Identification of Filamin A Mechanobinding Partner II: Fimbacin Is a Novel Actin Cross-Linking and Filamin A Binding Protein

LUZP1 Regulates Dendritic Spine Maturation and Synaptic Plasticity in the Hippocampal Dentate Gyrus of Mice

Leucine zipper protein 1 (LUZP1) functions in the maintenance and dynamics of the cytoskeleton by interacting with actin and microtubules. Deficiency or mutation of LUZP1 is associated with brain developmental disorders; however, its precise role in brain function remains unclear. We showed that LUZP1 localizes to actin and is highly expressed in CaMKIIα-expressing neurons within the mouse hippocampal dentate gyrus. Depletion of LUZP1 impedes dendritic spine maturation, which is characterized by excess immature filopodia and loss of mature mushroom spines both in vitro and in vivo. LUZP1 knockdown reduces spontaneous electrical activity and synaptic plasticity in hippocampal neurons. Conditional deletion of LUZP1 in CaMKIIα-expressing neurons causes impaired learning and memory behavior in mice of both sexes. Mechanistically, LUZP1 control dendritic maturation by directly interacting with filamin A and modulating the Rac1-PAK1 signaling pathway. These findings shed light on the role of LUZP1 in regulating synaptic plasticity and brain function.

Modulation of Gene Expression by Substrate Stiffness via Ubiquitination of Histone H2B by Ubiquitin-Conjugating Enzyme E2A/B

Animal cells adapt to the stiffness of their environment through mechanotransduction, a process in which mechanical signals are converted into biochemical responses, influencing key cellular processes such as growth and differentiation. We identified ubiquitin-conjugating enzymes E2 A and B (UBE2A/B) as mechanosensitive proteins that translocate between the nucleus and cytoplasm depending on force and substrate stiffness. Here, we hypothesized that UBE2A/B nuclear translocation on stiff substrates triggers gene expression via UBE2A/B-mediated ubiquitination of histone H2B lysine 120 (H2BK120). Chromatin immunoprecipitation sequencing (ChIP-seq) revealed distinct DNA fragments bound to monoubiquitinated H2B in cells cultured on soft (0.2 kPa) versus stiff (64 kPa) substrates. We identified 2245 gene regions binding to ubiquitinated histones on stiff substrates and 294 on soft substrates and further integrated RNA-seq and UBE2A/B knockdown data to pinpoint 179 stiff-specific and 18 soft-specific genes. Among these, filamin C (FLNC), leucine zipper protein 1 (LUZP1), and glutamate-rich WD repeat-containing protein 1 (GRWD1) showed higher expression on stiff substrates, with GRWD1 known for its role in cancer progression through cell cycle and gene regulation. These findings highlight how substrate stiffness modulates gene expression via UBE2A/B-mediated H2B ubiquitination.

Death-associated protein kinase 3 modulates migration and invasion of triple-negative breast cancer cells

Sixteen patient-derived xenografts (PDXs) were analyzed using a mass spectrometry (MS)-based kinase inhibitor pull-down assay (KIPA), leading to the observation that death-associated protein kinase 3 (DAPK3) is significantly and specifically overexpressed in the triple-negative breast cancer (TNBC) models. Validation studies confirmed enrichment of DAPK3 protein, in both TNBC cell lines and tumors, independent of mRNA levels. Genomic knockout of DAPK3 in TNBC cell lines inhibited in vitro migration and invasion, along with down-regulation of an epithelial-mesenchymal transition (EMT) signature, which was confirmed in vivo. The kinase and leucine-zipper domains within DAPK3 were shown by a mutational analysis to be essential for functionality. Notably, DAPK3 was found to inhibit the levels of desmoplakin (DSP), a crucial component of the desmosome complex, thereby explaining the observed migration and invasion effects. Further exploration with immunoprecipitation-mass spectrometry (IP-MS) identified that leucine-zipper protein 1 (LUZP1) is a preferential binding partner of DAPK3. LUZP1 engages in a leucine-zipper domain-mediated interaction that protects DAPK3 from proteasomal degradation. Thus, the DAPK3/LUZP1 heterodimer emerges as a newly discovered regulator of EMT/desmosome components that promote TNBC cell migration.

Regulation of Precise DNA Repair by Nuclear Actin Polymerization: A Chance for Improving Gene Therapy?

