Tensin: a potential link between the cytoskeleton and signal transduction

The molecular and clinical role of Tensin 1/2/3 in cancer

Tensin 1 was originally described as a focal adhesion adaptor protein, playing a role in extracellular matrix and cytoskeletal interactions. Three other Tensin proteins were subsequently discovered, and the family was grouped as Tensin. It is now recognized that these proteins interact with multiple cell signalling cascades that are implicated in tumorigenesis. To understand the role of Tensin 1-3 in neoplasia, current molecular evidence is categorized by the hallmarks of cancer model. Additionally, clinical data involving Tensin 1-3 are reviewed to investigate the correlation between cellular effects and clinical phenotype. Tensin proteins commonly interact with the tumour suppressor, DLC1. The ability of Tensin to promote tumour progression is directly correlated with DLC1 expression. Members of the Tensin family appear to have tumour subtype-dependent effects on oncogenesis; despite numerous data evidencing a tumour suppressor role for Tensin 2, association of Tensins 1-3 with an oncogenic role notably in colorectal carcinoma and pancreatic ductal adenocarcinoma is of potential clinical relevance. The complex interplay between these focal adhesion adaptor proteins and signalling pathways are discussed to provide an up to date review of their role in cancer biology.

Gene network analyses of larvae under different egg-protecting behaviors provide novel insights into immune response mechanisms of Amphioctopus fangsiao

Amphioctopus fangsiao was a representative economic species in cephalopods, which was vulnerable to marine bacteria. Vibrio anguillarum was a highly infectious pathogen that have recently been found to infect A. fangsiao and inhibit its growth and development. There were significant differences in the immune response mechanisms between egg-protected and egg-unprotected larvae. To explore larval immunity under different egg-protecting behaviors, we infected A. fangsiao larvae with V. anguillarum for 24 h and analyzed the transcriptome data about egg-protected and egg-unprotected larvae infected with 0, 4, 12, and 24 h using weighted gene co-expression networks (WGCNA) and protein-protein interaction (PPI) networks. Network analyses revealed a series of immune response processes after infection, and identified six key modules and multiple immune-related hub genes. Meanwhile, we found that ZNF family, such as ZNF32, ZNF160, ZNF271, ZNF479, and ZNF493 might play significant roles in A. fangsiao immune response processes. We first creatively combined WGCNA and PPI network analysis to deeply explore the immune response mechanisms of A. fangsiao larvae with different egg-protecting behaviors. Our results provided further insights into the immunity of V. anguillarum infected invertebrates, and laid the foundation for exploring the immune differences among cephalopods with different egg protecting behaviors.

CTEN Inhibits Tumor Angiogenesis and Growth by Targeting VEGFA Through Down-Regulation of β-Catenin in Breast Cancer

C-terminal tensin-like (CTEN) belongs to the tensin gene family, which encodes proteins that localize to focal adhesions and modulate integrin function. Accumulating studies have reported that CTEN expression can be upregulated or downregulated in different types of cancers, suggesting that CTEN has both oncogenic and tumor suppressor functions. In this study, by analyzing the expression level of CTEN in the human breast cancer (BRCA) samples from the clinically annotated genomic database, The Cancer Genome Atlas, we found that CTEN was downregulated in different BRCA subclasses, including luminal, human epidermal growth factor receptor 2 positive and triple-negative BRCA. Consistently, the protein level of CTEN was also reduced in BRCA based on the Proteomic Tumor Analysis Consortium. In contrast, vascular endothelial growth factor A (VEGFA), a signal protein that stimulates the formation of blood vessels, was upregulated in BRCA. CTEN overexpression in human umbilical vein endothelial cells and MCF7 significantly suppressed the expression of VEGFA, inhibited cell proliferation, migration, and tube formation in vitro. Mechanistically, CTEN bind to casitas B-lineage lymphoma (c-Cbl), an E3 ubiquitin-protein ligase, and decreased the β-catenin expression. In turn, the downregulation of β-catenin reduced the expression of VEGFA. Rescuing β-catenin expression effectively ameliorated the effect of CTEN overexpression in cell proliferation, migration, and tube formation. In conclusion, CTEN inhibited tumor angiogenesis by targeting VEGFA through c-Cbl-mediated down-regulation of β-catenin and may serve as a tumor suppressor in BRCA.

miR-152/TNS1 axis inhibits non-small cell lung cancer progression through Akt/mTOR/RhoA pathway

AIM

The purpose of the present study was to explore the function and mechanism of tensin 1 (TNS1) in non-small cell lung cancer (NSCLC) progression.

METHODS

The expression of TNS1 in NSCLC cells and tissues was assessed by RT-PCR and Western blot. Besides, Kaplan-Meier survival analysis was recruited to explore the association between TNS1 and NSCLC. Cell growth was analyzed by MTT and flow cytometry assay, while cell metastasis was determined by wound healing and transwell assays. The targeting relationship between TNS1 and miR-152 was assessed by luciferase activity assays. And Western blot was employed to determine the expression of related proteins of Akt/mTOR/RhoA pathway.

RESULTS

TNS1 level was boosted in NSCLC cells and tissues, related to the prognosis of NSCLC patients. Furthermore, it was proved that TNS1 promoted the growth and metastasis of NSCLC cells via Akt/mTOR/RhoA pathway. And miR-152 targeted TNS1 to affect the progression of NSCLC.

CONCLUSION

miR-152/TNS1 axis inhibits the progression of NSCLC by Akt/mTOR/RhoA pathway.

Understanding the role of integrins in breast cancer invasion, metastasis, angiogenesis, and drug resistance

Integrins are cell adhesion receptors, which are typically transmembrane glycoproteins that connect to the extracellular matrix (ECM). The function of integrins regulated by biochemical events within the cells. Understanding the mechanisms of cell growth by integrins is important in elucidating their effects on tumor progression. One of the major events in integrin signaling is integrin binding to extracellular ligands. Another event is distant signaling that gathers chemical signals from outside of the cell and transmit the signals upon cell adhesion to the inside of the cell. In normal breast tissue, integrins function as checkpoints to monitor effects on cell proliferation, while in cancer tissue these functions altered. The combination of tumor microenvironment and its associated components determines the cell fate. Hypoxia can increase the expression of several integrins. The exosomal integrins promote the growth of metastatic cells. Expression of certain integrins is associated with increased metastasis and decreased prognosis in cancers. In addition, integrin-binding proteins promote invasion and metastasis in breast cancer. Targeting specific integrins and integrin-binding proteins may provide new therapeutic approaches for breast cancer therapies. This review will examine the current knowledge of integrins' role in breast cancer.

