Recurrence of carcinomas due to cells that migrate away from the primary tumor is a major problem in cancer treatment. Immunohistochemical analyses of human carcinomas have consistently correlated up-regulation of the actin-bundling protein fascin with a clinically aggressive phenotype and poor prognosis. To understand the functional and mechanistic contributions of fascin, we undertook inducible short hairpin RNA (shRNA) knockdown of fascin in human colon carcinoma cells derived from an aggressive primary tumor. Fascin-depletion led to decreased numbers of filopodia and altered morphology of cell protrusions, decreased Rac-dependent migration on laminin, decreased turnover of focal adhesions, and, in vivo, decreased xenograft tumor development and metastasis. cDNA rescue of fascin shRNA-knockdown cells with wild-type green fluorescent protein-fascin or fascins mutated at the protein kinase C (PKC) phosphorylation site revealed that both the actin-bundling and active PKC-binding activities of fascin are required for the organization of filopodial protrusions, Rac-dependent migration, and tumor metastasis. Thus, fascin contributes to carcinoma migration and metastasis through dual pathways that impact on multiple subcellular structures needed for cell migration.
Cell adhesion to individual macromolecules of the extracellular matrix has dramatic effects on the subcellular localization of the actin-bundling protein fascin and on the ability of cells to form stable fascin microspikes. The actin-binding activity of fascin is down-regulated by phosphorylation, and we used two differentiated cell types, C2C12 skeletal myoblasts and LLC-PK1 kidney epithelial cells, to examine the hypothesis that cell adhesion to the matrix components fibronectin, laminin-1, and thrombospondin-1 differentially regulates fascin phosphorylation. In both cell types, treatment with the PKC activator 12-tetradecanoyl phorbol 13-acetate (TPA) or adhesion to fibronectin led to a diffuse distribution of fascin after 1 h. C2C12 cells contain the PKC family members α, γ, and λ, and PKCα localization was altered upon cell adhesion to fibronectin. Two-dimensional isoelectric focusing/SDS-polyacrylamide gels were used to determine that fascin became phosphorylated in cells adherent to fibronectin and was inhibited by the PKC inhibitors calphostin C and chelerythrine chloride. Phosphorylation of fascin was not detected in cells adherent to thrombospondin-1 or to laminin-1. LLC-PK1 cells expressing green fluorescent protein (GFP)-fascin also displayed similar regulation of fascin phosphorylation. LLC-PK1 cells expressing GFP-fascin S39A, a nonphosphorylatable mutant, did not undergo spreading and focal contact organization on fibronectin, whereas cells expressing a GFP-fascin S39D mutant with constitutive negative charge spread more extensively than wild-type cells. In contrast, C2C12 cells coexpressing S39A fascin with endogenous fascin remained competent to form microspikes on thrombospondin-1, and cells that expressed fascin S39D attached to thrombospondin-1 but did not form microspikes. Blockade of PKCα activity by TPA-induced down-regulation led to actin association of wild-type fascin in fibronectin-adherent C2C12 and LLC-PK1 cells but did not alter the distribution of S39A or S39D fascins. The association of fascin with actin in fibronectin-adherent cells was also evident in the presence of an inhibitory antibody to integrin α5 subunit. These novel results establish matrix-initiated PKC-dependent regulation of fascin phosphorylation at serine 39 as a mechanism whereby matrix adhesion is coupled to the organization of cytoskeletal structure.
The rapid turnover of actin filaments and the tertiary meshwork formation are regulated by a variety of actin-binding proteins. Protein phosphorylation of cofilin, an actin-binding protein that depolymerizes actin filaments, suppresses its function. Thus, cofilin is a terminal effector of signaling cascades that evokes actin cytoskeletal rearrangement. When wild-type LIMK2 and kinase-dead LIMK2 (LIMK2/KD) were respectively expressed in cells, LIMK2, but not LIMK2/KD, phosphorylated cofilin and induced formation of stress fibers and focal complexes. LIMK2 activity toward cofilin phosphorylation was stimulated by coexpression of activated Rho and Cdc42, but not Rac. Importantly, expression of activated Rho and Cdc42, respectively, induced stress fibers and filopodia, whereas both Rho- induced stress fibers and Cdc42-induced filopodia were abrogated by the coexpression of LIMK2/KD. In contrast, the coexpression of LIMK2/KD with the activated Rac did not affect Rac-induced lamellipodia formation. These results indicate that LIMK2 plays a crucial role both in Rho- and Cdc42-induced actin cytoskeletal reorganization, at least in part by inhibiting the functions of cofilin. Together with recent findings that LIMK1 participates in Rac-induced lamellipodia formation, LIMK1 and LIMK2 function under control of distinct Rho subfamily GTPases and are essential regulators in the Rho subfamilies-induced actin cytoskeletal reorganization.
cytoskeleton; actin depolymerization; LIM-kinase; Rho family GTPases; stress fibers
Fascin is an actin-bundling protein that is absent from most normal epithelia yet is upregulated in multiple forms of human carcinoma, where its expression correlates clinically with a poor prognosis. How fascin-1 transcription is activated in carcinoma cells is largely unknown, although the hypothesis of regulation by β-catenin signaling has received attention. The question is important because of the clinical significance of fascin expression in human carcinomas.
