Molecular cloning of chick cardiac muscle tensin. Full-length cDNA sequence, expression, and characterization

Tumor-infiltrating CD8+ T cells recognize a heterogeneously expressed functional neoantigen in clear cell renal cell carcinoma

Immune checkpoint inhibitors (ICIs) are used in cancer immunotherapy to block programmed death-1 and cytotoxic T-lymphocyte antigen 4, but the response rate for ICIs is still low and tumor cell heterogeneity is considered to be responsible for resistance to immunotherapy. Tumor-infiltrating lymphocytes (TILs) have an essential role in the anti-tumor effect of cancer immunotherapy; however, the specificity of TILs in renal cell carcinoma (RCC) is elusive. In this study, we analyzed a 58-year-old case with clear cell RCC (ccRCC) with the tumor showing macroscopic and microscopic heterogeneity. The tumor was composed of low-grade and high-grade ccRCC. A tumor cell line (1226 RCC cells) and TILs were isolated from the high-grade ccRCC lesion, and a TIL clone recognized a novel neoantigen peptide (YVVPGSPCL) encoded by a missense mutation of the tensin 1 (TNS1) gene in a human leukocyte antigen-C*03:03-restricted fashion. The TNS1 gene mutation was not detected in the low-grade ccRCC lesion and the TIL clone did not recognized low-grade ccRCC cells. The missense mutation of TNS1 encoding the S1309Y mutation was found to be related to cell migration by gene over-expression. These findings suggest that macroscopically and microscopically heterogenous tumors might show heterogenous gene mutations and reactivity to TILs.

Tensins - emerging insights into their domain functions, biological roles and disease relevance

Tensins are a family of focal adhesion proteins consisting of four members in mammals (TNS1, TNS2, TNS3 and TNS4). Their multiple domains and activities contribute to the molecular linkage between the extracellular matrix and cytoskeletal networks, as well as mediating signal transduction pathways, leading to a variety of physiological processes, including cell proliferation, attachment, migration and mechanical sensing in a cell. Tensins are required for maintaining normal tissue structures and functions, especially in the kidney and heart, as well as in muscle regeneration, in animals. This Review discusses our current understanding of the domain functions and biological roles of tensins in cells and mice, as well as highlighting their relevance to human diseases.

MethylationToActivity: a deep-learning framework that reveals promoter activity landscapes from DNA methylomes in individual tumors

Although genome-wide DNA methylomes have demonstrated their clinical value as reliable biomarkers for tumor detection, subtyping, and classification, their direct biological impacts at the individual gene level remain elusive. Here we present MethylationToActivity (M2A), a machine learning framework that uses convolutional neural networks to infer promoter activities based on H3K4me3 and H3K27ac enrichment, from DNA methylation patterns for individual genes. Using publicly available datasets in real-world test scenarios, we demonstrate that M2A is highly accurate and robust in revealing promoter activity landscapes in various pediatric and adult cancers, including both solid and hematologic malignant neoplasms.

Tensin regulates pharyngeal pumping in Caenorhabditis elegans

Tensin is a focal adhesion molecule that is known to regulate cell adhesion, migration, and proliferation. Although there are four tensin homologs (TNS1, TNS2, TNS3, and CTEN/TNS4) in mammals, only one tensin gene is found in Caenorhabditis elegans. Sequence analysis suggests that Caenorhabditis elegans tensin is slightly closer aligned with human TNS1 than with other human tensins. To establish the role of TNS1 in Caenorhabditis elegans, we have generated TNS1 knockout (KO) worms by CRISPR-Cas9 and homologous recombination directed repair approaches. Lack of TNS1 does not appear to affect the development or gross morphology of the worms. Nonetheless, defecation cycles are significantly longer in TNS1 KO worms. In addition, their pharyngeal pumping rate is markedly faster, which is likely due to a shorter pump duration in the KO worms. These findings indicate that TNS1 is not required for the development and survival of Caenorhabditis elegans but point to a critical role in modulating defecation and pharyngeal pumping rates.

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.

AMPK negatively regulates tensin-dependent integrin activity

Georgiadou et al. show that the major metabolic sensor AMPK regulates integrin activity and integrin-dependent processes in fibroblasts by modulating tensin levels. Loss of AMPK up-regulates tensin expression, triggering enhanced integrin activity in fibrillar adhesions, fibronectin remodeling, and traction stress.

