Mouse embryos co-cultured with PFN1-depleted cells failed to form actin cytoskeletal networks, whereas more F-actin formation in the direction of surrounding PFN1-intact endometrial epithelial cells was detected. Furthermore, significantly lower embryo attachment stability was observed in PFN1-depleted cells than in control cells. This may have been due to reduced endometrial receptivity caused by impaired actin cytoskeletal networks associated with PFN1 deficiency.

Conclusion

These observations definitively demonstrate an important role of PFN1 in mediating cell-cell adhesion during the initial stage of embryo implantation and suggest a potential therapeutic target or novel biomarker for patients suffering from implantation failure.

Postsynaptic Proteome of Non-Demented Individuals with Alzheimer's Disease Neuropathology

Some individuals, here referred to as Non-Demented with Alzheimer’s Neuropathology (NDAN), retain their cognitive function despite the presence of amyloid plaques and tau tangles typical of symptomatic Alzheimer’s disease (AD). In NDAN, unlike AD, toxic amyloid-β oligomers do not localize to the postsynaptic densities (PSDs). Synaptic resistance to amyloid-β in NDAN may thus enable these individuals to remain cognitively intact despite the AD-like pathology. The mechanism(s) responsible for this resistance remains unresolved and understanding such protective biological processes could reveal novel targets for the development of effective treatments for AD. The present study uses a proteomic approach to compare the hippocampal postsynaptic densities of NDAN, AD, and healthy age-matched persons to identify protein signatures characteristic for these groups. Subcellular fractionation followed by 2D gel electrophoresis and mass spectrometry were used to analyze the PSDs. We describe fifteen proteins which comprise the unique proteomic signature of NDAN PSDs, thus setting them apart from control subjects and AD patients.

ALS-causing mutations in profilin-1 alter its conformational dynamics: A computational approach to explain propensity for aggregation

Profilin-1 (PFN1) is a 140-amino-acid protein with two distinct binding sites―one for actin and one for poly-L-proline (PLP). The best-described function of PFN1 is to catalyze actin elongation and polymerization. Thus far, eight DNA mutations in the PFN1 gene encoding the PFN1 protein are associated with human amyotrophic lateral sclerosis (ALS). We and others recently showed that two of these mutations (Gly118Val or G118V and Cys71Gly or C71G) cause ALS in rodents. In vitro studies suggested that Met114Thr and Thr109Met cause the protein to behave abnormally and cause neurotoxicity. The mechanism by which a single amino acid change in human PFN1 causes the degeneration of motor neurons is not known. In this study, we investigated the structural perturbations of PFN1 caused by each ALS-associated mutation. We used molecular dynamics simulations to assess how these mutations alter the secondary and tertiary structures of human PFN1. Herein, we present our in silico data and analysis on the effect of G118V and T109M mutations on PFN1 and its interactions with actin and PLP. The substitution of valine for glycine reduces the conformational flexibility of the loop region between the α-helix and β-strand and enhances the hydrophobicity of the region. Our in silico analysis of T109M indicates that this mutation alters the shape of the PLP-binding site and reduces the flexibility of this site. Simulation studies of PFN1 in its wild type (WT) and mutant forms (both G118V and T109M mutants) revealed differential fluctuation patterns and the formation of salt bridges and hydrogen bonds between critical residues that may shed light on differences between WT and mutant PFN1. In particular, we hypothesize that the flexibility of the actin- and PLP-binding sites in WT PFN1 may allow the protein to adopt slightly different conformations in its free and bound forms. These findings provide new insights into how each of these mutations in PFN1 might increase its propensity for misfolding and aggregation, leading to its dysfunction.

