The LIM Protein Zyxin Binds CARP-1 and Promotes Apoptosis

The role of zyxin in signal transduction and its relationship with diseases

This review highlighted the pivotal role of zyxin, an essential cell focal adhesions protein, in cellular biology and various diseases. Zyxin can orchestrate the restructuring and dynamic alterations of the cellular cytoskeleton, which is involved in cell proliferation, adhesion, motility, and gene transcription. Aberrant zyxin expression is closely correlated with tumor cell activity and cardiac function in both tumorigenesis and cardiovascular diseases. Moreover, in fibrotic and inflammatory conditions, zyxin can modulate cellular functions and inflammatory responses. Therefore, a comprehensive understanding of zyxin is crucial for deciphering signal transduction networks and disease pathogenesis. Investigating its role in diseases holds promise for novel avenues in early diagnosis and therapeutic strategies. Nevertheless, targeting zyxin as a therapeutic focal point presents challenges in terms of specificity, safety, drug delivery, and resistance. Nonetheless, in-depth studies on zyxin and the application of precision medicine could offer new possibilities for personalized treatment modalities.

Zyxin inhibits the epithelial-mesenchymal transition process in gastric cancer by upregulating SIRT1

Tumor development relies on the stemness of cancer stem cells, which is regulated by environmental cues. Previous studies have shown that zyxin can inhibit the expression of genes for embryonic stem cell status. In the present study, the expression levels of zyxin protein in cancer tissues and adjacent noncancerous tissues from 73 gastric cancer patients with different clinical stages were analyzed by Western blot. We showed that the relative expression levels of zyxin in gastric cancer tissues (cancer tissues/adjacent tissues) were significantly downregulated in advanced clinical stages. Overexpression of zyxin inhibited the stemness and epithelial-mesenchymal transition (EMT) processes in gastric cancer cells. Zyxin also inhibited the proliferation, migration, and invasion but increased the sensitivity of cancer cells to drugs. Overexpression of zyxin in MKN45 cells inhibited tumor growth in nude mice. We show that the interactions between zyxin and SIRT1 led to the upregulation of SIRT1, reduced acetylation levels of histone H3 K9 and K23, decreased transcription levels of SNAI 1/2, and inhibition of the EMT process. This study demonstrated that zyxin negatively regulates the progression of gastric cancer by inhibiting the stemness of cancer stem cells and EMT. Our findings shed new light on the pathogenesis of gastric cancer.

Discoidin domain receptor-2 enhances secondary alveolar septation in mice by activating integrins and modifying focal adhesions

The extracellular matrix (ECM) of the pulmonary parenchyma must maintain the structural relationships among resident cells during the constant distortion imposed by respiration. This dictates that both the ECM and cells adapt to changes in shape, while retaining their attachment. Membrane-associated integrins and discoidin domain receptors (DDR) bind collagen and transmit signals to the cellular cytoskeleton. Although the contributions of DDR2 to collagen deposition and remodeling during osseous development are evident, it is unclear how DDR2 contributes to lung development. Using mice (smallie, Slie/Slie, DDR2Δ) bearing a spontaneous inactivating deletion within the DDR2 coding region, we observed a decrease in gas-exchange surface area and enlargement of alveolar ducts. Compared with fibroblasts isolated from littermate controls, DDR2Δ fibroblasts, spread more slowly, developed fewer lamellipodia, and were less responsive to the rigidity of neighboring collagen fibers. Activated β1-integrin (CD29) was reduced in focal adhesions (FA) of DDR2Δ fibroblasts, less phospho-zyxin localized to and fewer FA developed over ventral actin stress fibers, and the adhesions had a lower aspect ratio compared with controls. However, DDR2 deletion did not reduce cellular displacement of the ECM. Our findings indicate that DDR2, in concert with collagen-binding β1-integrins, regulates the timing and location of focal adhesion formation and how lung fibroblasts respond to ECM rigidity. Reduced rigidity sensing and mechano-responsiveness may contribute to the distortion of alveolar ducts, where the fiber cable-network is enriched and tensile forces are concentrated. Strategies targeting DDR2 could help guide fibroblasts to locations where tensile forces organize parenchymal repair.