Tight regulation of integrin activity is paramount for dynamic cellular functions such as cell matrix adhesion and mechanotransduction. Integrin activation is achieved through intracellular interactions at the integrin cytoplasmic tails and through integrin–ligand binding. In this study, we identify the metabolic sensor AMP-activated protein kinase (AMPK) as a β1-integrin inhibitor in fibroblasts. Loss of AMPK promotes β1-integrin activity, the formation of centrally located active β1-integrin– and tensin-rich mature fibrillar adhesions, and cell spreading. Moreover, in the absence of AMPK, cells generate more mechanical stress and increase fibronectin fibrillogenesis. Mechanistically, we show that AMPK negatively regulates the expression of the integrin-binding proteins tensin1 and tensin3. Transient expression of tensins increases β1-integrin activity, whereas tensin silencing reduces integrin activity in fibroblasts lacking AMPK. Accordingly, tensin silencing in AMPK-depleted fibroblasts impedes enhanced cell spreading, traction stress, and fibronectin fiber formation. Collectively, we show that the loss of AMPK up-regulates tensins, which bind β1-integrins, supporting their activity and promoting fibrillar adhesion formation and integrin-dependent processes.

Research advances on structure and biological functions of integrins

Integrins are an important family of adhesion molecules that were first discovered two decades ago. Integrins are transmembrane heterodimeric glycoprotein receptors consisting of α and β subunits, and are comprised of an extracellular domain, a transmembrane domain, and a cytoplasmic tail. Therein, integrin cytoplasmic domains may associate directly with numerous cytoskeletal proteins and intracellular signaling molecules, which are crucial for modulating fundamental cell processes and functions including cell adhesion, proliferation, migration, and survival. The purpose of this review is to describe the unique structure of each integrin subunit, primary cytoplasmic association proteins, and transduction signaling pathway of integrins, with an emphasis on their biological functions.

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.

Cell biology of mesangial cells: the third cell that maintains the glomerular capillary

The renal glomerulus consists of glomerular endothelial cells, podocytes, and mesangial cells, which cooperate with each other for glomerular filtration. We have produced monoclonal antibodies against glomerular cells in order to identify different types of glomerular cells. Among these antibodies, the E30 clone specifically recognizes the Thy1.1 molecule expressed on mesangial cells. An injection of this antibody into rats resulted in mesangial cell-specific injury within 15 min, and induced mesangial proliferative glomerulonephritis in a reproducible manner. We examined the role of mesangial cells in glomerular function using several experimental tools, including an E30-induced nephritis model, mesangial cell culture, and the deletion of specific genes. Herein, we describe the characterization of E30-induced nephritis, formation of the glomerular capillary network, mesangial matrix turnover, and intercellular signaling between glomerular cells. New molecules that are involved in a wide variety of mesangial cell functions are also introduced.

MicroRNA-548j functions as a metastasis promoter in human breast cancer by targeting Tensin1

MicroRNAs (miRNAs) are single-stranded, small non-coding RNA molecules that participate in important biological processes. Although the functions of many miRNAs in breast cancer metastasis have been established, the role of others remains to be characterized. To identify additional miRNAs involved in metastasis, we performed a genetic screen by transducing a Lenti-miR™ virus library into MCF-7 cells. Using transwell invasion assays we identified human miR-548j as an invasion-inducing miRNA. The endogenous levels of miR-548j expression in breast cancer cell lines were shown to correlate with invasiveness. Moreover, miR-548j was shown to stimulate breast cancer cell invasion and metastasis in vitro and in vivo, but had no effect on proliferation. Next, using a series of in vitro and in vivo experiments, we found that Tensin1 served as a direct and functional target of miR-548j. Both miR-548j and Tensin1 modulated the activation of Cdc42 to regulate cell invasion and siCdc42 or the selective Cdc42 inhibitor ML141 suppressed the pathway of miR-548j-mediated cell invasion. Furthermore, a strong correlation between miR-548j, Tensin1, metastasis and survival was observed using two sets of clinical breast cancer samples. Our findings demonstrate that miR-548j functions as a metastasis-promoting miRNA to regulate breast cancer cell invasion and metastasis by targeting Tensin1 and activating Cdc42, suggesting a potential therapeutic application in breast cancer.

