The PINCH-ILK-parvin complexes: assembly, functions and regulation

α-Parvin Expression in Breast Cancer Tissues: Correlation with Clinical Parameters and Prognostic Significance

Stromal cells play a critical role in the tumor microenvironment of breast cancer (BC), as they are recruited by tumor cells and regulate the metastatic spread. Though high expression of α-parvin, a member of the parvin family of actin-binding proteins, is reported to be associated with a poor prognosis and metastasis in several cancers, its role in carcinogenesis has not been thoroughly explored. Therefore, we aimed to examine the expression of α-parvin in BC patients by compartmentalizing and quantifying tissues to determine whether α-parvin can be a potential therapeutic target. We performed immunohistochemical (IHC) staining of α-parvin in BC tissues, and the IHC scores were calculated in the overall tissue, stroma, and epithelium using image analysis software. The expression of α-parvin was significantly higher in BC tissues (p = 0.0002) and BC stroma (p < 0.0001) than in normal tissues. Furthermore, all α-parvin scores were significantly positively correlated with the proliferation marker Ki67. The overall and stroma scores are associated with the tumor, (lymph) node, and metastasis (TNM) classification, stage, and grade. These results suggest that high expression of α-parvin in stroma is associated with BCs and might be a new predictive marker for diagnosing BC.

α-parvin controls chondrocyte column formation and regulates long bone development

Endochondral ossification requires proper control of chondrocyte proliferation, differentiation, survival, and organization. Here we show that knockout of α-parvin, an integrin-associated focal adhesion protein, from murine limbs causes defects in endochondral ossification and dwarfism. The mutant long bones were shorter but wider, and the growth plates became disorganized, especially in the proliferative zone. With two-photon time-lapse imaging of bone explant culture, we provide direct evidence showing that α-parvin regulates chondrocyte rotation, a process essential for chondrocytes to form columnar structure. Furthermore, loss of α-parvin increased binucleation, elevated cell death, and caused dilation of the resting zones of mature growth plates. Single-cell RNA-seq analyses revealed alterations of transcriptome in all three zones (i.e., resting, proliferative, and hypertrophic zones) of the growth plates. Our results demonstrate a crucial role of α-parvin in long bone development and shed light on the cellular mechanism through which α-parvin regulates the longitudinal growth of long bones.

CHILKBP protects against podocyte injury by preserving ZO-1 expression

Glomerular diseases afflict millions of people and impose an enormous burden on public healthcare costs worldwide. Identification of potential therapeutic targets for preventing glomerular diseases is of considerable clinical importance. CHILKBP is a focal adhesion protein and modulates a wide array of biological functions. However, little is known about the role of CHILKBP in glomerular diseases. To investigate the function of CHILKBP in maintaining the structure and function of podocytes in a physiologic setting, a mouse model (CHILKBP cKO) was generated in which CHILKBP gene was conditionally deleted in podocytes using the Cre-LoxP system. Ablation of CHILKBP in podocytes resulted in massive proteinuria and kidney failure in mice. Histologically, typical podocyte injury including podocyte loss, foot process effacement, and glomerulosclerosis was observed in CHILKBP cKO mice. Mechanistically, we identified ZO-1 as a key junctional protein that interacted with CHILKBP. Loss of CHILKBP in podocytes exhibited a significant reduction of ZO-1 expression, leading to abnormal actin organization, aberrant slit diaphragm protein expression and compromised podocyte filtration capacity. Restoration of CHILKBP or ZO-1 in CHILKBP-deficient podocytes effectively alleviated podocyte injury induced by the loss of CHILKBP in vitro and in vivo. Finally, we showed the glomerular expression of CHILKBP and ZO-1 was decreased in patients with proteinuric kidney diseases. Our findings reveal a novel signaling pathway consisting of CHILKBP and ZO-1 that plays an essential role in maintaining podocyte homeostasis and suggest novel therapeutic approaches to alleviate glomerular diseases.

The role of Actopaxin in tumor metastasis

Actopaxin is a newly discovered focal adhesions (FAs) protein, actin-binding protein and pseudopodia-enriched molecule. It can not only bind to a variety of FAs proteins (such as Paxillin, ILK and PINCH) and non-FAs proteins (such as TESK1, CdGAP, β2-adaptin, G3BP2, ADAR1 and CD29), but also participates in multiple signaling pathways. Thus, it plays a crucial role in regulating important processes of tumor metastasis, including matrix degradation, migration, and invasion, etc. This review covers the latest progress in the structure and function of Actopaxin, its interaction with other proteins as well as its involvement in regulating tumor development and metastasis. Additionally, the current limitations for Actopaxin related studies and the possible research directions on it in the future are also discussed. It is hoped that this review can assist relevant researchers to obtain a deep understanding of the role that Actopaxin plays in tumor progression, and also enlighten further research and development of therapeutic approaches for the treatment of tumor metastasis.

The explorations of dynamic interactions of paxillin at the focal adhesions

Paxillin is one of the most important adapters in integrin-mediated adhesions that performs numerous crucial functions relying on its dynamic interactions. Its structural behavior serves different purposes, providing a base for several activities. The various domains of paxillin display different functions in the whole process of cell movements and have a significant role in cell adhesion, migration, signal transmission, and protein-protein interactions. On the other hand, some paxillin-associated proteins provide a unique spatiotemporal mechanism for regulating its dynamic characteristics in the tissue homeostasis and make it a more complex and decisive protein at the focal adhesions. This review briefly describes the structural adaptations and molecular mechanisms of recruitment of paxillin into adhesions, explains paxillin's binding dynamics and impact on adhesion stability and turnover, and reveals a variety of paxillin-associated regulatory mechanisms and how paxillin is embedded into the signaling networks.

Parvin: A hub of intracellular signalling pathways regulating cellular behaviour and disease progression

α-actinin superfamily houses the family of parvins, comprising α, β and γ isoforms in the vertebrates and a single orthologue in the invertebrates. Parvin as an adaptor protein is a member of the ternary IPP-complex including Integrin Linked Kinase (ILK) and particularly-interesting-Cys-His-rich protein (PINCH). Each of the complex proteins showed a conserved lineage and was principally used by the evolutionarily primitive integrin-adhesome machinery to regulate cellular behaviour and signalling pathways. Parvin facilitated integrin mediated integration of the extracellular matrix with cytoskeletal framework culminating in regulation of cellular adhesion and spreading, cytoskeleton reorganisation and cell survival. Studies have established role of parvin in pregnancy, lactation, matrix degradation, blood vessel formation and in several diseases such as cancer, NAFLD and cardiac diseases etc. This review narrates the history of parvin discovery, its elaborate gene structure and conservation across phyla including cellular expression, localisation and interacting partners in vertebrates as well as invertebrates. The review further discusses how parvin acts as an epicentre of signalling pathways, its associated mutants and diseased conditions.

Patent Highlights February-March 2022

A snapshot of noteworthy recent developments in the patent literature of relevance to pharmaceutical and medical research and development.

Pinch2 regulates myelination in the mouse central nervous system

The extensive morphological changes of oligodendrocytes during axon ensheathment and myelination involve assembly of the Ilk-Parvin-Pinch (IPP) heterotrimeric complex of proteins to relay essential mechanical and biochemical signals between integrins and the actin cytoskeleton. Binding of Pinch1 and Pinch2 isoforms to Ilk is mutually exclusive and allows the formation of distinct IPP complexes with specific signaling properties. Using tissue-specific conditional gene ablation in mice, we reveal an essential role for Pinch2 during central nervous system myelination. Unlike Pinch1 gene ablation, loss of Pinch2 in oligodendrocytes results in hypermyelination and in the formation of pathological myelin outfoldings in white matter regions. These structural changes concur with inhibition of Rho GTPase RhoA and Cdc42 activities and phenocopy aspects of myelin pathology observed in corresponding mouse mutants. We propose a dual role for Pinch2 in preventing an excess of myelin wraps through RhoA-dependent control of membrane growth and in fostering myelin stability via Cdc42-dependent organization of cytoskeletal septins. Together, these findings indicate that IPP complexes containing Pinch2 act as a crucial cell-autonomous molecular hub ensuring synchronous control of key signaling networks during developmental myelination.