Cytoskeletal protein Zyxin in embryonic development: from controlling cell movements and pluripotency to regulating embryonic patterning

The Lim-domain protein Zyxin was initially identified as a minor actin cytoskeleton protein that regulates the assembly and repair of actin filaments. At the same time, additional functions revealed for Zyxin in recent decades indicate that this protein can also play an important role in regulating gene expression and cell differentiation. In this review, we analysed the data in the literature pointing to Zyxin as one of the possible molecular hubs linking morphogenetic cell movements with gene expression, stem cell status regulation and pattern formation during the most complex processes in organism life, embryogenesis.

Cellular force-sensing through actin filaments

The actin cytoskeleton orchestrates cell mechanics and facilitates the physical integration of cells into tissues, while tissue-scale forces and extracellular rigidity in turn govern cell behaviour. Here, we discuss recent evidence that actin filaments (F-actin), the core building blocks of the actin cytoskeleton, also serve as molecular force sensors. We delineate two classes of proteins, which interpret forces applied to F-actin through enhanced binding interactions: 'mechanically tuned' canonical actin-binding proteins, whose constitutive F-actin affinity is increased by force, and 'mechanically switched' proteins, which bind F-actin only in the presence of force. We speculate mechanically tuned and mechanically switched actin-binding proteins are biophysically suitable for coordinating cytoskeletal force-feedback and mechanical signalling processes, respectively. Finally, we discuss potential mechanisms mediating force-activated actin binding, which likely occurs both through the structural remodelling of F-actin itself and geometric rearrangements of higher-order actin networks. Understanding the interplay of these mechanisms will enable the dissection of force-activated actin binding's specific biological functions.

Expression of Zyxin in Non-Small Cell Lung Cancer-A Preliminary Study

Background: The potential involvement of zyxin (ZYX) in carcinogenesis has been investigated in many cancer types. However, there are a limited number of studies on the role of ZYX in the progression of non-small cell lung cancer (NSCLC). Since lung cancer is one of the most frequently diagnosed carcinomas, the aim of our study was to determine the localization and expression levels of ZYX in NSCLC and to correlate the results with the clinicopathological data. Materials and Methods: The expression of ZYX was assessed in NSCLC cases and in cell lines representing this tumor type. Levels of ZYX were determined in the clinical material using immunohistochemistry (IHC) and Western Blot. Real-time PCR was used to assess ZYX mRNA levels. The expression of ZYX was also checked in NSCLC cell lines using real-time PCR, Western Blot, and immunofluorescence/immunocytochemistry. Results: The results showed lower levels of ZYX in NSCLC cells compared with control tissues. This trend was observed at the protein and mRNA levels. The assays on the NSCLC model also demonstrated lower levels of ZYX in cancer cells compared with control cells. Conclusions: The decreased expression of ZYX in NSCLC may indicate a suppressor role of this protein in NSCLC.

Discovery of Novel Markers for Identifying Cognitive Decline Using Neuron-Derived Exosomes

Alzheimer's disease (AD), the predominant cause of late-life dementia, has a multifactorial etiology. Since there are few therapeutic options for symptomatic AD, research is increasingly focused on the identification of pre-symptomatic biomarkers. Recently, evaluation of neuron-derived exosomal markers has emerged as a promising novel approach for determining neuronal dysfunction. We aimed to identify novel neuron-derived exosomal markers that signify a transition from normal aging to Mild Cognitive Impairment (MCI) and then to clinically established AD, a sequence we refer to as AD progression. By using a Tandem Mass Tag-based quantitative proteomic approach, we identified a total of 360 neuron-derived exosomal proteins. Subsequent fuzzy c-means clustering revealed two clusters of proteins displaying trends of gradually increasing/decreasing expression over the period of AD progression (normal to MCI to AD), both of which were mainly involved in immune response-associated pathways, proteins within these clusters were defined as bridge proteins. Several differentially expressed proteins (DEPs) were identified in the progression of AD. The intersections of bridge proteins and DEPs were defined as key proteins, including C7 (Complement component 7), FERMT3 (Fermitin Family Member 3), CAP1 (Adenylyl cyclase-associated protein 1), ENO1 (Enolase 1), and ZYX (Zyxin), among which the expression patterns of C7 and ZYX were almost consistent with the proteomic results. Collectively, we propose that C7 and ZYX might be two novel neuron-derived exosomal protein markers, expression of which might be used to evaluate cognitive decline before a clinical diagnosis of AD is warranted.