Molecular physiology of the tensin brotherhood of integrin adaptor proteins

Numerous proteins have been identified as constituents of the adhesome, the totality of molecular components in the supramolecular assemblies known as focal adhesions, fibrillar adhesions and other kinds of adhesive contact. The transmembrane receptor proteins called integrins are pivotal adhesome members, providing a physical link between the extracellular matrix (ECM) and the actin cytoskeleton. Tensins are ever more widely investigated intracellular adhesome constituents. Involved in cell attachment and migration, cytoskeleton reorganization, signal transduction and other processes relevant to cancer research, tensins have recently been linked to functional properties of deleted in liver cancer 1 (DLC1) and a mitogen-activated protein kinases (MAPK), to cell migration in breast cancer, and to metastasis suppression in the kidney. Tensins are close relatives of phosphatase homolog/tensin homolog (PTEN), an extensively studied tumor suppressor. Such findings are recasting the earlier vision of tensin (TNS) as an actin-filament (F-actin) capping protein in a different light. This critical review aims to summarize current knowledge on tensins and thus to highlight key points concerning the expression, structure, function, and evolution of the various members of the TNS brotherhood. Insight is sought by comparisons with homologous proteins. Some historical points are added for perspective.

1H, 15N and 13C chemical shift assignments of the SH2 domain of human tensin2 (TENC1)

Tensin is an important cytoplasmic phosphoprotein localized to integrin-mediated focal adhesion. It links actin cytoskeleton to extracellular matrix through its N-terminal actin-binding domain and C-terminal phosphotyrosine-binding domain. Studies of knockout mice revealed the critical roles of tensin in skeletal muscle regeneration, renal function and regulation of cell migration. The SH2 domain of tensin interacts with various tyrosine-phosphorylated proteins thus functions as a platform for dis/assembly of signaling molecules. It has also been implicated in recruiting a tumor supperssor protein DLC1 (deleted in live cancer 1) to the focal adhesion, which is required for oncogenic inhibition effect of DLC1 in a phosphotyrosine-independent manner. Here, we report complete chemical shift assignments of the SH2 domain of human tensin2 determined by triple resonance experiments. The resonance assignments serve as a basis for our further functional studies and structure determination by NMR spectroscopy. (BMRB deposits with accession number 16472).

N-cadherin cell-cell adhesion complexes are regulated by fibronectin matrix assembly

Fibronectin is a principal component of the extracellular matrix. Soluble fibronectin molecules are assembled into the extracellular matrix as insoluble, fibrillar strands via a cell-dependent process. In turn, the interaction of cells with the extracellular matrix form of fibronectin stimulates cell functions critical for tissue repair. Cross-talk between cell-cell and cell-extracellular matrix adhesion complexes is essential for the organization of cells into complex, functional tissue during embryonic development and tissue remodeling. Here, we demonstrate that fibronectin matrix assembly affects the organization, composition, and function of N-cadherin-based adherens junctions. Using fibronectin-null mouse embryonic myofibroblasts, we identified a novel quaternary complex composed of N-cadherin, β-catenin, tensin, and actin that exists in the absence of a fibronectin matrix. In the absence of fibronectin, homophilic N-cadherin ligation recruited both tensin and α5β1 integrins into nascent cell-cell adhesions. Initiation of fibronectin matrix assembly disrupted the association of tensin and actin with N-cadherin, released α5β1 integrins and tensin from cell-cell contacts, stimulated N-cadherin reorganization into thin cellular protrusions, and decreased N-cadherin adhesion. Fibronectin matrix assembly has been shown to recruit α5β1 integrins and tensin into fibrillar adhesions. Taken together, these studies suggest that tensin serves as a common cytoskeletal link for integrin- and cadherin-based adhesions and that the translocation of α5β1 integrins from cell-cell contacts into fibrillar adhesions during fibronectin matrix assembly is a novel mechanism by which cell-cell and cell-matrix adhesions are coordinated.