Ras suppressor-1 (RSU1) exerts a tumor suppressive role with prognostic significance in lung adenocarcinoma

Ras suppressor-1 (RSU1), originally described as a suppressor of Ras oncogenic transformation, localizes to focal adhesions interacting with the ILK-PINCH-PARVIN (IPP) complex that exerts a well-established oncogenic role in cancer. However, RSU1 implication in lung cancer is currently unknown. Our study aims to address the role of RSU1 in lung adenocarcinoma (LUADC). We here show that RSU1 protein expression by immunohistochemistry is downregulated in LUADC human tissue samples and represents a significant prognostic indicator. In silico analysis of gene chip and RNA seq data validated our findings. Depletion of RSU1 by siRNA in lung cancer cells promotes anchorage-independent cell growth, cell motility and epithelial to mesenchymal transition (EMT). Silencing of RSU1 also alters IPP complex expression in lung cancer cells. The p29 RSU1 truncated isoform is detected in lung cancer cells, and its expression is downregulated upon RSU1 silencing, whereas it is overexpressed upon ILK overexpression. These findings suggest that RSU1 exerts a tumor suppressive role with prognostic significance in LUADC.

PINCH1 Promotes Fibroblast Migration in Extracellular Matrices and Influences Their Mechanophenotype

Cell migration performs a critical function in numerous physiological processes, including tissue homeostasis or wound healing after tissue injury, as well as pathological processes that include malignant progression of cancer. The efficiency of cell migration and invasion appears to be based on the mechano-phenotype of the cytoskeleton. The properties of the cytoskeleton depend on internal cytoskeletal and external environmental factors. A reason for this are connections between the cell and its local matrix microenvironment, which are established by cell-matrix adhesion receptors. Upon activation, focal adhesion proteins such as PINCH1 are recruited to sites where focal adhesions form. PINCH1 specifically couples through interactions with ILK, which binds to cell matrix receptors and the actomyosin cytoskeleton. However, the role of PINCH1 in cell mechanics regulating cellular motility in 3D collagen matrices is still unclear. PINCH1 is thought to facilitate 3D motility by regulating cellular mechanical properties, such as stiffness. In this study, PINCH1 wild-type and knock-out cells were examined for their ability to migrate in dense extracellular 3D matrices. Indeed, PINCH1 wild-type cells migrated more numerously and deeper in 3D matrices, compared to knock-out cells. Moreover, cellular deformability was determined, e.g., elastic modulus (stiffness). PINCH1 knock-out cells are more deformable (compliable) than PINCH1 wild-type cells. Migration of both PINCH1−/− cells and PINCH1fl/fl cells was decreased by Latrunculin A inhibition of actin polymerization, suggesting that actin cytoskeletal differences are not responsible for the discrepancy in invasiveness of the two cell types. However, the mechanical phenotype of PINCH1−/− cells may be reflected by Latrunculin A treatment of PINCH1fl/fl cells, as they exhibit resembling deformability to untreated PINCH1−/− cells. Moreover, an apparent mismatch exists between the elongation of the long axis and the contraction of the short axis between PINCH1fl/fl cells and PINCH1−/− cells following Latrunculin A treatment. There is evidence of this indicating a shift in the proxy values for Poisson’s ratio in PINCH1−/− cells compared with PINCH1fl/fl cells. This is probably attributable to modifications in cytoskeletal architecture. The non-muscle myosin II inhibitor Blebbistatin also reduced the cell invasiveness in 3D extracellular matrices but instead caused a stiffening of the cells. Finally, PINCH1 is apparently essential for providing cellular mechanical stiffness through the actin cytoskeleton, which regulates 3D motility.

An extremely streamlined macronuclear genome in the free-living protozoan Fabrea salina

Ciliated protists are among the oldest unicellular organisms with a heterotrophic lifestyle and share a common ancestor with Plantae. Unlike any other eukaryotes, there are two distinct nuclei in ciliates with separate germline and somatic cell functions. Here, we assembled a near-complete macronuclear genome of Fabrea salina, which belongs to one of the oldest clades of ciliates. Its extremely minimized genome (18.35 Mb) is the smallest among all free-living heterotrophic eukaryotes and exhibits typical streamlined genomic features, including high gene density, tiny introns, and shrinkage of gene paralogs. Gene families involved in hypersaline stress resistance, DNA replication proteins, and mitochondrial biogenesis are expanded, and the accumulation of phosphatidic acid may play an important role in resistance to high osmotic pressure. We further investigated the morphological and transcriptomic changes in the macronucleus during sexual reproduction and highlighted the potential contribution of macronuclear residuals to this process. We believe that the minimized genome generated in this study provides novel insights into the genome streamlining theory and will be an ideal model to study the evolution of eukaryotic heterotrophs.

ATP allosterically stabilizes integrin-linked kinase for efficient force generation

The pseudokinase integrin-linked kinase (ILK) is a central component of focal adhesions, cytoplasmic multiprotein complexes that integrate and transduce biochemical and mechanical signals from the extracellular environment into the cell and vice versa. However, the precise molecular functions, particularly the mechanosensory properties of ILK and the significance of retained adenosine triphosphate (ATP) binding, are still unclear. Combining molecular-dynamics simulations with cell biology, we establish a role for ATP binding to pseudokinases. We find that ATP promotes the structural stability of ILK, allosterically influences the interaction between ILK and its binding partner parvin at adhesions, and enhances the mechanoresistance of this complex. On the cellular level, ATP binding facilitates efficient traction force buildup, focal adhesion stabilization, and efficient cell migration.

Focal adhesions link the actomyosin cytoskeleton to the extracellular matrix regulating cell adhesion, shape, and migration. Adhesions are dynamically assembled and disassembled in response to extrinsic and intrinsic forces, but how the essential adhesion component integrin-linked kinase (ILK) dynamically responds to mechanical force and what role adenosine triphosphate (ATP) bound to this pseudokinase plays remain elusive. Here, we apply force–probe molecular-dynamics simulations of human ILK:α-parvin coupled to traction force microscopy to explore ILK mechanotransducing functions. We identify two key salt-bridge–forming arginines within the allosteric, ATP-dependent force-propagation network of ILK. Disrupting this network by mutation impedes parvin binding, focal adhesion stabilization, force generation, and thus migration. Under tension, ATP shifts the balance from rupture of the complex to protein unfolding, indicating that ATP increases the force threshold required for focal adhesion disassembly. Our study proposes a role of ATP as an obligatory binding partner for structural and mechanical integrity of the pseudokinase ILK, ensuring efficient cellular force generation and migration.