Through comparative genomics we made an unbiased analysis of the DNA sequence of the fascin-1 promoter region from six mammalian species. We identified two regions in which highly conserved motifs are concentrated. Luciferase promoter reporter assays for the human fascin-1 promoter were carried out in fascin-positive and -negative human breast and colon carcinoma cells, and in human dermal fibroblasts that are constitutively fascin-positive. In all fascin-positive cells, the region −219/+114 that contains multiple highly conserved motifs had strong transcriptional activity. The region −2953/−1582 appeared to contain repressor activity. By examining the effects of single or multiple point mutations of conserved motifs within the −219/+114 region on transcriptional reporter activity, we identified for the first time that the conserved CREB and AhR binding motifs are major determinants of transcriptional activity in human colon carcinoma cells. Chromatin immunoprecipitations for CREB, AhR or β-catenin from extracts from fascin-positive or -negative human colon carcinoma cells identified that CREB and AhR specifically associate with the −219/+114 region of the FSCN1 promoter in fascin-positive colon carcinoma cells. An association of β-catenin was not specific to fascin-positive cells.
Upregulation of fascin-1 in aggressive human carcinomas appears to have a multi-factorial basis. The data identify novel roles for CREB and AhR as major, specific regulators of FSCN-1 transcription in human carcinoma cells but do not support the hypothesis that β-catenin signaling has a central role.
Cell adhesion to extracellular matrix is an important physiological stimulus for organization of the actin-based cytoskeleton. Adhesion to the matrix glycoprotein thrombospondin-1 (TSP-1) triggers the sustained formation of F-actin microspikes that contain the actin-bundling protein fascin. These structures are also implicated in cell migration, which may be an important function of TSP-1 in tissue remodelling and wound repair. To further understand the function of fascin microspikes, we examined whether their assembly is regulated by Rho family GTPases. We report that expression of constitutively active mutants of Rac or Cdc42 triggered localization of fascin to lamellipodia, filopodia, and cell edges in fibroblasts or myoblasts. Biochemical assays demonstrated prolonged activation of Rac and Cdc42 in C2C12 cells adherent to TSP-1 and activation of the downstream kinase p21-activated kinase (PAK). Expression of dominant-negative Rac or Cdc42 in C2C12 myoblasts blocked spreading and formation of fascin spikes on TSP-1. Spreading and spike assembly were also blocked by pharmacological inhibition of F-actin turnover. Shear-loading of monospecific anti-fascin immunoglobulins, which block the binding of fascin to actin into cytoplasm, strongly inhibited spreading, actin cytoskeletal organization and migration on TSP-1 and also affected the motility of cells on fibronectin. We conclude that fascin is a critical component downstream of Rac and Cdc42 that is needed for actin cytoskeletal organization and cell migration responses to thrombospondin-1.
cell adhesion; cell motility; cytoskeleton; fascin; small G proteins
Mutation of a critical residue of fascin eliminates the protein’s actin-bundling activity but maintains its positive role in filopodia formation
Fascin is an evolutionarily conserved actin-binding protein that plays a key role in forming filopodia. It is widely thought that this function involves fascin directly bundling actin filaments, which is controlled by an N-terminal regulatory serine residue. In this paper, by studying cellular processes in Drosophila melanogaster that require fascin activity, we identify a regulatory residue within the C-terminal region of the protein (S289). Unexpectedly, although mutation (S289A) of this residue disrupted the actin-bundling capacity of fascin, fascin S289A fully rescued filopodia formation in fascin mutant flies. Live imaging of migrating macrophages in vivo revealed that this mutation restricted the localization of fascin to the distal ends of filopodia. The corresponding mutation of human fascin (S274) similarly affected its interaction with actin and altered filopodia dynamics within carcinoma cells. These data reveal an evolutionarily conserved role for this regulatory region and unveil a function for fascin, uncoupled from actin bundling, at the distal end of filopodia.
Fascin is a globular actin cross-linking protein, which plays a major role in forming parallel actin bundles in cell protrusions and is found to be associated with tumor cell invasion and metastasis in various type of cancers including oral squamous cell carcinoma (OSCC). Previously, we have demonstrated that fascin regulates actin polymerization and thereby promotes cell motility in K8-depleted OSCC cells. In the present study we have investigated the role of fascin in tumor progression of OSCC.
To understand the role of fascin in OSCC development and/or progression, fascin was overexpressed along with vector control in OSCC derived cells AW13516. The phenotype was studied using wound healing, Boyden chamber, cell adhesion, Hanging drop, soft agar and tumorigenicity assays. Further, fascin expression was examined in human OSCC samples (N = 131) using immunohistochemistry and level of its expression was correlated with clinico-pathological parameters of the patients.
Fascin overexpression in OSCC derived cells led to significant increase in cell migration, cell invasion and MMP-2 activity. In addition these cells demonstrated increased levels of phosphorylated AKT, ERK1/2 and JNK1/2. Our in vitro results were consistent with correlative studies of fascin expression with the clinico-pathological parameters of the OSCC patients. Fascin expression in OSCC showed statistically significant correlation with increased tumor stage (P = 0.041), increased lymph node metastasis (P = 0.001), less differentiation (P = 0.005), increased recurrence (P = 0.038) and shorter survival (P = 0.004) of the patients.
In conclusion, our results indicate that fascin promotes tumor progression and activates AKT and MAPK pathways in OSCC-derived cells. Further, our correlative studies of fascin expression in OSCC with clinico-pathological parameters of the patients indicate that fascin may prove to be useful in prognostication and treatment of OSCC.