Comprehensive analysis of phosphorylation sites in Tensin1 reveals regulation by p38MAPK

Tensin1 is the archetype of a family of focal adhesion proteins. Tensin1 has a phosphotyrosine binding domain that binds the cytoplasmic tail of β-integrin, a Src homology 2 domain that binds focal adhesion kinase, p130Cas, and the RhoGAP called deleted in liver cancer-1, a phosphatase and tensin homology domain that binds protein phosphatase-1α and other regions that bind F-actin. The association between tensin1 and these partners affects cell polarization, migration, and invasion. In this study we analyzed the phosphorylation of human S-tag-tensin1 expressed in HEK293 cells by mass spectrometry. Peptides covering >90% of the sequence initially revealed 50 phosphorylated serine/phosphorylated threonine (pSer/pThr) but no phosphorylated tyrosine (pTyr) sites. Addition of peroxyvanadate to cells to inhibit protein tyrosine phosphatases exposed 10 pTyr sites and addition of calyculin A to cells to inhibit protein phosphatases type 1 and 2A gave a total of 62 pSer/pThr sites. We also characterized two sites modified by O-linked N-acetylglucosamine. Tensin1 F302A, which does not bind protein phosphatase-1, showed > twofold enhanced phosphorylation of seven sites. The majority of pSer/pThr have adjacent proline (Pro) residues and we show endogenous p38 mitogen activated protein kinase (MAPK) associated with and phosphorylated tensin1 in an in vitro kinase assay. Recombinant p38α MAPK also phosphorylated S-tag-tensin1, resulting in decreased binding with deleted in liver cancer-1. Activation of p38 MAPK in cells by sorbitol-induced hyperosmotic stress increased phosphorylation of S-tag-tensin1, which reduced binding to deleted in liver cancer-1 and increased binding to endogenous pTyr proteins, including p130Cas and focal adhesion kinase. These data demonstrate that tensin1 is extensively phosphorylated on Ser/Thr residues in cells and phosphorylation by p38 MAPK regulates the specificity of the tensin1 Src homology 2 domain for binding to different proteins. Tensin1 provides a hub for connecting signaling pathways involving p38 MAP kinase, tyrosine kinases and RhoGTPases.

Myogenic differentiation in atrium-derived adult cardiac pluripotent cells and the transcriptional regulation of GATA4 and myogenin on ANP promoter

We established cardiac pluripotent stem-like cells from the left atrium (LA-PCs) of adult rat hearts. These cells could differentiate not only into beating myocytes but also into cells of other lineages, including adipocytes and endothelial cells in the methylcellulose-based medium containing interleukin-3 (IL-3), interleukin-6 (IL-6), and stem cell factor (SCF). In particular, IL-3 and SCF contributed to the differentiation into cardiac troponin I-positive cells. Notably, small population of LA-PCs coexpressed GATA4 and myogenin, which are markers specific to cardiomyocytes and skeletal myocytes, respectively, and could differentiate into both cardiac and skeletal myocytes. Therefore, we investigated the involvement of these two tissue-specific transcription factors in the cardiac transcriptional activity. Coexpression of GATA4 and myogenin synergistically activated GATA4-specific promoter of the atrial natriuretic peptide gene. This combinatorial function was shown to be dependant on the GATA site, but independent of the E-box. The results of chromatin immunoprecipitation and electrophoretic mobility shift assays suggested that myogenin bound to GATA4 on the GATA elements and the C-terminal Zn-finger domain of GATA4 and the N-terminal region of myogenin were required for this synergistic activation of transcription. Taken together, these two transcription factors could be involved in the myogenesis of LA-PCs.

Regulation of actin assembly associated with protrusion and adhesion in cell migration

To migrate, a cell first extends protrusions such as lamellipodia and filopodia, forms adhesions, and finally retracts its tail. The actin cytoskeleton plays a major role in this process. The first part of this review (sect. II) describes the formation of the lamellipodial and filopodial actin networks. In lamellipodia, the WASP-Arp2/3 pathways generate a branched filament array. This polarized dendritic actin array is maintained in rapid treadmilling by the concerted action of ADF, profilin, and capping proteins. In filopodia, formins catalyze the processive assembly of nonbranched actin filaments. Cell matrix adhesions mechanically couple actin filaments to the substrate to convert the treadmilling into protrusion and the actomyosin contraction into traction of the cell body and retraction of the tail. The second part of this review (sect. III) focuses on the function and the regulation of major proteins (vinculin, talin, tensin, and alpha-actinin) that control the nucleation, the binding, and the barbed-end growth of actin filaments in adhesions.

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.