Although more difficult to detect than in the cytoplasm, it is now clear that actin polymerization occurs in the nucleus and that it plays a role in the specific processes of the nucleus such as transcription, replication, and DNA repair. A number of studies suggest that nuclear actin polymerization is promoting precise DNA repair by homologous recombination, which could potentially be of help for precise genome editing and gene therapy. This review summarizes the findings and describes the challenges and chances in the field.

LUZP1 regulates the maturation of contractile actomyosin bundles

Contractile actomyosin bundles play crucial roles in various physiological processes, including cell migration, morphogenesis, and muscle contraction. The intricate assembly of actomyosin bundles involves the precise alignment and fusion of myosin II filaments, yet the underlying mechanisms and factors involved in these processes remain elusive. Our study reveals that LUZP1 plays a central role in orchestrating the maturation of thick actomyosin bundles. Loss of LUZP1 caused abnormal cell morphogenesis, migration, and the ability to exert forces on the environment. Importantly, knockout of LUZP1 results in significant defects in the concatenation and persistent association of myosin II filaments, severely impairing the assembly of myosin II stacks. The disruption of these processes in LUZP1 knockout cells provides mechanistic insights into the defective assembly of thick ventral stress fibers and the associated cellular contractility abnormalities. Overall, these results significantly contribute to our understanding of the molecular mechanism involved in actomyosin bundle formation and highlight the essential role of LUZP1 in this process.

Leucine zipper protein 1 (LUZP1) regulates the constriction velocity of the contractile ring during cytokinesis

There has been a great deal of research on cell division and its mechanisms; however, its processes still have many unknowns. To find novel proteins that regulate cell division, we performed the screening using siRNAs and/or the expression plasmid of the target genes and identified leucine zipper protein 1 (LUZP1). Recent studies have shown that LUZP1 interacts with various proteins and stabilizes the actin cytoskeleton; however, the function of LUZP1 in mitosis is not known. In this study, we found that LUZP1 colocalized with the chromosomal passenger complex (CPC) at the centromere in metaphase and at the central spindle in anaphase and that these LUZP1 localizations were regulated by CPC activity and kinesin family member 20A (KIF20A). Mass spectrometry analysis identified that LUZP1 interacted with death-associated protein kinase 3 (DAPK3), one regulator of the cleavage furrow ingression in cytokinesis. In addition, we found that LUZP1 also interacted with myosin light chain 9 (MYL9), a substrate of DAPK3, and comprehensively inhibited MYL9 phosphorylation by DAPK3. In line with a known role for MYL9 in the actin-myosin contraction, LUZP1 suppression accelerated the constriction velocity at the division plane in our time-lapse analysis. Our study indicates that LUZP1 is a novel regulator for cytokinesis that regulates the constriction velocity of the contractile ring.

The Role of Mechanotransduction in Contact Inhibition of Locomotion and Proliferation

Contact inhibition (CI) represents a crucial tumor-suppressive mechanism responsible for controlling the unbridled growth of cells, thus preventing the formation of cancerous tissues. CI can be further categorized into two distinct yet interrelated components: CI of locomotion (CIL) and CI of proliferation (CIP). These two components of CI have historically been viewed as separate processes, but emerging research suggests that they may be regulated by both distinct and shared pathways. Specifically, recent studies have indicated that both CIP and CIL utilize mechanotransduction pathways, a process that involves cells sensing and responding to mechanical forces. This review article describes the role of mechanotransduction in CI, shedding light on how mechanical forces regulate CIL and CIP. Emphasis is placed on filamin A (FLNA)-mediated mechanotransduction, elucidating how FLNA senses mechanical forces and translates them into crucial biochemical signals that regulate cell locomotion and proliferation. In addition to FLNA, trans-acting factors (TAFs), which are proteins or regulatory RNAs capable of directly or indirectly binding to specific DNA sequences in distant genes to regulate gene expression, emerge as sensitive players in both the mechanotransduction and signaling pathways of CI. This article presents methods for identifying these TAF proteins and profiling the associated changes in chromatin structure, offering valuable insights into CI and other biological functions mediated by mechanotransduction. Finally, it addresses unanswered research questions in these fields and delineates their possible future directions.