Integrin-Linked Kinase Reduces H3K9 Trimethylation to Enhance Herpes Simplex Virus 1 Replication

Histone modifications control the lytic gene expression of herpes simplex virus 1 (HSV-1). The heterochromatin mark, trimethylation of histone H3 on lysine (K) 9 (H3K9me3), is detected on HSV-1 genomes at early phases of infection to repress viral gene transcription. However, the components and mechanisms involved in the process are mostly unknown. Integrin-linked kinase (ILK) is activated by PI3K to phosphorylate Akt and promote several RNA virus infections. Akt has been shown to enhance HSV-1 infection, suggesting a pro-viral role of ILK in HSV-1 infection that has not been addressed before. Here, we reveal that ILK enhances HSV-1 replication in an Akt-independent manner. ILK reduces the accumulation of H3K9me3 on viral promoters and replication compartments. Notably, ILK reduces H3K9me3 in a manner independent of ICP0. Instead, we show an increased binding of H3K9 methyltransferase SUV39H1 and corepressor TRIM28 on viral promoters in ILK knockdown cells. Knocking down SUV39H1 or TRIM28 increases HSV-1 lytic gene transcription in ILK knockdown cells. These results show that ILK antagonizes SVU39H1- and TRIM28-mediated repression on lytic gene transcription. We further demonstrate that ILK knockdown reduces TRIM28 phosphorylation on serine 473 and 824 in HSV-1-infected cells, suggesting that ILK facilitates TRIM28 phosphorylation to abrogate its inhibition on lytic gene transcription. OSU-T315, an ILK inhibitor, suppresses HSV-1 replication in cells and mice. In conclusion, we demonstrate that ILK decreases H3K9me3 on HSV-1 DNA by reducing SUV39H1 and TRIM28 binding. Moreover, our results suggest that targeting ILK could be a broad-spectrum antiviral strategy for DNA and RNA virus infections, especially for DNA viruses controlled by histone modifications.

The focal adhesion protein Integrin-Linked Kinase (ILK) as an important player in breast cancer pathogenesis

Cell-extracellular matrix interactions, or focal adhesions (FA), are crucial for tissue homeostasis but are also implicated in cancer. Integrin-Linked Kinase (ILK) is an abundantly expressed FA protein involved in multiple signaling pathways. Here, we reviewed the current literature on the role of ILK in breast cancer (BC). Articles included in vitro and in vivo experiments as well as studies in human BC samples. ILK attenuation via silencing or pharmaceutical inhibition, leads to apoptosis or inhibition of epithelial-to-mesenchymal transition, and cell invasion whereas ILK overexpression suppresses anoikis and promotes tumor growth and metastasis. Finally, ILK is upregulated in BC tumors and its expression is associated with grade, and metastasis. Therefore, ILK should be evaluated as a potential anti-cancer pharmaceutical target.

PINCH-1 promotes Δ1-pyrroline-5-carboxylate synthase expression and contributes to proline metabolic reprogramming in lung adenocarcinoma

Proline metabolic reprogramming is intimately involved in cancer progression. We recently identified a critical role of PINCH-1, a cell-extracellular matrix (ECM) adhesion protein whose expression is elevated in lung adenocarcinoma, in the promotion of proline biosynthesis, fibrosis and lung adenocarcinoma growth. How PINCH-1 promotes proline biosynthesis, however, was incompletely understood. In this study, we show that PINCH-1 promotes the expression of Δ¹-pyrroline-5-carboxylate synthase (P5CS), a key enzyme that links glutamate metabolism to proline biosynthesis. Depletion of PINCH-1 from lung adenocarcinoma cells reduced the protein but not mRNA level of P5CS, resulting in down-regulation of the cellular level of P5C and cell proliferation. Treatment of the cells with protease inhibitor leupeptin effectively reversed PINCH-1 deficiency-induced reduction of the P5CS level. At the molecular level, PINCH-1, through its LIM2 domain, physically associated with P5CS in lung adenocarcinoma cells. Re-expression of wild type PINCH-1, but not that of the PINCH-1 LIM2 deletion mutant, in PINCH-1 deficient lung adenocarcinoma cells restored P5CS expression, proline biosynthesis and cell proliferation. Finally, P5CS expression, like that of PINCH-1, is elevated in human and mouse lung adenocarcinoma. Using a mouse model of lung adenocarcinoma in which PINCH-1 is conditionally ablated, we show that knockout of PINCH-1 from lung adenocarcinoma effectively reduced the P5CS level in vivo. Our results reveal an important role of PINCH-1 in the promotion of P5CS expression, which likely contributes to proline metabolic reprogramming and consequently lung adenocarcinoma progression.

How signaling pathways link extracellular mechano-environment to proline biosynthesis: A hypothesis: PINCH-1 and kindlin-2 sense mechanical signals from extracellular matrix and link them to proline biosynthesis

We propose a signaling pathway in which cell-extracellular matrix (ECM) adhesion components PINCH-1 and kindlin-2 sense mechanical signals from ECM and link them to proline biosynthesis, a vital metabolic pathway for macromolecule synthesis, redox balance, and ECM remodeling. ECM stiffening promotes PINCH-1 expression via integrin signaling, which suppresses dynamin-related protein 1 (DRP1) expression and mitochondrial fission, resulting in increased kindlin-2 translocation into mitochondria and interaction with Δ¹ -pyrroline-5-carboxylate (P5C) reductase 1 (PYCR1). Kindlin-2 interaction with PYCR1 protects the latter from proteolytic degradation, leading to elevated PYCR1 level. Additionally, PINCH-1 promotes P5C synthase (P5CS) expression and P5C synthesis, which, together with increased PYCR1 level, support augmented proline biosynthesis. This signaling pathway is frequently activated in fibrosis and cancer, resulting in increased proline biosynthesis and excessive collagen matrix production, which in turn further promotes ECM stiffening. Targeting this signaling pathway, therefore, may provide an effective strategy for alleviating fibrosis and cancer progression.

A Potential Role for Integrin-Linked Kinase in Colorectal Cancer Growth and Progression via Regulating Senescence and Immunity

Integrin-linked kinase (ILK) has been implicated as a molecular driver and mediator in both inflammation and tumorigenesis of the colon. ILK functions as an adaptor and mediator protein linking the extracellular matrix with downstream signaling pathways. ILK is broadly expressed in many human tissues and cells. It is also overexpressed in many cancers, including colorectal cancer (CRC). Inflammation, as evidenced by inflammatory bowel disease (IBD), is one of the highest risk factors for initiating CRC. This has led to the hypothesis that targeting ILK therapeutically could have potential in CRC, as it regulates different cellular processes associated with CRC development and progression as well as inflammation in the colon. A number of studies have indicated an ILK function in senescence, a cellular process that arrests the cell cycle while maintaining active metabolism and transcription. Senescent cells produce different secretions collectively known as the senescence-associated secretory phenotype (SASP). The SASP secretions influence infiltration of different immune cells, either positively for clearing senescent cells or negatively for promoting tumor growth, reflecting the dual role of senescence in cancer. However, a role for ILK in senescence and immunity in CRC remains to be determined. In this review, we discuss the possible role for ILK in senescence and immunity, paying particular attention to the relevance of ILK in CRC. We also examine how activating Toll-like receptors (TLRs) and their agonists in CRC could trigger immune responses against cancer, as a combination therapy with ILK inhibition.

Complex structures of Rsu1 and PINCH1 reveal a regulatory mechanism of the ILK/PINCH/Parvin complex for F-actin dynamics

Communications between actin filaments and integrin-mediated focal adhesion (FA) are crucial for cell adhesion and migration. As a core platform to organize FA proteins, the tripartite ILK/PINCH/Parvin (IPP) complex interacts with actin filaments to regulate the cytoskeleton-FA crosstalk. Rsu1, a Ras suppressor, is enriched in FA through PINCH1 and plays important roles in regulating F-actin structures. Here, we solved crystal structures of the Rsu1/PINCH1 complex, in which the leucine-rich-repeats of Rsu1 form a solenoid structure to tightly associate with the C-terminal region of PINCH1. Further structural analysis uncovered that the interaction between Rsu1 and PINCH1 blocks the IPP-mediated F-actin bundling by disrupting the binding of PINCH1 to actin. Consistently, overexpressing Rsu1 in HeLa cells impairs stress fiber formation and cell spreading. Together, our findings demonstrated that Rsu1 is critical for tuning the communication between F-actin and FA by interacting with the IPP complex and negatively modulating the F-actin bundling.