Tensin

Tensin is a cytoplasmic phosphoprotein that localized to integrin-mediated focal adhesions. It binds to actin filaments and contains a phosphotyrosine-binding (PTB) domain, which interacts with the cytoplasmic tails of beta integrin. These interactions allow tensin to link actin filaments to integrin receptors. In addition, tensin has an Src Homology 2 (SH2) domain capable of interacting with tyrosine-phosphorylated proteins. Furthermore, several factors induce tyrosine phosphorylation of tensin. Thus, tensin functions as a platform for dis/assembly of signaling complexes at focal adhesions by recruiting tyrosine-phosphorylated signaling molecules through the SH2 domain, and also by providing interaction sites for other SH2-containing proteins. Analysis of knockout mice has demonstrated critical roles of tensin in renal function, muscle regeneration, and cell migration. Therefore, tensin and its downstream signaling molecules may be targets for therapeutic interventions in renal disease, wound healing and cancer.

Beginning and ending an actin filament: control at the barbed end

Dynamic actin filaments contribute to cell migration, organelle movements, memory, and gene regulation. These dynamic processes are often regulated by extracellular and?or cell cycle signals. Regulation targets, not actin itself, but the factors that determine it's dynamic properties. Thus, filament nucleation, rate and duration of elongation, and depolymerization are each controlled with regard to time and?or space. Two mechanisms exist for nucleating filaments de novo, the Arp23 complex and the formins; multiple pathways regulate each. A new filament elongates rapidly but transiently before its barbed end is capped. Rapid capping allows the cell to maintain fine temporal and spatial control over F-actin distribution. Modulation of capping protein activity and its access to barbed ends is emerging as a site of local regulation. Finally, to maintain a steady state filaments must depolymerize. Depolymerization can limit the rate of new filament nucleation and elongation. The activity of ADF?cofilin, which facilitates depolymerization, is also regulated by multiple inputs. This chapter describes (1) mechanism and regulation of new filament formation, (2) mechanism of enhancing elongation at barbed ends, (3) capping proteins and their regulators, and (4) recycling of actin monomers from filamentous actin (F-actin) back to globular actin (G-actin).

blistery encodes Drosophila tensin protein and interacts with integrin and the JNK signaling pathway during wing development

Tensin is an actin-binding protein that is localized in focal adhesions. At focal adhesion sites, tensin participates in the protein complex that establishes transmembrane linkage between the extracellular matrix and cytoskeletal actin filaments. Even though there have been many studies on tensin as an adaptor protein, the role of tensin during development has not yet been clearly elucidated. Thus, this study was designed to dissect the developmental role of tensin by isolating Drosophila tensin mutants and characterizing its role in wing development. The Drosophila tensin loss-of-function mutations resulted in the formation of blisters in the wings, which was due to a defective wing unfolding process. Interestingly, by(1)-the mutant allele of the gene blistery (by)-also showed a blistered wing phenotype, but failed to complement the wing blister phenotype of the Drosophila tensin mutants, and contains Y62N/T163R point mutations in Drosophila tensin coding sequences. These results demonstrate that by encodes Drosophila tensin protein and that the Drosophila tensin mutants are alleles of by. Using a genetic approach, we have demonstrated that tensin interacts with integrin and also with the components of the JNK signaling pathway during wing development; overexpression of by in wing imaginal discs significantly increased JNK activity and induced apoptotic cell death. Collectively, our data suggest that tensin relays signals from the extracellular matrix to the cytoskeleton through interaction with integrin, and through the modulation of the JNK signal transduction pathway during Drosophila wing development.

Integrin beta cytoplasmic domain interactions with phosphotyrosine-binding domains: a structural prototype for diversity in integrin signaling