Fascin; Cell migration; Invasion; Metastasis; OSCC
Background & Aims
Pancreatic ductal adenocarcinoma (PDAC) is often lethal because it is highly invasive and metastasizes rapidly. The actin-bundling protein fascin has been identified as a biomarker of invasive and advanced PDAC and regulates cell migration and invasion in vitro. We investigated fascin expression and its role in PDAC progression in mice.
We used KRasG12D p53R172H Pdx1-Cre (KPC) mice to investigate the effects of fascin deficiency on development of pancreatic intraepithelial neoplasia (PanIn), PDAC, and metastasis. We measured levels of fascin in PDAC cell lines and 122 human resected PDAC samples, along with normal ductal and acinar tissues; we associated levels with patient outcomes.
Pancreatic ducts and acini from control mice and early-stage PanINs from KPC mice were negative for fascin, but approximately 6% of PanIN3 and 100% of PDAC expressed fascin. Fascin-deficient KRasG12D p53R172H Pdx1-Cre mice had longer survival times, delayed onset of PDAC, and a lower PDAC tumor burdens than KPC mice; loss of fascin did not affect invasion of PDAC into bowel or peritoneum in mice. Levels of slug and fascin correlated in PDAC cells; slug was found to regulate transcription of Fascin along with the epithelial−mesenchymal transition. In PDAC cell lines and cells from mice, fascin concentrated in filopodia and was required for their assembly and turnover. Fascin promoted intercalation of filopodia into mesothelial cell layers and cell invasion. Nearly all human PDAC samples expressed fascin, and higher fascin histoscores correlated with poor outcomes, vascular invasion, and time to recurrence.
The actin-bundling protein fascin is regulated by slug and involved in late-stage PanIN and PDAC formation in mice. Fascin appears to promote formation of filopodia and invasive activities of PDAC cells. Its levels in human PDAC correlate with outcomes and time to recurrence, indicating it might be a marker or therapeutic target for pancreatic cancer.
Pancreas; Tumor Progression; Actin Cytoskeleton; EMT; EMT, epithelial to mesenchymal transition; FKPC, fascin-deficient KRasG12D p53R172H Pdx1-Cre; KPC, KRasG12D p53R172H Pdx1-Cre; MC, mesothelial cell; PanIN, pancreatic intraepithelial neoplasia; PDAC, pancreatic ductal adenocarcinoma; Tf, transcription factor
During cellular migration, regulated actin assembly takes place at the cell leading edge, with continuous disassembly deeper in the cell interior. Actin polymerization at the plasma membrane results in the extension of cellular protrusions in the form of lamellipodia and filopodia. To understand how cells regulate the transformation of lamellipodia into filopodia, and to determine the major factors that control their transition, we studied actin self-assembly in the presence of Arp2/3 complex, WASp-VCA and fascin, the major proteins participating in the assembly of lamellipodia and filopodia. We show that in the early stages of actin polymerization fascin is passive while Arp2/3 mediates the formation of dense and highly branched aster-like networks of actin. Once filaments in the periphery of an aster get long enough, fascin becomes active, linking the filaments into bundles which emanate radially from the aster's surface, resulting in the formation of star-like structures. We show that the number of bundles nucleated per star, as well as their thickness and length, is controlled by the initial concentration of Arp2/3 complex ([Arp2/3]). Specifically, we tested several values of [Arp2/3] and found that for given initial concentrations of actin and fascin, the number of bundles per star, as well as their length and thickness are larger when [Arp2/3] is lower. Our experimental findings can be interpreted and explained using a theoretical scheme which combines Kinetic Monte Carlo simulations for aster growth, with a simple mechanistic model for bundles' formation and growth. According to this model, bundles emerge from the aster's (sparsely branched) surface layer. Bundles begin to form when the bending energy associated with bringing two filaments into contact is compensated by the energetic gain resulting from their fascin linking energy. As time evolves the initially thin and short bundles elongate, thus reducing their bending energy and allowing them to further associate and create thicker bundles, until all actin monomers are consumed. This process is essentially irreversible on the time scale of actin polymerization. Two structural parameters, L, which is proportional to the length of filament tips at the aster periphery and b, the spacing between their origins, dictate the onset of bundling; both depending on [Arp2/3]. Cells may use a similar mechanism to regulate filopodia formation along the cell leading edge. Such a mechanism may allow cells to have control over the localization of filopodia by recruiting specific proteins that regulate filaments length (e.g., Dia2) to specific sites along lamellipodia.
Microtubule (MT) destabilization promotes the formation of actin stress fibers and enhances the contractility of cells, however, mechanism involved in the coordinated regulation of MTs and the actin cytoskeleton is poorly understood. LIM kinase 1 (LIMK1) regulates actin polymerization by phosphorylating the actin depolymerization factor (ADF), cofilin. Here we report that LIMK1 is also involved in the MTs destabilization. In endothelial cells, endogenous LIMK1 co-localizes with MTs and forms a complex with tubulin via PDZ domain. MTs destabilization induced by thrombin or nocodazole resulted in decrease of LIMK1 colocalization with MTs. Overexpression of wild type LIMK1 resulted in MTs destabilization whereas kinase-dead mutant of LIMK1 (KD) did not affect MTs stability. Importantly, downregulation of endogenous LIMK1 by siRNA resulted in abrogation of the thrombin-induced MTs destabilization and the inhibition of thrombin-induced actin polymerization. Expression of ROCK2, which phosphorylates and activates LIMK1, decreases dramatically the interaction of LIMK1 with tubulin but increases its interaction with actin. Interestingly, expression of KD- or siRNA-LIMK1 prevents thrombin induced microtubule destabilization and Factin formation suggesting that LIMK1 activity is required for thrombin-induced modulation of microtubule destabilization and actin polymerization. Our findings indicate that LIMK1 may coordinate microtubules and actin cytoskeleton.