A mechanoresponsive PINCH-1-Notch2 interaction regulates smooth muscle differentiation of human placental mesenchymal stem cells

Extracellular matrix (ECM) stiffness plays an important role in the decision making process of smooth muscle differentiation of mesenchymal stem cells (MSCs) but the underlying mechanisms are incompletely understood. Here we show that a signaling axis consisting of PINCH-1 and Notch2 is critically involved in mediating the effect of ECM stiffness on smooth muscle differentiation of MSCs. Notch2 level is markedly increased in ECM stiffness-induced smooth muscle differentiation of human placental MSCs. Knockdown of Notch2 from human placental MSCs effectively inhibits ECM stiffness-induced smooth muscle differentiation, whereas overexpression of North intracellular domain (NICD2) is sufficient to drive human placental MSC differentiation toward smooth muscle cells. At the molecular level, Notch2 directly interacts with PINCH-1. The interaction of Notch2 with PINCH-1 is significantly increased in response to ECM stiffness favoring smooth muscle differentiation. Furthermore, depletion of PINCH-1 from human placental MSCs reduces Notch2 level and consequently suppresses ECM stiffness-induced smooth muscle differentiation. Re-expression of PINCH-1, but not that of a Notch2-binding defective PINCH-1 mutant, in PINCH-1 knockdown human placental MSCs restores smooth muscle differentiation. Finally, overexpression of NICD2 is sufficient to override PINCH-1 deficiency-induced defect in smooth muscle differentiation. Our results identify an ECM stiffness-responsive PINCH-1-Notch2 interaction that is critically involved in ECM stiffness-induced smooth muscle differentiation of human placental MSCs.

RSU-1 interaction with prohibitin-2 links cell-extracellular matrix detachment to downregulation of ERK signaling

Cell–extracellular matrix (ECM) detachment is known to decrease extracellular signal–regulated kinase (ERK) signaling, an intracellular pathway that is central for control of cell behavior. How cell–ECM detachment is linked to downregulation of ERK signaling, however, is incompletely understood. We show here that focal adhesion protein Ras Suppressor 1 (RSU1) plays a critical role in cell–ECM detachment induced suppression of ERK signaling. We have identified prohibitin 2 (PHB2), a component of membrane lipid rafts, as a novel binding protein of RSU1, and mapped a major RSU1-binding site to PHB2 amino acids 150 to 206 in the C-terminal region of the PHB/SPFH (stomatin/prohibitin/flotillin/HflKC) domain. The PHB2 binding is mediated by multiple sites located in the N-terminal leucine-rich repeat region of RSU1. Depletion of PHB2 suppressed cell–ECM adhesion–induced ERK activation. Furthermore, cell–ECM detachment increased RSU1 association with membrane lipid rafts and interaction with PHB2. Finally, knockout of RSU1 or inhibition of RSU1 interaction with PHB2 by overexpression of the major RSU1-binding PHB2 fragment (amino acids 150–206) effectively suppressed the cell–ECM detachment induced downregulation of ERK signaling. Additionally, expression of venus-tagged wild-type RSU1 restored ERK signaling, while expression of venus-tagged PHB2-binding defective RSU1 mutant in which the N-terminal leucine-rich repeat region is deleted did not. Taken together, Our findings identify a novel RSU1-PHB2 signaling axis that senses cell–ECM detachment and links it to decreased ERK signaling.

PINCH-1 regulates mitochondrial dynamics to promote proline synthesis and tumor growth

Reprograming of proline metabolism is critical for tumor growth. Here we show that PINCH-1 is highly expressed in lung adenocarcinoma and promotes proline synthesis through regulation of mitochondrial dynamics. Knockout (KO) of PINCH-1 increases dynamin-related protein 1 (DRP1) expression and mitochondrial fragmentation, which suppresses kindlin-2 mitochondrial translocation and interaction with pyrroline-5-carboxylate reductase 1 (PYCR1), resulting in inhibition of proline synthesis and cell proliferation. Depletion of DRP1 reverses PINCH-1 deficiency-induced defects on mitochondrial dynamics, proline synthesis and cell proliferation. Furthermore, overexpression of PYCR1 in PINCH-1 KO cells restores proline synthesis and cell proliferation, and suppresses DRP1 expression and mitochondrial fragmentation. Finally, ablation of PINCH-1 from lung adenocarcinoma in mouse increases DRP1 expression and inhibits PYCR1 expression, proline synthesis, fibrosis and tumor growth. Our results identify a signaling axis consisting of PINCH-1, DRP1 and PYCR1 that regulates mitochondrial dynamics and proline synthesis, and suggest an attractive strategy for alleviation of tumor growth.

RSU-1 Maintains Integrity of Caenorhabditis elegans Vulval Muscles by Regulating α-Actinin

Egg-laying behavior in Caenorhabditis elegans is a well-known model for investigating fundamental cellular processes. In egg-laying, muscle contraction is the relaxation of the vulval muscle to extrude eggs from the vulva. Unlike skeletal muscle, vulval muscle lacks visible striations of the sarcomere. Therefore, vulval muscle must counteract the mechanical stress, caused by egg extrusion and body movement, from inducing cell-shape distortion by maintaining its cytoskeletal integrity. However, the underlying mechanisms that regulate the cellular integrity in vulval muscles remain unclear. Here, we demonstrate that C. elegans egg-laying requires proper vulval muscle 1 (vm1), in which the actin bundle organization of vm1 muscles is regulated by Ras suppressor protein 1 (RSU-1). In the loss of RSU-1, as well as Ras^LET-60 overactivation, blister-like membrane protrusions and disorganized actin bundles were observed in the vm1 muscles. Moreover, Ras^LET-60 depletion diminished the defected actin-bundles in rsu-1 mutant. These results reveal the genetic interaction of RSU-1 and Ras^LET-60 in vivo In addition, our results further demonstrated that the fifth to seventh leucine-rich region of RSU-1 is required to promote actin-bundling protein, α-actinin, for actin bundle stabilization in the vm1 muscles. This expands our understanding of the molecular mechanisms of actin bundle organization in a specialized smooth muscle.

A PINCH-1-Smurf1 signaling axis mediates mechano-regulation of BMPR2 and stem cell differentiation

Mechanical cues from extracellular matrix exert strong effects on stem cell differentiation. This study finds that a signaling axis consisting of PINCH-1, Smurf1, and BMPR2 senses mechanical signals from extracellular matrix and regulates BMP signaling and mesenchymal stem cell differentiation.

Mechano-environment plays multiple critical roles in the control of mesenchymal stem cell (MSC) fate decision, but the underlying signaling mechanisms remain undefined. We report here a signaling axis consisting of PINCH-1, SMAD specific E3 ubiquitin protein ligase 1 (Smurf1), and bone morphogenetic protein type 2 receptor (BMPR2) that links mechano-environment to MSC fate decision. PINCH-1 interacts with Smurf1, which inhibits the latter from interacting with BMPR2 and consequently suppresses BMPR2 degradation, resulting in augmented BMP signaling and MSC osteogenic differentiation (OD). Extracellular matrix (ECM) stiffening increases PINCH-1 level and consequently activates this signaling axis. Depletion of PINCH-1 blocks stiff ECM-induced BMP signaling and OD, whereas overexpression of PINCH-1 overrides signals from soft ECM and promotes OD. Finally, perturbation of either Smurf1 or BMPR2 expression is sufficient to block the effects of PINCH-1 on BMP signaling and MSC fate decision. Our findings delineate a key signaling mechanism through which mechano-environment controls BMPR2 level and MSC fate decision.