Multiplexed labeling of cellular proteins with split fluorescent protein tags

Self-complementing split fluorescent proteins (split FP1-10/11) have become an important labeling tool in live-cell protein imaging. However, current split FP systems to label multiple proteins in single cells have a fundamental limitation in the number of proteins that can be simultaneously labeled. Here, we describe an approach to expand the number of orthogonal split FP systems with spectrally distinct colors. By combining rational design and cycles of directed evolution, we expand the spectral color palette of FP1-10/11. We also circularly permutate GFP and synthesize the β-strand 7, 8, or 10 system. These split GFP pairs are not only capable of labeling proteins but are also orthogonal to the current FP1-10/11 pairs, offering multiplexed labeling of cellular proteins. Our multiplexing approach, using the new orthogonal split FP systems, demonstrates simultaneous imaging of four distinct proteins in single cells; the resulting images reveal nuclear localization of focal adhesion protein Zyxin.

Cell density-dependent proteolysis by HtrA1 induces translocation of zyxin to the nucleus and increased cell survival

Proteases modulate critical processes in cutaneous tissue repair to orchestrate inflammation, cell proliferation and tissue remodeling. However, the functional consequences and implications in healing impairments of most cleavage events are not understood. Using iTRAQ-based Terminal Amine Isotopic Labeling of Substrates (TAILS) we had characterized proteolytic signatures in a porcine wound healing model and identified two neo-N termini derived from proteolytic cleavage of the focal adhesion protein and mechanotransducer zyxin. Here, we assign these proteolytic events to the activity of either caspase-1 or serine protease HtrA1 and analyze the biological relevance of the resultant zyxin truncations. By cellular expression of full-length and truncated zyxin proteins, we demonstrate nuclear translocation of a C-terminal zyxin fragment that could also be generated in vitro by HtrA1 cleavage and provide evidence for its anti-apoptotic activities, potentially by regulating the expression of modulators of cell proliferation, protein synthesis and genome stability. Targeted degradomics correlated endogenous generation of the same zyxin fragment with increased cell density in human primary dermal fibroblasts. Hence, this newly identified HtrA1-zyxin protease signaling axis might present a novel mechanism to transiently enhance cell survival in environments of increased cell density like in wound granulation tissue.

Antagonizing binding of cell cycle and apoptosis regulatory protein 1 (CARP-1) to the NEMO/IKKγ protein enhances the anticancer effect of chemotherapy

NF-κB is a pro-inflammatory transcription factor that critically regulates immune responses and other distinct cellular pathways. However, many NF-κB-mediated pathways for cell survival and apoptosis signaling in cancer remain to be elucidated. Cell cycle and apoptosis regulatory protein 1 (CARP-1 or CCAR1) is a perinuclear phosphoprotein that regulates signaling induced by anticancer chemotherapy and growth factors. Although previous studies have reported that CARP-1 is a part of the NF-κB proteome, regulation of NF-κB signaling by CARP-1 and the molecular mechanism(s) involved are unclear. Here, we report that CARP-1 directly binds the NF-κB-activating kinase IκB kinase subunit γ (NEMO or NF-κB essential modulator) and regulates the chemotherapy-activated canonical NF-κB pathway. Importantly, blockade of NEMO-CARP-1 binding diminished NF-κB activation, indicated by reduced phosphorylation of its subunit p65/RelA by the chemotherapeutic agent adriamycin (ADR), but not NF-κB activation induced by tumor necrosis factor α (TNFα), interleukin (IL)-1β, or epidermal growth factor. High-throughput screening of a chemical library yielded a small molecule inhibitor of NEMO-CARP-1 binding, termed selective NF-κB inhibitor 1 (SNI)-1). We noted that SNI-1 enhances chemotherapy-dependent growth inhibition of a variety of cancer cells, including human triple-negative breast cancer (TNBC) and patient-derived TNBC cells in vitro, and attenuates chemotherapy-induced secretion of the pro-inflammatory cytokines TNFα, IL-1β, and IL-8. SNI-1 also enhanced ADR or cisplatin inhibition of murine TNBC tumors in vivo and reduced systemic levels of pro-inflammatory cytokines. We conclude that inhibition of NEMO-CARP-1 binding enhances responses of cancer cells to chemotherapy.

