Reversible tumorigenesis induced by deficiency of vasodilator-stimulated phosphoprotein

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.

Role of vasodilator-stimulated phosphoprotein in RANKL-differentiated murine macrophage RAW264.7 cells: Modulation of NF-κB, c-Fos and NFATc1 transcription factors

Vasodilator-stimulated phosphoprotein (VASP) is essential for osteoclast differentiation, and reduced VASP expression results in depressed osteoclast differentiation. Previously, we demonstrated the importance of VASP and Ras-related C3 botulinum toxin substrate 1 interactions in osteosarcoma cell migration and metastasis using Mg-63 and Saos2 cells. However, the molecular details of the functional role of VASP in cell motility and migration remain to be elucidated. The present study demonstrated that VASP affects the expression of αV-integrin, tartrate-resistant acid phosphatase (TRAP) and lamellipodia protrusion in RAW 264.7 murine macrophage cells. The RAW 264.7 mouse monocyte macrophage cell line was used as an osteoclast precursor. RAW 264.7 cells were treated with 50 ng/ml of receptor activator of nuclear factor κ-Β ligand (RANKL) in order to induce cell differentiation (osteoclastogenesis). Small interfering RNA (siRNA) was used to silence VASP, and RT-PCR and western blotting were used to determine the expression for genes and proteins, respectively. TRAP staining as a histochemical marker for osteoclast and fluorescent microscopy for lamellipodia protrusion was performed. RANKL treatment significantly increased the gene and protein expression of VASP, αV-integrin and TRAP in RAW 264.7 cells. Silencing of VASP significantly reduced the RANKL-induced expression of αV-integrin, TRAP and lamellipodia protrusion. In addition, knockdown of VASP attenuated RANKL-stimulated activation of NF-κB, c-Fos and nuclear factor of activated T cells cytoplasmic 1 transcription factors, and the phosphorylation of the p65 and IκBα. These results suggest the critical role of VASP in regulating osteoclast differentiation, which should be further explored in osteosarcoma research.

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.

Betulinic acid inhibits cell proliferation and migration in gastric cancer by targeting the NF-κB/VASP pathway

Gastric cancer (GC) is one of the most common malignant neoplasms of the digestive system, with China leading in terms of morbidity and mortality rates. Betulinic acid (BA) is a widely-occurring pentacyclic triterpenoid that has been reported to exhibit potent anti-inflammatory, antioxidant, and antitumor activities. BA can combat tumors by inducing apoptosis, regulating cell cycle, and inhibiting autophagy, but its mechanism of action in the context of GC is unclear. A preliminary study found that higher expression of vasodilator-stimulated phosphoprotein (VASP) was correlated with migration in the GC cell line. In this study, BGC-823 cells and MNK45 cells were treated with BA for investigating its effect on the proliferation and migration of cells. Moreover, the expression of VASP and upstream signal molecules were also investigated in this background. The results showed BA could inhibit the proliferation and migration the GC cells. Furthermore, NF-κB acted as a transcription factor to upregulate VASP expression. Moreover, BA could downregulate the expression of VASP at the protein and mRNA level by inhibiting NF-κB activity. In conclusion, these results suggest that BA could inhibit the expression of VASP by negatively regulating NF-κB, thereby inhibiting the proliferation and migration of the GC cells. Our study provides a theoretical basis for exploring the molecular mechanism underlying BA-induced inhibition of proliferation and migration in GC cells.

CREB1/Lin28/miR-638/VASP Interactive Network Drives the Development of Breast Cancer

Breast cancer is one of the most common malignant tumors worldwide. Metastasis remains the leading cause of death in breast cancer patients. Research on the mechanism of breast cancer metastasis has become a core issue in breast cancer research. Our previous series of studies have shown that VASP, as a key oncogene, plays an important role in the development of various tumors such as breast cancer. In this study, we find that miR-638 can target to inhibit VASP expression, and Lin28 acts as an RNA-binding protein to regulate the processing of miR-638, which inhibits its maturation and promotes the expression of VASP. In addition, we also find that CREB1 acts as a transcription factor that binds to the promoter of Lin28 gene and activates the Lin28/miR-638/VASP pathway. Furthermore, CREB1 can also directly bind to the promoter of VASP, and activate VASP expression, forming a CREB/Lin28/miR-638/VASP interactive network, which plays an important role in promoting cell proliferation and migration in breast cancer. Our study explained the mechanism of CREB1/Lin28/miR-638/VASP network promoting the development of breast cancer, which further elucidated the mechanism of VASP as a key oncogene, and also provided a theoretical basis for expanding new approaches to tumor biotherapy.