Activation of Human Peripheral Blood Eosinophils by Cytokines in a Comparative Time-Course Proteomic/Phosphoproteomic Study

Activated eosinophils contribute to airway dysfunction and tissue remodeling in asthma and thus are considered to be important factors in asthma pathology. We report here comparative proteomic and phosphoproteomic changes upon activation of eosinophils using eight cytokines individually and in selected cytokine combinations in time-course reactions. Differential protein and phosphoprotein expressions were determined by mass spectrometry after 2-dimensional gel electrophoresis (2DGE) and by LC-MS/MS. We found that each cytokine-stimulation produced significantly different changes in the eosinophil proteome and phosphoproteome, with phosphoproteomic changes being more pronounced and having an earlier onset. Furthermore, we observed that IL-5, GM-CSF, and IL-3 showed the greatest change in protein expression and phosphorylation, and this expression differed markedly from those of the other five cytokines evaluated. Comprehensive univariate and multivariate statistical analyses were employed to evaluate the comparative results. We also monitored eosinophil activation using flow cytometry (FC) analysis of CD69. In agreement with our proteomic studies, FC indicated that IL-5, GM-CSF, and IL-3 were more effective than the other five cytokines studied in stimulating a cell surface CD69 increase indicative of eosinophil activation. Moreover, selected combinations of cytokines revealed proteomic patterns with many proteins in common with single cytokine expression patterns but also showed a greater effect of the two cytokines employed, indicating a more complex signaling pathway that was reflective of a more typical inflammatory pathology.

Alterative Expression and Localization of Profilin 1/VASPpS157 and Cofilin 1/VASPpS239 Regulates Metastatic Growth and Is Modified by DHA Supplementation

Profilin 1, cofilin 1, and vasodialator-stimulated phosphoprotein (VASP) are actin-binding proteins (ABP) that regulate actin remodeling and facilitate cancer cell metastases. miR-17-92 is highly expressed in metastatic tumors and profilin1 and cofilin1 are predicted targets. Docosahexaenoic acid (DHA) inhibits cancer cell proliferation and adhesion. These studies tested the hypothesis that the metastatic phenotype is driven by changes in ABPs including alternative phosphorylation and/or changes in subcellular localization. In addition, we tested the efficacy of DHA supplementation to attenuate or inhibit these changes. Human lung cancer tissue sections were analyzed for F-actin content and expression and cellular localization of profilin1, cofilin1, and VASP (S157 or S239 phosphorylation). The metastatic phenotype was investigated in A549 and MLE12 cells lines using 8 Br-cAMP as a metastasis inducer and DHA as a therapeutic agent. Migration was assessed by wound assay and expression measured by Western blot and confocal analysis. miR-17-92 expression was measured by qRT-PCR. Results indicated increased expression and altered cellular distribution of profilin1/VASP(pS157), but no changes in cofilin1/VASP(pS239) in the human malignant tissues compared with normal tissues. In A549 and MLE12 cells, the expression patterns of profilin1/VASP(pS157) or cofilin1/VASP(pS239) suggested an interaction in regulation of actin dynamics. Furthermore, DHA inhibited cancer cell migration and viability, ABP expression and cellular localization, and modulated expression of miR-17-92 in A549 cells with minimal effects in MLE12 cells. Further investigations are warranted to understand ABP interactions, changes in cellular localization, regulation by miR-17-92, and DHA as a novel therapeutic. Mol Cancer Ther; 15(9); 2220-31. ©2016 AACR.

DHA-mediated regulation of lung cancer cell migration is not directly associated with Gelsolin or Vimentin expression

AIMS

Deaths associated with cancer metastasis have steadily increased making the need for newer, anti-metastatic therapeutics imparative. Gelsolin and vimentin, actin binding proteins expressed in metastatic tumors, participate in actin remodelling and regulate cell migration. Docosahexaenoic acid (DHA) limits cancer cell proliferation and adhesion but the mechanisms involved in reducing metastatic phenotypes are unknown. We aimed to investigate the effects of DHA on gelsolin and vimentin expression, and ultimately cell migration and proliferation, in this context.

MAIN METHODS

Non-invasive lung epithelial cells (MLE12) and invasive lung cancer cells (A549) were treated with DHA (30μmol/ml) or/and 8 bromo-cyclic adenosine monophosphate (8 Br-cAMP) (300μmol/ml) for 6 or 24h either before (pre-treatment) or after (post-treatment) plating in transwells. Migration was assessed by the number of cells that progressed through the transwell. Gelsolin and vimentin expression were measured by Western blot and confocal microscopy in cells, and by immunohistochemistry in human lung cancer biopsy samples.