The role of zyxin in regulation of malignancies

Focal adhesions are highly dynamic multi-protein complexes found at the cell surface and effectively link the cell's internal cytoskeleton to a complex mixture of macromolecules known as the extracellular matrix and mediate transmission of signals from the extracellular matrix to the nucleus. Zyxin is one of the key focal adhesion proteins and is also found to shuttle in the nucleus. Although the mechanism of shuttling to the nucleus unclear, it moves out from the nucleus through a leucine-rich nuclear export signal sequence. It is known to contribute to fundamental cellular activities such as cell migration, adhesion and proliferation by interacting with a variety of cellular proteins. It is also linked with a number of cancers such as melanoma, hepatocellular carcinoma, oral squamous-cell carcinoma, Ewing sarcoma and prostate cancer. However, in many cases, the precise mechanisms by which the absence or presence of zyxin contributes to cancer progression or suppression is unknown. Thus, more work is required to gain insights into how zyxin modulates cellular functions in relationship to cancer. This review summarises the role of zyxin in cancer, with an emphasis on conflicting roles in prostate cancer.

Mapping hyper-susceptibility to colitis-associated colorectal cancer in FVB/NJ mice

Inbred strains of mice differ in susceptibility to colitis-associated colorectal cancer (CA-CRC). We tested 10 inbred strains of mice for their response to azoxymethane/dextran sulfate sodium-induced CA-CRC and identified a bimodal inter-strain distribution pattern when tumor multiplicity was used as a phenotypic marker of susceptibility. The FVB/NJ strain was particularly susceptible showing a higher tumor burden than any other susceptible strains (12.5-week post-treatment initiation). FVB/NJ hyper-susceptibility was detected as early as 8-week post-treatment initiation with FVB/NJ mice developing 5.5-fold more tumors than susceptible A/J or resistant B6 control mice. Linkage analysis by whole genome scan in informative (FVB/NJ×C3H/HeJ)F2 mice identified a novel susceptibility locus designated as C olon c ancer s usceptibility 6 (Ccs6) on proximal mouse chromosome 6. When gender was used as a covariate, a LOD score of 5.4 was computed with the peak marker being positioned at rs13478727, 43.8 Mbp. Mice homozygous for FVB/NJ alleles at this locus had increased tumor multiplicity compared to homozygous C3H/HeJ mice. Positional candidates in this region of chromosome 6 were analyzed with respect to a possible role in carcinogenesis and a role in inflammatory response using a new epigenetic gene scoring tool (Myeloid Inflammation Score).

PTHrP attenuates osteoblast cell death and apoptosis induced by a novel class of anti-cancer agents

The effectiveness of chemotherapeutic agents often limits their use due to their negative effects on normal cells. Apoptosis regulatory protein (CARP)-1 functional mimetics (CFMs) belong to a novel class of compounds that possess anti-cancer properties with potential utility in breast and other cancers. In this study, we investigated the growth inhibitory action of CFM-4 and -5 in bone-forming osteoblasts and role of a skeletal regulator, parathyroid hormone (PTH)-related peptide (PTHrP), which is frequently associated with oncologic pathologies. MC3T3E1-clone4 (MC-4) or primary osteoblasts were treated with CFMs. Western blots were performed to determine specific protein expressions. MTT, TUNEL assay, ethidium bromide/acridine orange staining, and ApoAlert caspase profiling were used to investigate cell viability and apoptosis of osteoblasts. Immunofluorescence staining was performed to observe intracellular localization of CARP-1. Our studies revealed that CFM-4 and -5 suppressed growths of mature differentiated, but not proliferating, MC-4 cells and PTHrP attenuated this effect. Mechanistically, induction of CARP-1 protein by CFM-4 and -5 was partially decreased by PTHrP. While CARP-1 increased by CFM-4 or -5 correlated with activated caspase-3, PTHrP remarkably blocked caspase-3 activation. PTHrP also influenced translocation of CFM-induced CARP-1 from the nucleus to the cytoplasm. Our data identify a new function of PTHrP in maintaining osteoblast homeostasis in chemotherapy and define a role of CARP-1 in this process. The crosstalk of PTHrP and CFM-4 and -5 signaling highlights the importance of CFMs as potential anti-cancer therapeutics in breast and other cancers which adversely affect bone.