LIMK1, LIMK-domain-containing kinase 1; ROCK2, Rho kinase 2; ADF, actin depolymerization factor ; PAK, p21 activated kinases; HUVEC, human umbilical vein endothelial cells; MAPs, microtubule-associated proteins; GEF, guanine nucleotide exchange factor; HBSS, Hank’s balanced salt solution; PBS, phosphate buffered saline; BSA, bovine serum albumin; GST, glutathione S-transferase
The majority of thymomas are histologically characterized by tumor-infiltrating lymphocytes. Mature dendritic cells (DCs) are known to assemble lymphocytes through antigen presentation to T lymphocytes. Fascin, a 55-kDa actin-binding protein and a known marker for mature DCs, regulates filaments necessary for the formation of filopodia in cell migration. Moreover, fascin expression in various epithelial neoplasms has recently been reported to be associated with invasion of tumor cells and clinically aggressive manifestations. In the present study, we investigated fascin expression immunohistochemically in tissues of thymomas and thymic carcinomas surgically resected at our institute. A total of 34 thymomas and 5 thymic carcinomas were included. The amount and immunohistochemical intensity of both fascin+ DCs and tumor epithelium were counted and assessed, and the clinicopathological data were also scored. Statistical analyses revealed that the amount of fascin+ DCs with the formation of clusters was associated with lymphocyte-rich variants (p=0.002) and cortical differentiation (p=0.037) of thymoma with complication from myasthenia gravis (p=0.002). The quantity of fascin+ epithelium was associated with a strong intensity of fascin in infiltrating DCs (p=0.002) with the formation of clusters (p=0.002) and favorable prognosis, as assessed by the Masaoka staging system (p=0.001). The amount of infiltrating DCs (p=0.024) and fascin+ epithelium were lower in thymic carcinoma. It was concluded that fascin+ epithelium may induce tumor immunity through the surveillance activity of fascin+ DCs in thymic neoplasms, thus improving prognosis.
thymoma; immunohistochemistry; fascin; dendritic cell; tumor immunity
Stereocilia are actin-filled protrusions that permit mechanotransduction in the
internal ear. To identify proteins that organize the cytoskeleton of
stereocilia, we scrutinized the hair-cell transcriptome of zebrafish. One
promising candidate encodes fascin 2b, a filamentous actin-bundling protein
found in retinal photoreceptors. Immunolabeling of zebrafish hair cells and the
use of transgenic zebrafish that expressed fascin 2b fused to green fluorescent
protein demonstrated that fascin 2b localized to stereocilia specifically. When
filamentous actin and recombinant fusion protein containing fascin 2b were
combined in vitro to determine their dissociation constant, a
Kd≈0.37 µM was observed. Electron
microscopy showed that fascin 2b-actin filament complexes formed parallel actin
bundles in vitro. We demonstrated that expression of fascin 2b
or espin, another actin-bundling protein, in COS-7 cells induced the formation
of long filopodia. Coexpression showed synergism between these proteins through
the formation of extra-long protrusions. Using phosphomutant fascin 2b proteins,
which mimicked either a phosphorylated or a nonphosphorylated state, in COS-7
cells and in transgenic hair cells, we showed that both formation of long
filopodia and localization of fascin 2b to stereocilia were dependent on serine
38. Overexpression of wild-type fascin 2b in hair cells was correlated with
increased stereociliary length relative to controls. These findings indicate
that fascin 2b plays a key role in shaping stereocilia.
After birth, stem cells in the subventricular zone (SVZ) generate neuroblasts that migrate along the rostral migratory stream (RMS) to become interneurons in the olfactory bulb (OB). This migration is a fundamental event controlling the proper integration of new neurons in a pre-existing synaptic network. Many regulators of neuroblast migration have been identified; however, still very little is known about the intracellular molecular mechanisms controlling this process. Here, we show that the actin-bundling protein fascin is highly upregulated in mouse SVZ-derived migratory neuroblasts. Fascin-1ko mice display an abnormal RMS and a smaller OB. Bromodeoxyuridine labeling experiments show that lack of fascin significantly impairs neuroblast migration, but does not appear to affect cell proliferation. Moreover, fascin depletion substantially alters the polarized morphology of rat neuroblasts. Protein kinase C (PKC)-dependent phosphorylation of fascin on Ser39 regulates its actin-bundling activity. In vivo postnatal electroporation of phosphomimetic (S39D) or nonphosphorylatable (S39A) fascin variants followed by time-lapse imaging of brain slices demonstrates that the phospho-dependent modulation of fascin activity ensures efficient neuroblast migration. Finally, fluorescence lifetime imaging microscopy studies in rat neuroblasts reveal that the interaction between fascin and PKC can be modulated by cannabinoid signaling, which controls neuroblast migration in vivo. We conclude that fascin, whose upregulation appears to mark the transition to the migratory neuroblast stage, is a crucial regulator of neuroblast motility. We propose that a tightly regulated phospho/dephospho-fascin cycle modulated by extracellular signals is required for the polarized morphology and migration in neuroblasts, thus contributing to efficient neurogenesis.