A Novel Mutation in the IL6R Gene Identified in a Family with Asthma Patients

Background: Allergic diseases, including asthma, atopic dermatitis, allergic rhinitis, and food allergies, are caused by both environmental and genetic factors. The allergic condition, where genetic factors make up the largest proportion (up to 95%), is asthma. Aim: To identify polymorphisms and mutations in potentially disease-causing genes in a family affected with allergic asthma. Methods: Whole exome sequencing of the index patient was performed via next-generation sequencing. Variants in known allergy-associated susceptibility genes were identified by comparison with the reference genome GRChr37. Results: Seven common polymorphisms and three rare mutations were identified in the allergy-susceptibility genes of the index patient. Only four of these variants co-segregated with a second patient in the same family. These variants occurred in the TENS1, NPSR1, RAD50, and IL6R genes. Discussion: The variants observed in TENS1 and NPSR1 are relatively common (minor allele frequency, MAF ∼0.4), whereas the mutation in RAD50 is rare (MAF 0.0035). The mutation identified in IL6R (S409P) has never been found before. IL6R encodes an important receptor of the inflammatory system. The mutation occurs in the intracellular domain within a tyrosine-based motif, which is required for sorting of the IL6R protein to the basolateral side of polarized cells. It is likely that this rare mutation contributes-together with the other variants-to the predisposition to asthma and other allergic diseases.

The SSC15 QTL-Rich Region Mutations Affecting Intramuscular Fat and Production Traits in Pigs

One of the more interesting regions in the pig genome is on chromosome 15 (115,800,000-122,100,000, SSC15, Sus scrofa 11.1) that has high quantitative trait locus (QTL) density associated with fattening, slaughter and meat quality characteristics. The SSC15 region encodes over 80 genes and a few miRNA sequences where potential genetic markers can be found. The goal of the study was to evaluate the effects of SSC15 mutations associated with villin 1 (VIL1), tensin 1 (TNS1), obscurin-like 1 (OBSL1) genes and with one long non-coding RNA (lncRNA) on productive pig traits and to enrich the genetic marker pool in further selection purpose. The potential genetic markers were identified using the targeted enrichment DNA sequencing (TEDNA-seq) of chromosome 15 region. The selected mutations were genotyped by using HRM, PCR and PCRRFLP methods. The association study was performed using the general linear model (GLM) in the sas program that included over 600 pigs of 5 Polish populations. The rs332253419 VIL1 mutation shows a significant effect on intramuscular fat (IMF) content in Duroc population where AA pigs had a 16% higher level than heterozygotes. The IMF content is also affected by the OBSL1 mutation, and the differences between groups are even up to 30%, but it is strongly dependent on breed factor. The OBSL1 mutation also significantly influences the meat yellowness, backfat thickness and pH level. The performed study delivers valuable information that could be highly useful during the development of the high-throughput genotyping method for further selection purposes in pigs. The OBSL1 and VIL1 mutations seem to be the most promising DNA marker showing a high effect on IMF level.

Regulation and modulation of PTEN activity

PTEN (Phosphatase and tensin homolog deleted on chromosome ten) is a tumor suppressor that is frequently mutated in most human cancers. PTEN is a lipid and protein phosphatase that antagonizes PI3K/AKT pathway through lipid phosphatase activity at the plasma membrane. More recent studies showed that, in addition to the putative role of PTEN as a PI(3,4,5)P3 3-phosphatase, it is a PI(3,4)P2 3-phosphatase during stimulation of class I PI3K signaling pathway by growth factor. Although PTEN tumor suppressor function via it's lipid phosphatase activity occurs primarily in the plasma membrane, it can also be found in the nucleus, in cytoplasmic organelles and extracellular space. PTEN has also shown phosphatase independent functions in the nucleus. PTEN can exit from the cell through exosomal export or secretion and has a tumor suppressor function in adjacent cells. PTEN has a critical role in growth, the cell cycle, protein synthesis, survival, DNA repair and migration. Understanding the regulation of PTEN function, activity, stability, localization and its dysregulation outcomes and also the intracellular and extracellular role of PTEN and paracrine role of PTEN-L in tumor cells as an exogenous therapeutic agent can help to improve clinical conceptualization and treatment of cancer.

Elevated transgelin/TNS1 expression is a potential biomarker in human colorectal cancer

Transgelin is an actin-binding protein that regulates cell motility and other important cellular functions. Previous studies have suggested that transgelin expression is associated with cancer development and progression, but its specific role in colorectal cancer (CRC) remains controversial. We analyzed expression of transgelin and its candidate downstream target, tensin 1 (TNS1), in CRC patients using the ONCOMINE, Protein Atlas, and OncoLnc databases. Transgelin and TNS1 mRNA and protein levels were higher in CRC patients and CRC cell lines than in normal tissues and cells. Survival analyses using the OncoLnc database revealed that elevated TAGLN/TNS1 levels were associated with a poor overall survival in CRC patients. Transgelin suppression using siRNA decreased TNS1 expression in CRC cells, demonstrating that transgelin induces the TNS1 expression. Importantly, suppression of transgelin or TNS1 using siRNA decreased proliferation and invasiveness of CRC cells. These results suggest that transgelin/TNS1 signaling promotes CRC cell proliferation and invasion, and that transgelin/TNS1 expression levels could potentially serve as a prognostic and therapeutic target in CRC patients.

Tensin 1 Is Essential for Myofibroblast Differentiation and Extracellular Matrix Formation

Myofibroblasts, the primary effector cells that mediate matrix remodeling during pulmonary fibrosis, rapidly assemble an extracellular fibronectin matrix. Tensin (TNS) 1 is a key component of specialized cellular adhesions (fibrillar adhesions) that bind to extracellular fibronectin fibrils. We hypothesized that TNS1 may play a role in modulating myofibroblast-mediated matrix formation. We found that TNS1 expression is increased in fibroblastic foci from lungs with idiopathic pulmonary fibrosis. Transforming growth factor (TGF)-β profoundly up-regulates TNS1 expression with kinetics that parallel the expression of the myofibroblast marker, smooth muscle α-actin. TGF-β-induced TNS1 expression is dependent on signaling through the TGF-β receptor 1 and is Rho coiled-coiled kinase/actin/megakaryoblastic leukemia-1/serum response factor dependent. Small interfering RNA-mediated knockdown of TNS1 disrupted TGF-β-induced myofibroblast differentiation, without affecting TGF-β/Smad signaling. In contrast, loss of TNS1 resulted in disruption of focal adhesion kinase phosphorylation, focal adhesion formation, and actin stress fiber development. Finally, TNS1 was essential for the formation of fibrillar adhesions and the assembly of nascent fibronectin and collagen matrix in myofibroblasts. In summary, our data show that TNS1 is a novel megakaryoblastic leukemia-1-dependent gene that is induced during pulmonary fibrosis. TNS1 plays an essential role in TGF-β-induced myofibroblast differentiation and myofibroblast-mediated formation of extracellular fibronectin and collagen matrix. Targeted disruption of TNS1 and associated signaling may provide an avenue to inhibit tissue fibrosis.