CARP-1/CCAR1: a biphasic regulator of cancer cell growth and apoptosis

Targeted cancer therapy using small molecule inhibitors (SMIs) has been useful in targeting the tumor cells while sparing the normal cells. Despite clinical success of many targeted therapies, their off-target effects and development of resistance are emerging as significant and challenging problems. Thus, there is an urgent need to identify targets to devise new means to treat cancers and their drug-resistant phenotypes. CARP-1/CCAR1 (Cell division cycle and apoptosis regulator 1), a peri-nuclear phospho-protein, plays a dynamic role in regulating cell growth and apoptosis by serving as a co-activator of steroid/thyroid nuclear receptors, β-catenin, Anaphase Promoting Complex/Cyclosome (APC/C) E3 ligase, and tumor suppressor p53. CARP-1/CCAR1 also regulates chemotherapy-dependent apoptosis. CARP-1/CCAR1 functional mimetics (CFMs) are a novel SMIs of CARP-1/CCAR1 interaction with APC/C. CFMs promote apoptosis in a manner independent of p53. CFMs are potent inhibitors of a variety of cancer cells including the drug (Adriamycin or Tamoxifen)-resistant breast cancer cells but not the immortalized breast epithelial cells, while a nano-lipid formulation of the lead compound CFM-4 improves its bioavailability and efficacy in vivo when administered orally. This review focuses on the background and pleiotropic roles of CARP-1/CCAR1 as well as its apoptosis signaling mechanisms in response to chemotherapy in cancer cells.

Loss of the mechanotransducer zyxin promotes a synthetic phenotype of vascular smooth muscle cells

Background

Exposure of vascular smooth muscle cells (VSMCs) to excessive cyclic stretch such as in hypertension causes a shift in their phenotype. The focal adhesion protein zyxin can transduce such biomechanical stimuli to the nucleus of both endothelial cells and VSMCs, albeit with different thresholds and kinetics. However, there is no distinct vascular phenotype in young zyxin-deficient mice, possibly due to functional redundancy among other gene products belonging to the zyxin family. Analyzing zyxin function in VSMCs at the cellular level might thus offer a better mechanistic insight. We aimed to characterize zyxin-dependent changes in gene expression in VSMCs exposed to biomechanical stretch and define the functional role of zyxin in controlling the resultant VSMC phenotype.

Methods and Results

DNA microarray analysis was used to identify genes and pathways that were zyxin regulated in static and stretched human umbilical artery–derived and mouse aortic VSMCs. Zyxin-null VSMCs showed a remarkable shift to a growth-promoting, less apoptotic, promigratory and poorly contractile phenotype with ≈90% of the stretch-responsive genes being zyxin dependent. Interestingly, zyxin-null cells already seemed primed for such a synthetic phenotype, with mechanical stretch further accentuating it. This could be accounted for by higher RhoA activity and myocardin-related transcription factor-A mainly localized to the nucleus of zyxin-null VSMCs, and a condensed and localized accumulation of F-actin upon stretch.

Conclusions

At the cellular level, zyxin is a key regulator of stretch-induced gene expression. Loss of zyxin drives VSMCs toward a synthetic phenotype, a process further consolidated by exaggerated stretch.

Molecular dissection of the mechanism by which EWS/FLI expression compromises actin cytoskeletal integrity and cell adhesion in Ewing sarcoma

Ewing sarcoma is the second-most-common bone cancer in children. Driven by an oncogenic chromosomal translocation that results in the expression of an aberrant transcription factor, EWS/FLI, the disease is typically aggressive and micrometastatic upon presentation. Silencing of EWS/FLI in patient-derived tumor cells results in the altered expression of hundreds to thousands of genes and is accompanied by dramatic morphological changes in cytoarchitecture and adhesion. Genes encoding focal adhesion, extracellular matrix, and actin regulatory proteins are dominant targets of EWS/FLI-mediated transcriptional repression. Reexpression of genes encoding just two of these proteins, zyxin and α5 integrin, is sufficient to restore cell adhesion and actin cytoskeletal integrity comparable to what is observed when the EWS/FLI oncogene expression is compromised. Using an orthotopic xenograft model, we show that EWS/FLI-induced repression of α5 integrin and zyxin expression promotes tumor progression by supporting anchorage-independent cell growth. This selective advantage is paired with a tradeoff in which metastatic lung colonization is compromised.

