Actin-bundling Protein Research Articles

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 RasLET-60 overactivation, blister-like membrane protrusions and disorganized actin bundles were observed in the vm1 muscles. Moreover, RasLET-60 depletion diminished the defected actin-bundles in rsu-1 mutant. These results reveal the genetic interaction of RSU-1 and RasLET-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.

Transgelin-2 and phosphoregulation of the LIC2 subunit of dynein govern mitotic spindle orientation.

The molecular motor dynein is essential for mitotic spindle orientation, which defines the axis of cell division. The light intermediate chain subunits, LIC1 and LIC2, define biochemically and functionally distinct vertebrate dynein complexes, with LIC2-dynein playing a crucial role in ensuring spindle orientation. We reveal a novel, mitosis-specific interaction of LIC2-dynein with the cortical actin-bundling protein transgelin-2. Transgelin-2 is required for maintaining proper spindle length, equatorial metaphase chromosome alignment, spindle orientation and timely anaphase onset. We show that transgelin-2 stabilizes the cortical recruitment of LGN-NuMA, which together with dynein is required for spindle orientation. The opposing actions of transgelin-2 and LIC2-dynein maintain optimal cortical levels of LGN-NuMA. In addition, we show that the highly conserved serine 194 phosphorylation of LIC2 is required for proper spindle orientation, by maintaining mitotic centrosome integrity to ensure optimal astral microtubule nucleation. The work reveals two specific mechanisms through which LIC2-dynein regulates mitotic spindle orientation; namely, through a new interactor transgelin-2, which is required for engagement of LGN-NuMA with the actin cortex, and through mitotic phosphoregulation of LIC2 to control microtubule nucleation from the poles.This article has an associated First Person interview with the first author of the paper.

F-actin-bundling sites are conserved in proteins with villin-type headpiece domains.

Villin is a major actin-bundling protein that assembles the brush border of intestinal and renal epithelial cells. The villin “headpiece” domain and the actin-binding residues within it regulate its actin-bundling function. Substantial experimental and theoretical information about the three-dimensional structure of the isolated villin headpiece, including a description of the actin-binding residues within the headpiece, is available. Despite that, the actin-bundling site in the full-length (FL) villin protein remains unidentified. We used this existing villin headpiece nuclear magnetic resonance data and performed mutational analysis and functional assays to identify the actin-bundling site in FL human villin protein. By careful evaluation of these conserved actin-binding residues in human advillin protein, we demonstrate their functional significance in the over 30 proteins that contain a villin-type headpiece domain. Our study is the first that combines the available structural data on villin headpiece with functional assays to identify the actin-binding residues in FL villin that regulate its filament-bundling activity. Our findings could have wider implications for other actin-bundling proteins that contain a villin-type headpiece domain.

ILK silencing inhibits migration and invasion of more invasive glioblastoma cells by downregulating ROCK1 and Fascin-1.

Glioblastoma multiforme (GBM) is the most aggressive type of brain tumor and it is associated with poor survival. Integrin-linked kinase (ILK) is a serine/threonine protein pseudo-kinase that binds to the cytoplasmic domains of β1 and β3 integrins and has been previously shown to promote invasion and metastasis in many cancer types, including GBM. However, little is known regarding the exact molecular mechanism implicating ILK in GBM aggressiveness. In this study, we used two brain cell lines, the non-invasive neuroglioma H4 cells, and the highly invasive glioblastoma A172 cells, which express ILK in much higher levels than H4. We studied the effect of ILK silencing on the metastatic behavior of glioblastoma cells in vitro and elucidate the underlying molecular mechanism. We showed that siRNA-mediated silencing of ILK inhibits cell migration and invasion of the highly invasive A172 cells while it does not affect the migratory and invasive capacity of H4 cells. These data were also supported by respective changes in the expression of Rho-associated kinase 1 (ROCK1), fascin actin-bundling protein 1 (FSCN1), and matrix metalloproteinase 13 (MMP13), which are known to regulate cell migration and invasion. Our findings were further corroborated by analyzing the Cancer Genome Atlas Glioblastoma Multiforme (TCGA-GBM) dataset. We conclude that ILK promotes glioblastoma cell invasion through activation of ROCK1 and FSCN1 in vitro, providing a more exact molecular mechanism for its action.