Tensin Is Expressed in Glomerular Mesangial Cells and Is Related to Their Attachment to Surrounding Extracellular Matrix

Glomerular expression of tensin was immunohistochemically studied in normal and diseased rat kidneys to determine whether tensin might be related to specific binding in individual glomerular cells. Normal rat kidneys displayed an intense immunofluorescence reaction for tensin along the basal aspects of proximal and distal tubule cells and parietal epithelial cells of Bowman's capsules. In glomeruli, a positive reaction for tensin was detected only in the mesangial areas. Immunoelectron microscopy revealed a positive reaction in the mesangial cell (MC) processes. RT-PCR and immunoprecipitation demonstrated mRNA and protein levels of tensin in cultured rat MCs. Mesangial tensin expression was decreased when the mesangium was injured by Habu snake venom. During the regenerative process after mesangiolysis, tensin expression was not detected in early-phase proliferating MCs that did not have extracellular matrix (ECM). The expression of tensin recovered in late-phase proliferating MCs, which became attached to regenerated ECM. It appears that tensin is related to MC attachment to surrounding ECM, which suggests that signal transduction regulated by tensin may be related to a specific mechanism of MC matrix regeneration. Furthermore, tensin can act as a marker for rat MCs because the expression of tensin was detected only in MCs in glomeruli.

PTEN

The importance of PTEN in cellular function is underscored by the frequency of its deregulation in cancer. PTEN tumor-suppressor activity depends largely on its lipid phosphatase activity, which opposes PI3K/AKT activation. As such, PTEN regulates many cellular processes, including proliferation, survival, energy metabolism, cellular architecture, and motility. More than a decade of research has expanded our knowledge about how PTEN is controlled at the transcriptional level as well as by numerous posttranscriptional modifications that regulate its enzymatic activity, protein stability, and cellular location. Although the role of PTEN in cancers has long been appreciated, it is also emerging as an important factor in other diseases, such as diabetes and autism spectrum disorders. Our understanding of PTEN function and regulation will hopefully translate into improved prognosis and treatment for patients suffering from these ailments.

Identification of cellular proteins that interact with human cytomegalovirus immediate-early protein 1 by protein array assay

Human cytomegalovirus (HCMV) gene expression during infection is characterized as a sequential process including immediate-early (IE), early (E), and late (L)-stage gene expression. The most abundantly expressed gene at the IE stage of infection is the major IE (MIE) gene that produces IE1 and IE2. IE1 has been the focus of study because it is an important protein, not only for viral gene expression but also for viral replication. It is believed that IE1 plays important roles in viral gene regulation by interacting with cellular proteins. In the current study, we performed protein array assays and identified 83 cellular proteins that interact with IE1. Among them, seven are RNA-binding proteins that are important in RNA processing; more than half are nuclear proteins that are involved in gene regulations. Tumorigenesis-related proteins are also found to interact with IE1, implying that the role of IE1 in tumorigenesis might need to be reevaluated. Unexpectedly, cytoplasmic proteins, such as Golgi autoantigen and GGA1 (both related to the Golgi trafficking protein), are also found to be associated with IE1. We also employed a coimmunoprecipitation assay to test the interactions of IE1 and some of the proteins identified in the protein array assays and confirmed that the results from the protein array assays are reliable. Many of the proteins identified by the protein array assay have not been previously reported. Therefore, the functions of the IE1-protein interactions need to be further explored in the future.

Phylogenetic analysis, expression patterns, and transcriptional regulation of human CTEN gene

Cten is a focal adhesion molecule and a member of the tensin family. Its expression is highly enriched in the prostate and placenta, suggesting that cten gene might be closely associated with mammalian species. Recent studies have reported that cten expression is frequently up-regulated in a variety of cancers and its levels appear to correlate with tumorigenicity. Here, we have (1) analyzed cten sequences of various species to build a phylogenetic tree, (2) examined cten mRNA levels in human and mouse tissues to establish its expression profiles, and (3) determined the promoter region of human CTEN gene in cell lines and in a mouse model to understand its transcriptional regulation. Our analyses indicate that all currently known cten genes are present in mammals. The prostate and placenta are the two most cten abundant tissues in human and mouse, meanwhile brain and lung also express low levels of cten. Results from cell culture reporter assays demonstrate that a 327-bp fragment is the shortest functional promoter. All functional promoter constructs produce 40- to 160-fold increases in luciferase reporter activities in normal prostate cells, whereas lower activities (<40-fold) are detected in non-prostatic cell lines. To evaluate CTEN promoter activity in mice and develop a new tissue specific Cre recombinase mouse model, we have established pCTEN-Cre:R26R mice by crossing R26R β-galactosidase reporter mice with pCTEN-Cre transgenic mice, in which the 327-bp cten promoter drives the expression of Cre recombinase. X-gal analysis has shown strong β-galactosidase activities in the prostate, brain, and few other tissues in pCTEN-Cre:R26R mice. Altogether, we have identified the promoter region of human cten gene and provided a useful tool for investigating cell lineages and generating tissue-specific knockout or knockin mice.

Vascular hypertrophy-associated hypertension of profilin1 transgenic mouse model leads to functional remodeling of peripheral arteries

Increased mechanical stress/hypertension in the vessel wall triggers the hypertrophic signaling pathway, resulting in structural remodeling of vasculature. Vascular hypertrophy of resistance vessels leads to reduced compliance and elevation of blood pressure. We showed before that increased expression of profilin1 protein in the medial layer of the aorta induces stress fiber formation, triggering the hypertrophic signaling resulting in vascular hypertrophy and, ultimately, hypertension in older mice. Our hypothesis is that profilin1 induced vascular hypertrophy in resistance vessels, which led to elevation of blood pressure, both of which contributed to the modulation of vascular function. Our results showed significant increases in the expression of alpha(1)- and beta(1)-integrins (280 + or - 6.3 and 325 + or - 7.4%, respectively) and the activation of the Rho/Rho-associated kinase (ROCK) II pathway (260 and 350%, respectively, P < 0.05) in profilin1 mesenteric arteries. The activation of Rho/ROCK led to the inhibition of endothelial nitric oxide synthase expression (39 + or - 5.4%; P < 0.05) and phosphorylation (35 + or - 4.5%; P < 0.05) but also an increase in myosin light chain 20 phosphorylation (372%, P < 0.05). There were also increases in hypertrophic signaling pathways in the mesenteric arteries of profilin1 mice such as phospho-extracellular signal-regulated kinase 1/2 and phospho-c-Jun NH(2)-terminal kinase (312.15 and 232.5%, respectively, P < 0.05). Functional analyses of mesenteric arteries toward the vasoactive drugs were assessed using wire-myograph and showed significant increases in the vascular responses of profilin1 mesenteric arteries toward phenylephrine, but significant decreases in response toward ROCK inhibitor Y-27632, ACh, sodium nitrite, and cytochalasin D. The changes in vascular responses in the mesenteric arteries of profilin1 mice are due to vascular hypertrophy and the elevation of blood pressure in the profilin1 transgenic mice.

CTEN/tensin 4 expression induces sensitivity to paclitaxel in prostate cancer

BACKGROUND

Recently, we established paclitaxel-resistant prostate cancer cell lines (PC-3-TxR and DU145-TxR). To determine the mechanisms of paclitaxel resistance in PC-3-TxR cells, we compared the gene expression profiles between PC-3 and PC-3-TxR cells. Our results indicated that expression of the C-terminal tensin like protein (CTEN, tensin 4) gene was down-regulated by 10-fold in PC-3-TxR cells. We investigated the possibility that CTEN overexpression restores paclitaxel sensitivity.