Coordinated Expression of Ras Suppressor 1 (RSU-1) and Growth Differentiation Factor 15 (GDF15) Affects Glioma Cell Invasion

Glioblastoma multiforme (GBM) is the most aggressive type of brain tumor due to its invasive phenotype. Ras suppressor 1 (RSU-1) is a cell-extracellular matrix adhesion protein and we recently found that it promotes cell invasion in aggressive cells and inhibits it in non-invasive. Growth differentiation factor-15 (GDF15) is known to be involved in actin cytoskeleton reorganization and metastasis. In this study, we used three brain cell lines (H4, SW1088 and A172) with increasing RSU-1 expression levels and invasive capacity and decreasing GDF15 levels to investigate the interplay between RSU-1 and GDF15 with regard to cell invasion. Four experimental approaches were used: (a) GDF15 treatment, (b) Rsu-1 silencing, (c) GDF15 silencing, and (d) combined GDF15 treatment and RSU-1 silencing. We found that the differential expression of RSU-1 and GDF15 in H4 and A172 cells leading to inhibition of cell invasion in H4 cells and promotion in A172 through respective changes in PINCH1, RhoA and MMP-13 expression. Interestingly SW1088, with intermediate RSU-1 and GDF15 expression, were not affected by any treatment. We conclude that there is a strong connection between RSU-1 and GDF15 in H4, SW1088 and A172 cells and the relative expression of these two proteins is fundamental in affecting their invasive fate.

Depletion of Ras Suppressor-1 (RSU-1) promotes cell invasion of breast cancer cells through a compensatory upregulation of a truncated isoform

Extracellular matrix (ECM)-adhesion proteins and actin cytoskeleton are pivotal in cancer cell invasion. Ras Suppressor-1 (RSU-1), a cell-ECM adhesion protein that interacts with PINCH-1, thus being connected to Integrin Linked Kinase (ILK), alpha-parvin (PARVA), and actin cytoskeleton, is up-regulated in metastatic breast cancer (BC) samples. Apart from the originally-identified gene (RSU-1L), an alternatively-spliced isoform (RSU-1-X1) has been reported. We used non-invasive MCF-7 cells, expressing only RSU-1L, and highly invasive MDA-MB-231-LM2 expressing both isoforms and generated stable shRNA-transduced cells lacking RSU-1L, while the truncated RSU-1-X1 isoform was depleted by siRNA-mediated silencing. RSU-1L depletion in MCF-7 cells resulted in complete abrogation of tumor spheroid invasion in three-dimensional collagen gels, whereas it promoted MDA-MB-231-LM2 invasion, through a compensatory upregulation of RSU-1-X1. When RSU-1-X1 was also eliminated, RSU-1L-depletion-induced migration and invasion were drastically reduced being accompanied by reduced urokinase plasminogen activator expression. Protein expression analysis in 23 human BC samples corroborated our findings showing RSU-1L to be upregulated and RSU-1-X1 downregulated in metastatic samples. We demonstrate for the first time, that both RSU-1 isoforms promote invasion in vitro while RSU-1L elimination induces RSU-1-X1 upregulation to compensate for the loss. Hence, we propose that both isoforms should be blocked to effectively eliminate metastasis.

α-Parvin promotes breast cancer progression and metastasis through interaction with G3BP2 and regulation of TWIST1 signaling

Identification of molecular alterations driving breast cancer progression is critical for the development of effective therapy. In this study, we show that the level of α-parvin is elevated in triple-negative breast cancer cells. The depletion of α-parvin from triple-negative breast cancer cells effectively inhibits breast cancer cell growth, migration, and invasion in vitro, and tumor progression and metastasis in vivo. At the molecular level, we identify Ras-GTPase-activing protein SH3-domain-binding protein 2 (G3BP2) as an α-parvin-binding protein. Knockdown of α-parvin promotes G3BP2 interaction with TWIST1, increases ubiquitination and proteasome-dependent degradation of TWIST1, and consequently reduces the cellular level of TWIST1 and its downstream signaling. Importantly, the depletion of G3BP2 reverses the reduction in the level and signaling of TWIST1 and the suppression of breast cancer progression induced by the loss of α-parvin. Furthermore, the re-expression of an α-parvin mutant in which the G3BP2-binding site is ablated, unlike that of wild-type α-parvin, in α-parvin-deficient breast cancer cells, is unable to restore the level and signaling of TWIST1 and promote breast cancer progression. Finally, we show that protein level of α-parvin is highly positively correlated with that of TWIST1 in human triple-negative breast cancer patients. Our studies reveal a novel signaling pathway consisting of α-parvin, G3BP2, and TWIST1 that regulates breast cancer progression and metastasis, and suggest that the activation of this signaling pathway is a key factor for driving the progression and poor clinical outcome of human ER-negative breast cancer.

Muscarinic m2 receptor-mediated actin polymerization via PI3 kinase γ and integrin-linked kinase in gastric smooth muscle

BACKGROUND

Actin polymerization plays an important role in smooth muscle contraction. Integrin-linked kinase (ILK) was shown to mediate actin polymerization in airway smooth muscle. The role of ILK in actin polymerization in response to m2 receptor activation was not in gastric smooth muscle.

METHODS

Phosphorylation of paxillin, neuronal Wiskott-Aldrich syndrome protein (N-WASp), and association of paxillin with GEF proteins (Cool2/αPix [Cool2/PAK-interacting exchange factor alpha], Cool1/βPix [Cool1/PAK-interacting exchange factor beta], and DOCK 180 [Dedicator of cytokinesis]) and N-WASp with Arp2/3 complex were measured by western blot. Activation of Cdc42 was determined using an antibody for activated Cdc42. Actin polymerization was measured as an increase in F-actin/G-actin ratio.

RESULTS

Phosphorylation of paxillin, an association of paxillin with GEF proteins, Cdc42 activity, and actin polymerization were increased in response to m2 receptor activation in gastric smooth muscle cells. The increases in paxillin phosphorylation, Cdc42 activity, and actin polymerization were inhibited by a PI3Kγ inhibitor (AS-605240), ILK siRNA, and ILK dominant negative mutant (ILK [R211]). Increase in actin polymerization was also inhibited by Cdc42 dominant negative mutant (Cdc42 [T17N]). Increases in the association of paxillin with GEF proteins, phosphorylation of N-WASp and its association with Arp2/3 complex were inhibited by ILK (R211).

CONCLUSION

In gastric smooth muscle cells, activation of PI3Kγ by muscarinic m2 receptors causes ILK-dependent phosphorylation of paxillin, an association of paxillin with Cdc42 GEF proteins and activation of Cdc42, which, in turn, causes phosphorylation of N-WASp and its association with Arp2/3 complex leading to actin polymerization.