Fascin, an actin‐binding protein, is usually expressed at a low level in normal epithelium, but is markedly up regulated in several types of carcinomas. Reports on fascin expression in oesophageal squamous cell carcinoma (ESCC) and precancerous lesions remain rare.
To show the roles of fascin in the progression from normal epithelium to invasive ESCC.
Fascin expression in 102 sections embedded in paraffin wax, including samples of normal mucosa (n = 20), dysplasia (n = 10), ESCC (n = 62) and special sections (n = 10) of a full‐length mucosa layer from the distant margin to the cancer focus of the excised oesophagus, and 49 fresh specimens of ESCC was analysed by immunohistochemistry, western blot and real‐time reverse transcription‐polymerase chain reaction. Fascin expression in ESCC cell lines was also investigated.
In the immunohistochemical study, the positive rate of fascin was significantly higher in the tumour tissue than in the normal epithelium (p = 0.020), but no significant difference was shown between ESCC and dysplasia (p = 1.000). Immunostaining for fascin was only apparent in the basal layer of the normal epithelium. However, in the dysplasia, positive staining was observed in most of the heterogeneous cells from the basal layer to the granular layer of the epithelium. Fascin expression was seen to increase progressively from the normal epithelium to invasive ESCC. Up regulation of fascin was observed in 87.76% (43/49) and 77.55% (38/49) of the specimens, respectively, using western blot and real‐time reverse transcription‐polymerase chain reaction assays; 80% (4/5) of ESCC cell lines also expressed fascin at a high level. Furthermore, overexpression of fascin was markedly correlated with cell proliferation and lymph node metastasis.
These findings suggested that fascin was associated with the transformation and development of ESCC and implicated the potential of fascin as a novel biomarker that would allow the tumour to be identified at an early stage in high‐risk individuals.
LIM kinase 1 (LIMK1) is expressed in both cytoplasmic and nuclear compartments, and is a key regulator of cytoskeletal organization involved in cell migration and proliferation. LIMK1 levels are increased in several human cancers, with LIMK1 over-expression in prostate and breast cancer cells leading to tumor progression. While it has been presumed that the mechanism by which LIMK1 promotes cancer progression is via its cytoplasmic effects, the role of nuclear vs cytoplasmic LIMK1 in the tumorigenic process has not been examined.
To determine if cytoplasmic or nuclear LIMK1 expression correlated with breast cancer, we performed immunohistochemical (IHC) analysis of breast tissue microarrays (TMAs), The IHC analysis of breast TMAs revealed that 76% of malignant breast tissue samples strongly expressed LIMK1 in the cytoplasm, with 52% of these specimens also expressing nuclear LIMK1. Only 48% of benign breast samples displayed strong cytoplasmic LIMK1 expression and 27% of these expressed nuclear LIMK1. To investigate the respective roles of cytoplamsic and nuclear LIMK1 in breast cancer progression, we targeted GFP-LIMK1 to cytoplasmic and nuclear subcellular compartments by fusing nuclear export signals (NESs) or nuclear localization sequences (NLS), respectively, to the amino-terminus of GFP-LIMK1. Stable pools of MDA-MB-231 cells were generated by retroviral transduction, and fluorescence microscopy revealed that GFP alone (control) and GFP-LIMK1 were each expressed in both the cytoplasm and nucleus of MDA-MB-231 cells, whereas NLS-GFP-LIMK1 was expressed in the nucleus and NES-GFP-LIMK1 was expressed in the cytoplasm. Western blot analyses revealed equal expression of GFP-LIMK1 and NES-GFP-LIMK1, with NLS-GFP-LIMK1 expression being less but equal to endogenous LIMK1. Also, Western blotting revealed increased levels of phospho-cofilin, phospho-FAK, phospho-paxillin, phospho-Src, phospho-AKT, and phospho-Erk1/2 in cells expressing all GFP-LIMK1 fusions, compared to GFP alone. Invasion assays revealed that all GFP-LIMK1 fusions increased MDA-MB-231 cell invasion ~1.5-fold, compared to GFP-only control cells. Tumor xenograft studies in nude mice revealed that MDA-MB-231 cells stably expressing GFP-LIMK, NLS-GFP-LIMK1 and NES-GFP-LIMK1 enhanced tumor growth 2.5-, 1.6- and 4.7-fold, respectively, compared to GFP-alone.
Taken together, these data demonstrate that LIMK1 activity in both the cytoplasmic and nuclear compartments promotes breast cancer progression, underscoring that nuclear LIMK1 contributes to the transforming function of LIMK1.
RhoGDIs are negative regulators of small GTP-binding proteins of the Rho family, which have essential cellular functions in most aspects of actin-based morphology and motility processes. They extract Rho proteins from membranes, keep them in inactive rhoGDI/Rho complexes and eventually deliver them again to specific membranes in response to cellular signals. RhoGDI3, the most divergent member of the rhoGDI family, is well suited to document the underlying molecular mechanisms, since the active and inactive forms of its cellular target, RhoG, have well-separated subcellular localizations. In this study, we investigate trafficking structures and molecular interactions involved in rhoGDI3-mediated shuttling of RhoG between the Golgi and the plasma membrane.