Circular RNA circSATB2 promotes progression of non-small cell lung cancer cells

BackgroundLung cancer has high morbidity and mortality worldwide with non-small cell lung cancer (NSCLC) accounting for 85% of the cases. Therapies for lung cancer have relatively poor outcomes and further improvements are required. Circular RNAs have been reported to participate in the occurrence and progression of cancer. Information on the functions and mechanism of circRNAs in lung cancer is limited and needs more exploration.MethodsWe detected expression of genes and proteins by qPCR and western blot. Function of circSATB2 was investigated using RNA interference and overexpression assays. Location of circSATB2 was assessed by fluorescence in situ hybridization (FISH). Interaction of circSATB2, miR-326 and FSCN1 was confirmed by dual-luciferase reporter assay.ResultsData from the investigation showed that circSATB2 was highly expressed in NSCLC cells and tissues. circSATB2 positively regulated fascin homolog 1, actin-bundling protein 1 (FSCN1) expression via miR-326 in lung cancer cells. Furthermore, circSATB2 can be transferred by exosomes and promote the proliferation, migration and invasion of NSCLC cells, as well as induce abnormal proliferation in normal human bronchial epithelial cells. Also, circSATB2 was highly expressed in serumal exosomes from lung cancer patients with high sensitivity and specificity for clinical detection and was related to lung cancer metastasis.ConclusionscircSATB2 participated in the progression of NSCLC and was differentially expressed in lung cancer tissue and serumal exosomes. circSATB2 may be potential biomarker for the diagnosis of NSCLC.

Dynamin regulates the dynamics and mechanical strength of the actin cytoskeleton as a multifilament actin-bundling protein.

The dynamin GTPase is known to bundle actin filaments, but the underlying molecular mechanism and physiological relevance remain unclear. Our genetic analyses revealed a function of dynamin in propelling invasive membrane protrusions during myoblast fusion in vivo. Using biochemistry, total internal reflection fluorescence microscopy, electron microscopy and cryo-electron tomography, we show that dynamin bundles actin while forming a helical structure. At its full capacity, each dynamin helix captures 12-16 actin filaments on the outer rim of the helix. GTP hydrolysis by dynamin triggers disassembly of fully assembled dynamin helices, releasing free dynamin dimers/tetramers and facilitating Arp2/3-mediated branched actin polymerization. The assembly/disassembly cycles of dynamin promote continuous actin bundling to generate mechanically stiff actin super-bundles. Super-resolution and immunogold platinum replica electron microscopy revealed dynamin along actin bundles at the fusogenic synapse. These findings implicate dynamin as a unique multifilament actin-bundling protein that regulates the dynamics and mechanical strength of the actin cytoskeletal network.

Osteogenesis imperfecta mutations in plastin 3 lead to impaired calcium regulation of actin bundling

Mutations in actin-bundling protein plastin 3 (PLS3) emerged as a cause of congenital osteoporosis, but neither the role of PLS3 in bone development nor the mechanisms underlying PLS3-dependent osteoporosis are understood. Of the over 20 identified osteoporosis-linked PLS3 mutations, we investigated all five that are expected to produce full-length protein. One of the mutations distorted an actin-binding loop in the second actin-binding domain of PLS3 and abolished F-actin bundling as revealed by cryo-EM reconstruction and protein interaction assays. Surprisingly, the remaining four mutants fully retained F-actin bundling ability. However, they displayed defects in Ca2+ sensitivity: two of the mutants lost the ability to be inhibited by Ca2+, while the other two became hypersensitive to Ca2+. Each group of the mutants with similar biochemical properties showed highly characteristic cellular behavior. Wild-type PLS3 was distributed between lamellipodia and focal adhesions. In striking contrast, the Ca2+-hyposensitive mutants were not found at the leading edge but localized exclusively at focal adhesions/stress fibers, which displayed reinforced morphology. Consistently, the Ca2+-hypersensitive PLS3 mutants were restricted to lamellipodia, while chelation of Ca2+ caused their redistribution to focal adhesions. Finally, the bundling-deficient mutant failed to co-localize with any F-actin structures in cells despite a preserved F-actin binding through a non-mutation-bearing actin-binding domain. Our findings revealed that severe osteoporosis can be caused by a mutational disruption of the Ca2+-controlled PLS3’s cycling between adhesion complexes and the leading edge. Integration of the structural, biochemical, and cell biology insights enabled us to propose a molecular mechanism of plastin activity regulation by Ca2+.