A Novel Approach to Orthotopic Hepatocyte Transplantation Engineered With Liver Hydrogel for Fibrotic Livers, Enhancing Cell-Cell Interaction and Angiogenesis

Hepatocyte transplantation (HCT) is a potential bridging therapy or an alternative to liver transplantation. Conventionally, single-cell hepatocytes are injected via the portal vein. This strategy, however, has yet to overcome poor cell engraftment and function. Therefore, we developed an orthotopic HCT method using a liver-derived extracellular matrix (L-ECM) gel. PXB cells (flesh mature human hepatocytes) were dispersed into the hydrogel solution in vitro, and the gel solution was immediately gelated in 37°C incubators to investigate the affinity between mature human hepatocyte and the L-ECM gel. During the 3-day cultivation in hepatocyte medium, PXB cells formed cell aggregates via cell-cell interactions. Quantitative analysis revealed human albumin production in culture supernatants. For the in vivo assay, PXB cells were encapsulated in the L-ECM gel and transplanted between the liver lobes of normal rats. Pathologically, the L-ECM gel was localized at the transplant site and retained PXB cells. Cell survival and hepatic function marker expression were verified in another rat model wherein thioacetamide was administered to induce liver fibrosis. Moreover, cell-cell interactions and angiogenesis were enhanced in the L-ECM gel compared with that in the collagen gel. Our results indicate that L-ECM gels can help engraft transplanted hepatocytes and express hepatic function as a scaffold for cell transplantation.

Identification of Filamin A Mechanobinding Partner III: SAV1 Specifically Interacts with Filamin A Mechanosensitive Domain 21

Filamin A (FLNA) cross-links actin filaments and mediates mechanotransduction by force-induced conformational changes of its domains. FLNA's mechanosensitive immunoglobulin-like repeats (R) interact with each other to create cryptic binding sites, which can be exposed by physiologically relevant mechanical forces. Using the FLNA mechanosensing domains as an affinity ligand followed by stable isotope labeling by amino acids in cell culture (SILAC)-based proteomics, we recently identified smoothelin and fimbacin as FLNA mechanobinding proteins. Here, using the mechanosensing domain as an affinity ligand and two labeled amino acids, we identify salvador homologue 1 (SAV1), a component of the Hippo pathway kinase cascade, as a new FLNA mechanobinding partner. We demonstrate that SAV1 specifically interacts with the cryptic C-D cleft of FLNA R21 and map the FLNA-binding site on SAV1. We show that point mutations on the R21 C strand block the SAV1 interaction and find that SAV1 contains a FLNA-binding motif in the central region (¹¹⁶Phe-¹²⁴Val). Point mutations F116A and T118A (FT/AA) disrupt the interaction. A proximity ligation assay reveals that their interaction occurs in the cytosol in an actin polymerization-dependent manner. Although SAV1 is typically found in the cytosol, disrupting the interaction between SAV1 and FLNA causes SAV1 to diffuse to the nucleus and YAP1 to diffuse to the cytosol in an inverse relationship. These results suggest that FLNA mediates regulation of the Hippo pathway through actin polymerization-dependent interaction with SAV1.

The force-dependent filamin A-G3BP1 interaction regulates phase-separated stress granule formation

Filamin A (FLNA) is an actin crosslinking protein that mediates mechanotransduction. External and internal mechanical forces, through the actin cytoskeleton, can induce conformational changes of the FLNA molecule to expose cryptic binding sites for its binding partners. Here, we identified Ras GTPase-activating protein SH3 domain-binding protein 1 (G3BP1) as a new FLNA mechanobinding partner. Unlike other FLNA binding partners to the mechanosensing domain repeat 21 (R21), G3BP1 requires an additional neighboring repeat R22 to interact. We demonstrated that their interaction occurs in the cytosol of living cells in an actin polymerization-dependent manner. We also mapped the FLNA-binding site on G3BP1 and found that a F360A point mutation in the RNA recognition motif disrupts the interaction. RNA interfered with the FLNA-G3BP1 interaction, and FLNA did not localize in RNA-rich stress granules (SGs). Disruption of the interaction was sufficient to promote phase-separated SG formation, and arsenite treatment further stimulated the formation of SGs. Taken together, these data identify G3BP1 as a new mechanobinding protein that interacts with the FLNA mechanosensing domain R21 and suggest that SG formation is partially regulated by mechanical force.