Knockdown of RAC1 and VASP gene expression inhibits breast cancer cell migration

The ability of tumor cells to migrate is biologically fundamental for tumorigenesis, growth, metastasis and invasion. The present study examined the role of Ras-related C3 botulinum toxin substrate (RAC1) and vasodilator-stimulated phosphoprotein (VASP) in breast cancer cell migration. According to data in Kaplan, Oncomine and The Cancer Genome Atlas, increased expression levels of RAC1 and VASP in breast cancer are associated with decreased cancer cell differentiation, advanced pathological stage and more aggressive tumor subtypes, while increased VASP mRNA expression levels are positively correlated with a poor prognosis in patients with breast cancer. The short hairpin (sh)RNA technique was employed to knock down the expression of RAC1 or VASP. Stable interference with the expression of RAC1 or VASP using RAC1-shRNA or VASP-shRNA, respectively, was established in MCF-7 breast cancer cells. In RAC1-shRNA or VASP-shRNA cells, the protein expression levels of RAC1 or VASP were significantly downregulated compared with control cells. The proliferation and migration rates of the RAC1-shRNA or VASP-shRNA cells were significantly lower compared with control cells. It was observed that the protein expression levels of VASP also decreased in RAC1-shRNA cells compared with control cells. The results revealed that RAC1 and VASP may serve important roles in promoting the migration of MCF-7 breast cancer cells, and that VASP may among the downstream signaling molecules associated with RAC1.

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.

Tumor suppressor berberine binds VASP to inhibit cell migration in basal-like breast cancer

Berberine is a plant-derived compound used in traditional Chinese medicine, which has been shown to inhibit cell proliferation and migration in breast cancer. On the other hand, vasodilator-stimulated phosphoprotein (VASP) promotes actin filament elongation and cell migration. We previously showed that VASP is overexpressed in high-motility breast cancer cells. Here we investigated whether the anti-tumorigenic effects of berberine are mediated by binding VASP in basal-like breast cancer. Our results show that berberine suppresses proliferation and migration of MDA-MB-231 cells as well as tumor growth in MDA-MB-231 nude mouse xenografts. We also show that berberine binds to VASP, inducing changes in its secondary structure and inhibits actin polymerization. Our study reveals the mechanism underlying berberine's inhibition of cell proliferation and migration in basal-like breast cancer, highlighting the use of berberine as a potential adjuvant therapeutic agent.

The phosphorylation status of VASP at serine 322 can be predictive for aggressiveness of invasive ductal carcinoma

Vasodilator-stimulated phosphoprotein (VASP) signaling is critical for dynamic actin reorganization processes that define the motile phenotype of cells. Here we show that VASP is generally highly expressed in normal breast tissue and breast cancer. We also show that the phosphorylation status of VASP at S322 can be predictive for breast cancer progression to an aggressive phenotype. Our data indicate that phosphorylation at S322 is gradually decreased from normal breast to DCIS, luminal/ER+, HER2+ and basal-like/TN phenotypes. Similarly, the expression levels of PKD2, the kinase that phosphorylates VASP at this site, are decreased in invasive ductal carcinoma samples of all three groups. Overall, the phosphorylation status of this residue may serve as an indicator of aggressiveness of breast tumors.

Regulation of Cancer Cell Behavior by the Small GTPase Rab13

The members of the Rab family of GTPases are master regulators of cellular membrane trafficking. With ∼70 members in humans, Rabs have been implicated in all steps of membrane trafficking ranging from vesicle formation and transport to vesicle docking/tethering and fusion. Vesicle trafficking controls the localization and levels of a myriad of proteins, thus regulating cellular functions including proliferation, metabolism, cell-cell adhesion, and cell migration. It is therefore not surprising that impairment of Rab pathways is associated with diseases including cancer. In this review, we highlight evidence supporting the role of Rab13 as a potent driver of cancer progression.