KEY FINDINGS

A significant decrease in cell migration was detected for A549 cells treated with DHA verses control but this same decrease was not seen in MLE12 cells. DHA and 8 Br-cAMP altered gelsolin and vimentin expression but no clear pattern of change was observed. Immunofluorescence staining indicated slightly higher vimentin expression in human lung tissue that was malignant compared to control.

SIGNIFICANCE

Collectively, our data indicate that DHA inhibits cancer cell migration and further suggests that vimentin and gelsolin may play secondary roles in cancer cell migration and proliferation, but are not the primary regulators.

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

Vasodilator-stimulated phosphoprotein (VASP) can catalyze actin polymerization by elongating actin filaments. The elongation mechanism involves VASP oligomerization and its binding to profilin, a G-actin chaperone. Actin polymerization is required for tension generation during the contraction of airway smooth muscle (ASM); however, the role of VASP in regulating actin dynamics in ASM is not known. We stimulated ASM cells and tissues with the contractile agonist acetylcholine (ACh) or the adenylyl cyclase activator, forskolin (FSK), a dilatory agent. ACh and FSK stimulated VASP Ser(157) phosphorylation by different kinases. Inhibition of VASP Ser(157) phosphorylation by expression of the mutant VASP S157A in ASM tissues suppressed VASP phosphorylation and membrane localization in response to ACh, and also inhibited contraction and actin polymerization. ACh but not FSK triggered the formation of VASP-VASP complexes as well as VASP-vinculin and VASP-profilin complexes at membrane sites. VASP-VASP complex formation and the interaction of VASP with vinculin and profilin were inhibited by expression of the inactive vinculin mutant, vinculin Y1065F, but VASP phosphorylation and membrane localization were unaffected. We conclude that VASP phosphorylation at Ser(157) mediates its localization at the membrane, but that VASP Ser(157) phosphorylation and membrane localization are not sufficient to activate its actin catalytic activity. The interaction of VASP with activated vinculin at membrane adhesion sites is a necessary prerequisite for VASP-mediated molecular processes necessary for actin polymerization. Our results show that VASP is a critical regulator of actin dynamics and tension generation during the contractile activation of ASM.

Serine phosphorylation of vasodilator-stimulated phosphoprotein (VASP) regulates colon cancer cell survival and apoptosis

AIMS

In colon cancer, disease recurrence and death are associated with abnormal tumor cell survival. Vasodilator-stimulated phosphoprotein (VASP) is an actin binding protein regulating cell shape and polarity through the F-actin cytoskeleton, whose activity is controlled by cAMP-dependent phosphorylation at Ser157 and cGMP-dependent phosphorylation at Ser239. This study examined the role of differential VASP Ser phosphorylation in regulating cell survival and apoptosis in human colon carcinoma cells.

MAIN METHODS

Selective inhibition of VASP Ser157 or Ser239 phosphorylation in colon cancer cells was performed with specific phosphomutant constructs. F-actin organization was examined by confocal microscopy, and the balance of cell survival and death assessed by measuring acridine orange and ethidium bromide staining, caspase-3 and BAD-pS112 expression and DNA fragmentation.

KEY FINDINGS

In human colon carcinoma cells suppression of VASP Ser157 phosphorylation reduced F-actin content and survival and increased apoptosis, while inhibition of VASP Ser239 phosphorylation increased F-actin content and survival and reduced cell death. Also, while 8Br-cAMP induced VASP Ser157 phosphorylation and reduced cell death, treatments with 8CPT-cGMP elevated VASP Ser239 phosphorylation and promoted apoptosis.

SIGNIFICANCE

These findings suggest that differential VASP Ser phosphorylation represents a unique therapeutic target to control cell survival and death behavior in colon cancer. In particular, pharmacological manipulation of VASP Ser phosphorylation could be exploited to affect the malignant actin cytoskeleton and induce apoptosis in colorectal cancer cells.