Inhibition of Breast Cancer Cell Invasion by Ras Suppressor-1 (RSU-1) Silencing Is Reversed by Growth Differentiation Factor-15 (GDF-15)

Extracellular matrix (ECM)-related adhesion proteins are important in metastasis. Ras suppressor-1 (RSU-1), a suppressor of Ras-transformation, is localized to cell–ECM adhesions where it interacts with the Particularly Interesting New Cysteine-Histidine rich protein (PINCH-1), being connected to Integrin Linked Kinase (ILK) and alpha-parvin (PARVA), a direct actin-binding protein. RSU-1 was also found upregulated in metastatic breast cancer (BC) samples and was recently demonstrated to have metastasis-promoting properties. In the present study, we transiently silenced RSU-1 in BC cells, MCF-7 and MDA-MB-231. We found that RSU-1 silencing leads to downregulation of Growth Differentiation Factor-15 (GDF-15), which has been associated with both actin cytoskeleton reorganization and metastasis. RSU-1 silencing also reduced the mRNA expression of PINCH-1 and cell division control protein-42 (Cdc42), while increasing that of ILK and Rac regardless of the presence of GDF-15. However, the downregulation of actin-modulating genes PARVA, RhoA, Rho associated kinase-1 (ROCK-1), and Fascin-1 following RSU-1 depletion was completely reversed by GDF-15 treatment in both cell lines. Moreover, complete rescue of the inhibitory effect of RSU-1 silencing on cell invasion was achieved by GDF-15 treatment, which also correlated with matrix metalloproteinase-2 expression. Finally, using a graph clustering approach, we corroborated our findings. This is the first study providing evidence of a functional association between RSU-1 and GDF-15 with regard to cancer cell invasion.

Mechanisms and consequences of constitutive activation of integrin-linked kinase in acute myeloid leukemia

Integrin-linked kinase (ILK) has emerged as a critical adaptor and mediator protein in cell signaling pathways that is commonly deregulated in acute myeloid leukemia (AML). This has led to the expectation that therapeutic targeting of ILK may be a useful option in treating leukemia. Although ILK can regulate many cellular processes, including cell differentiation, survival, migration, apoptosis and production of pro-inflammatory cytokines, its role in promoting AML is still unclear. However, its ability to mediate phosphorylation and regulate the important hematopoietic stem cell regulators protein kinase B (AKT) and glycogen synthase kinase-3β supports ILK as an attractive target for the development of novel anticancer therapeutics. In this review, we summarize the existing knowledge of ILK signaling and its impact on cytokines, paying particular attention to the relevance of ILK signaling in AML. We also discuss the rationale for targeting ILK in the treatment of AML and conclude with perspectives on the future of ILK-targeted therapy in AML.

Identification of Ras suppressor-1 (RSU-1) as a potential breast cancer metastasis biomarker using a three-dimensional in vitro approach

Breast cancer (BC) is the most common malignant disease in women, with most patients dying from metastasis to distant organs, making discovery of novel metastasis biomarkers and therapeutic targets imperative. Extracellular matrix (ECM)-related adhesion proteins as well as tumor matrix stiffness are important determinants for metastasis. As traditional two-dimensional culture does not take into account ECM stiffness, we employed 3-dimensional collagen I gels of increasing concentration and stiffness to embed BC cells of different invasiveness (MCF-7, MDA-MB-231 and MDA-MB-231-LM2) or tumor spheroids. We tested the expression of cell-ECM adhesion proteins and found that Ras Suppressor-1 (RSU-1) is significantly upregulated in increased stiffness conditions. Interestingly, RSU-1 siRNA-mediated silencing inhibited Urokinase Plasminogen Activator, and metalloproteinase-13, whereas tumor spheroids formed from RSU-1-depleted cells lost their invasive capacity in all cell lines and stiffness conditions. Kaplan-Meier survival plot analysis corroborated our findings showing that high RSU-1 expression is associated with poor prognosis for distant metastasis-free and remission-free survival in BC patients. Taken together, our results indicate the important role of RSU-1 in BC metastasis and set the foundations for its validation as potential BC metastasis marker.

Alterations in the host transcriptome in vitro following Rift Valley fever virus infection

Rift Valley fever virus (RVFV) causes major outbreaks among livestock, characterized by "abortion storms" in which spontaneous abortion occurs in almost 100% of pregnant ruminants. Humans can also become infected with mild symptoms that can progress to more severe symptoms, such as hepatitis, encephalitis, and hemorrhagic fever. The goal of this study was to use RNA-sequencing (RNA-seq) to analyze the host transcriptome in response to RVFV infection. G2/M DNA damage checkpoint, ATM signaling, mitochondrial dysfunction, regulation of the antiviral response, and integrin-linked kinase (ILK) signaling were among the top altered canonical pathways with both the attenuated MP12 strain and the fully virulent ZH548 strain. Although several mRNA transcripts were highly upregulated, an increase at the protein level was not observed for the selected genes, which was at least partially due to the NSs dependent block in mRNA export. Inhibition of ILK signaling, which is involved in cell motility and cytoskeletal reorganization, resulted in reduced RVFV replication, indicating that this pathway is important for viral replication. Overall, this is the first global transcriptomic analysis of the human host response following RVFV infection, which could give insight into novel host responses that have not yet been explored.

Molecular mechanisms involved in podocyte EMT and concomitant diabetic kidney diseases: an update

Epithelial–mesenchymal transition (EMT) is a tightly regulated process by which epithelial cells lose their hallmark epithelial characteristics and gain the features of mesenchymal cells. For podocytes, expression of nephrin, podocin, P-cadherin, and ZO-1 is downregulated, the slit diaphragm (SD) will be altered, and the actin cytoskeleton will be rearranged. Diabetes, especially hyperglycemia, has been demonstrated to incite podocyte EMT through several molecular mechanisms such as TGF-β/Smad classic pathway, Wnt/β-catenin signaling pathway, Integrins/integrin-linked kinase (ILK) signaling pathway, MAPKs signaling pathway, Jagged/Notch signaling pathway, and NF-κB signaling pathway. As one of the most fundamental prerequisites to develop ground-breaking therapeutic options to prevent the development and progression of diabetic kidney disease (DKD), a comprehensive understanding of the molecular mechanisms involved in the pathogenesis of podocyte EMT is compulsory. Therefore, the purpose of this paper is to update the research progress of these underlying signaling pathways and expound the podocyte EMT-related DKDs.

Chimeric Genes in Deletions and Duplications Associated with Intellectual Disability

We report on three nonrelated patients with intellectual disability and CNVs that give rise to three new chimeric genes. All the genes forming these fusion transcripts may have an important role in central nervous system development and/or in gene expression regulation, and therefore not only their deletion or duplication but also the resulting chimeric gene may contribute to the phenotype of the patients. Deletions and duplications are usually pathogenic when affecting dose-sensitive genes. Alternatively, a chimeric gene may also be pathogenic by different gain-of-function mechanisms that are not restricted to dose-sensitive genes: the emergence of a new polypeptide that combines functional domains from two different genes, the deregulated expression of any coding sequence by the promoter region of a neighboring gene, and/or a putative dominant-negative effect due to the preservation of functional domains of partially truncated proteins. Fusion oncogenes are well known, but in other pathologies, the search for chimeric genes is disregarded. According to our findings, we hypothesize that the frequency of fusion transcripts may be much higher than suspected, and it should be taken into account in the array-CGH analyses of patients with intellectual disability.

Integrin associated proteins differentially regulate neutrophil polarity and directed migration in 2D and 3D

Directed neutrophil migration in blood vessels and tissues is critical for proper immune function; however, the mechanisms that regulate three-dimensional neutrophil chemotaxis remain unclear. It has been shown that integrins are dispensable for interstitial three-dimensional (3D) leukocyte migration; however, the role of integrin regulatory proteins during directed neutrophil migration is not known. Using a novel microfluidic gradient generator amenable to 2D and 3D analysis, we found that the integrin regulatory proteins Kindlin-3, RIAM, and talin-1 differentially regulate neutrophil polarization and directed migration to gradients of chemoattractant in 2D versus 3D. Both talin-1-deficient and RIAM-deficient neutrophil-like cells had impaired adhesion, polarization, and migration on 2D surfaces whereas in 3D the cells polarized but had impaired 3D chemotactic velocity. Kindlin-3 deficient cells were able to polarize and migrate on 2D surfaces but had impaired directionality. In a 3D environment, Kindlin-3 deficient cells displayed efficient chemotaxis. These findings demonstrate that the role of integrin regulatory proteins in cell polarity and directed migration can be different in 2D and 3D.