METHODS

We investigated how knockdown and overexpression of CTEN in androgen-independent cell lines affect paclitaxel sensitivity by colony formation assay and growth inhibition assay. To determine the mechanisms by which CTEN affects paclitaxel sensitivity, we investigated the relationships between CTEN and F-actin or epidermal growth factor receptor (EGFR) in PC-3 cells. We also examined the association between expression of CTEN and grade of prostate cancer by immunohistochemistry using tissue microarray analysis.

RESULTS

Down-regulation of CTEN, which is located in the cytoskeleton, played an important role in paclitaxel resistance in PC-3-TxR cells. Knockdown of CTEN expression in PC-3 cells induced paclitaxel resistance. Overexpression of CTEN in PC-3-TxR and DU145-TxR cells restored paclitaxel sensitivity. CTEN expression was inversely correlated with F-actin and EGFR expression. Then knockdown of actin and EGFR in PC-3-TxR cells recovered paclitaxel sensitivity, indicating that CTEN down-regulation mediates paclitaxel resistance through elevation of EGFR and actin expression. Moreover, CTEN expression was inversely correlated with Gleason score.

CONCLUSIONS

These results strongly suggested that CTEN plays an important role in paclitaxel sensitivity and that CTEN expression level may be a prognostic predictive factor for PCa patients.

Upregulation of Hic-5 in glomerulosclerosis and its regulation of mesangial cell apoptosis

Glomerulosclerosis is characterized by the loss of glomerular cells by apoptosis and deposition of collagen type I into the normal collagen IV-containing mesangial matrix. We sought to determine the alterations that might contribute to these changes by performing proteomic analysis of rat mesangial cell lysates comparing cells cultured on normal collagen type IV to those grown on abnormal collagen type I surfaces. Subculture on collagen type I was associated with changed expression of several proteins, including a significant upregulation of the paxillin-like LIM protein, hydrogen-peroxide-induced clone 5 (Hic-5), and increased the susceptibility of the cells to apoptosis in response to physiological triggers. When we knocked down Hic-5 (using siRNA), we found mesangial cells grown on collagen type I were protected from apoptosis to the same degree as untreated cells grown on collagen type IV. Further we found that the level of Hic-5 in vivo was almost undetectable in control rats but increased dramatically in the glomerular mesangium of remnant kidneys 90 and 120 days after subtotal nephrectomy. This induction of Hic-5 paralleled the upregulation of mesangial collagen type I expression and glomerular cell apoptosis. Our results suggest that Hic-5 is pivotal in mediating the response of mesangial cells to attachment on abnormal extracellular matrix during glomerular scarring.

Role and significance of focal adhesion proteins in hepatocellular carcinoma

Focal adhesions are structural links between the extracellular matrix and actin cytoskeleton. They are important sites where dynamic alterations of proteins in the focal contacts are involved during cell movement. Focal adhesions are composed of diverse molecules, for instance, receptors, structural proteins, adaptors, GTPase, kinases and phosphatases. These molecules play critical roles in normal physiological events such as cellular adhesion, movement, cytoskeletal structure and intracellular signaling pathways. In cancers, aberrant expression and altered functions of focal adhesion proteins contribute to adverse tumor behavior. It is evident that these proteins do not function alone, but rather associate and work together in the process of tumor development and cancer metastasis. Focal adhesion proteins have been shown to play critical roles in hepatocellular carcinoma. Understanding the molecular interactions and mechanisms of the interconnected focal adhesion proteins is of particular importance in understanding mechanisms underlying hepatocellular carcinoma progression and development of potential effective treatment.

Cyclic peptidyl inhibitors of Grb2 and tensin SH2 domains identified from combinatorial libraries

Cyclic peptides provide attractive lead compounds for drug discovery and excellent molecular probes in biomedical research. In this work, a novel method has been developed for the high-throughput synthesis, screening, and identification of cyclic peptidyl ligands against macromolecular targets. Support-bound cyclic phosphotyrosyl peptide libraries containing randomized amino acid sequences and different ring sizes (theoretical diversity of 3.2 x 10(6)) were synthesized and screened against the SH2 domains of Grb2 and tensin. Potent, selective inhibitors were identified from the libraries and were generally more effective than the corresponding linear peptides. One of the inhibitors selected against the Grb2 SH2 domain inhibited human breast cancer cell growth and disrupted actin filaments. This method should be applicable to the development of cyclic peptidyl inhibitors against other protein domains, enzymes, and receptors.

Association of the tensin N-terminal protein-tyrosine phosphatase domain with the alpha isoform of protein phosphatase-1 in focal adhesions

Focal adhesions attach cultured cells to the extracellular matrix, and we found endogenous protein phosphatase-1alpha isoform (PP1alpha) localized in adhesions across the entire area of adherent fibroblasts. However, in fibroblasts migrating into a scrape wound or spreading after replating PP1alpha did not appear in adhesions near the leading edge but was recruited into other adhesions coincident in time and space with incorporation of tensin. Endogenous tensin and PP1alpha co-precipitated from cell lysates with isoform-specific PP1 antibodies. Chemical cross-linking of focal adhesion preparations with Lomant's reagent demonstrated molecular proximity of endogenous PP1alpha and tensin, whereas neither focal adhesion kinase nor vinculin was cross-linked and co-precipitated with PP1alpha, suggesting distinct spatial subdomains within adhesions. Transient expression of truncated tensin showed the N-terminal 360 residues, which comprise a protein-tyrosine phosphatase domain, alone were sufficient for isoform-selective co-precipitation of co-expressed PP1alpha. Human prostate cancer PC3 cells are deficient in tensin relative to fibroblasts and have fewer, mostly peripheral adhesions. Transient expression of green fluorescent protein tensin in these cancer cells induced formation of adhesions and recruited endogenous PP1alpha into those adhesions. Thus, the protein-tyrosine phosphatase domain of tensin exhibits isoform-specific association with PP1alpha in a restricted spatial region of adhesions that are formed during cell migration.

A chemical approach to the identification of tensin-binding proteins

Many protein-protein interactions are mediated by small modular domains, which recognize short peptide motifs in their partner proteins. However, for the great majority of these domains, the identity of their partner proteins remains unknown. In this work, a chemical/bioinformatics approach has been developed to identify phosphotyrosyl (pY) proteins that bind to tensin, a protein involved in the formation of actin cytoskeleton and signal transduction. A pY peptide library was chemically synthesized and screened against the Src homology 2 (SH2) domain of tensin to identify the peptide motifs that bind to the SH2 domain. Next, protein databases were searched for proteins containing the SH2 domain-binding peptide motifs. Finally, the potential tensin-binding proteins were confirmed (or disproved) by in vitro pull-down and coimmunoprecipitation assays. This procedure identified phosphoinositide-dependent kinase-1 and downstream of tyrosine kinase 2 as novel tensin-binding proteins. In addition, a cell-permeable pY peptide was designed as tensin SH2 domain inhibitor, which caused the disruption of actin filaments in NIH 3T3 cells. This method should be generally applicable to other modular domains that recognize small peptide motifs.