Herpes simplex virus type 1 entry into epithelial MDCKII cells: role of VASP activities

VASP is an actin-regulatory protein that links signalling to remodelling of the cytoskeleton. We investigated the role of VASP during entry of herpes simplex viruses into epithelial MDCKII cells. As VASP functions are regulated by phosphorylations, the phosphorylation pattern was determined upon infection. Phosphorylated VASP decreased temporarily at 15 and 30 min after infection. The impact of phosphorylated VASP was addressed by overexpression of phosphomimetic VASP mutants. Our results revealed that phosphorylated VASP slightly reduced the number of infected cells. Expression studies with deletion mutants further indicated minor effects of VASP on infection efficiency, whereas RNA interference studies demonstrated that reduced VASP expression did not suppress infection. We conclude that VASP activities alone may contribute to herpes simplex virus infection to only a minor extent.

Latrunculin B facilitates Shiga toxin 1 transcellular transcytosis across T84 intestinal epithelial cells

Shiga toxins (Stx), released into the intestinal lumen by enterohemorrhagic Escherichia coli (EHEC), are major virulence factors responsible for gastrointestinal and systemic illnesses. These pathologies are believed to be due to the action of the toxins on endothelial cells, which express the Stx receptor, the glycosphingolipid Gb3. To reach the endothelial cells, Stx must translocate across the intestinal epithelial monolayer. This process is poorly understood. We investigated Stx1 movement across the intestinal epithelial T84 cell model and the role of actin turnover in this transcytosis. We showed that changes in the actin cytoskeleton due to latrunculin B, but not cytochalasin D or jasplakinolide, significantly facilitate toxin transcytosis across T84 monolayers. This trafficking is transcellular and completely inhibited by tannic acid, a cell impermeable plasma membrane fixative. This indicates that actin turnover could play an important role in Stx1 transcellular transcytosis across intestinal epithelium in vitro. Since EHEC attachment to epithelial cells causes an actin rearrangement, this finding may be highly relevant to Stx-induced disease.

Immunocell-array for molecular dissection of multiple signaling pathways in mammalian cells

The knowledge of signaling pathways that are triggered by physiological and pathological conditions or drug treatment is essential for the comprehension of the biological events that regulate cellular responses. Recently novel platforms based on "reverse-phase protein arrays" have proven to be useful in the study of different pathways, but they still lack the possibility to detect events in the complexity of a cellular context. We developed an "immunocell-array" of cells on chip where, upon cell plating, growing, drug treatment, and fixation, by spotting specific antibodies we can detect the localization and state of hundreds of proteins involved in specific signaling pathways. By applying this technology to mammalian cells we analyzed signaling proteins involved in the response to DNA damage and identified a chromatin remodeling pathway following bleomycin treatment. We propose our technology as a new tool for the array-based multiplexed analysis of signaling pathways in drug response screening, for the proteomics of profiling patient cells, and ultimately for the high throughput screening of antibodies for immunofluorescence applications.

Alterations in vasodilator-stimulated phosphoprotein (VASP) phosphorylation: associations with asthmatic phenotype, airway inflammation and beta2-agonist use

BACKGROUND

Vasodilator-stimulated phosphoprotein (VASP) mediates focal adhesion, actin filament binding and polymerization in a variety of cells, thereby inhibiting cell movement. Phosphorylation of VASP via cAMP and cGMP dependent protein kinases releases this "brake" on cell motility. Thus, phosphorylation of VASP may be necessary for epithelial cell repair of damage from allergen-induced inflammation. Two hypotheses were examined: (1) injury from segmental allergen challenge increases VASP phosphorylation in airway epithelium in asthmatic but not nonasthmatic normal subjects, (2) regular in vivo beta2-agonist use increases VASP phosphorylation in asthmatic epithelium, altering cell adhesion.

METHODS

Bronchial epithelium was obtained from asthmatic and non-asthmatic normal subjects before and after segmental allergen challenge, and after regularly inhaled albuterol, in three separate protocols. VASP phosphorylation was examined in Western blots of epithelial samples. DNA was obtained for beta2-adrenergic receptor haplotype determination.