Interaction of LARP4 to filamin A mechanosensing domain regulates cell migrations

Filamin A (FLNA) is an actin cross-linking protein that mediates mechanotransduction. Force-dependent conformational changes of FLNA molecule expose cryptic binding site of FLNA, allowing interaction with partners such as integrin, smoothelin, and fimbacin. Here, we identified La-related protein 4 (LARP4) as a new FLNA mechanobinding partner. LARP4 specifically interacts with the cleft formed by C and D strands of immunoglobulin-like repeat 21 (R21) which is blocked by A strand of R20 without force. We validated the interaction between LARP4 and FLNA R21 both in vivo and in vitro. We also determined the critical amino acid that is responsible for the interaction and generated the non-FLNA-binding mutant LARP4 (F277A in human: F273A in mouse Larp4) that disrupts the interaction. Fluorescence recovery after photobleaching (FRAP) of GFP-labeled LARP4 in living cells demonstrated that mutant LARP4 diffuses faster than WT LARP4. Proximity ligation assay (PLA) also confirmed their interaction and disruption of actin polymerization diminishes the interaction. Data mining of RNAseq analysis of LARP4 knockdown (KD) HEK293T cells suggested that LARP4 is involved in morphogenesis and cell motility. Consistent with this prediction, we found that KD of LARP4 increases cell migration speed and expression of the F277A mutant LARP4 in LARP4-KD cells also leads to a higher cell migration speed compared to WT LARP4. These results demonstrated that the LARP4 interaction with FLNA regulates cell migration.

LUZP1: A new player in the actin-microtubule cross-talk

LUZP1 (leucine zipper protein 1) was first described as being important for embryonic development. Luzp1 null mice present defective neural tube closure and cardiovascular problems, which cause perinatal death. Since then, LUZP1 has also been implicated in the etiology of diseases like the 1p36 and the Townes-Brocks syndromes, and the molecular mechanisms involving this protein started being uncovered. Proteomics studies placed LUZP1 in the interactomes of the centrosome-cilium interface, centriolar satellites, and midbody. Concordantly, LUZP1 is an actin and microtubule-associated protein, which localizes to the centrosome, the basal body of primary cilia, the midbody, actin filaments and cellular junctions. LUZP1, like its interactor EPLIN, is an actin-stabilizing protein and a negative regulator of primary cilia formation. Moreover, through the regulation of actin, LUZP1 has been implicated in the regulation of cell cycle progression, cell migration and epithelial cell apical constriction. This review discusses the latest findings concerning LUZP1 molecular functions and implications in disease development.

The Extracellular Matrix Stiffening: A Trigger of Prostate Cancer Progression and Castration Resistance?

Despite advancements made in diagnosis and treatment, prostate cancer remains the second most diagnosed cancer among men worldwide in 2020, and the first in North America and Europe. Patients with localized disease usually respond well to first-line treatments, however, up to 30% develop castration-resistant prostate cancer (CRPC), which is often metastatic, making this stage of the disease incurable and ultimately fatal. Over the last years, interest has grown into the extracellular matrix (ECM) stiffening as an important mediator of diseases, including cancers. While this process is increasingly well-characterized in breast cancer, a similar in-depth look at ECM stiffening remains lacking for prostate cancer. In this review, we scrutinize the current state of literature regarding ECM stiffening in prostate cancer and its potential association with disease progression and castration resistance.

Actin-Associated Proteins and Small Molecules Targeting the Actin Cytoskeleton

Actin-associated proteins (AAPs) act on monomeric globular actin (G-actin) and polymerized filamentous actin (F-actin) to regulate their dynamics and architectures which ultimately control cell movement, shape change, division; organelle localization and trafficking. Actin-binding proteins (ABPs) are a subset of AAPs. Since actin was discovered as a myosin-activating protein (hence named actin) in 1942, the protein has also been found to be expressed in non-muscle cells, and numerous AAPs continue to be discovered. This review article lists all of the AAPs discovered so far while also allowing readers to sort the list based on the names, sizes, functions, related human diseases, and the dates of discovery. The list also contains links to the UniProt and Protein Atlas databases for accessing further, related details such as protein structures, associated proteins, subcellular localization, the expression levels in cells and tissues, mutations, and pathology. Because the actin cytoskeleton is involved in many pathological processes such as tumorigenesis, invasion, and developmental diseases, small molecules that target actin and AAPs which hold potential to treat these diseases are also listed.