FSCN1 as prognostic marker in borderline tumors of the ovary.

e18061 Background: Risk factors for invasive recurrence of borderline tumours (BOT) of the ovary are needed. The actin-bundling protein Fascin-1 (FSCN1) is involved in alteration of adhesion and cell motility and has been associated with invasion and metastasis in different cancers. Methods: We studied a retrospective cohort of 124 bordeline tumors of the ovary (BOT) with validated diagnosis by an independent pathologist for expression of FSCN1 as potential prognostic biomarker. Results: We found strong expression of the actin-bundling protein FSCN1 in 62 of these tumors. FSCN1 positive patients were slightly younger (46.9±2.2 vs. 53.3±2.3 years, P = 0.049). Expression of FSCN1 was more frequently detected in BOT with serous compared to mucinous histotype (58/78 [74.4%] vs. 3/41 [7.3%], p < 0.001), and in cases with micropapillary pattern (25/28 [89.3%] vs. 38/98 [38.8%], P < 0.001). In addition, a non significant trend was observed for more frequent expression of FSCN1 among cases with implants (8/10 [80.0%] vs. 55/116 [47.4%], P = 0.095). When we compared progression free survival of the patients we found numerical lower but not statistically significant PFS rates of 90.5±6.4% vs. 94.4±5.4% for 10 years, and 81.4±10.3% vs. 94.4±5.4% for 15 years, in BOT with FSCN1 expression compared to those tumors negative for FSCN1, respectively. Conclusions: Our analysis suggests an association of FSCN1 expression in BOT with micropapillary pattern and implants, which have been linked to inferior prognosis. Cases with FSCN1 expression in our cohort displayed numerical lower PFS rates prompting further studies of this marker.

The actin-bundling protein L-plastin regulates NLRP3 inflammasome activation in macrophages

Abstract In macrophages, inflammasome pathways induce IL-1β release and pyroptotic cell death to clear infections. For example, NLRP3 inflammasome activation in lung resident alveolar macrophages (AMs) is crucial in controlling pneumonia. We have found that mice lacking the actin-bundling protein L-plastin (LPL−/−) mice are highly susceptible to Streptococcus pnuemoniae lung infection and produce less IL-1β. LPL is also required for podosome formation. Podosomes are integrin-based sites of adhesion that anchor the actin cytoskeleton of AMs to the extracellular environment. As such, AMs can sense their mechanical environment via podosomes. We have found that AMs lacking LPL exhibit defective NLRP3 inflammasome activation in ex-vivo stimulation. Specifically, LPL is required for ASC oligomerization and downstream IL-1β processing after NLRP3 assembly. Since LPL also supports mechanosensitive integrin signaling, we hypothesized that LPL might link contact-based mechanosensation to inflammasome activation in macrophages. To test this hypothesis, we challenged LPL−/− mice with bleomycin, as bleomycin-induced lung injury and fibrosis is thought to be dependent upon NLRP3 activation. LPL−/− mice were resistant to bleomycin-induced lung injury, suggesting a previously unrecognized mechanosensitive mechanism regulating inflammasome activation in macrophages. We propose that the increased lung stiffness in fibrotic lung exerts mechanical stress on AMs and thus may contribute in inflammasome signaling. Increased understanding how mechanical signaling regulates may thus aid in developing therapies to treat lung pathologies i.e. acute respiratory distress syndrome (ARDS), COPD and lung fibrosis.