Regulation of VASP by phosphorylation: consequences for cell migration

Phosphorylations control all aspects of vasodilator-stimulated phospho-protein (VASP) function. Mapped phosphorylation sites include Y39, S157, S239, T278, and S322, and multiple kinases have been shown to mediate their phosphorylation. Recently, Protein Kinase D1 (PKD1) as a direct kinase for S157 and S322 joined this group. While S157 phosphorylation generally seems to serve as a signal for membrane localization, phosphorylations at S322 or at S239 and T278 have opposite effects on F-actin accumulation. In migrating cells, S322 phosphorylation increases filopodia numbers and length, while S239/T278 phosphorylations decrease these and also disrupt formation of focal adhesions. Therefore, the kinases mediating these phosphorylations can be seen as switches needed to facilitate cell motility.

HIF-1α acts downstream of TNF-α to inhibit vasodilator-stimulated phosphoprotein expression and modulates the adhesion and proliferation of breast cancer cells

Metastasis is the leading cause of death in breast cancer patients. Recent evidence suggests that inflammation-related cytokine tumor necrosis factor-alpha (TNF-α) is implicated in tumor invasion and metastasis, but the mechanism of its involvement remains elusive. In this study, we employed MCF-7 breast cancer cells as an experimental model to demonstrate that TNF-α inhibits breast cancer cell adhesion and cell proliferation through hypoxia inducible factor-1alpha (HIF-1α) mediated suppression of vasodilator-stimulated phosphoprotein (VASP). We observed that TNF-α treatment attenuated the adhesion and proliferation of MCF-7 cells it also dramatically increased HIF-1α expression and decreased VASP expression. Through a variety of approaches, including promoter assay, electrophoretic mobility shift assay (EMSA), and chromatin immunoprecipitation (ChIP), we identified VASP as a direct target gene of HIF-1α. In addition, we confirmed that HIF-1α mediated the repression of VASP expression by TNF-α in MCF-7 cells. We also demonstrated that exogenous VASP expression or knockdown of HIF-1α relieved TNF-α induced inhibition of cell adhesion and proliferation. We identified a novel TNF-α/HIF-1α/VASP axis in which HIF-1α acts downstream of TNF-α to inhibit VASP expression and modulate the adhesion and proliferation of breast cancer cells. These data provide new insight into the potential anti-tumor effects of TNF-α.

MicroRNA-610 inhibits the migration and invasion of gastric cancer cells by suppressing the expression of vasodilator-stimulated phosphoprotein

Vasodilator-stimulated phosphoprotein (VASP) has been implicated in the establishment of cancerous phenotypes. However, the role of VASP in gastric cancer progression and metastasis remains poorly understood. Here, we demonstrated that VASP was upregulated by epidermal growth factor (EGF) and promoted the migration and invasion of gastric cancer cells. Then we explored the regulatory mechanisms responsible for high expression of VASP in gastric cancer. Based on miRNA expression profiling of the paired gastric cancer tissues and their adjacent non-tumour gastric tissues 18 miRNAs were identified including microRNA-610 (miR-610) which were down-regulated in gastric cancer. Next, we observed an inverse correlation between VASP and miR-610 expression levels in gastric cancer cells after EGF stimulation. Then we performed bioinformatics analysis, Western blot and reverse transcription polymerase chain reaction (RT-PCR) analysis and luciferase assay to establish that miR-610 directly targets VASP 3'-UTR and inhibits its expression. Functionally, we demonstrated that miR610-mediated inhibition of VASP expression resulted in a significant reduction in the migration and invasion properties of gastric cancer cells. The identification of miR-610 as a novel miRNA regulated by EGF that targets VASP in gastric cancer cells suggests that EGF-miR610-VASP axis may be exploited for therapeutic intervention to inhibit gastric cancer progression and metastasis.