Epithelial Protein Lost in Neoplasm, EPLIN, the Cellular and Molecular Prospects in Cancers

Epithelial Protein Lost In Neoplasm (EPLIN), also known as LIMA1 (LIM Domain And Actin Binding 1), was first discovered as a protein differentially expressed in normal and cancerous cell lines. It is now known to be key to the progression and metastasis of certain solid tumours. Despite a slow pace in understanding the biological role in cells and body systems, as well as its clinical implications in the early years since its discovery, recent years have witnessed a rapid progress in understanding the mechanisms of this protein in cells, diseases and indeed the body. EPLIN has drawn more attention over the past few years with its roles expanding from cell migration and cytoskeletal dynamics, to cell cycle, gene regulation, angiogenesis/lymphangiogenesis and lipid metabolism. This concise review summarises and discusses the recent progress in understanding EPLIN in biological processes and its implications in cancer.

Chromatin remodeling factor CECR2 forms tissue-specific complexes with CCAR2 and LUZP1

Chromatin remodeling complexes alter chromatin structure to control access to DNA and therefore control cellular processes such as transcription, DNA replication, and DNA repair. CECR2 is a chromatin remodeling factor that plays an important role in neural tube closure and reproduction. Loss-of-function mutations in Cecr2 result primarily in the perinatal lethal neural tube defect exencephaly, with non-penetrant mice that survive to adulthood exhibiting subfertility. CECR2 forms a complex with ISWI proteins SMARCA5 and/or SMARCA1, but further information on the structure and function of the complex is not known. We therefore have identified candidate components of the CECR2-containing remodeling factor (CERF) complex in embryonic stem (ES) cells through mass spectroscopy. Both SMARCA5 and SMARCA1 were confirmed to be present in CERF complexes in ES cells and testis. However, novel proteins CCAR2 and LUZP1 are CERF components in ES cells but not testis. This tissue specificity in mice suggests these complexes may also have functional differences. Furthermore, LUZP1, loss of which is also associated with exencephaly, appears to play a role in stabilizing the CERF complex in ES cells. Keywords: CECR2, LUZP1, CCAR2, Chromatin remodeling factor, Neural tube defects.

The Overexpression of NMHC IIA Promoted Invasion and Metastasis of Nasopharyngeal Carcinoma Cells

Background: Nasopharyngeal carcinoma (NPC) is a kind of head and neck squamous cell carcinoma (HNSCC) with a strong tendency for metastasis and recurrence. Non-muscle myosin heavy chain IIA (NMHC IIA) plays important roles in recurrence and metastasis of cancers. However, the function and mechanism of NMHC IIA expression in NPC remain unclear. Methods: A receiver operating characteristic (ROC) curve was constructed for 141 specimens of HNSCC tissues and 44 control samples from The Cancer Genome Atlas (TCGA) database. Co-expressed genes with MYH9 were identified using LinkedOmics. Transcription factors (TFs) and miRNA regulation network were constructed using Networkanalyst. The migration and invasion ability of nasopharyngeal carcinoma cells were evaluated by in vitro migration and matrigel invasion assays, respectively. Results: The public microarray results showed that MYH9 expression levels were upregulated in HNSCC tissues compared with the matched adjacent normal tissues in this study (p<0.0001). The AUC of MYH9 reached up to 0.8303 at a cutoff value of 175.2, with a sensitivity and specificity of 70.21% and 86.36%, respectively. MYH9 expression was increased in lymph node metastasis HNSCC tumors compared with that in tumors without lymph node metastasis (p<0.05) and showed a strong positive association with expression of FLNA. High MYH9 and FLNA expression were related with poorer overall survival in HNSCC. MYH9 with positively associated genes regulated focal adhesion, cell-substrate junction assembly and cell morphogenesis were involved in differentiation using GO and KEGG analysis. MYH9 was correlated with a network of TFs including SP1, SRF, JUN and FOS in HNSCC. The suppression of endogenous NMHC IIA decreased cellular migration and invasion in HNE1 cells and reduced the expression of phosphorylation of EGFR, AKT and ERK. The over-expression of NMHC IIA increased cellular migration and invasion in COS-7 cells and increased the expression of phosphorylation of EGFR, AKT and ERK. Conclusion: Expression of NMHC IIA mRNA was higher in HNSCC than in the adjacent normal tissues. NMHC IIA expression was increased in lymph node metastasis HNSCC tumors compared with tumors without lymph node metastasis. High MYH9 was association with poorer overall survival in HNSCC. NMHC IIA expression increased the invasion and metastasis abilities of the nasopharyngeal cancer cell line in vitro by augmenting the expression of phosphorylation of EGFR, AKT and ERK. These findings will be beneficial for providing an effectively therapeutic strategy for NPC.