Fascin Activates β-Catenin Signaling and Promotes Breast Cancer Stem Cell Function Mainly Through Focal Adhesion Kinase (FAK): Relation With Disease Progression.

Cancer stem cells (CSCs), a rare population of tumor cells with high self-renewability potential, have gained increasing attention due to their contribution to chemoresistance and metastasis. We have previously demonstrated a critical role for the actin-bundling protein (fascin) in mediating breast cancer chemoresistance through activation of focal adhesion kinase (FAK). The latter is known to trigger the β-catenin signaling pathway. Whether fascin activation of FAK would ultimately trigger β-catenin signaling pathway has not been elucidated. Here, we assessed the effect of fascin manipulation in breast cancer cells on triggering β-catenin downstream targets and its dependence on FAK. Gain and loss of fascin expression showed its direct effect on the constitutive expression of β-catenin downstream targets and enhancement of self-renewability. In addition, fascin was essential for glycogen synthase kinase 3β inhibitor–mediated inducible expression and function of the β-catenin downstream targets. Importantly, fascin-mediated constitutive and inducible expression of β-catenin downstream targets, as well as its subsequent effect on CSC function, was at least partially FAK dependent. To assess the clinical relevance of the in vitro findings, we evaluated the consequence of fascin, FAK, and β-catenin downstream target coexpression on the outcome of breast cancer patient survival. Patients with coexpression of fascinhigh and FAKhigh or high β-catenin downstream targets showed the worst survival outcome, whereas in fascinlow, patient coexpression of FAKhigh or high β-catenin targets had less significant effect on the survival. Altogether, our data demonstrated the critical role of fascin-mediated β-catenin activation and its dependence on intact FAK signaling to promote breast CSC function. These findings suggest that targeting of fascin–FAK-β-catenin axis may provide a novel therapeutic approach for eradication of breast cancer from the root.

Functional Heterogeneity within the Developing Zebrafish Epicardium

SummaryThe epicardium is essential during cardiac development, homeostasis, and repair, and yet fundamental insights into its underlying cell biology, notably epicardium formation, lineage heterogeneity, and functional cross-talk with other cell types in the heart, are currently lacking. In this study, we investigated epicardial heterogeneity and the functional diversity of discrete epicardial subpopulations in the developing zebrafish heart. Single-cell RNA sequencing uncovered three epicardial subpopulations with specific genetic programs and distinctive spatial distribution. Perturbation of unique gene signatures uncovered specific functions associated with each subpopulation and established epicardial roles in cell adhesion, migration, and chemotaxis as a mechanism for recruitment of leukocytes into the heart. Understanding which mechanisms epicardial cells employ to establish a functional epicardium and how they communicate with other cardiovascular cell types during development will bring us closer to repairing cellular relationships that are disrupted during cardiovascular disease.

Investigation of promoter methylation of FSCN1 gene and FSCN1 protein expression in differentiated thyroid carcinomas.

FSCN1 gene encodes an actin-bundling protein, FSCN1, which is involved in formation of actin-based structures that contribute to cell migration. High levels of FSCN1 expression is observed in cells with extended membranes and protrusions. Moreover, up-regulation of FSCN1 has been reported in several epithelial carcinomas. Therefore, FSCN1 is thought to play a role in cell movement and invasion. However, the mechanism behind FSCN1 up-regulation is not known. We investigated the expression of FSCN1 using immunohistochemistry. Methylation-specific PCR was adopted to analyze the methylation status of FSCN1 promoter as a potential regulatory mechanism in FSCN1 expression. The samples included papillary thyroid carcinoma, follicular thyroid carcinoma and goiter samples (controls). Methylation of FSCN1 promoter was observed in 50% of follicular, 48.6% of papillary and 60% of controls. The promoter was unmethylated in 16.7% of follicular samples, 5.7% of papillary samples and 26.7% of controls. In the remaining 33.3% of follicular and 45.7% of papillary samples as well as 13.3% of controls, both methylated and unmethylated alleles were amplified, a condition referred to as semi-methylation. The results showed that FSCN1 promoter was significantly hypomethylated in papillary cases while the methylation status was not significantly altered in follicular cases. On the other hand, FSCN1 was expressed in only nine papillary samples. Regarding protein expression and methylation status, we suggest that hypomethylation of FSCN1 promoter in papillary thyroid carcinoma does not lead to overexpression of FSCN1 and that there might be other regulatory mechanisms involved in FSCN1 up-regulation.