Reverse interactomics: decoding protein–protein interactions with combinatorial peptide libraries

Identification of binding partners is the crucial first step towards understanding the biological function of a protein. Many protein-protein interactions occur via modular domains that recognize short peptide motifs in their target proteins. Here we describe a chemical/bioinformatics approach for predicting the binding partners of modular domains. The optimal binding motif(s) of a protein domain is identified by screening a combinatorial peptide library. The resulting consensus sequence is used to search protein and genomic databases for potential binding proteins, which are subsequently confirmed (or disproved) by conventional protein binding assays (e.g. pull-down and co-immunoprecipitation).

Tensin2 variant 3 is associated with aggressive tumor behavior in human hepatocellular carcinoma

Tensins are a new family of proteins that act as an important link among extracellular matrix, actin cytoskeleton, and signal transduction and have been implicated in human cancers. Tensin2 was initially identified in a search for new tensin family members that share extensive sequence homology with tensin1. Tensin2 was highly expressed in liver tissues. A recent study reported that one of the splicing variants of tensin2, variant 3, promotes cell migration. In the present study, we aimed to elucidate the role of variant 3 in hepatocarcinogenesis by assessing the expression of variant 3 mRNA in hepatocellular carcinoma (HCC) tissue and ectopically expressing variant 3 in HCC cell lines. Analysis of variant 3 expression in human HCC tissue revealed it was overexpressed in 46% (23/50) of tumor tissues as compared with the corresponding nontumorous livers. High expression of variant 3 was significantly associated with venous invasion (P = .037), tumor microsatellite formation (P = .022), and tumor nonencapsulation (P = .049). Our ectopic expression study showed that variant 3 significantly promoted the cell growth and motility of HCC cells. The clonal transfectants of variant 3 were more closely packed and resulted in a higher saturation density than in the control vector transfectants. Variant 3 expression also enhanced the proliferation rate in culture and in vivo tumorigenicity in nude mice. In conclusion, we reveal a novel role for variant 3 in the progression of HCC and suggest the feasibility of elevated variant 3 expression as a tumor progression marker for HCC.

Cleavage of tensin during cytoskeleton disruption in YTX-induced apoptosis

Yessotoxin (YTX) is a marine algal toxin previously shown to induce apoptosis in L6 and BC3H1 myoblast cell lines. Disassembly of the F-actin cytoskeleton and cleavage of tensin, a cytoskeletal protein localised at the focal adhesion contacts, appear during this apoptotic process. Tensin binds to actin filaments at the focal adhesion contacts and it links the actin cytoskeleton to the extracellular matrix (ECM). This binding occurs via integrin receptors and it makes tensin a potential link between the actin cytoskeleton and signal transduction. This study evaluates disruption in the F-actin cytoskeleton and change of tensin in myoblast cell lines exposed to 100 nM YTX up to 72 h. YTX treatment cleaves tensin and makes it translocate to the cell centre. Tensin has normally a role in the maintenance of cell shape and YTX-treatment may therefore alter the shape of the cells. YTX exposure also induces formation of lamellas associated with pseudopodia. Alternative linkages and cytoskeletal proteins anchoring the actin filaments to focal contacts remain to be identified.

Disruption of polycystin-1 function interferes with branching morphogenesis of the ureteric bud in developing mouse kidneys

The polycystic kidney disease (PKD1) gene-encoded protein, polycystin-1, is developmentally regulated, with highest expression levels seen in normal developing kidneys, where it is distributed in a punctate pattern at the basal surface of ureteric bud epithelia. Overexpression in ureteric epithelial cell membranes of an inhibitory pMyr-GFP-PKD1 fusion protein via a retroviral (VVC) delivery system and microinjection into the ureteric bud lumen of embryonic day 11 mouse metanephric kidneys resulted in disrupted branching morphogenesis. Using confocal quantitative analysis, significant reductions were measured in the numbers of ureteric bud branch points and tips, as well as in the total ureteric bud length, volume and area, while significant increases were seen as dilations of the terminal branches, where significant increases in outer diameter and volumes were measured. Microinjection of an activating 5TM-GFP-PKD1 fusion protein had an opposite effect and showed significant increases in ureteric bud length and area. These are the first studies to experimentally manipulate polycystin-1 expression by transduction in the embryonic mouse kidney and suggest that polycystin-1 plays a critical role in the regulation of epithelial morphogenesis during renal development.

Integrity of actin fibers and microtubules influences metastatic tumor cell adhesion

Tumor cell adhesion within host organ microvasculature, its stabilization and invasion into host organ parenchyma appear to be important steps during formation of distant metastasis. These interactions of circulating tumor cells with the host organs occur in the presence of fluid shear forces and soluble and cellular environmental conditions of the blood that can modulate their cellular responses and possibly their metastatic efficiency. Cytoskeletal components, such as actin filaments and microtubules, can regulate biophysical characteristics and cellular signaling of the circulating cells. Therefore, we investigated the role of these cytoskeletal structures for early steps during metastasis formation in vivo and in vitro. Using an intravital observation technique, tumor cell adhesion of colon carcinoma cells within the hepatic microcirculation of rats and their invasion into liver parenchyma was observed. Disruption of actin filaments increased cell adhesion, whereas tubulin disruption inhibited adhesive interactions in vivo. The impairment of the cytoskeleton modulated adhesion-mediated cell signaling via focal adhesion kinase (FAK) and paxillin under flow conditions in vitro. In the presence of fluid flow, focal adhesions were enlarged and hyperphosphorylated, whereas stress fibers were reduced compared to static cell adhesion. Disruption of microtubules, however, partially inhibited these effects. Combining the in vivo and in vitro results, our study suggested that changes in cell rigidity and avidity of cell adhesion molecules after disruption of cytoskeletal components appear to be more important for initial adhesive interactions in vivo than their interference with adhesion-mediated cellular signal transduction.

Transcriptional changes following restoration of SERCA2a levels in failing rat hearts

Heart failure is characterized at the cellular level by impaired contractility and abnormal Ca2+ homeostasis. We have previously shown that restoration of a key enzyme that controls intracellular Ca(2+) handling, the sarcoplasmic reticulum Ca2+ ATPase (SERCA2a), induces functional improvement in heart failure. We used high-density oligonucleotide arrays to explore the effects of gene transfer of SERCA2a on genetic reprogramming in a model of heart failure. A total of 1,300 transcripts were identified to be unmodified by the effect of virus alone. Of those, 251 transcripts were found to be up- or down-regulated upon failure. A total of 51 transcripts which were either up--(27) or down--(24) regulated in heart failure were normalized to the nonfailing levels by the restoration of SERCA2a by gene transfer. The microarray analysis identified new genes following SERCA2a restoration in heart failure, which will give us insights into their role in the normalization of multiple pathways within the failing cell.

