Tandem LIM domain-containing proteins, LIMK1 and LMO1, directly bind to force-bearing keratin intermediate filaments.

The cytoskeleton of the cell is constantly exposed to physical forces that regulate cellular functions. Selected members of the LIM (Lin-11, Isl-1, and Mec-3) domain-containing protein family accumulate along force-bearing actin fibers, with evidence supporting that the LIM domain is solely responsible for this force-induced interaction. However, LIM domain's force-induced interactions are not limited to actin. LIMK1 and LMO1, both containing only two tandem LIM domains, are recruited to force-bearing keratin fibers in epithelial cells. This unique recruitment is mediated by their LIM domains and regulated by the sequences outside the LIM domains. Based on in vitro reconstitution of this interaction, LIMK1 and LMO1 directly interact with stretched keratin 8/18 fibers. These results show that LIM domain's mechano-sensing abilities extend to the keratin cytoskeleton, highlighting the diverse role of LIM proteins in force-regulated signaling.

Matrix viscoelasticity promotes liver cancer progression in the pre-cirrhotic liver.

Type 2 diabetes mellitus is a major risk factor for hepatocellular carcinoma (HCC). Changes in extracellular matrix (ECM) mechanics contribute to cancer development1,2, and increased stiffness is known to promote HCC progression in cirrhotic conditions3,4. Type 2 diabetes mellitus is characterized by an accumulation of advanced glycation end-products (AGEs) in the ECM; however, how this affects HCC in non-cirrhotic conditions is unclear. Here we find that, in patients and animal models, AGEs promote changes in collagen architecture and enhance ECM viscoelasticity, with greater viscous dissipation and faster stress relaxation, but not changes in stiffness. High AGEs and viscoelasticity combined with oncogenic ß-catenin signalling promote HCC induction, whereas inhibiting AGE production, reconstituting the AGE clearance receptor AGER1 or breaking AGE-mediated collagen cross-links reduces viscoelasticity and HCC growth. Matrix analysis and computational modelling demonstrate that lower interconnectivity of AGE-bundled collagen matrix, marked by shorter fibre length and greater heterogeneity, enhances viscoelasticity. Mechanistically, animal studies and 3D cell cultures show that enhanced viscoelasticity promotes HCC cell proliferation and invasion through an integrin-ß1-tensin-1-YAP mechanotransductive pathway. These results reveal that AGE-mediated structural changes enhance ECM viscoelasticity, and that viscoelasticity can promote cancer progression in vivo, independent of stiffness.

Tensins in Kidney Function and Diseases.

Tensins are focal adhesion proteins that regulate various biological processes, such as mechanical sensing, cell adhesion, migration, invasion, and proliferation, through their multiple binding activities that transduce critical signals across the plasma membrane. When these molecular interactions and/or mediated signaling are disrupted, cellular activities and tissue functions are compromised, leading to disease development. Here, we focus on the significance of the tensin family in renal function and diseases. The expression pattern of each tensin in the kidney, their roles in chronic kidney diseases, renal cell carcinoma, and their potentials as prognostic markers and/or therapeutic targets are discussed in this review.

Phase transition of tensin-1 during the focal adhesion disassembly and cell division.

Biomolecular condensates are nonmembranous structures that are mainly formed through liquid-liquid phase separation. Tensins are focal adhesion (FA) proteins linking the actin cytoskeleton to integrin receptors. Here, we report that GFP-tagged tensin-1 (TNS1) proteins phase-separate to form biomolecular condensates in cells. Live-cell imaging showed that new TNS1 condensates are budding from the disassembling ends of FAs, and the presence of these condensates is cell cycle dependent. TNS1 condensates dissolve immediately prior to mitosis and rapidly reappear while postmitotic daughter cells establish new FAs. TNS1 condensates contain selected FA proteins and signaling molecules such as pT308Akt but not pS473Akt, suggesting previously unknown roles of TNS1 condensates in disassembling FAs, as the storage of core FA components and the signaling intermediates.

Transient regulation of focal adhesion via Tensin3 is required for nascent oligodendrocyte differentiation.