Cell cycle and apoptosis regulatory protein (CARP)-1 is expressed in osteoblasts and regulated by PTH

Bone mass is dependent on osteoblast proliferation, differentiation and life-span of osteoblasts. Parathyroid hormone (PTH) controls osteoblast cell cycle regulatory proteins and suppresses mature osteoblasts apoptosis. Intermittent administration of PTH increases bone mass but the mechanism of action are complex and incompletely understood. Cell Cycle and Apoptosis Regulatory Protein (CARP)-1 (aka CCAR1) is a novel transducer of signaling by diverse agents including cell growth and differentiation factors. To gain further insight into the molecular mechanism, we investigated involvement of CARP-1 in PTH signaling in osteoblasts. Immunostaining studies revealed presence of CARP-1 in osteoblasts and osteocytes, while a minimal to absent levels were noted in the chondrocytes of femora from 10 to 12-week old mice. Treatment of 7-day differentiated MC3T3-E1 clone-4 (MC-4) mouse osteoblastic cells and primary calvarial osteoblasts with PTH for 30min to 5h followed by Western blot analysis showed 2- to 3-fold down-regulation of CARP-1 protein expression in a dose- and time-dependent manner compared to the respective vehicle treated control cells. H-89, a Protein Kinase A (PKA) inhibitor, suppressed PTH action on CARP-1 protein expression indicating PKA-dependent mechanism. PMA, a Protein Kinase C (PKC) agonist, mimicked PTH action, and the PKC inhibitor, GF109203X, partially blocked PTH-dependent downregulation of CARP-1, implying involvement of PKC. U0126, a Mitogen-Activated Protein Kinase (MAPK) Kinase (MEK) inhibitor, failed to interfere with CARP-1 suppression by PTH. In contrast, SB203580, p38 inhibitor, attenuated PTH down-regulation of CARP-1 suggesting that PTH utilized an Extracellular Signal Regulated Kinase (ERK)-independent but p38 dependent pathway to regulate CARP-1 protein expression in osteoblasts. Immunofluorescence staining of differentiated osteoblasts further revealed nuclear to cytoplasmic translocation of CARP-1 protein following PTH treatment. Collectively, our studies identified CARP-1 for the first time in osteoblasts and suggest its potential role in PTH signaling and bone anabolic action.

ZYX-1, the unique zyxin protein of Caenorhabditis elegans, is involved in dystrophin-dependent muscle degeneration

In vertebrates, zyxin is a LIM-domain protein belonging to a family composed of seven members. We show that the nematode Caenorhabditis elegans has a unique zyxin-like protein, ZYX-1, which is the orthologue of the vertebrate zyxin subfamily composed of zyxin, migfilin, TRIP6, and LPP. The ZYX-1 protein is expressed in the striated body-wall muscles and localizes at dense bodies/Z-discs and M-lines, as well as in the nucleus. In yeast two-hybrid assays ZYX-1 interacts with several known dense body and M-line proteins, including DEB-1 (vinculin) and ATN-1 (α-actinin). ZYX-1 is mainly localized in the middle region of the dense body/Z-disk, overlapping the apical and basal regions containing, respectively, ATN-1 and DEB-1. The localization and dynamics of ZYX-1 at dense bodies depend on the presence of ATN-1. Fluorescence recovery after photobleaching experiments revealed a high mobility of the ZYX-1 protein within muscle cells, in particular at dense bodies and M-lines, indicating a peripheral and dynamic association of ZYX-1 at these muscle adhesion structures. A portion of the ZYX-1 protein shuttles from the cytoplasm into the nucleus, suggesting a role for ZYX-1 in signal transduction. We provide evidence that the zyx-1 gene encodes two different isoforms, ZYX-1a and ZYX-1b, which exhibit different roles in dystrophin-dependent muscle degeneration occurring in a C. elegans model of Duchenne muscular dystrophy.