Preservation of human limbal epithelial progenitor cells on carbodiimide cross-linked amniotic membrane via integrin-linked kinase-mediated Wnt activation

The Wnt pathway is a major signaling pathway that regulates corneal epithelial stem cells. However, little is known about how the ultrastructure of the limbal epithelial basement membrane (EBM) affects Wnt activity. Due to its enhanced matrix stability, the cross-linked amniotic membrane (AM) has gained increasing interest in the field of regenerative medicine. For the first time, we used EDC/NHS cross-linked denuded AM (CLDAM) as a simulated EBM substrate to investigate this mechanism. Human limbal epithelial (HLE) cells were cultured on dishes (HLE/dish), denuded AM (HLE/DAM) or CLDAM (HLE/CLDAM). Compared with HLE/dish or HLE/DAM cultures, HLE/CLDAM cultures showed greater BrdU retention and colony formation efficiency and expressed higher levels of p63, ABCG2, integrin β1, and integrin-linked kinase (ILK). Nuclear β-catenin and TCF-4 levels were higher in HLE/CLDAM cultures compared with HLE cells cultured on collagen IV, laminin, Matrigel, or DAM. Silencing of ILK in HLE/CLDAM cultures resulted in decreased levels of nuclear β-catenin, TCF-4 and deltaNp63α, whereas cytokeratin 12 expression increased. Over-expression of ILK in HLE/dish cultures had the opposite effects. Accordingly, we proposed that the CLDAM matrix, with its higher rigidity and rougher ultrastructure, better preserved HLE progenitor cells in vitro, possibly by activating integrin β1/ILK, which indirectly activated Wnt/β-catenin and subsequently deltaNp63α. Crosstalk between the integrin β1/ILK and Wnt/β-catenin pathways appears to play a crucial role in limbal progenitor cell survival on EBM.

STATEMENT OF SIGNIFICANCE

We demonstrated the superior capability of carbodiimide cross-linked denuded amniotic membrane (CLDAM) than natural DAM to preserve limbo-corneal epithelial progenitor cells in vitro, then we used CLDAM as a simulated epithelial basement membrane (EBM) to study how EBM maintains limbal epithelial stem cells (LESCs). We found that integrin-linked kinase (ILK) is an important mediator that transfers survival signals detected by integrin β1 to the Wnt/β-catenin pathway, which in turn up-regulates deltaNp63α, a master gene that regulates LESC function. The rougher surface of the limbal EBM suggests that the surface complexity of the LESC niche may be important in regulating LESC function, which is triggered by the recognition of topographic cues by integrin β1, followed by activation of the ILK/Wnt/β-catenin/p63 cascade.

Interaction of infectious spleen and kidney necrosis virus ORF119L with PINCH leads to dominant-negative inhibition of integrin-linked kinase and cardiovascular defects in zebrafish

Infectious spleen and kidney necrosis virus (ISKNV) is the type species of the Megalocytivirus genus, Iridoviridae family, causing a severe systemic disease with high mortality in mandarin fish (Siniperca chuatsi) in China and Southeast Asia. At present, the pathogenesis of ISKNV infection is still not fully understood. Based on a genome-wide bioinformatics analysis of ISKNV-encoded proteins, we found that ISKNV open reading frame 119L (ORF119L) is predicted to encode a three-ankyrin-repeat (3ANK)-domain-containing protein, which shows high similarity to the dominant negative form of integrin-linked kinase (ILK); i.e., viral ORF119L lacks the ILK kinase domain. Thus, we speculated that viral ORF119L might affect the host ILK complex. Here, we demonstrated that viral ORF119L directly interacts with particularly interesting Cys-His-rich protein (PINCH) and affects the host ILK-PINCH interaction in vitro in fathead minnow (FHM) cells. In vivo ORF119L overexpression in zebrafish (Danio rerio) embryos resulted in myocardial dysfunctions with disintegration of the sarcomeric Z disk. Importantly, ORF119L overexpression in zebrafish highly resembles the phenotype of endogenous ILK inhibition, either by overexpressing a dominant negative form of ILK or by injecting an ILK antisense morpholino oligonucleotide. Intriguingly, ISKNV-infected mandarin fish develop disorganized sarcomeric Z disks in cardiomyocytes. Furthermore, phosphorylation of AKT, a downstream effector of ILK, was remarkably decreased in ORF119L-overexpressing zebrafish embryos. With these results, we show that ISKNV ORF119L acts as a domain-negative inhibitor of the host ILK, providing a novel mechanism for the megalocytivirus pathogenesis.

IMPORTANCE

Our work is the first to show the role of a dominant negative inhibitor of the host ILK from ISKNV (an iridovirus). Mechanistically, the viral ORF119L directly binds to the host PINCH, attenuates the host PINCH-ILK interaction, and thus impairs ILK signaling. Intriguingly, ORF119L-overexpressing zebrafish embryos and ISKNV-infected mandarin fish develop similar disordered sarcomeric Z disks in cardiomyocytes. These findings provide a novel mechanism for megalocytivirus pathogenesis.

Parvin-ILK: An intimate relationship

Integrin-linked kinase (ILK), PINCH and Parvin proteins form the IPP-complex that has been established as a core component of the integrin-actin link. Our recent genetic studies on Drosophila parvin, reveal that loss of function mutant defects phenocopy those observed upon loss of ILK or PINCH in the muscle and the wing, strengthening the notion that these proteins function together in the organism. Our work identified that ILK is necessary and sufficient for parvin subcellular localization, corroborating previous data indicating a direct association between these two proteins. Further genetic epistasis analysis of the IPP-complex assembly at integrin adhesion sites reveals that depending on the cell context each component is required differently. At the muscle attachment sites of the embryo, ILK is placed upstream in the hierarchy of genetic interactions required for the IPP-complex assembly. By contrast, in the wing epithelium the three proteins are mutually interdependent. Finally, we uncovered a novel property for the CH1-domain of parvin: its recruitment at the integrin-containing junctions in an ILK-dependent manner. Apparently, this ability of the CH1-domain is controlled by the inter-CH linker region. Thus, an intramolecular interaction within parvin could serve as a putative regulatory mechanism controlling the ILK-Parvin interaction.

Symmetric exchange of multi-protein building blocks between stationary focal adhesions and the cytosol

How can the integrin adhesome get self-assembled locally, rapidly, and correctly as diverse cell-matrix adhesion sites? Here, we investigate this question by exploring the cytosolic state of integrin-adhesome components and their dynamic exchange between adhesion sites and cytosol. Using fluorescence cross-correlation spectroscopy (FCCS) and fluorescence recovery after photobleaching (FRAP) we found that the integrin adhesome is extensively pre-assembled already in the cytosol as multi-protein building blocks for adhesion sites. Stationary focal adhesions release symmetrically the same types of protein complexes that they recruit, thereby keeping the cytosolic pool of building blocks spatiotemporally uniform. We conclude a model in which multi-protein building blocks enable rapid and modular self-assembly of adhesion sites and symmetric exchange of these building blocks preserves their specifications and thus the assembly logic of the system.DOI: http://dx.doi.org/10.7554/eLife.02257.001.