Bimolecular fluorescence complementation and acceptor-photobleaching FRET experiments suggest that rhoGDI3 and RhoG form complexes on Golgi and vesicular structures in mammalian cells. 4D-videomicroscopy confirms this localization, and show that RhoG/rhoGDI3-labelled structures are less dynamic than RhoG and rhoGDI3-labeled vesicles, consistent with the inhibitory function of rhoGDI3. Next, we identify the Exocyst subunit Sec3 as a candidate rhoGDI3 partner in cells. RhoGDI3 relocates a subcomplex of the Exocyst (Sec3 and Sec8) from the cytoplasm to the Golgi, while Sec6 is unaffected. Remarkably, Sec3 increases the level of GTP-bound endogenous RhoG, the RhoG-dependent induction of membrane ruffles, and the formation of intercellular tunneling nanotube-like protrusions.
Altogether, our study identifies a novel link between vesicular traffic and the regulation of Rho proteins by rhoGDIs. It also suggests that components of the Exocyst machinery may be involved in RhoG functions, possibly regulated by rhoGDI3.
RhoGDI; RhoGDI3; guanine nucleotide dissociation inhibitor; Rho; RhoG; small GTPase; Exocyst; Sec3; Sec6; Sec8; vesicular traffic; membrane protrusions; tunneling nanotubes; videomicroscopy; bimolecular fluorescence complementation
Fascin is an actin bundling protein involved in filopodia assembly and cancer invasion and metastasis of multiple epithelial cancer types. Fascin forms stable actin bundles with slow dissociation kinetics in vitro  and is regulated by phosphorylation of serine 39 by protein kinase C (PKC) . Cancer cells use invasive finger-like protrusions termed invadopodia to invade into and degrade extracellular matrix. Invadopodia have highly dynamic actin that is assembled by both Arp2/3 complex and formins [3, 4]; they also contain components of membrane trafficking machinery such as dynamin and cortactin  and have been compared with focal adhesions and podosomes [6, 7]. We show that fascin is an integral component of invadopodia and that it is important for the stability of actin in invadopodia. The phosphorylation state of fascin at S39, a PKC site, contributes to its regulation at invadopodia. We further implicate fascin in invasive migration into collagen I-Matrigel gels and particularly in cell types that use an elongated mesenchymal type of motility in 3D. We provide a potential molecular mechanism for how fascin increases the invasiveness of cancer cells and we compare invadopodia with invasive filopod-like structures in 3D.
Ras GTPases mediate numerous biological processes through their ability to cycle between an inactive GDP-bound form and an active GTP-bound form. Guanine nucleotide exchange factors (GEFs) favor the formation of the active Ras-GTP, whereas GTPase activating proteins (GAPs) promote the formation of inactive Ras-GDP. Numerous studies have established complex signaling cross-talks between Ras GTPases and other members of the superfamily of small GTPases. GEFs were thought to play a major role in these cross-talks. However, recently GAPs were also shown to play crucial roles in these processes. Among RasGAPs, Nf1 is of special interest. Nf1 is responsible for the genetic disease Neurofibromatosis type I, and recent data strongly suggest that this RasGAP connects different signaling pathways.
In order to know if the RasGAP Nf1 might play a role in connecting Ras GTPases to other small GTPase pathways, we systematically looked for new partners of Nf1, by performing a yeast two-hybrid screening on its SecPH domain. LIMK2, a major kinase of the Rho/ROCK/LIMK2/cofilin pathway, was identified in this screening. We confirmed this interaction by co-immunoprecipitation experiments, and further characterized it. We also demonstrated its specificity: the close related homolog of LIMK2, LIMK1, does not interact with the SecPH domain of Nf1. We then showed that SecPH partially inhibits the kinase activity of LIMK2 on cofilin. Our results furthermore suggest a precise mechanism for this inhibition: in fact, SecPH would specifically prevent LIMK2 activation by ROCK, its upstream regulator.
Although previous data had already connected Nf1 to actin cytoskeleton dynamics, our study provides for the first time possible detailed molecular requirements of this involvement. Nf1/LIMK2 interaction and inhibition allows to directly connect neurofibromatosis type I to actin cytoskeleton remodeling, and provides evidence that the RasGAP Nf1 mediates a new cross-talk between Ras and Rho signaling pathways within the superfamily of small GTPases.
Catenins were first characterized as linking the cytoplasmic domains of cadherin cell-cell adhesion molecules to the cortical actin cytoskeleton. In addition to their essential role in modulating cadherin adhesivity, catenins have more recently been indicated to participate in cell and developmental signaling pathways. beta-Catenin, for example, associates directly with at least two receptor tyrosine kinases and transduces developmental signals within the Wnt pathway. Catenins also complex with the tumor suppressor protein adenomatous polyposis coli (APC), which appears to have a role in regulating cell proliferation. We have used the yeast two-hybrid method to reveal that fascin, a bundler of actin filaments, binds to beta-catenin's central Armadillo repeat domain. Western blotting of immunoprecipitates from cell line and mouse and rat brain extracts indicate that this interaction exists in vivo. Fascin and beta-catenin's association was further substantiated in vitro using purified proteins isolated from recombinant bacterial and baculoviral sources. Immunoprecipitation analysis indicates that fascin additionally binds to plakoglobin, which is highly homologous to beta-catenin but not to p120cas, a newly described catenin which contains a more divergent Armadillo-repeat domain. Immunoprecipitation, in vitro competition, and domain-mapping experiments demonstrate that fascin and E-cadherin utilize a similar binding site within beta-catenin, such that they form mutually exclusive complexes with beta-catenin. Immunofluorescence microscopy reveals that fascin and beta-catenin colocalize at cell-cell borders and dynamic cell leading edges of epithelial and endothelial cells. In addition to cell-cell borders, cadherins were unexpectedly observed to colocalize with fascin and beta-catenin at cell leading edges. It is conceivable that beta-catenin participates in modulating cytoskeletal dynamics in association with the microfilament-bundling protein fascin, perhaps in a coordinate manner with its functions in cadherin and APC complexes.