A functional mouse retroposed gene Rps23r1 reduces Alzheimer's beta-amyloid levels and tau phosphorylation

Senile plaques consisting of beta-amyloid (Abeta) and neurofibrillary tangles composed of hyperphosphorylated tau are major pathological hallmarks of Alzheimer's disease (AD). Elucidation of factors that modulate Abeta generation and tau hyperphosphorylation is crucial for AD intervention. Here, we identify a mouse gene Rps23r1 that originated through retroposition of ribosomal protein S23. We demonstrate that RPS23R1 protein reduces the levels of Abeta and tau phosphorylation by interacting with adenylate cyclases to activate cAMP/PKA and thus inhibit GSK-3 activity. The function of Rps23r1 is demonstrated in cells of various species including human, and in transgenic mice overexpressing RPS23R1. Furthermore, the AD-like pathologies of triple transgenic AD mice were improved and levels of synaptic maker proteins increased after crossing them with Rps23r1 transgenic mice. Our studies reveal a new target/pathway for regulating AD pathologies and uncover a retrogene and its role in regulating protein kinase pathways.

Protein kinase G as a therapeutic target for the treatment of metastatic colorectal cancer

Colorectal cancer is a leading cause of cancer-related death in the world and there is an urgent need for new strategies to combat this disease. Findings from several independent laboratories have converged on cGMP signaling as an exciting new therapeutic target, but the mechanisms remain controversial. A key intracellular effector of cGMP is protein kinase G (PKG). This article reviews the scientific literature concerning PKG effects on tumor development and progression, and discusses possible strategies for its exploitation in future cancer therapies. Studies from several independent laboratories have described novel anti-tumor effects of PKG in colon cancer cells that include inhibition of tumor growth and angiogenesis. While more preclinical research is warranted to better understand signaling mechanisms, these properties support the notion that PKG is a novel cancer target.

Role of Ena/VASP proteins in homeostasis and disease

The actin cytoskeleton is required for many important processes during embryonic development. In later stages of life, important homeostatic processes depend on the actin cytoskeleton, such as immune response, haemostasis and blood vessel preservation. Therefore, the function of the actin cytoskeleton must be tightly regulated, and aberrant regulation may cause disease. A growing number of proteins have been described to bind and regulate the actin cytoskeleton. Amongst them, Ena/VASP proteins function as anti-capping proteins, thereby directly modulating the actin ultrastructure. Ena/VASP function is regulated by their recruitment into protein complexes downstream of plasma membrane receptors and by phosphorylation. As regulators of the actin ultrastructure, Ena/VASP proteins are involved in crucial cellular functions, such as shape change, adhesion, migration and cell-cell interaction and hence are important targets for therapeutic intervention. In this chapter, we will first describe the structure, function and regulation of Ena/VASP proteins. Then, we will review the involvement of Ena/VASP proteins in the development of human diseases. Growing evidence links Ena/VASP proteins to important human diseases, such as thrombosis, cancer, arteriosclerosis, cardiomyopathy and nephritis. Finally, present and future perspectives for the development of therapeutic molecules interfering with Ena/VASP-mediated protein-protein interactions are presented.

Effect of matrine on HeLa cell adhesion and migration

This study sought to explore the role of matrine in the metastasis of cancer cells and to gain insight into the possible mechanism of matrine's ability to inhibit cancer metastasis. Accordingly, changes in vasodilator-stimulated phosphoprotein (VASP) phosphorylation and in cAMP-dependent protein kinase (PKA) activity during cell detachment and reattachment were first investigated. After administration of matrine (50 microg/ml), the decrease in VASP phosphorylation paralleled the decrease in PKA activity. Matrine was found to significantly inhibit HeLa cell adhesion to collagen I. To determine the effect of matrine on the migration of HeLa cells, we analysed the migratory behaviour of HeLa cells in a two and three-dimensional cell migration assay. In a two-dimensional cell migration assay, the average cell migration velocity was significantly reduced by matrine compared with the control. Moreover, in a three-dimensional cell migration assay performed with the Transwell system, HeLa cells treated with matrine (50 microg/ml) were found to migrate less than the control cells. These data suggest that the inhibitory effect of matrine may be produced by decreased phosphorylation of VASP due to inhibition of the activity of PKA during HeLa cell adhesion and migration.

Differential expression of VASP in normal lung tissue and lung adenocarcinomas

BACKGROUND

Vasodilator stimulated phosphoprotein (VASP) is associated with focal adhesions and is thought to have an important role in actin filament assembly and cell motility. We hypothesise that an increase in the expression of VASP is involved in the progression and invasion of lung adenocarcinomas in parallel to tumour progression. A study was undertaken to analyse VASP expression in normal lung tissue and lung adenocarcinomas.