The cytoplasmic domains (tails) of heterodimeric integrin adhesion receptors mediate integrins' biological functions by binding to cytoplasmic proteins. Most integrin beta tails contain one or two NPXYF motifs that can form beta turns. These motifs are part of a canonical recognition sequence for phosphotyrosine-binding (PTB) domains, protein modules that are present in a wide variety of signaling and cytoskeletal proteins. Indeed, talin and ICAP1-alpha bind to integrin beta tails by means of a PTB domain-NPXY ligand interaction. To assess the generality of this interaction we examined the binding of a series of recombinant PTB domains to a panel of short integrin beta tails. In addition to the known integrin-binding proteins, we found that Numb (a negative regulator of Notch signaling) and Dok-1 (a signaling adaptor involved in cell migration) and their isolated PTB domain bound to integrin tails. Furthermore, Dok-1 physically associated with integrin alpha IIb beta 3. Mutations of the integrin beta tails confirmed that these interactions are canonical PTB domain-ligand interactions. First, the interactions were blocked by mutation of an NPXY motif in the integrin tail. Second, integrin class-specific interactions were observed with the PTB domains of Dab, EPS8, and tensin. We used this specificity, and a molecular model of an integrin beta tail-PTB domain interaction to predict critical interacting residues. The importance of these residues was confirmed by generation of gain- and loss-of-function mutations in beta 7 and beta 3 tails. These data establish that short integrin beta tails interact with a large number of PTB domain-containing proteins through a structurally conserved mechanism.

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.

Effects of cytochalasin D and latrunculin B on mechanical properties of cells

Actin microfilaments transmit traction and contraction forces generated within a cell to the extracellular matrix during embryonic development, wound healing and cell motility, and to maintain tissue structure and tone. Therefore, the state of the actin cytoskeleton strongly influences the mechanical properties of cells and tissues. Cytochalasin D and Latrunculin are commonly used reagents that, by different mechanisms, alter the state of actin polymerization or the organization of actin filaments. We have investigated the effect of a wide range of Cytochalasin D and Latrunculin B concentrations (from 40 pM to 10 microM) on the mechanical properties of the cells within fibroblast populated collagen matrices. Contractile force and dynamic stiffness were measured by uniaxial stress-strain testing. The range of effective concentrations of Cytochalasin D (200 pM-2 microM) was broader than that of Latrunculin B (20 nM-200 nM). Activating the cells by serum did not change the effective range of Cytochalasin D concentrations but shifted that of Latrunculin B upward by tenfold. Simple mathematical binding models based on the presumed mechanisms of action of Cytochalasin D and Latrunculin B simulated the concentration-dependent mechanical changes reasonably well. This study shows a strong dependence of the mechanical properties of cells and tissues on the organization and degree of polymerization of actin filaments.

Molecular cloning and characterization of human trabeculin-alpha, a giant protein defining a new family of actin-binding proteins

We describe the molecular cloning and characterization of a novel giant human cytoplasmic protein, trabeculin-alpha (M(r) = 614,000). Analysis of the deduced amino acid sequence reveals homologies with several putative functional domains, including a pair of alpha-actinin-like actin binding domains; regions of homology to plakins at either end of the giant polypeptide; 29 copies of a spectrin-like motif in the central region of the protein; two potential Ca(2+)-binding EF-hand motifs; and a Ser-rich region containing a repeated GSRX motif. With similarities to both plakins and spectrins, trabeculin-alpha appears to have evolved as a hybrid of these two families of proteins. The functionality of the actin binding domains located near the N terminus was confirmed with an F-actin binding assay using glutathione S-transferase fusion proteins comprising amino acids 9-486 of the deduced peptide. Northern and Western blotting and immunofluorescence studies suggest that trabeculin is ubiquitously expressed and is distributed throughout the cytoplasm, though the protein was found to be greatly up-regulated upon differentiation of myoblasts into myotubes. Finally, the presence of cDNAs similar to, yet distinct from, trabeculin-alpha in both human and mouse suggests that trabeculins may form a new subfamily of giant actin-binding/cytoskeletal cross-linking proteins.

Modulation of cellular apoptotic potential: contributions to oncogenesis

The importance of apoptosis as a natural means to eliminate unwanted or damaged cells has been realized over the past decade. Many components required to exercise programmed cell death have been identified and shown to pre-exist in most, if not all, cells. Such ubiquity requires that apoptosis be tightly controlled and suggests the propensity of cells to trigger the cellular death machinery can be regulated. Recently, several signaling pathways have been demonstrated to impact the apoptotic potential of cells, most notably the phosphatidylinositol 3' kinase (PI3'K) pathway. The 3' phosphorylated lipid products generated by this enzyme promote activation of a protein-serine kinase, PKB/AKT, which is necessary and sufficient to confer cell PI3'K-dependent survival signals. The relevance of this pathway to human cancer was revealed by the recent finding that the product of the PTEN tumor suppressor gene acts to antagonize PI3'K. This review focuses on the regulation and mechanisms by which PKB activation protects cells and the oncologic consequences of dysregulation of the pathway.