The differentiation of oligodendroglia from oligodendrocyte precursor cells (OPCs) to complex and extensive myelinating oligodendrocytes (OLs) is a multistep process that involves large-scale morphological changes with significant strain on the cytoskeleton. While key chromatin and transcriptional regulators of differentiation have been identified, their target genes responsible for the morphological changes occurring during OL myelination are still largely unknown. Here, we show that the regulator of focal adhesion, Tensin3 (Tns3), is a direct target gene of Olig2, Chd7, and Chd8, transcriptional regulators of OL differentiation. Tns3 is transiently upregulated and localized to cell processes of immature OLs, together with integrin-ß1, a key mediator of survival at this transient stage. Constitutive <i>Tns3</i> loss of function leads to reduced viability in mouse and humans, with surviving knockout mice still expressing Tns3 in oligodendroglia. Acute deletion of <i>Tns3</i> in vivo, either in postnatal neural stem cells (NSCs) or in OPCs, leads to a twofold reduction in OL numbers. We find that the transient upregulation of Tns3 is required to protect differentiating OPCs and immature OLs from cell death by preventing the upregulation of p53, a key regulator of apoptosis. Altogether, our findings reveal a specific time window during which transcriptional upregulation of Tns3 in immature OLs is required for OL differentiation likely by mediating integrin-ß1 survival signaling to the actin cytoskeleton as OL undergo the large morphological changes required for their terminal differentiation.

Endothelial DLC1 is dispensable for liver and kidney function in mice.

DLC1 is a focal adhesion molecule that regulates cell polarity, proliferation, migration, and survival. DLC1 functions as a tumor suppressor and its expression is often down-regulated in various malignant neoplasms of epithelial origin. Recent studies have suggested that lack of DLC1 in endothelial cells may contribute to the development of angiosarcoma, and that DLC1 mutations have been identified in patients with nephrotic syndrome, a disease mainly due to leaky glomerular filtration barriers. To demonstrate whether lack of endothelial DLC1 induces angiosarcoma and/or damages glomerular capillaries leading to nephrotic syndrome, we have extended our analyses on endothelial cell-specific DLC1 knockout mice with focuses on their liver and kidney function. Mice were monitored up to 24 months of age. However, no histological or clinical difference was found between DLC1 knockout and wild type mice, indicating that lack of endothelial DLC1 alone does not compromise kidney and liver function in mice.

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.

Direct Observations of Silver Nanowire-Induced Frustrated Phagocytosis among NR8383 Lung Alveolar Macrophages.

The interaction of long nanowires and living cells is directly related to nanowires' nanotoxicity and health impacts. Interactions of silver nanowires (AgNWs) and macrophage cell lines (NR8383) were investigated using laser scanning confocal microscopy and single cell compression (SCC). With high-resolution imaging and mechanics measurement of individual cells, AgNW-induced frustrated phagocytosis was clearly captured in conjunction with structural and property changes of cells. While frustrated phagocytosis is known for long microwires and long carbon nanotubes, this work reports first direct observations of frustrated phagocytosis of AgNWs among living cells in situ. In the case of partial penetration of AgNWs into NR8383 cells, confocal imaging revealed actin participation at the entry sites, whose behavior differs from microwire-induced frustrated phagocytosis. The impacts of frustrated phagocytosis on the cellular membrane and cytoskeleton were also quantified by measuring the mechanical properties using SCC. Taken collectively, this study reveals the structural and property characteristics of nanowire-induced frustrated phagocytosis, which deepens our understanding of nanowire-cell interactions and nanocytotoxicity.

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.

Hyperactivity of Mek in TNS1 knockouts leads to potential treatments for cystic kidney diseases.

Cystic kidney disease is the progressive development of multiple fluid-filled cysts that may severely compromise kidney functions and lead to renal failure. TNS1 (tensin-1) knockout mice develop cystic kidneys and die from renal failure. Here, we have established TNS1-knockout MDCK cells and applied 3D culture system to investigate the mechanism leading to cyst formation. Unlike wild-type MDCK cells, which form cysts with a single lumen, TNS1-knockout cysts contain multiple lumens and upregulated Mek/Erk activities. The multiple lumen phenotype and Mek/Erk hyperactivities are rescued by re-expression of wild-type TNS1 but not the TNS1 mutant lacking a fragment essential for its cell-cell junction localization. Furthermore, Mek inhibitor treatments restore the multiple lumens back to single lumen cysts. Mek/Erk hyperactivities are also detected in TNS1-knockout mouse kidneys. Treatment with the Mek inhibitor trametinib significantly reduces the levels of interstitial infiltrates, fibrosis and dilated tubules in TNS1-knockout kidneys. These studies establish a critical role of subcellular localization of TNS1 in suppressing Mek/Erk signaling and maintaining lumenogenesis, and provide potential therapeutic strategies by targeting the Mek/Erk pathway for cystic kidney diseases.

Force-induced recruitment of cten along keratin network in epithelial cells.