In vitro studies have identified LIMK2 as a key downstream effector of Rho GTPase-induced changes in cytoskeletal organization. LIMK2 is phosphorylated and activated by Rho associated coiled-coil kinases (ROCKs) in response to a variety of growth factors. The biochemical targets of LIMK2 belong to a family of actin binding proteins that are potent modulators of actin assembly and disassembly. Although numerous studies have suggested that LIMK2 regulates cell morphology and motility, evidence supportive of these functions in vivo has remained elusive. In this study, a knockout mouse was created that abolished LIMK2 biochemical activity resulting in a profound inhibition of epithelial sheet migration during eyelid development. In the absence of LIMK2, nascent eyelid keratinocytes differentiate and acquire a pre-migratory phenotype but the leading cells fail to nucleate filamentous actin and remain immobile causing an eyes open at birth (EOB) phenotype. The failed nucleation of actin was associated with significant reductions in phosphorylated cofilin, a major LIMK2 biochemical substrate and potent modulator of actin dynamics. These results demonstrate that LIMK2 activity is required for keratinocyte migration in the developing eyelid.
Neurofibromin regulates cell motility via three distinct GTPase pathways acting through two different domains, the Ras GTPase-activating protein-related domain (GRD) and the pre-GRD domain. First, the GRD domain inhibits Ras-dependent changes in cell motility through the mitogen activated protein cascade. Second, it also regulates Rho-dependent (Ras-independent) changes by activating LIM kinase 2 (LIMK2), an enzyme that phosphorylates and inactivates cofilin (an actin-depolymerizing factor). Third, the pre-GRD domain acts through the Rac1 GTPase, that activate the P21 activated kinase 1 (PAK1)-LIMK1-cofilin pathway. We employed molecular modeling to identify a novel inhibitor of LIMK1/2. The active sites of an ephrin-A receptor (EphA3) and LIMK2 showed marked similarity (60%). On testing a known inhibitor of EphA3, we found that it fits to the LIMK1/2-ATP binding site and to the latter's substrate-binding pockets. We identified a similar compound, T56-LIMKi, and found that it inhibits LIMK1/2 kinase activities. It blocked the phosphorylation of cofilin which led to actin severance and inhibition of tumor cell migration, tumor cell growth, and anchorage-independent colony formation in soft agar. Because modulation of LIMK by neurofibromin is not affected by the Ras inhibitor Salirasib, we examined the combined effect of Salirasib and T56-LIMKi each of which can affect cell motility by a distinct pathway. We found that their combined action on cell proliferation and stress-fiber formation in neurofibromin-deficient cells was synergistic. We suggest that this drug combination may be developed for treatment of neurofibromatosis and cancer.
Cofilin; Ras; Rac; Rho; LIMK
Fascin-1 is an actin-bundling protein expressed in many human carcinomas, although absent from most normal epithelia. Fascin-1 promotes filopodia formation, migration and invasion in carcinoma cells; in mouse xenograft tumor models it contributes to metastasis. Fascin-1 is an interesting candidate biomarker for aggressive, metastatic carcinomas but data from individual studies of human tumors have not yet been pooled systematically.
This systematic review was conducted in accordance with PRISMA guidelines, using fixed and random effects models, as appropriate, to undertake meta-analysis.
A total of 26 immunohistochemical studies of 5 prevalent human carcinomas were identified for meta-analysis. Fascin-1 was associated with increased risk of mortality for breast (pooled hazard ratio, (HR) = 2.58; 95% confidence interval (CI) 1.48 to 4.52; P = 0.001), colorectal (HR = 1.60 (1.37 to 1.86; P <0.001) and esophageal carcinomas (HR = 1.35; CI 1.13 to 1.60; P = 0.001). There was no evidence of association of fascin-1 with mortality in gastric and lung carcinomas. Fascin-1 was associated with increased risk of disease progression in breast (HR = 2.48; CI 1.38 to 4.46; P = 0.002) and colorectal carcinomas (HR = 2.12; CI 1.00 to 4.47; P = 0.05), but not with progression of lung carcinomas (HR = 0.95; CI 0.49 to 1.85; P = 0.9). Fascin-1 was associated with increased risk of lymph node metastasis in colorectal (pooled risk ratio (RR) = 1.47; CI 1.26 to 1.71; P <0.001) and gastric carcinomas (RR = 1.43; CI 1.21 to 1.70; P <0.001). There was no evidence of association of fascin-1 with lymph node metastasis in lung or esophageal carcinomas. Fascin-1 was associated with increased risk of distant metastasis in colorectal (RR = 1.70; CI 1.18 to 2.45; P = 0.004) and gastric carcinomas (RR = 1.93; CI 1.21 to 3.33; P = 0.02). No association with distant metastasis in esophageal carcinomas was observed. Pooling across all the carcinomas provided strong evidence for association of fascin-1 with increased risk of mortality (HR = 1.44; CI 1.24 to 1.68; P <0.001; n = 3,645), lymph node metastasis (RR = 1.36; CI 1.18 to 1.55; P <0.001; n = 2,906) and distant metastasis (1.76; 1.34 to 2.32; P <0.001; n = 1,514).