Sensing Actin Dynamics through Adherens Junctions

We study punctate adherens junctions (pAJs) to determine how short-lived cadherin clusters and relatively stable actin bundles interact despite differences in dynamics. We show that pAJ-linked bundles consist of two distinct regions-the bundle stalk (AJ-BS) and a tip (AJ-BT) positioned between cadherin clusters and the stalk. The tip differs from the stalk in a number of ways: it is devoid of the actin-bundling protein calponin, and exhibits a much faster F-actin turnover rate. While F-actin in the stalk displays centripetal movement, the F-actin in the tip is immobile. The F-actin turnover in both the tip and stalk is dependent on cadherin cluster stability, which in turn is regulated by F-actin. The close bidirectional coupling between the stability of cadherin and associated F-actin shows how pAJs, and perhaps other AJs, allow cells to sense and coordinate the dynamics of the actin cytoskeleton in neighboring cells-a mechanism we term "dynasensing."

Long-term live-cell microscopy with labeled nanobodies delivered by laser-induced photoporation.

Fluorescence microscopy is the method of choice for studying intracellular dynamics. However, its success depends on the availability of specific and stable markers. A prominent example of markers that are rapidly gaining interest are nanobodies (Nbs, ~ 15 kDa), which can be functionalized with bright and photostable organic fluorophores. Due to their relatively small size and high specificity, Nbs offer great potential for high-quality long-term subcellular imaging, but suffer from the fact that they cannot spontaneously cross the plasma membrane of live cells. We have recently discovered that laser-induced photoporation is well suited to deliver extrinsic labels to living cells without compromising their viability. Being a laser-based technology, it is readily compatible with light microscopy and the typical cell recipients used for that. Spurred by these promising initial results, we demonstrate here for the first time successful long-term imaging of specific subcellular structures with labeled nanobodies in living cells. We illustrate this using Nbs that target GFP/YFP-protein constructs accessible in the cytoplasm, actin-bundling protein Fascin, and the histone H2A/H2B heterodimers. With an efficiency of more than 80% labeled cells and minimal toxicity (~ 2%), photoporation proved to be an excellent intracellular delivery method for Nbs. Time-lapse microscopy revealed that cell division rate and migration remained unaffected, confirming excellent cell viability and functionality. We conclude that laser-induced photoporation labeled Nbs can be easily delivered into living cells, laying the foundation for further development of a broad range of Nbs with intracellular targets as a toolbox for long-term live-cell microscopy.

Regulation of Bone Resorption by the Actin-Bundling Protein L-Plastin in Osteoclasts

Osteoporosis is related to estrogen deficiency and aging. Bone loss can also occur as a result of inflammation-associated diseases such as rheumatoid arthritis and periodontitis, which share several pathologic features with osteoporosis. Estrogen deficiency is associated with increased osteoclast activation, decreased osteoblast function, and increased inflammatory bone-resorbing cytokines (e.g., interleukin-1, -6, and tumor necrosis factor –α). The differentiation of osteoclasts is regulated by the cytokines macrophage colony-stimulating factor, RANK ligand, and osteoprotegerin secreted by osteoblasts. Bone resorption is the unique function of osteoclasts. Podosomes are essential features of osteoclast migration. Podosomes are F-actin rich structures joined radially by actin fibers called F-actin cloud. Upon attachment to the bone surface, osteoclasts reorganize their cytoskeleton to form sealing zones. Sealing zone formation is required for efficient bone resorption to occur by osteoclasts. Integrin αvβ3 and TNF-alpha mediated signaling mechanisms regulate the assembly/disassembly of podosomes during migration and the organization of sealing zones during bone resorption. A brief description is provided on these aspects in this review.