LUZP1 Controls Cell Division, Migration and Invasion Through Regulation of the Actin Cytoskeleton

LUZP1 is a centrosomal and actin cytoskeleton-localizing protein that regulates both ciliogenesis and actin filament bundling. As the cytoskeleton and cilia are implicated in metastasis and tumor suppression, we examined roles for LUZP1 in the context of cancer. Here we show that LUZP1 exhibits frequent genomic aberrations in cancer, with a predominance of gene deletions. Furthermore, we demonstrate that CRISPR/Cas9-mediated loss of Luzp1 in mouse fibroblasts promotes cell migration and invasion features, reduces cell viability, and increases cell apoptosis, centriole numbers, and nuclear size while altering the actin cytoskeleton. Loss of Luzp1 also induced changes to ACTR3 (Actin Related Protein 3, also known as ARP3) and phospho-cofilin ratios, suggesting regulatory roles in actin polymerization, beyond its role in filament bundling. Our results point to an unprecedented role for LUZP1 in the regulation of cancer features through the control of actin cytoskeleton.

LUZP1 and the tumor suppressor EPLIN modulate actin stability to restrict primary cilia formation

Cilia and flagella are microtubule-based cellular projections with important sensory and motility functions. Their absence or malfunction is associated with a growing number of human diseases collectively referred to as ciliopathies. However, the fundamental mechanisms underpinning cilia biogenesis and functions remain only partly understood. Here, we show that depleting LUZP1 or its interacting protein, EPLIN, increases the levels of MyosinVa at the centrosome and primary cilia formation. We further show that LUZP1 localizes to both actin filaments and the centrosome/basal body. Like EPLIN, LUZP1 is an actin-stabilizing protein that regulates actin dynamics, at least in part, by mobilizing ARP2 to the centrosomes. Both LUZP1 and EPLIN interact with known ciliogenesis and cilia-length regulators and as such represent novel players in actin-dependent centrosome to basal body conversion. Ciliogenesis deregulation caused by LUZP1 or EPLIN loss may thus contribute to the pathology of their associated disease states.

The function and pathogenic mechanism of filamin A

Filamin A(FLNa) is an actin-binding protein, which participates in the formation of the cytoskeleton, anchors a variety of proteins in the cytoskeleton and regulates cell adhesion and migration. It is involved in signal transduction, cell proliferation and differentiation, pseudopodia formation, vesicle transport, tumor resistance and genetic diseases by binding with interacting proteins. In order to fully elucidate the structure, function and pathogenesis of FLNa, we summarized all substances which directly or indirectly act on FLNa so far, upstream and downstream targets which having effect on it, signaling pathways and their functions. It also recorded the expression and effect of FLNa in different diseases, including hereditary disease and tumors.

A microtubule-LUZP1 association around tight junction promotes epithelial cell apical constriction

Apical constriction is critical for epithelial morphogenesis, including neural tube formation. Vertebrate apical constriction is induced by di-phosphorylated myosin light chain (ppMLC)-driven contraction of actomyosin-based circumferential rings (CRs), also known as perijunctional actomyosin rings, around apical junctional complexes (AJCs), mainly consisting of tight junctions (TJs) and adherens junctions (AJs). Here, we revealed a ppMLC-triggered system at TJ-associated CRs for vertebrate apical constriction involving microtubules, LUZP1, and myosin phosphatase. We first identified LUZP1 via unbiased screening of microtubule-associated proteins in the AJC-enriched fraction. In cultured epithelial cells, LUZP1 was found localized at TJ-, but not at AJ-, associated CRs, and LUZP1 knockout resulted in apical constriction defects with a significant reduction in ppMLC levels within CRs. A series of assays revealed that ppMLC promotes the recruitment of LUZP1 to TJ-associated CRs, where LUZP1 spatiotemporally inhibits myosin phosphatase in a microtubule-facilitated manner. Our results uncovered a hitherto unknown microtubule-LUZP1 association at TJ-associated CRs that inhibits myosin phosphatase, contributing significantly to the understanding of vertebrate apical constriction.