Nexilin: a novel actin filament-binding protein localized at cell-matrix adherens junction

We isolated two novel actin filament (F-actin)-binding proteins from rat brain and rat 3Y1 fibroblast. They were splicing variants, and we named brain big one b-nexilin and fibroblast small one s-nexilin. b-Nexilin purified from rat brain was a protein of 656 amino acids (aa) with a calculated molecular weight of 78,392, whereas s-nexilin, encoded by the cDNA isolated from rat 3Y1 cells by the reverse transcriptase-PCR method, was a protein of 606 aa with a calculated molecular weight of 71,942. b-Nexilin had two F-actin- binding domains (ABDs) at the NH2-terminal and middle regions, whereas s-nexilin had one ABD at the middle region because 64 aa residues were deleted and 14 aa residues were inserted in the first NH2-terminal ABD of b-nexilin, and thereby the first ABD lost its activity. b- and s-nexilins bound along the sides of F-actin, but only b-nexilin showed F-actin cross-linking activity. b-Nexilin was mainly expressed in brain and testis, whereas s-nexilin was mainly expressed in testis, spleen, and fibroblasts, such as rat 3Y1 and mouse Swiss 3T3 cells, but neither b- nor s-nexilin was detected in liver, kidney, or cultured epithelial cells. An immunofluorescence microscopic study revealed that s-nexilin was colocalized with vinculin, talin, and paxillin at cell- matrix adherens junction (AJ) and focal contacts, but not at cell-cell AJ, in 3Y1 cells. Overexpressed b- and s-nexilins were localized at focal contacts but not at cell-cell AJ. These results indicate that nexilin is a novel F-actin-binding protein localized at cell-matrix AJ.

Progressive kidney degeneration in mice lacking tensin

Tensin is a focal adhesion phosphoprotein that binds to F-actin and contains a functional Src homology 2 domain. To explore the biological functions of tensin, we cloned the mouse tensin gene, determined its program of expression, and used gene targeting to generate mice lacking tensin. Even though tensin is expressed in many different tissues during embryogenesis, tensin null mice developed normally and appeared healthy postnatally for at least several months. Over time, -/- mice became frail because of abnormalities in their kidneys, an organ that expresses high levels of tensin. Mice with overt signs of weakness exhibited signs of renal failure and possessed multiple large cysts in the proximal kidney tubules, but even in tensin null mice with normal blood analysis, cysts were prevalent. Ultrastructurally, noncystic areas showed typical cell-matrix junctions that readily labeled with antibodies against other focal adhesion molecules. In abnormal regions, cell-matrix junctions were disrupted and tubule cells lacked polarity. Taken together, our data imply that, in the kidney, loss of tensin leads to a weakening, rather than a severing, of focal adhesion. All other tissues appeared normal, suggesting that, in most cases, tensin's diverse functions are redundant and may be compensated for by other focal adhesion proteins.

The N-terminal domains of tensin and auxilin are phosphatase homologues

Tensin, an actin filament capping protein, and auxilin, a component of receptor-mediated endocytosis, are known to have 350 residue regions of significant sequence similarity near their N-termini (Schröder et al., 1995, Eur J Biochem 228:297-304). Here we demonstrate that these regions are homologous, not only to each other, but also to the catalytic domain of a putative protein tyrosine phosphatase (PTP) from Saccharomyces cerevisiae and to other PTPs. We propose that the PTP-like portion of the homology region of tensin and auxilin represents a distinct domain. A detailed sequence comparison indicates that the PTP-like domain in tensin is unlikely to exhibit phosphatase activity, whereas in auxilin it may possess a different phosphatase specificity from tyrosine phosphatases. It is probable that the PTP-like domains in tensin and auxilin mediate binding interactions with phosphorylated polypeptides; they may therefore represent members of a distinct class of phosphopeptide recognition domain.

p130CAS forms a signaling complex with the adapter protein CRKL in hematopoietic cells transformed by the BCR/ABL oncogene