The actin-bundling protein L-plastin-A double-edged sword: Beneficial for the immune response, maleficent in cancer.

The dynamic organization of the actin cytoskeleton into bundles and networks is orchestrated by a large variety of actin-binding proteins. Among them, the actin-bundling protein L-plastin is normally expressed in hematopoietic cells, where it is involved in the immune response. However, L-plastin is also often ectopically expressed in malignant cancer cells of non-hematopoietic origin and is even considered as a marker for cancer progression. Post-translational modification modulates L-plastin activity. In particular, L-plastin Ser5 phosphorylation has been shown to be important for the immune response in leukocytes as well as for invasion and metastasis formation of carcinoma cells. This chapter discusses the physiological and pathological role of L-plastin with a special focus on the importance of L-plastin Ser5 phosphorylation for the protein functions. The potential use of Ser5 phosphorylated L-plastin as a biomarker and/or therapeutic target will be evoked.

Features of fascin expression in the small intestine of rats exposed to processed Eucheuma seaweed

This study focuses on the assessment of fascin expression in the small intestinal tissue of rats orally administered a food additive E407a (processed Eucheuma seaweed), which is widely used to improve the texture of food products. The issue of its safety is under debate nowadays. Small intestinal expression of fascin, an actin-bundling cytoskeletal protein involved in the formation of filopodia and microspikes, was evaluated immunohistochemically in 9 rats exposed to 140 mg of E407a per kg of weight daily during two weeks and 8 control animals. Fascin was found to be upregulated both in the lamina propria and epithelia of the small intestine in rats administered processed Eucheuma seaweed compared with the control group. Thus, oral consumption of E407a is associated with overexpression of fascin in the small intestine of rats.

Abstract C053: NP-G2-044, a novel fascin inhibitor, blocks tumor metastasis and increases antitumor immune response

Abstract Filopodia are finger-like plasma membrane protrusions that are formed upon remodeling of the actin cytoskeleton beneath the plasma membrane. Fascin protein is the main actin-bundling protein in filopodia and invadopodia which are fundamental to cell shape and motility events. Human fascin expression is low or absent in normal adult epithelial cells but highly expressed in metastatic tumors and in antigen-presenting dendritic cells within the tumor microenvironment. Elevated levels of fascin are correlated with poor prognosis and short survival due to aggressive phenotypes with increased lymph node and distant metastases. Mouse genetic studies demonstrate that deletion of fascin gene delays tumor development, slows tumor growth, reduces metastatic colonization, and increases overall survival. These mouse genetic studies provide strong evidence for fascin’s role in tumor initiation, tumor progression and tumor metastasis, making it an attractive target for drug development. Chemical libraries were screened to identify small-molecule compounds that specifically inhibit the biochemical function of fascin to bundle actin filaments. The inhibitors were optimized to produce the lead compound, NP-G2-044. Preclinical studies showed that fascin inhibitors increase the overall survival of tumor-bearing mice and reinvigorate anti-tumor immune response in syngeneic mouse models of breast, lung, pancreatic and prostate tumors. Fascin protein levels are increased in conventional dendritic cells (cDCs) in the immunosuppressive tumor microenvironment. The number of intra-tumoral activated cDCs is increased following fascin inhibitor treatment. Moreover, together with anti-PD-1 antibody, fascin inhibition markedly increases the number of Ki67+ proliferating and Granzyme-B+ activated CD8+ killer T-cells in tumor tissue. These data demonstrate that fascin inhibitors simultaneously act on tumor cells to block tumor metastasis and on intratumoral DCs to reinvigorate anti-tumor immune response. We are currently conducting a first-in-human phase 1 trial of NP-G2-044 in patients with advanced or metastatic solid tumor malignancies. Citation Format: Vincent Chung, Frank Tsai, Komal Jhaveri, Yufeng Wang, Daniel D Von Hoff, Edward G Garmey, J. Jillian Zhang, Xin-Yun Huang. NP-G2-044, a novel fascin inhibitor, blocks tumor metastasis and increases antitumor immune response [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr C053. doi:10.1158/1535-7163.TARG-19-C053