Changes in PINCH levels in the CSF of HIV+ individuals correlate with hpTau and CD4 count

Several studies report associations between the particularly interesting new cysteine histidine-rich (PINCH) protein and HIV-associated CNS disease. PINCH is detected in the CSF of HIV patients, and changes in levels during disease may be indicative of changes in disease status over time. PINCH binds hyperphosphorylated Tau (hpTau) in the brain and CSF, but little is known about the relevance of these interactions to HIV CNS disease. In this study, PINCH and hpTau levels were assessed in three separate CSF samples collected longitudinally from 20 HIV+ participants before and after initiating antiretroviral therapy or before and after a change in the treatment regimen. The intervals were approximately 1 (T2) and 3-7 (T3) months from the initial visit (baseline, T1). Correlational analyses were conducted for CSF levels of PINCH and hpTau and other variables including blood CD4 T-cell count, plasma and CSF viral burden, CSF neopterin, white blood cell (WBC) count, and antiretroviral CNS penetration effectiveness (CPE). Values for PINCH and hpTau were determined for each patient by calculating the fold changes between the second (T2) and third measurements (T3) from the baseline measurement (T1). Statistical analyses showed that the fold changes in CSF PINCH protein from T1 to T2 were significantly higher in participants with CD4 counts >200 cells/mm(3) at T2 compared to those with CD4 counts <200 cells/mm(3) at T2. This trend persisted irrespective of plasma or CSF viral burden or antiretroviral therapy CPE scores. The fold changes in PINCH levels between T1 and T2, and T1 and T3 were highly correlated to the fold changes in hpTau at T2/T1 and T3/T1 (correlation coefficient = 0.69, p < 0.001; correlation coefficient = 0.83, p < 0.0001, respectively). In conclusion, in these HIV participants, changes in CSF levels of PINCH appear to correlate with changes in blood CD4 count and with changes in CSF hpTau levels, but not with plasma or CSF viral burden, neopterin, WBC, or antiretroviral regimen CPE.

Nephrin phosphorylation regulates podocyte adhesion through the PINCH-1-ILK-α-parvin complex

Nephrin, a structural molecule, is also a signaling molecule after phosphorylation. Inhibition of nephrin phosphorylation is correlated with podocyte injury. The PINCH-1-ILK-α-parvin (PIP) complex plays a crucial role in cell adhesion and cytoskeleton formation. We hypothesized that nephrin phosphorylation influenced cytoskeleton and cell adhesion in podocytes by regulating the PIP complex. The nephrin phosphorylation, PIP complex formation, and F-actin in Wistar rats intraperitoneally injected with puromycin aminonucleoside were gradually decreased but increased with time, coinciding with the recovery from glomerular/podocyte injury and proteinuria. In cultured podocytes, PIP complex knockdown resulted in cytoskeleton reorganization and decreased cell adhesion and spreading. Nephrin and its phosphorylation were unaffected after PIP complex knockdown. Furthermore, inhibition of nephrin phosphorylation suppressed PIP complex expression, disorganized podocyte cytoskeleton, and decreased cell adhesion and spreading. These findings indicate that alterations in nephrin phosphorylation disorganize podocyte cytoskeleton and decrease cell adhesion through a PIP complex-dependent mechanism.

PINCH expression in relation to radiation response in co-cultured colon cancer cells and in rectal cancer patients

Particularly interesting new cysteine-histidine rich protein (PINCH), involved in cell spreading, motility and proliferation, has been shown to enhance radioresistance in colon cancer cell lines. The expression of PINCH in relation to radiation was studied in co-cultured colon cancer cells. Furthermore, the clinical significance between PINCH and radiotherapy (RT) was analyzed in rectal cancer patients with or without RT. The relative PINCH expression in colon cancer (KM12C) cells cultured separately and in co-culture was examined by western blotting and real-time PCR, and was analyzed over a period of 8 and 24 h after radiation. PINCH expression was immunohistochemically examined in 137 primary rectal tumors for which 65 cases did not receive RT and 72 cases received RT. PINCH expression tended to decrease from that in the separately cultured KM12C cells without radiation to that in cells with radiation at 8 h (P=0.060); while in the co-cultured cells, no significant difference was found (P=0.446). In patients with RT, strong PINCH expression was related to worse survival, when compared to patients with weak expression, independent of TNM stage, degree of differentiation, age and p53 status (P=0.029, RR 4.03, 95% CI 1.34‑12.1). No survival relationship for the patients without RT was observed (P=0.287). A statistical interaction analysis between PINCH, RT and survival showed a trend towards significance (P=0.057). In conclusion, PINCH predicts survival in rectal cancer patients with RT, but not in patients without RT. The expression of PINCH may be regulated by radiation and by environmental factors surrounding the cells.

Suppression of actopaxin impairs hepatocellular carcinoma metastasis through modulation of cell migration and invasion

Early reports suggested that actopaxin, a member of the focal adhesion proteins, regulates cell migration. Here we investigated whether actopaxin is involved in hepatocellular carcinoma (HCC) progression and metastasis. We examined actopaxin expression in human HCC samples using immunohistochemistry and western blotting. The functional and molecular effect of actopaxin was studied in vitro by overexpression in a nonmetastatic HCC cell line, as well as repression in a metastatic cell line. The in vivo effect of actopaxin repression was studied in nonobese diabetic and severe combined immunodeficient mice. We found that actopaxin was frequently overexpressed in human HCC patients and its overexpression positively correlated with tumor size, stage, and metastasis. Actopaxin expression also correlated with the metastatic potential of HCC cell lines. Actopaxin overexpression induced the invasion and migration ability of nonmetastatic HCC cells, whereas down-regulation of actopaxin reverted the invasive phenotypes and metastatic potential of metastatic HCC cells through regulating the protein expression of certain focal adhesion proteins including ILK, PINCH, paxillin, and cdc42, as well as regulating the epithelial-mesenchymal transition pathway. Furthermore, there was a close association between actopaxin and CD29. HCC cells with stronger CD29 expression showed a higher actopaxin level, whereas actopaxin repression attenuated CD29 activity. Finally, actopaxin down-regulation enhanced the chemosensitivity of HCC cells towards oxaliplatin treatment by way of a collective result of suppression of survivin protein, β-catenin, and mammalian target of rapamycin pathways and up-regulation of p53.

CONCLUSION

This study provides concrete evidence of a significant role of actopaxin in HCC progression and metastasis, by way of regulation of cell invasiveness and motility, an epithelial-mesenchymal transition process, and chemosensitivity to cytotoxic drugs.

α-Catulin drives metastasis by activating ILK and driving an αvβ3 integrin signaling axis

α-Catulin is an oncoprotein that helps sustain proliferation by preventing cellular senescence. Here, we report that α-catulin also drives malignant invasion and metastasis. α-Catulin was upregulated in highly invasive non-small cell lung cancer (NSCLC) cell lines, where its ectopic expression or short-hairpin RNA-mediated attenuation enhanced or limited invasion or metastasis, respectively. α-Catulin interacted with integrin-linked kinase (ILK), a serine/threonine protein kinase implicated in cancer cell proliferation, antiapoptosis, invasion, and angiogenesis. Attenuation of ILK or α-catulin reciprocally blocked cell migration and invasion induced by the other protein. Mechanistic investigations revealed that α-catulin activated Akt-NF-κB signaling downstream of ILK, which in turn led to increased expression of fibronectin and integrin αvβ3. Pharmacologic or antibody-mediated blockade of NF-κB or αvβ3 was sufficient to inhibit α-catulin-induced cell migration and invasion. Clinically, high levels of expression of α-catulin and ILK were associated with poor overall survival in patients with NSCLC. Taken together, our study shows that α-catulin plays a critical role in cancer metastasis by activating the ILK-mediated Akt-NF-κB-αvβ3 signaling axis.