The Philadelphia chromosome (Ph) translocation generates a chimeric tyrosine kinase oncogene, BCR/ABL, which causes chronic myelogenous leukemia (CML) and a type of acute lymphoblastic leukemia (ALL). In primary samples from virtually all patients with CML or Ph+ALL, the CRKL adapter protein is tyrosine phosphorylated and physically associated with p210(BCR/ABL). CRKL has one SH2 domain and two SH3 domains and is structurally related to c-CRK-II (CRK) and the v-Crk oncoprotein. We have previously shown that CRKL, but not the related adapter protein c-CRK, is tyrosine phosphorylated in cell lines transformed by BCR/ABL, and that CRKL binds to BCR/ABL through the CRKL-SH3 domains. Furthermore, the CRKL-SH2 domain has been shown to bind one or more cellular proteins, one of which is p120(CBL). Here we demonstrate that another cellular protein linked to BCR/ABL through the CRKL-SH2 domain is p130(CAS). p130(CAS) was found to be tyrosine phosphorylated and associated with CRKL in BCR/ABL expressing cell lines and in samples obtained from CML and ALL patients, but not in samples from controls. In both normal and BCR/ABL transformed cells, p130(CAS) was detected in focal adhesion-like structures, as was BCR/ABL. In normal cells, the focal adhesion proteins tensin, p125(FAK), and paxillin constitutively associated with p130(CAS). However, in BCR/ABL transformed cells, the interaction between p130(CAS) and tensin was disrupted, while the associations between p130(CAS), p125(FAK), and paxillin were unaffected. These results suggest that the BCR/ABL oncogene could alter the function of p130(CAS) in at least three ways: tyrosine phosphorylation, inducing constitutive binding of CRKL to a domain in p130(CAS) containing Tyr-X-X-Pro motifs (substrate domain), and disrupting the normal interaction of p130(CAS) with the focal adhesion protein tensin. These alterations in the structure of signaling proteins in focal adhesion like structures could contribute to the known adhesion abnormalities in CML cells.

Platelet-derived growth factor-induced formation of tensin and phosphoinositide 3-kinase complexes

Tensin is an SH2 domain-containing cytoskeletal protein that binds to and caps actin filaments. Investigation of signal transduction mechanisms associated with tensin revealed the presence of phosphoinositide 3-kinase (PI 3-kinase) activity in tensin immunoprecipitates from platelet-derived growth factor-treated cells. Association of PI 3-kinase activity with tensin was transitory, and the amount of activity was approximately 1% of the total PI 3-kinase activity found in anti-phosphotyrosine (anti-pY) immunoprecipitates. In vitro, PI 3-kinase activity associated with the SH2 domain of tensin in a platelet-derived growth factor-dependent manner. The optimal phosphopeptide binding specificity of the SH2 domain of tensin was determined to be phospho-Y (E or D), N, (I, V, or F). Synthetic phosphopeptides containing the sequence YENI could specifically block the association of PI 3-kinase activity with tensin in a dose-dependent manner. These results suggest that PI 3-kinase interacts with the cytoskeleton via the SH2 domain of tensin and may play an important role in platelet-derived growth factor-induced cytoskeletal reorganization that is concomitant with cell migration and proliferation.

Signal transduction by cell adhesion receptors

Over the last few years, it has become clear that cell adhesion receptors function in signal transduction processes leading to the regulation of cell growth and differentiation. Signal transduction by both integrins and CAMs has been shown to involve activation of tyrosine kinases, while CAM signaling in neural cells involves G proteins as well. In the case of integrins, some of the downstream signaling events intersect with the Ras pathway, particularly the activation of MAP kinases. In fibroblasts, integrin mediated anchorage to the substratum regulates cell cycle traverse, while in epithelial cells, loss of anchorage can trigger programmed cell death. In many cell types, but particularly monocytic cells, integrin ligation has a profound impact on gene expression. Preliminary evidence also implicates CAMs and selectins in gene regulation. A consistent theme in signal transduction mediated by adhesion receptors concerns the role of the cytoskeleton. Integrin mediated signaling processes are interrupted by cytoskeletal disassembly. Identification of the APC and neurofibromatosis type 2 tumor suppressors suggest that cytoskeletal complexes also play a key role in signaling by cadherins and CD44, respectively. Thus, signaling by cell adhesion receptors may involve aspects that impinge on previously known signaling pathways including the RTK/Ras pathway and serpentine receptor/G protein pathways. However, novel aspects of signal transduction involving cytoskeletal assemblies may also be critical.