METHODS

Human lung tissues with adenocarcinomas (n = 26) were used. Normal lung tissue specimens (n = 14) were taken from areas a standard distance (3 cm) from resected adenocarcinomas of patients who underwent surgical lung resection. Adenocarcinomas were classified according to pathological staging and histopathological grades. Tissues were stained for VASP using immunohistochemistry.

RESULTS

Normal lung pneumocytes showed no VASP expression while alveolar macrophages had the strongest immunoreactivity for VASP. Bronchial epithelium (surface epithelium, goblet cells) and bronchial gland cells had a very weak immunoreactivity for VASP. Adenocarcinomas had significantly greater VASP expression than normal epithelium (p < 0.001). Moreover, VASP expression in adenocarcinomas increased significantly with more advanced tumour stage (p < 0.001).

CONCLUSIONS

The spatial and differential expression of VASP in normal lung tissue and lung adenocarcinomas suggests that it is likely to be involved in the differentiation of normal lung cells to adenocarcinomas. The significant increase in the expression of VASP in adenocarcinomas in parallel to pathological staging suggests that it may regulate the invasive behaviour of lung adenocarcinomas as adenocarcinoma invasion is increased in more advanced tumours.

Vasodilator-stimulated phosphoprotein regulates proliferation and growth inhibition by nitric oxide in vascular smooth muscle cells

OBJECTIVE

Vasodilator-stimulated phosphoprotein (VASP) was identified as a substrate for cGMP-dependent protein kinase (PKG) and cAMP-dependent protein kinase (PKA). It is preferentially phosphorylated at serine239 by PKG, whereas serine157 is a preferred phosphorylation site for PKA. In addition, serine157 is phosphorylated by PKC in response to serum. We have investigated the effects of VASP and VASP phosphorylation at serine157 and serine239 on smooth muscle cell (SMC) proliferation and nitric oxide (NO)-mediated growth inhibition.

METHODS AND RESULTS

Aortic SMCs derived from VASP-deficient mice were transduced with retroviral vectors encoding either wild-type VASP or VASP mutants (S157A-VASP and S239A-VASP), in which serine157 and serine239, respectively, were replaced by a nonphosphorylatable amino acid, alanine. Expression of wt-VASP and S239A-VASP significantly increased proliferation, whereas expression of S157A-VASP was inhibitory. Expression of S239A-VASP rendered SMCs less sensitive to growth inhibition by the NO donor, S-nitroso-n-acetylpenicillamine, when compared with cells expressing wt-VASP. Similar effects were observed in cultured rat SMCs in which wt-VASP, S157A-VASP, and S239A-VASP were expressed.

CONCLUSIONS

Our data suggest that VASP phosphorylation at serine157 is required for the growth-stimulatory effect of VASP in SMCs, whereas VASP phosphorylation at serine239 is involved in the growth inhibitory effects of NO on SMCs.

Ena/VASP proteins: regulators of the actin cytoskeleton and cell migration

Ena/VASP proteins are a conserved family of actin regulatory proteins made up of EVH1, EVH2 domains, and a proline-rich central region. They have been implicated in actin-based processes such as fibroblast migration, axon guidance, and T cell polarization and are important for the actin-based motility of the intracellular pathogen Listeria monocytogenes. Mechanistically, these proteins associate with barbed ends of actin filaments and antagonize filament capping by capping protein (CapZ). In addition, they reduce the density of Arp2/3-dependent actin filament branches and bind Profilin at sites of actin polymerization. Vertebrate Ena/VASP proteins are substrates for PKA/PKG serine/threonine kinases. Phosphorylation by these kinases appears to modulate Ena/VASP function within cells, although the mechanism underlying this regulation remains to be determined.