Epidermal Growth Factor Modulates Tyrosine Phosphorylation of a Novel Tensin Family Member, Tensin3

Here, we report the identification of a new tensin family member, tensin3, and its role in epidermal growth factor (EGF) signaling pathway. Human tensin3 cDNA encodes a 1445 amino acid sequence that shares extensive homology with tensin1, tensin2, and COOH-terminal tensin-like protein. Tensin3 is expressed in various tissues and in different cell types such as endothelia, epithelia, and fibroblasts. The potential role of tensin3 in EGF-induced signaling pathway is explored. EGF induces tyrosine phosphorylation of tensin3 in MDA-MB-468 cells in a time- and dose-dependent manner, but it is independent of an intact actin cytoskeleton or phosphatidylinositol 3-kinase. Activation of EGF receptor is necessary but not sufficient for tyrosine phosphorylation of tensin3. It also requires Src family kinase activities. Furthermore, tensin3 forms a complex with focal adhesion kinase and p130Cas in MDA-MB-468 cells. Addition of EGF to the cells induces dephosphorylation of these two molecules, leads to disassociation of the tensin3-focal adhesion kinase-p130Cas complex, and enhances the interaction between tensin3 and EGF receptor. Our results demonstrate that tensin3 may function as a platform for the disassembly of EGF-related signaling complexes at focal adhesions.

Tensin Stabilizes Integrin Adhesive Contacts in Drosophila

We report the functional characterization of the Drosophila ortholog of tensin, a protein implicated in linking integrins to the cytoskeleton and signaling pathways. A tensin null was generated and is viable with wing blisters, a phenotype characteristic of loss of integrin adhesion. In tensin mutants, mechanical abrasion is required during wing expansion to cause wing blisters, suggesting that tensin strengthens integrin adhesion. The localization of tensin requires integrins, talin, and integrin-linked kinase. The N-terminal domain and C-terminal PTB domain of tensin provide essential recruitment signals. The intervening SH2 domain is not localized on its own. We suggest a model where tensin is recruited to sites of integrin adhesion via its PTB and N-terminal domains, localizing the SH2 domain so that it can interact with phosphotyrosine-containing proteins, which stabilize the integrin link to the cytoskeleton.

FAK promotes organization of fibronectin matrix and fibrillar adhesions

Targeted disruption of the focal adhesion kinase (FAK) gene in mice is lethal at embryonic day 8.5 (E8.5). Vascular defects in FAK-/- mice result from the inability of FAK-deficient endothelial cells to organize themselves into vascular network. We found that, although fibronectin (FN) levels were similar, its organization was less fibrillar in both FAK-/- endothelial cells and mesoderm of E8.5 FAK-/- embryos, as well as in mouse embryonic fibroblasts isolated from mutant embryos. FAK catalytic activity, proline-rich domains, and location in focal contacts were all required for proper allocation and patterning of FN matrix. Cells lacking FAK in focal adhesions fail to translocate supramolecular complexes of integrin-bound FN and focal adhesion proteins along actin filaments to form mature fibrillar adhesions. Taken together, our data suggest that proper FN allocation and organization are dependent on FAK-mediated remodeling of focal adhesions.

Physiologic role of decidual beta1 integrin and focal adhesion kinase in embryonic implantation

Implantation refers to a series of interactions between embryo and endometrium including hatching, attachment, and outgrowth. We investigated the expression and function of beta1 integrin and focal adhesion kinase (FAK) in human decidual cells during implantation. Immunofluorescent staining localized beta1 integrin to surfaces of cultured decidual cells. Double staining for beta1 integrin and mediators of intracellular signaling involving beta1 integrin, such as FAK and vinculin, colocalized beta1 integrin with these substances, suggesting that human decidual cells express beta1 integrin in the focal adhesion region. We next investigated the actions of beta1 integrin and FAK in implantation by co-culturing mouse embryos and human decidual cells. Mouse blastocysts attached to cultured decidual cells after embryo hatching, usually within 24 h of culture initiation. Blastocysts attached to decidual cells exhibited extensive outgrowth at 48 h. Treatment of decidual cells with an antibody against beta1 integrin or with an antisense FAK oligonucleotide did not affect hatching or attachment of blastocysts, but either one could inhibit outgrowth. Thus, it was concluded that human decidual beta1 integrin and FAK participate in this final step of implantation.

Caspase-dependent cleavage of tensin induces disruption of actin cytoskeleton during apoptosis

Members of both calpain and caspase protease families can degrade several components of focal adhesions, leading to disassembly of these complexes. In this report, we investigated the disappearance of tensin from cell adhesion sites of chicken embryonic fibroblast cells (CEFs) exposed to etoposide and demonstrated that loss of tensin from cell adhesions during etoposide-induced apoptosis may be due to degradation of tensin by caspase-3. Tensin cleavage by caspase-3 at the sequence DYPD(1226)G separates the amino-terminal region containing the actin binding domain and the carboxyl-terminal region containing the SH2 domain. The resultant carboxyl-terminal fragment of tensin is unable to bind phosphoinositide 3-kinase (PI3-kinase) transducing cell survival signaling. We also demonstrated that overexpression of the amino-terminal tensin fragment induced disruption of actin cytoskeleton in chicken embryonic fibroblasts. Therefore, caspase-mediated cleavage of tensin contributes to the disruption of actin organization and interrupts ECM-mediated survival signals through phosphatidylinositol 3-kinase.

Indomethacin delays gastric restitution: association with the inhibition of focal adhesion kinase and tensin phosphorylation and reduced actin stress fibers

Repair of superficial gastric mucosal injury is accomplished by the process of restitution-migration of epithelial cells to restore continuity of the mucosal surface. Actin filaments, focal adhesions, and focal adhesion kinase (FAK) play crucial roles in cell motility essential for restitution. We studied whether epidermal growth factor (EGF) and/or indomethacin (IND) affect cell migration, actin stress fiber formation, and/or phosphorylation of FAK and tensin in wounded gastric monolayers. Human gastric epithelial monolayers (MKN 28 cells) were wounded and treated with either vehicle or 0.5 mM IND for 16 hr followed by EGF. EGF treatment significantly stimulated cell migration and actin stress fiber formation, and increased FAK localization to focal adhesions, and phosphorylation of FAK and tensin, whereas IND inhibited all these at the baseline and EGF-stimulated conditions. IND-induced inhibition of FAK phosphorylation preceded changes in actin polymerization, indicating that actin depolymerization might be the consequence of decreased FAK activity. In in vivo experiments, rats received either vehicle or IND (5 mg/kg i.g.), and 3 min later, they received water or 5% hypertonic NaCl; gastric mucosa was obtained at 1, 4, and 8 hr after injury. Four and 8 hr after hypertonic injury, FAK phosphorylation was induced in gastric mucosa compared with controls. IND pretreatment significantly delayed epithelial restitution in vivo, and reduced FAK phosphorylation and recruitment to adhesion points, as well as actin stress fiber formation in migrating surface epithelial cells. Our study indicates that FAK, tensin, and actin stress fibers are likely mediators of EGF-stimulated cell migration in wounded human gastric monolayers and potential targets for IND-induced inhibition of restitution.