RESULTS

Although VASP phosphorylation increased, it was not significantly greater after allergen challenge in asthmatics or normals. However, VASP phosphorylation in epithelium of nonasthmatic normal subjects was double that observed in asthmatic subjects, both at baseline and after challenge. Regularly inhaled albuterol significantly increased VASP phosphorylation in asthmatic subjects in both unchallenged and antigen challenged lung segment epithelium. There was also a significant increase in epithelial cells in the bronchoalveolar lavage of the unchallenged lung segment after regular inhalation of albuterol but not of placebo. The haplotypes of the beta2-adrenergic receptor did not appear to associate with increased or decreased phosphorylation of VASP.

CONCLUSION

Decreased VASP phosphorylation was observed in epithelial cells of asthmatics compared to nonasthmatic normals, despite response to beta-agonist. The decreased phosphorylation does not appear to be associated with a particular beta2-adrenergic receptor haplotype. The observed decrease in VASP phosphorylation suggests greater inhibition of actin reorganization which is necessary for altering attachment and migration required during epithelial repair.

Activation of Rac-1 and Cdc42 stabilizes the microvascular endothelial barrier

We have demonstrated previously that the Rho family GTPase Rac-1 is required for maintenance of endothelial barrier functions in mouse microvascular myocardial endothelial (MyEnd) cells in vitro as well as in rat mesenteric microvessels in vivo. In this study, we tested the hypothesis that specific activation of Rac-1 would stabilize microvascular endothelial barrier functions. For this purpose we used Escherichia coli Cytotoxic necrotizing factor (CNF-1) under conditions (300 ng/ml, 120 min) where it strongly activated Rac-1 and Cdc42 but not Rho A in MyEnd cells. Under these conditions, CNF-1 induced translocation of the actin-binding proteins cortactin and vasodilator-stimulated phosphoprotein (VASP) to cell junctions, increased the junction-associated actin filament belt, and reduced monolayer permeability. We also tested the effect of CNF-1 on endothelial barrier properties in vivo using single-perfused mesenteric microvessels. In contrast to cultured microvascular monolayers, CNF-1 did not reduce baseline barrier functions assayed as hydraulic conductivity (Lp). However, following 120 min pretreatment, CNF-1 significantly attenuated the peak Lp increase in response to platelet-activating factor (PAF, 10 nM) to 12.6+/-4 x 10(-7) cm/(s cmH(2)O) compared to 46.2+/-10 x 10(-7) cm/(s cmH(2)O) in experiments using PAF alone. These experiments indicate that activation of Rac-1 and Cdc42 stabilizes microvascular endothelial barrier functions in vitro and in vivo, likely by increasing the junction-associated actin cytoskeleton.

Comparative microarray analysis of basal gene expression in mouse Hepa-1c1c7 wild-type and mutant cell lines

Hepa-1c1c7 wild-type and benzo[a]pyrene-resistant derived mutant cell lines have been used to elucidate pathways and mechanisms involving the aryl hydrocarbon receptor (AhR). However, there has been little focus on other biological processes which may differ between the isolated lines. In this study, mouse cDNA microarrays representing 4858 genes were used to examine differences in basal gene expression between mouse Hepa-1c1c7 wild-type and c1 (truncated Cyp1a1 protein), c4 (AhR nuclear translocator, ARNT, deficient), and c12 (low AhR levels) mutant cell lines. Surprisingly, c1 mutants exhibited the greatest number of gene expression changes compared to wild-type cells, followed by c4 and c12 lines, respectively. Differences in basal gene expression were consistent with cell line specific variations in morphology, mitochondrial activity, and proliferation rate. MTT and direct cell count assays indicate both c4 and c12 mutants exhibit increased proliferative activity when compared to wild-type cells, while the c1 mutants exhibited decreased activity. This study further characterizes Hepa-1c1c7 wild-type and mutant cells and identifies significant differences in biological processes that should be considered when conducting comparative mechanistic studies with these lines.