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

Transformation progression of epithelial cells involves alterations in their morphology, polarity, and adhesive characteristics, all of which are associated with the loss and/or reorganization of actin structures. To identify the underlying mechanism of formation of the adhesion-dependent, circumferential actin network, the expression and localization of the actin binding and regulating proteins (ABPs), vinculin, VASP, and profilin were evaluated. Experimental depolarization of epithelial cells results in the loss of normal F-actin structures and the transient upregulation of vinculin, VASP, and profilin. This response is due to the loss of cell-cell, and not cell-substrate interactions, since cells that no longer express focal adhesions or stress fibers are still sensitive to changes in adhesion and manifest this in the altered profile of expression of these ABPs. Transient upregulation is dependent upon de novo protein synthesis, and protein kinase-, but not phosphatase-sensitive signal transduction pathway(s). Inhibition of the synthesis of these proteins is accompanied by dephosphorylation of the ribosomal S6 protein, but does not involve inhibition of the PI3-kinase-Akt-mTOR pathway. Constitutive expression of VASP results in altered cell morphology and adhesion and F-actin and vinculin structures. V12rac1 expressing epithelial cells are constitutively nonadhesive, malignantly transformed, and constitutively express high levels of these ABPs, with altered subcellular localizations. Transformation suppression is accompanied by the restoration of normal levels of the three ABPs, actin structures, adhesion, and epithelial morphology. Thus, vinculin, VASP, and profilin are coordinately regulated by signal transduction pathways that effect a translational response. Additionally, their expression profile maybe indicative of the adhesion and transformation status of epithelial cells.

Disruption of cardiac Ena-VASP protein localization in intercalated disks causes dilated cardiomyopathy

Vasodilator-stimulated phosphoprotein (VASP) and mammalian enabled (Mena) are actin cytoskeleton and signaling modulators. Ena-VASP proteins share an identical domain organization with an NH2-terminal Ena VASP homology (EVH1) domain, which mediates the binding of these proteins to FPPPP-motif containing partners such as zyxin and vinculin. VASP and Mena are abundantly expressed in the heart. However, previous studies showed that disruption by gene targeting of VASP or Mena genes in mice did not reveal any cardiac phenotype, whereas mice lacking both VASP and Mena died during embryonic development. To determine the in vivo function of Ena-VASP proteins in the heart, we used a dominant negative strategy with cardiac-specific expression of the VASP-EVH1 domain. Transgenic mice with cardiac myocyte-restricted, alpha-myosin heavy chain promoter-directed expression of the VASP-EVH1 domain were generated. Overexpression of the EVH1 domain resulted in specific displacement of both VASP and Mena from cardiac intercalated disks. VASP-EVH1 transgenic mice developed dilated cardiomyopathy with myocyte hypertrophy and bradycardia, which resulted in early postnatal lethality in mice with high levels of transgene expression. The results demonstrate that Ena-VASP proteins may play an important role in intercalated disk function at the interface between cardiac myocytes.

Actin-based motility: stop and go with Ena/VASP proteins

Proteins of the Ena/VASP (Enabled/vasodilator-stimulated phosphoprotein) family are involved in Abl and/or cyclic nucleotide-dependent protein kinase signaling pathways. These proteins are also crucial factors in regulating actin dynamics and associated processes such as cell-cell adhesion, platelet function and actin-based motility of both cytopathogenic Listeria and their eukaryotic host cells. Although biochemical mechanisms have emerged depicting Ena/VASP proteins as enhancers of actin filament formation, increasing evidence also suggests that these proteins have inhibitory functions in integrin regulation, cell motility and axon guidance.

Transcriptional regulation and function during the human cell cycle

We report here the transcriptional profiling of the cell cycle on a genome-wide scale in human fibroblasts. We identified approximately 700 genes that display transcriptional fluctuation with a periodicity consistent with that of the cell cycle. Systematic analysis of these genes revealed functional organization within groups of coregulated transcripts. A diverse set of cytoskeletal reorganization genes exhibit cell-cycle-dependent regulation, indicating that biological pathways are redirected for the execution of cell division. Many genes involved in cell motility and remodeling of the extracellular matrix are expressed predominantly in M phase, indicating a mechanism for balancing proliferative and invasive cellular behavior. Transcripts upregulated during S phase displayed extensive overlap with genes induced by DNA damage; cell-cycle-regulated transcripts may therefore constitute coherent programs used in response to external stimuli. Our data also provide clues to biological function for hundreds of previously uncharacterized human genes.