Molecular Tuning of Filamin A Activities in the Context of Adhesion and Migration

The dynamic organization of actin cytoskeleton meshworks relies on multiple actin-binding proteins endowed with distinct actin-remodeling activities. Filamin A is a large multi-domain scaffolding protein that cross-links actin filaments with orthogonal orientation in response to various stimuli. As such it plays key roles in the modulation of cell shape, cell motility, and differentiation throughout development and adult life. The essentiality and complexity of Filamin A is highlighted by mutations that lead to a variety of severe human disorders affecting multiple organs. One of the most conserved activity of Filamin A is to bridge the actin cytoskeleton to integrins, thereby maintaining the later in an inactive state. We here review the numerous mechanisms cells have developed to adjust Filamin A content and activity and focus on the function of Filamin A as a gatekeeper to integrin activation and associated adhesion and motility.

Primary Cilia, Ciliogenesis and the Actin Cytoskeleton: A Little Less Resorption, A Little More Actin Please

Primary cilia are microtubule-based organelles that extend from the apical surface of most mammalian cells, forming when the basal body (derived from the mother centriole) docks at the apical cell membrane. They act as universal cellular "antennae" in vertebrates that receive and integrate mechanical and chemical signals from the extracellular environment, serving diverse roles in chemo-, mechano- and photo-sensation that control developmental signaling, cell polarity and cell proliferation. Mutations in ciliary genes cause a major group of inherited developmental disorders called ciliopathies. There are very few preventative treatments or new therapeutic interventions that modify disease progression or the long-term outlook of patients with these conditions. Recent work has identified at least four distinct but interrelated cellular processes that regulate cilia formation and maintenance, comprising the cell cycle, cellular proteostasis, signaling pathways and structural influences of the actin cytoskeleton. The actin cytoskeleton is composed of microfilaments that are formed from filamentous (F) polymers of globular G-actin subunits. Actin filaments are organized into bundles and networks, and are attached to the cell membrane, by diverse cross-linking proteins. During cell migration, actin filament bundles form either radially at the leading edge or as axial stress fibers. Early studies demonstrated that loss-of-function mutations in ciliopathy genes increased stress fiber formation and impaired ciliogenesis whereas pharmacological inhibition of actin polymerization promoted ciliogenesis. These studies suggest that polymerization of the actin cytoskeleton, F-actin branching and the formation of stress fibers all inhibit primary cilium formation, whereas depolymerization or depletion of actin enhance ciliogenesis. Here, we review the mechanistic basis for these effects on ciliogenesis, which comprise several cellular processes acting in concert at different timescales. Actin polymerization is both a physical barrier to both cilia-targeted vesicle transport and to the membrane remodeling required for ciliogenesis. In contrast, actin may cause cilia loss by localizing disassembly factors at the ciliary base, and F-actin branching may itself activate the YAP/TAZ pathway to promote cilia disassembly. The fundamental role of actin polymerization in the control of ciliogenesis may present potential new targets for disease-modifying therapeutic approaches in treating ciliopathies.

Mechanotransduction, nanotechnology, and nanomedicine

Mechanotransduction, a conversion of mechanical forces into biochemical signals, is essential for human development and physiology. It is observable at all levels ranging from the whole body, organs, tissues, organelles down to molecules. Dysregulation results in various diseases such as muscular dystrophies, hypertension-induced vascular and cardiac hypertrophy, altered bone repair and cell deaths. Since mechanotransduction occurs at nanoscale, nanosciences and applied nanotechnology are powerful for studying molecular mechanisms and pathways of mechanotransduction. Atomic force microscopy, magnetic and optical tweezers are commonly used for force measurement and manipulation at the single molecular level. Force is also used to control cells, topographically and mechanically by specific types of nano materials for tissue engineering. Mechanotransduction research will become increasingly important as a sub-discipline under nanomedicine. Here we review nanotechnology approaches using force measurements and manipulations at the molecular and cellular levels during mechanotransduction, which has been increasingly play important role in the advancement of nanomedicine.