The cytoskeleton provides structural integrity to cells and serves as a key component in mechanotransduction. Tensins are thought to provide a force-bearing linkage between integrins and the actin cytoskeleton; yet, direct evidence of tensin's role in mechanotransduction is lacking. We here report that local force application to epithelial cells using a micrometer-sized needle leads to rapid accumulation of cten (tensin 4), but not tensin 1, along a fibrous intracellular network. Surprisingly, cten-positive fibers are not actin fibers; instead, these fibers are keratin intermediate filaments. The dissociation of cten from tension-free keratin fibers depends on the duration of cell stretch, demonstrating that the external force favors maturation of cten-keratin network interactions over time and that keratin fibers retain remarkable structural memory of a cell's force-bearing state. These results establish the keratin network as an integral part of force-sensing elements recruiting distinct proteins like cten and suggest the existence of a mechanotransduction pathway via keratin network.

Identification of subcellular targeting sequences of Cten reveals its role in cell proliferation.

Spatial and temporal subcellular localization plays critical roles in regulating protein function. Cten (C-terminal tensin like) is a member of the tensin family. Cten recruits signaling molecules, such as DLC1, to focal adhesions, modulates homeostasis of receptor tyrosine kinases, including EGFR and c-Met, and promotes cell migration. These functions are likely controlled by Cten localization at focal adhesions and/or in the cytoplasm. In addition, Cten has been detected in the nucleus by which mechanism is unknown. To this end, we have examined the distribution of Cten in various cell lines, determined primary sequence requirements for its nuclear and focal adhesion localizations, and analyzed potential roles of nuclear Cten. Our results show that a proportion of Cten translocates to nuclei in cancer cell lines and that nuclear exporting of Cten is a CRM1-dependent process. A nuclear localization sequence and a nuclear export sequence are identified within Cten. In addition, like other tensins, Cten contains two independent focal adhesion binding sites. Although further expression of recombinant Cten showed no effect on cancer cell proliferation, silencing of Cten significantly reduced cell growth. Furthermore, expression of Cten mutants either with defective nuclear export sequence or tagged with SV40 nuclear localization sequence promoted cell growth. These results suggest that nuclear Cten contributes to cancer cell proliferation. Our findings identify a molecular mechanism for regulating Cten protein trafficking in mammalian cells and provide new insights into the dynamics of focal adhesion complexes in health and disease.

Tensins.

Su Hao Lo provides an introduction to the tensin family of focal adhesion proteins.

Down-regulation of DLC1 in endothelial cells compromises the angiogenesis process.

DLC1 is a RhoGAP-containing tumor suppressor that inhibits angiogenesis by repressing VEGF production in epithelial cells. Here we report the roles of DLC1 in endothelial cells. Silencing of DLC1 (siDLC1) enhances cell migration but reduces tube formation activities of human umbilical vein endothelial cells (HUVECs). Biochemically, RhoA activity and paxillin protein level are markedly increased in siDLC1 HUVECs. Although further silencing of RhoA restores the cell migration phenotype, the tube formation defect and up-regulated paxillin level remain unchanged. On the other hand, paxillin knockdown rescues tube formation and migration phenotypes but not the up-regulated RhoA activity. These results indicate that DLC1 regulates endothelial cell migration through RhoA and paxillin independently and controls tube formation mainly via paxillin. To further determine endothelial DLC1's function, we have generated endothelial specific knockout mice (DLC1-Tek). DLC1-Tek mice appear to be normal and healthy but their angiogenesis processes are compromised as shown in gel plug and aortic ring sprouting assays. Analysis of endothelial cells isolated from DLC1-Tek mice has further affirmed the cellular and biochemical phenotypes established in siDLC1 HUVECs. Our studies have demonstrated a positive regulatory role of endothelial DLC1 in angiogenesis.

Down-regulation of tensin2 enhances tumorigenicity and is associated with a variety of cancers.

Tensin family members, including tensin2 (TNS2), are present as major components of the focal adhesions. The N-terminal end of TNS2 contains a C1 region (protein kinase C conserved region 1) that is not found in other tensin members. Three isoforms of TNS2 have been identified with previous reports describing the shortest V3 isoform as lacking the C1 region. Although TNS2 is known to regulate cell proliferation and migration, its role in tumorigenicity is controversial. By gain-of-function overexpression approaches, results supporting either promotion or reduction of cancer cell tumorigenicity were reported. Here we report that the complete V3 isoform also contains the C1 region and describe the expression patterns of the three human TNS2 isoforms. By loss-of-function approaches, we show that silencing of TNS2 up-regulates the activities of Akt, Mek, and IRS1, and increases tumorigenicities in A549 and Hela cells. Using public database analyses we found that TNS2 is down-regulated in head and neck, esophageal, breast, lung, liver, and colon cancer. In addition, patients with low TNS2 expression showed poor relapse-free survival rates for breast and lung cancers. These results strongly suggest a role of tensin2 in suppressing cell transformation and reduction of tumorigenicity.