Tensin1 and a previously undocumented family member, tensin2, positively regulate cell migration

Tensin is a focal adhesion molecule that binds to actin filaments and participates in signaling pathways. In this study, we have characterized a previously undocumented tensin family member, tensin2/KIAA 1075. Human tensin2 cDNA encodes a 1,285-aa sequence that shares extensive homology with tensin1 at its amino- and carboxyl-terminal ends, which include the actin-binding domain, the Src homology 2 (SH2) domain, and the phosphotyrosine binding (PTB) domain. Analysis of the genomic structures of tensin1 and tensin2 further confirmed that they represent a single gene family. Examination of tensin2 mRNA distribution revealed that heart, kidney, skeletal muscle, and liver were tissues of high expression. The endogenous and recombinant tensin2 were expressed as a 170-kDa protein in NIH 3T3 cells. The subcellular localization of tensin2 was determined by transfection of green fluorescence protein (GFP)-tensin2 fusion construct. The results indicated that tensin2 is also localized to focal adhesions. Finally, functional analysis of tensin genes has demonstrated that expression of tensin genes is able to promote cell migration on fibronectin, indicating that the tensin family plays a role in regulating cell motility.

Analysis of PTEN/MMAC1 alteration in neuroblastoma

Neuroblastoma is the most common extracranial solid tumor in children. Although it has been reported that loss of heterozygosity at various loci, including 10q, frequently occurs in neuroblastoma, a bona fide tumor suppressor gene has not been identified. Recently, a gene mapped to chromosome 10q23, PTEN/MMAC1, was identified as a tumor suppressor gene that inhibits cell survival and cell proliferation by catalyzing the dephosphorylation of phosphatidylinositol 3,4,5-triphosphate. To screen for mutations of this gene in neuroblastoma, we analyzed 11 primary neuroblastoma tumors and 16 neuroblastoma cell lines for PTEN/MMAC1 mutations and deletions. All nine exons of the PTEN/MMAC1 gene were examined using the polymerase chain reaction-single strand conformational polymorphism assay and sequencing. Only one of the cell lines showed a mutation, a 1-bp frameshift deletion in exon 7, and an allelic loss in the opposite allele was revealed by a microsatellite analysis. Our results indicate that the disruption of the PTEN/MMAC1 gene is not a frequent event in neuroblastoma, and suggest that this disruption may be responsible for malignant progression in only a limited proportion of cases of neuroblastoma.

Focal adhesion kinase and p130Cas mediate both sarcomeric organization and activation of genes associated with cardiac myocyte hypertrophy

Hypertrophic terminally differentiated cardiac myocytes show increased sarcomeric organization and altered gene expression. Previously, we established a role for the nonreceptor tyrosine kinase Src in signaling cardiac myocyte hypertrophy. Here we report evidence that p130Cas (Cas) and focal adhesion kinase (FAK) regulate this process. In neonatal cardiac myocytes, tyrosine phosphorylation of Cas and FAK increased upon endothelin (ET) stimulation. FAK, Cas, and paxillin were localized in sarcomeric Z-lines, suggesting that the Z-line is an important signaling locus in these cells. Cas, alone or in cooperation with Src, modulated basal and ET-stimulated atrial natriuretic peptide (ANP) gene promoter activity, a marker of cardiac hypertrophy. Expression of the C-terminal focal adhesion-targeting domain of FAK interfered with localization of endogenous FAK to Z-lines. Expression of the Cas-binding proline-rich region 1 of FAK hindered association of Cas with FAK and impaired the structural stability of sarcomeres. Collectively, these results suggest that interaction of Cas with FAK, together with their localization to Z-lines, is critical to assembly of sarcomeric units in cardiac myocytes in culture. Moreover, expression of the focal adhesion-targeting and/or the Cas-binding proline-rich regions of FAK inhibited ANP promoter activity and suppressed ET-induced ANP and brain natriuretic peptide gene expression. In summary, assembly of signaling complexes that include the focal adhesion proteins Cas, FAK, and paxillin at Z-lines in the cardiac myocyte may regulate, either directly or indirectly, both cytoskeletal organization and gene expression associated with cardiac myocyte hypertrophy.

A role of tensin in skeletal-muscle regeneration

Regeneration of skeletal muscle requires the activation, proliferation, differentiation and fusion of satellite cells to generate new muscle fibres. This study was designed to determine the role of tensin in this process. Cardiotoxin was used to induce regeneration in the anterior tibial muscles of tensin-knockout and wild-type mice. From histological analysis, we found that the regeneration process lasted longer in knockout than in wild-type mice. To investigate the mechanism involved in this delay, we examined each regeneration step in animals and cultured primary cells. We found fewer proliferating myogenic cells identified by bromodeoxyuridine and desmin double labelling in knockout mice on the first 2 days after injury. Expression of myosin, paxillin, dystrophin and dystrophin-associated proteins were delayed in knockout mice. Withdrawal from the cell cycle was less efficient in isolated knockout myoblasts, and the fusion capacity was reduced in these cells as well. These defects in regeneration most likely contributed to the 9-fold increase of centrally nucleated fibres occurring in the non-injected knockout mice. Our results demonstrated clearly that tensin plays a role in skeletal-muscle regeneration.

PTEN mutations in malignant gliomas and their relation with meningeal gliomatosis

A putative tumor suppressor, the PTEN gene at chromosome 10q23. was identified and found to be mutated in many different human tumors. PTEN was recently found to be also involved in focal cell adhesion and cell migration. To identify the role of PTEN gene in malignant gliomas. we used PCR-SSCP and direct sequencing methods to examine 44 malignant gliomas comprising 29 cases without and 15 cases with meningeal gliomatosis. In malignant gliomas without meningeal gliomatosis, 2/29 (7%) of the cases showed alteration of the PTEN gene. In contrast, 5/15 (33%) of malignant gliomas with meningeal gliomatosis cases showed this alteration. These findings indicate that PTEN gene mutation contributes not only to the neoplastic evolution in gliomas but also to the meningeal dissemination of glioma cells.

Resting murine neutrophils express functional alpha 4 integrins that signal through Src family kinases

There is mounting evidence that alpha(4) (CD49d) integrins are involved in neutrophil recruitment and function during inflammatory responses. We report that all resting murine neutrophils derived from bone marrow or peripheral blood express easily detectable levels of alpha(4) integrins on their surface. These alpha(4) integrins were functional, as demonstrated by stimulation of respiratory burst when neutrophils adhered to surfaces coated with the murine vascular cell adhesion molecule-1 (mVCAM-1). Adhesion occurred via alpha(4) integrins, as preincubation of neutrophils with an anti-alpha(4)-specific Ab inhibited attachment to mVCAM-1. Direct cross-linking of the alpha(4) integrin subunit by surface-bound mAbs also elicited superoxide release and release of the secondary granule marker, lactoferrin. The functional responses that occurred downstream of alpha(4) integrin cross-linking required signaling by Src family kinases. Neutrophils derived from hck(-/-)fgr(-/-)lyn(-/-) triple-knockout or hck(-/-)fgr(-/-) double-knockout mice failed to undergo respiratory burst when plated on mVCAM-1. Triple mutant neutrophils were also defective in release of both superoxide and lactoferrin when plated on surfaces coated with mAbs directed against alpha(4). Correlated with impaired alpha(4)-induced functional responses, triple-mutant neutrophils also failed to spread and tightly adhere to anti-alpha(4) mAb-coated surfaces. This is the first direct evidence that functional alpha(4) integrins are expressed by murine PMNs, and that these surface molecules can mediate cellular responses such as tight adhesion, spreading, sustained respiratory burst, and specific granule release in vitro. Moreover the alpha(4) integrins, like all other integrins tested, use the Src family kinases to transduce intracellular signals.