LUZP1, a novel regulator of primary cilia and the actin cytoskeleton, is a contributing factor in Townes-Brocks Syndrome

Primary cilia are sensory organelles crucial for cell signaling during development and organ homeostasis. Cilia arise from centrosomes and their formation and function is governed by numerous factors. Through our studies on Townes-Brocks Syndrome (TBS), a rare disease linked to abnormal cilia formation in human fibroblasts, we uncovered the leucine-zipper protein LUZP1 as an interactor of truncated SALL1, a dominantly-acting protein causing the disease. Using TurboID proximity labeling and pulldowns, we show that LUZP1 associates with factors linked to centrosome and actin filaments. Here, we show that LUZP1 is a cilia regulator. It localizes around the centrioles and to actin cytoskeleton. Loss of LUZP1 reduces F-actin levels, facilitates ciliogenesis and alters Sonic Hedgehog signaling, pointing to a key role in cytoskeleton-cilia interdependency. Truncated SALL1 increases the ubiquitin proteasome-mediated degradation of LUZP1. Together with other factors, alterations in LUZP1 may be contributing to TBS etiology.

Structure and Function of Filamin C in the Muscle Z-Disc

Filamin C (FLNC) is one of three filamin proteins (Filamin A (FLNA), Filamin B (FLNB), and FLNC) that cross-link actin filaments and interact with numerous binding partners. FLNC consists of a N-terminal actin-binding domain followed by 24 immunoglobulin-like repeats with two intervening calpain-sensitive hinges separating R15 and R16 (hinge 1) and R23 and R24 (hinge-2). The FLNC subunit is dimerized through R24 and calpain cleaves off the dimerization domain to regulate mobility of the FLNC subunit. FLNC is localized in the Z-disc due to the unique insertion of 82 amino acid residues in repeat 20 and necessary for normal Z-disc formation that connect sarcomeres. Since phosphorylation of FLNC by PKC diminishes the calpain sensitivity, assembly, and disassembly of the Z-disc may be regulated by phosphorylation of FLNC. Mutations of FLNC result in cardiomyopathy and muscle weakness. Although this review will focus on the current understanding of FLNC structure and functions in muscle, we will also discuss other filamins because they share high sequence similarity and are better characterized. We will also discuss a possible role of FLNC as a mechanosensor during muscle contraction.

Proteomic Analysis of miR-195 and miR-497 Replacement Reveals Potential Candidates that Increase Sensitivity to Oxaliplatin in MSI/P53wt Colorectal Cancer Cells

Most patients with advanced colorectal cancer (CRC) eventually develop resistance to systemic combination therapy. miR-195-5p and miR-497-5p are downregulated in CRC tissues and associated with drug resistance. Sensitization to 5-FU, oxaliplatin, and irinotecan by transfection with miR-195-5p and miR-497-5p mimics was studied using cell viability and clonogenic assays in cell lines HCT116, RKO, DLD-1, and SW480. In addition, proteomic analysis of transfected cells was implemented to identify potential targets. Significantly altered proteins were subjected to STRING (protein-protein interaction networks) database analysis to study the potential mechanisms of drug resistance. Cell viability analysis of transfected cells revealed increased sensitivity to oxaliplatin in microsatellite instable (MSI)/P53 wild-type HCT116 and RKO cells. HCT116 transfected cells formed significantly fewer colonies when treated with oxaliplatin. In sensitized cells, proteomic analysis showed 158 and 202 proteins with significantly altered expression after transfection with miR-195-5p and miR-497-5p mimics respectively, of which CHUK and LUZP1 proved to be coinciding downregulated proteins. Resistance mechanisms of these proteins may be associated with nuclear factor kappa-B signaling and G1 cell-cycle arrest. In conclusion, miR-195-5p and miR-497-5p replacement enhanced sensitivity to oxaliplatin in treatment naïve MSI/P53 wild-type CRC cells. Proteomic analysis revealed potential miRNA targets associated with the cell-cycle which possibly bare a relation with chemotherapy sensitivity.