ΔNp63α Transcriptionally Regulates the Expression of CTEN That Is Associated with Prostate Cell Adhesion.

p63 is a member of the p53 transcription factor family and a linchpin of epithelial development and homeostasis. p63 drives the expression of many target genes involved in cell survival, adhesion, migration and cancer. In this study, we identify C-terminal tensin-like (CTEN) molecule as a downstream target of ΔNp63α, the predominant p63 isoform expressed in epithelium. CTEN belongs to the tensin family and is mainly localized to focal adhesions, which mediate many biological events such as cell adhesion, migration, proliferation and gene expression. Our study demonstrate that ΔNp63 and CTEN are both highly expressed in normal prostate epithelial cells and are down-regulated in prostate cancer. In addition, reduced expression of CTEN and ΔNp63 is correlated with prostate cancer progression from primary tumors to metastatic lesions. Silencing of ΔNp63 leads to decreased mRNA and protein levels of CTEN. ΔNp63α induces transcriptional activity of the CTEN promoter and a 140-bp fragment upstream of the transcription initiation site is the minimal promoter region required for activation. A putative binding site for p63 is located between -61 and -36 within the CTEN promoter and mutations of the critical nucleotides in this region abolish ΔNp63α-induced promoter activity. The direct interaction of ΔNp63α with the CTEN promoter was demonstrated using a chromatin immunoprecipitation (ChIP) assay. Moreover, impaired cell adhesion caused by ΔNp63α depletion is rescued by over-expression of CTEN, suggesting that CTEN is a downstream effector of ΔNp63α-mediated cell adhesion. In summary, our findings demonstrate that ΔNp63α functions as a trans-activation factor of CTEN promoter and regulates cell adhesion through modulating CTEN. Our study further contributes to the potential regulatory mechanisms of CTEN in prostate cancer progression.

Tensin1 positively regulates RhoA activity through its interaction with DLC1.

DLC1 is a RhoGAP-containing tumor suppressor and many of DLC1's functions are absolutely dependent on its RhoGAP activity. Through its RhoGAP domain, DLC1 inhibits the activity of RhoA GTPase, which regulates actin cytoskeleton networks and dis/assembly of focal adhesions. Tensin1 (TNS1) is a focal adhesion molecule that links the actin cytoskeleton to integrins and forms signaling complexes through its multiple binding domains. Here, we report that TNS1 enhances RhoA activity in a DLC1-dependent manner. This is accomplished by binding to DLC1 through TNS1's C2, SH2, and PTB domains. Point mutations at these three sites disrupt TNS1's interaction with DLC1 as well as its effect on RhoA activity. The biological relevance of this TNS1-DLC1-RhoA signaling axis is investigated in TNS1 knockout (KO) cells and mice. Endothelial cells isolated from TNS1 KO mice or those silenced with TNS1 siRNA show significant reduction in proliferation, migration, and tube formation activities. Concomitantly, the RhoA activity is down-regulated in TNS1 KO cells and this reduction is restored by further silencing of DLC1. Furthermore, the angiogenic process is compromised in TNS1 KO mice. These studies demonstrate that TNS1 binds to DLC1 and fine-tunes its RhoGAP activity toward RhoA and that the TNS1-DLC1-RhoA signaling axis is critical in regulating cellular functions that lead to angiogenesis.

Genetic association analyses highlight biological pathways underlying mitral valve prolapse.

Nonsyndromic mitral valve prolapse (MVP) is a common degenerative cardiac valvulopathy of unknown etiology that predisposes to mitral regurgitation, heart failure and sudden death. Previous family and pathophysiological studies suggest a complex pattern of inheritance. We performed a meta-analysis of 2 genome-wide association studies in 1,412 MVP cases and 2,439 controls. We identified 6 loci, which we replicated in 1,422 cases and 6,779 controls, and provide functional evidence for candidate genes. We highlight LMCD1 (LIM and cysteine-rich domains 1), which encodes a transcription factor and for which morpholino knockdown of the ortholog in zebrafish resulted in atrioventricular valve regurgitation. A similar zebrafish phenotype was obtained with knockdown of the ortholog of TNS1, which encodes tensin 1, a focal adhesion protein involved in cytoskeleton organization. We also showed expression of tensin 1 during valve morphogenesis and describe enlarged posterior mitral leaflets in Tns1(-/-) mice. This study identifies the first risk loci for MVP and suggests new mechanisms involved in mitral valve regurgitation, the most common indication for mitral valve repair.