Actin-Bundling Proteins (Actinin-4 and Fascin-1) are Involved in the Development of Pancreatic Intraepithelial Neoplasia (PanIN)

Fascin-1 and actinin-4 are involved in key processes of tumor cell adhesion, migration and metastasis. Actinin-4 plays an important role in promotion of cell proliferation, whereas fascin-1 regulates cellular motility. Its over-expression leads to the loss of cell adhesion and metastasis. The aim of our study was to assess fascin-1 and actinin-4 expression in normal pancreatic ducts and in pancreatic intraepithelial neoplasia (PanIN) - precursor lesion of pancreatic ductal adenocarcinoma (PDAC). The study involved 70 patients treated surgically due to PDAC, cysts and pancreatitis, who had also been diagnosed with pancreatic intraepithelial neoplasia. Fascin-1 and actinin-4 expressions were evaluated using the immunohistochemistry method. A statistically significant relationship was observed between the expression of fascin-1 and actinin-4 (cytoplasmic) and patients' age (P=0.01, P=0.002, respectively). The expression of fascin-1 and actinin-4 was associated with the diagnosis (P<0.001,P=0.04, respectively). Statistical analysis revealed correlations of fascin-1 and actinin-4 expressions with the presence and grade of PanIN (P < 0.001, P=0.002, respectively). The expression of these proteins was observed in each degree of PanIN and increased with the pancreatic intraepithelial neoplasia progression. The expression of fascin-1 and actinin-4 is connected with the degree of PanIN advancement and depends on the type of the primary disease. Overexpression of these proteins may be linked to cytological and architectural abnormalities observed in advanced PanIN. Elevated expression of fascin-1 and actinin-4 indicates the role of these proteins in the progression from PanIN to PDAC.

Mice lacking plastin-3 display a specific defect of cortical bone acquisition.

Although inactivating mutations of PLS3, encoding the actin-bundling protein plastin-3, have been identified to cause X-linked osteoporosis, the cellular and molecular influence of PLS3 on bone remodeling is poorly defined. Moreover, although a previous study has demonstrated moderate osteopenia in 12 week-old Pls3-deficient mice based on μCT scanning, there is no reported analysis of such a model on the basis of undecalcified histology and bone-specific histomorphometry. To fill this knowledge gap we applied a deep phenotyping approach and studied Pls3-deficient mice at different ages. Surprisingly, we did not detect significant differences between wildtype and Pls3-deficient littermates with respect to trabecular bone mass, and the same was the case for all histomorphometric parameters determined at 12 weeks of age. Remarkably however, the cortical thickness in both, tibia and femur, was significantly reduced in Pls3-deficient mice in all age groups. We additionally studied the ex vivo behavior of Pls3-deficient primary osteoblasts, which displayed moderately impaired mineralization capacity. Of note, while most osteoblastogenesis markers were not differentially expressed between wildtype and Pls3-deficient cultures, the expression of Sfrp4 was significantly reduced in the latter, a potentially relevant finding, since Sfrp4 inactivation, in mice and humans, specifically causes cortical thinning. We finally addressed the question, if Pls3-deficiency would impair the osteoanabolic influence of parathyroid hormone (PTH). For this purpose we applied daily injection of PTH into wildtype and Pls3-deficient mice and found a similar response regardless of the genotype. Taken together, our data reveal that Pls3-deficiency in mice only recapitulates the cortical bone phenotype of individuals with X-linked osteoporosis by negatively affecting the early stage of cortical bone acquisition.