Neoplastic transformation and tumorigenesis associated with sam68 protein deficiency in cultured murine fibroblasts

Sam68 is a multimeric 68-kDa RNA-binding nuclear protein of unknown function that interacts with, and is tyrosine-phosphorylated by, the oncogenic protein Src during mitosis. Random homozygous knock-out (RHKO) is a retroviral-based antisense RNA strategy that can identify chromosomal genes whose functional disablement leads to reversible tumorigenic capabilities. Here we report that RHKO-induced Sam68 deficiency results in neoplastic transformation of murine NIH3T3 fibroblasts. Whereas simple haploinsufficiency of Sam68 produced by insertion mutagenesis in a single chromosomal allele did not detectably affect cell growth, reduction of Sam68 protein to <25% of the wild type level was associated with anchorage-independent growth, defective contact inhibition, and the ability to form metastatic tumors in nude mice. These properties were reversed by cessation of RHKO inactivation. Our findings, which indicate that the Sam68 protein level can prominently affect cell proliferation, implicate Sam68 function in tumorigenesis. Consistent with these results is evidence that cells undergoing mitosis show a dramatic reduction in the level of Sam68 protein.

Antisense RNA-mediated deficiency of the calpain protease, nCL-4, in NIH3T3 cells is associated with neoplastic transformation and tumorigenesis

We previously have described the use of an antisense RNA strategy termed random homozygous knock-out (RHKO) to identify negative regulators of cell proliferation. Here we report the discovery that RHKO-mediated deficiency of the nCL-4 calpain protease results in cellular transformation of and tumorigenesis by murine NIH3T3 fibroblasts. We isolated cell clones able to form colonies on 0.5% soft agar and found that these cells generated tumors when injected subcutaneously into nude mice. The gene inactivated by RHKO was identified as nCL-4 by genomic library screening, transcript analysis, and DNA sequencing. Anchorage-independent growth, as indicated by colony formation on soft agar, was reversed by reversal of antisense-mediated homozygous inactivation, but continued haplo-insufficiency of nCL-4 resulting from insertional mutagenesis of one nCL-4 allele was associated with persistent tumorigenesis. nCL-4 cDNA expressed in naive 3T3 cells in the antisense, but not sense, direction under control of the cytomegalovirus early promoter reproduced the anchorage-independent growth effects of RHKO. Our results implicate deficiency of the nCL-4 calpain protease in neoplastic transformation.

While E1A can facilitate epithelial cell transformation by several dominant oncogenes, the C-terminus seems only to regulate rac and cdc42 function, but in both epithelial and fibroblastic cells

Epithelial and fibroblast cells were differentially susceptible to transformation by oncogenic src, ras, mos, raf, rac, and cdc42 and the influence of adenovirus E1A. In contrast to NIH 3T3 cells, which are easily transformed by all the oncogenes tested, epithelial cells were more resistant to transformation by the same oncogenes. Transformation efficiency of both primary and immortal epithelial cells by E1B, V12ras, v-src, v-raf, and v-mos was increased by cotransfection of E1A 12S, which enables these cells to overcome the M1/M2 mortality blocks, which are not present in NIH 3T3 cells. NIH 3T3 cell transformation by these oncogenes was not altered by E1A. Although V12cdc42 or V12rac1 alone could produce foci on NIH 3T3 cells, morphological conversion was observed only in the presence of a hypertransforming E1A mutant and not WT E1A. Epithelial cells were not transformed by V12cdc42 or V12rac1, even in the presence of WT or mutant E1A, but could be transformed by coexpression of mos/raf and rac/cdc42, and the resultant phenotype was affected by the E1A C-terminus. Hypertransformation, which has previously been reported with ras and E1A C-terminal mutants, turns out to be due to a synergy with rac/cdc42, but not ERK/MAPK or PI3K ras effectors. Like V12rac, expression of the E1A hypertransforming mutant resulted in the upregulation of vinculin and VASP, concomitant with the altered organization of the actin cytoskeleton in these cells. The results show that in addition to requiring abrogation of M1/M2 mortality blocks, primary epithelial cells require activation of the ERK MAPK cascade and rearrangement of the actin CSK to achieve transformation. In addition, the E1A C-terminus regulates rac/cdc42 function in both epithelial and fibroblast cells to affect the extent of transformation progression.