Zyxin is a novel target for β-amyloid peptide: characterization of its role in Alzheimer's pathogenesis

Zyxin is an adaptor protein recently identified as a novel regulator of the homeodomain-interacting protein kinase 2 (HIPK2)-p53 signaling in response to DNA damage. We recently reported an altered conformational state of p53 in tissues from patients with Alzheimer 's disease (AD), because of a deregulation of HIPK2 activity, leading to an impaired and dysfunctional response to stressors. Here, we examined the molecular mechanisms underlying the deregulation of HIPK2 activity in two cellular models, HEK-293 cells and SH-SY5Y neuroblastoma cells differentiated with retinoic acid over-expressing the amyloid precursor protein, focusing on the evidence that zyxin expression is important to maintain HIPK2 protein stability. We demonstrated that both beta-amyloid (Aβ) 1-40 and 1-42 induce zyxin deregulation, thus affecting the transcriptional repressor activity of HIPK2 onto its target promoter, metallothionein 2A, which is in turn responsible for the induction of an altered conformational state of p53. We demonstrate for the first time that zyxin is a novel target of Aβ activities in AD. These results may help the studies on the pathogenesis of AD, through the fine dissection of events related to beta-amyloid activities.

Tandem zyxin LIM sequences do not enhance force sensitive accumulation

The ability to sense mechanical forces is vital to cell physiology. Yet, the molecular basis of mechano-signaling remains unclear. Previous studies have shown that zyxin, a focal adhesion protein, is recruited at force-bearing sites on the actin cytoskeleton and, therefore, identifying zyxin as a mechano-sensing protein candidate. Furthermore, zyxin accumulation at force-bearing sites requires the LIM domain located at the C-terminus of zyxin. The zyxin LIM domain consists of three LIM motifs, each containing two zinc-binding sites. Since individual LIM motifs do not accumulate at focal adhesions or force-bearing sites, we hypothesize that multiple zyxin LIM domains increase force sensitivity. Using a miniature force sensor and GFP-tagged LIM variants, we quantified the relationship between single, tandem dimer and trimer LIM protein localization and traction forces. While the presence of extra LIM domains affected VASP recruitment to focal adhesions, force sensitivity was not enhanced over the single LIM domain. Therefore, zyxin force sensitivity is optimal with a single LIM domain, while additional LIM domains fail to enhance force sensitivity.

Stretch-induced actin remodeling requires targeting of zyxin to stress fibers and recruitment of actin regulators

Mechanical stimulation induces zyxin-dependent actin cytoskeletal reinforcement. Stretch induces MAPK activation, zyxin phosphorylation, and recruitment to actin stress fibers, independent of p130Cas. Zyxin's C-terminal LIM domains are required for stretch-induced targeting to stress fibers, and zyxin's N-terminus is necessary for actin remodeling.

Reinforcement of actin stress fibers in response to mechanical stimulation depends on a posttranslational mechanism that requires the LIM protein zyxin. The C-terminal LIM region of zyxin directs the force-sensitive accumulation of zyxin on actin stress fibers. The N-terminal region of zyxin promotes actin reinforcement even when Rho kinase is inhibited. The mechanosensitive integrin effector p130Cas binds zyxin but is not required for mitogen-activated protein kinase–dependent zyxin phosphorylation or stress fiber remodeling in cells exposed to uniaxial cyclic stretch. α-Actinin and Ena/VASP proteins bind to the stress fiber reinforcement domain of zyxin. Mutation of their docking sites reveals that zyxin is required for recruitment of both groups of proteins to regions of stress fiber remodeling. Zyxin-null cells reconstituted with zyxin variants that lack either α-actinin or Ena/VASP-binding capacity display compromised response to mechanical stimulation. Our findings define a bipartite mechanism for stretch-induced actin remodeling that involves mechanosensitive targeting of zyxin to actin stress fibers and localized recruitment of actin regulatory machinery.