Absence of PTEN/MMAC1 gene mutations in lung adenocarcinomas induced by N-nitrosobis(2-hydroxypropyl)amine in rats

Mutations of the phosphatase and tensin homolog deleted on chromosome ten/mutated in multiple advanced cancers 1 (PTEN/MMAC1) gene were investigated in lung adenocarcinomas induced by N-nitrosobis(2-hydroxypropyl)amine (BHP) in rats. Male Wistar rats (6 weeks old) were given 2000 ppm BHP in their drinking water for 12 weeks and maintained without further treatment until they were killed at week 25. Total RNA was extracted from 15 adenocarcinomas and mutations of the PTEN/MMAC1 gene were investigated by reverse transcription-polymerase chain reaction-restriction-single-strand conformation polymorphism analysis. No mutations were detected, and loss or decrease of expression of PTEN/MMAC1 mRNA was also not found in any of the cases. These results suggest that alterations of the PTEN/MMAC1 gene may not be involved in the development of adenocarcinomas induced by BHP in rats.

Role of the cytoskeleton in adhesion stabilization of human colorectal carcinoma cells to extracellular matrix components under dynamic conditions of laminar flow

Adhesion stabilization of malignant cells in the microcirculation is necessary for successful metastasis formation. The adhesion of colon carcinoma cells to microcirculation extracellular matrix (ECM) components is mediated, in part, by integrins that can be intracellularly linked to cytoskeletal proteins. Thus the functional status of at least certain integrins can be regulated by complex interactions with cytosolic, cytoskeletal and membrane-bound proteins. Wall shear stress caused by fluid flow also influences cellular functions, such as cell morphology, cytoskeletal arrangements and cell signaling. Using a parallel plate laminar flow chamber dynamic adhesion of human HT-29 colon carcinoma cells to collagen was investigated and compared with cell adhesion under static conditions. Cells were pretreated with cytochalasin D, nocodazole, colchicine or acrylamide to disrupt actin filaments, microtubules or intermediate filaments. Disruption of actin filaments completely inhibited all types of adhesive interactions. In contrast, impairment of tubulin polymerization or disruption of intermediate filaments resulted in different effects on static and dynamic adhesion. Treatment with acrylamide did not interfere with dynamic cell adhesion, whereas under static conditions it partially reduced adhesion rates. Under dynamic conditions increased initial adhesive interactions between HT-29 cells and collagen were found after disruption of microtubules, and the adherent cells demonstrated extensive crawling on collagen surfaces. In contrast, under static adhesion disrupting microtubules did not affect cell adhesion rates. Cytochalasin D and acrylamide were found to inhibit Tyr-phosphorylation of FAK and paxillin, whereas microtubule disrupting agents at low but not high concentrations increased phosphorylation of these focal adhesion proteins. Our results revealed that cytoskeletal components appear to be involved in adhesion stabilization of HT-29 cells to ECM components, and hydrodynamic shear forces modulate this involvement. Tyr-phosphorylation of focal adhesion proteins, such as paxillin and FAK, appears to be a part of this cytoskeleton-mediated process.

Lipid phosphatases in the immune system

In the last 10 years we have come to appreciate the central role that phosphatidylinositol (PI)-3,4,5-P(3)plays in regulating a vast array of biological responses to extracellular signals. The level of this phospholipid is low in resting cells but increases rapidly in response to growth factor/cytokine-stimulated plasma membrane recruitment and activation of PI-3-kinase. Within the last 3 years three enzymes, SHIP, SHIP2 and PTEN, that play key roles in regulating the level of PI-3,4,5-P(3)have been cloned. In this review I have attempted to summarize our current knowledge regarding these three intriguing phosphatases.

A novel PTEN mutation in a Japanese patient with Cowden disease

Cowden disease (CD) is an autosomal dominant syndrome characterized by multiple hamartomatous lesions and an increased risk for malignancies. Recent evidence has indicated that the PTEN gene, encoding a protein tyrosine phosphatase, is the CD susceptibility gene. However, another line of evidence has suggested that CD might be genetically heterogeneous. Clinical features of CD are variable, and there are interfamilial differences in the expression of skin lesions. Therefore, information on PTEN mutations in CD patients should be accumulated to clarify the genotype-phenotype correlation. In the present study, we found heterozygous germline mutations of PTEN in all of three Japanese patients with CD examined, indicating no genetic heterogeneity among our patients. The mutations included two non-sense mutations of R335X and R130X, and a mis-sense mutation of C136R. To the best of our knowledge, the C136R mutation has not previously been reported in CD patients. This novel mutation was located outside the core motif of the phosphatase domain of PTEN protein, where most of the missense mutations previously reported in CD patients were clustered. Mucocutaneous manifestations were far fewer in the patient with this mutation than in the patients with nonsense mutations. Whether the phenotypic difference in mucocutaneous features was due to the different mutations remains unclear.

Cytoskeletal tumor suppressors that block oncogenic RAS signaling

Several distinct peptides or drugs that block the Rho family GTPases-mediated pathways were found to suppress RAS-induced malignant phenotype. They include (1) C3 enzyme that selectively inactivates Rho, (2) ACK42, a peptide that blocks the interaction of CDC42 with its effectors such as ACKs, (3) PAK18, a peptide that blocks the activation of PAK and membrane ruffling, and (4) actin-binding drugs, chaetoglobosin K (CK) and MKT-077, that block membrane ruffling by capping and bundling actin filaments, respectively.

Cytoskeletal disruption induces T cell apoptosis by a caspase-3 mediated mechanism

T cell apoptosis can be triggered by different mechanisms that lead to distinctive features such as cell shrinkage, membrane blebbing, phosphatidylserine externalization, and internucleosomal DNA fragmentation. Prevailing models for the induction of apoptosis place the cytoskeleton as a distal target of the death effector molecules ('executioners'). However, the cytoskeleton can also play a role in the induction of apoptosis as suggested by the finding that cytoskeletal disruption can induce apoptosis. The mechanism by which this occurs is unknown. Here, we report that T cell apoptosis by cytoskeletal disruption involves a protein synthesis-independent mechanism leading to up-regulation of caspase-3 protease activity and increased accessibility of active caspase-3 to its substrate. Thus, cytoskeleton integrity may regulate the subcellular compartmentalization of death effector molecules.