Defining the role of TRIP6 in cell physiology and cancer

Integrating signals from the ECM (extracellular matrix) via the cell surface into the nucleus is an essential feature of multicellular life and often malfunctions in cancer. To date many signal transducers known as shuttle proteins have been identified that act as both: a cytoskeletal and a signalling protein. Here, we highlight the interesting member of the Zyxin family TRIP6 [thyroid receptor interactor protein 6; also designated ZRP-1 (zyxin-related protein 1)] and review current literature to define its role in cell physiology and cancer. TRIP6 is a versatile scaffolding protein at FAs (focal adhesions) involved in cytoskeletal organization, coordinated cell migration and tissue invasion. Via its LIM and TDC domains TRIP6 interacts with different components of the LPA (lysophosphatidic acid), NF-κB (nuclear factor κB), glucocorticoid and AMPK (AMP-activated protein kinase) signalling pathway and thereby modulates their activity. Within the nucleus TRIP6 acts as a transcriptional cofactor regulating the transcriptional responses of these pathways. Moreover, intranuclear TRIP6 associates with proteins ensuring telomere protection and hence may contribute to genome stability. Accordingly, TRIP6 is engaged in key cellular processes such as cell proliferation, differentiation and survival. These diverse functions of TRIP6 are found to be dysregulated in various cancers and may have pleiotropic roles in tumour initiation, tumour growth and metastasis, which turn TRIP6 into an attractive candidate for cancer diagnosis and targeted therapy.

The LIM domain protein, CRIP2, promotes apoptosis in esophageal squamous cell carcinoma

The group 2 LIM domain protein, Cysteine-rich intestinal protein 2 (CRIP2) was found to play an important role in esophageal squamous cell carcinoma (ESCC) tumorigenesis. Subcellular fractionation studies show that CRIP2 is expressed in the nucleus. Real-time quantitative PCR shows CRIP2 expression is down-regulated in ESCC tissues and cell lines. Functional studies reveal that CRIP2 reduces colony formation, growth, and invasion abilities. Furthermore, over-expression of CRIP2 induces apoptosis through induction of active caspases 3 and 9 proteins. In conclusion, this study shows CRIP2 plays an important role in the development of ESCC.

Antagonists of anaphase-promoting complex (APC)-2-cell cycle and apoptosis regulatory protein (CARP)-1 interaction are novel regulators of cell growth and apoptosis

CARP-1/CCAR1, a perinuclear phosphoprotein, is a regulator of cell growth and apoptosis signaling. Although CARP-1 is a regulator of chemotherapy-dependent apoptosis, it is also a part of the NF-κB proteome and a co-activator of steroid/thyroid nuclear receptors as well as β-catenin signaling. Our yeast two-hybrid screen revealed CARP-1 binding with the anaphase-promoting complex/cyclosome E3 ubiquitin ligase component APC-2 protein. CARP-1 also binds with anaphase-promoting complex/cyclosome co-activators Cdc20 and Cdh1. Following mapping of the minimal epitopes involved in CARP-1 binding with APC-2, a fluorescence polarization assay was established that indicated a dissociation constant (K(d)) of 480 nm for CARP-1/APC-2 binding. Fluorescence polarization assay-based high throughput screening of a chemical library yielded several small molecule antagonists of CARP-1/APC-2 binding, termed CARP-1 functional mimetics. CFM-4 (1(2-chlorobenzyl)-5'-phenyl-3'H-spiro[indoline-3,2'-[1,3,4]thiadiazol]-2-one), a lead compound, binds with and stimulates CARP-1 expression. CFM-4 prevents CARP-1 binding with APC-2, causes G(2)M cell cycle arrest, and induces apoptosis with an IC(50) range of 10-15 μm. Apoptosis signaling by CFM-4 involves activation of caspase-8 and -9 and caspase-mediated ubiquitin-proteasome pathway-independent loss of cyclin B1 and Cdc20 proteins. Depletion of CARP-1, however, interferes with CFM-4-dependent cell growth inhibition, activation of caspases, and apoptosis. Because CFM-4 also suppresses growth of drug-resistant human breast cancer cells without affecting the growth of human breast epithelial MCF-10A cells, elevating CARP-1 by CFM-4 and consequent apoptosis could in principle be exploited to further elucidate, and perhaps effectively target, often deregulated cell cycle pathways in pathological conditions, including cancer.