Fascin-1 is associated consistently with increased risk of mortality in breast, colorectal and esophageal carcinomas and with metastasis in colorectal and gastric carcinomas. The results were stable to various sensitivity analyses and did not vary by predefined subgroups. These data will assist rational decision making for focusing investigations of fascin-1 as a biomarker or therapeutic target onto the most relevant carcinomas.
Fascin-1; carcinoma; mortality; metastasis; meta-analysis
Fascin, a conserved actin-bundling protein, is not only cytoplasmic but also localizes to the nucleus and nuclear periphery in both Drosophila and mammalian cell contexts. In Drosophila, prostaglandin signaling regulates this localization. In addition, Fascin plays a critical role in nucleolar architecture in both Drosophila and mammalian cells.
Fascin, a highly conserved actin-bundling protein, localizes and functions at new cellular sites in both Drosophila and multiple mammalian cell types. During Drosophila follicle development, in addition to being cytoplasmic, Fascin is in the nuclei of the germline-derived nurse cells during stages 10B–12 (S10B–12) and at the nuclear periphery during stage 13 (S13). This localization is specific to Fascin, as other actin-binding proteins, Villin and Profilin, do not exhibit the same subcellular distribution. In addition, localization of fascin1 to the nucleus and nuclear periphery is observed in multiple mammalian cell types. Thus the regulation and function of Fascin at these new cellular locations is likely to be highly conserved. In Drosophila, loss of prostaglandin signaling causes a global reduction in nuclear Fascin and a failure to relocalize to the nuclear periphery. Alterations in nuclear Fascin levels result in defects in nucleolar morphology in both Drosophila follicles and cultured mammalian cells, suggesting that nuclear Fascin plays an important role in nucleolar architecture. Given the numerous roles of Fascin in development and disease, including cancer, our novel finding that Fascin has functions within the nucleus sheds new light on the potential roles of Fascin in these contexts.
Precise regulation of the dendritic spine actin cytoskeleton is critical for neurodevelopment and neuronal plasticity, but how neurons spatially control actin dynamics is not well defined. Here, we identify direct palmitoylation of the actin regulator LIM kinase-1 (LIMK1) as a novel mechanism to control spine-specific actin dynamics. A conserved palmitoyl-motif is necessary and sufficient to target LIMK1 to spines and to anchor LIMK1 in spines. ShRNA knockdown/rescue experiments reveal that LIMK1 palmitoylation is essential for normal spine actin polymerization, for spine-specific structural plasticity and for long-term spine stability. Palmitoylation is critical for LIMK1 function because this modification not only controls LIMK1 targeting, but is also essential for LIMK1 activation by its membrane-localized upstream activator PAK. These novel roles for palmitoylation in the spatial control of actin dynamics and kinase signaling provide new insights into structural plasticity mechanisms and strengthen links between dendritic spine impairments and neuropathological conditions.
Neurons transmit information from one cell to the next by passing signals across junctions called synapses. For the neurons that receive these signals, these junctions are found on fine branch-like structures called dendrites that stick out of the cell. Dendrites themselves are decorated with smaller structures called dendritic spines, which typically receive information from one other neuron via a single synapse. Dendritic spines form in response to the signaling activity of the neuron, and problems with forming these spines have been linked to conditions such as autism and schizophrenia.
Dendritic spines are created by the cell's cytoskeleton—a network of proteins that creates a constantly changing internal scaffold that shapes cells. One cytoskeleton protein called actin exists as thin filaments that can be extended or broken up by other proteins. It is not fully understood how actin is regulated in the dendritic spines. However, some researchers thought that the proteins that control the formation of the actin filaments would need to be localized to the dendritic spines to ensure that the spines form correctly.
Some proteins can be made to localize to cell membranes by attaching a molecule called palmitic acid to them. Previous research has suggested that this ‘palmitoylation’ process is particularly important in neurons. Through a combination of experimental techniques, George et al. now show that palmitoylation is required to localize a protein called LIMK1, which regulates the construction of actin filaments, to the tips of dendritic spines. Further experiments showed that blocking the palmitoylation of LIMK1 alters how actin filaments form, makes spines unstable and causes synapses to be lost.
George et al. also discovered that palmitoylation is necessary for LIMK1 to be activated by another protein that is found at dendritic spine membranes. This ‘dual-control’ mechanism makes it possible to precisely control where actin filaments form within dendritic spines. In addition to LIMK1, several other enzymes are also modified by palmitoylation. It will therefore be interesting to determine whether this dual control mechanism is broadly used by neurons to precisely regulate the structure and function of individual spines and synapses.
DHHC; dendritic spines; protein trafficking; LTP; glutamate; LIMK1; rat
Stromal cell-derived factor 1 α (SDF-1α), the ligand for G-protein-coupled receptor CXCR4, is a chemotactic factor for T lymphocytes. LIM kinase 1 (LIMK1) phosphorylates cofilin, an actin-depolymerizing and -severing protein, at Ser-3 and regulates actin reorganization. We investigated the role of cofilin phosphorylation by LIMK1 in SDF-1α-induced chemotaxis of T lymphocytes. SDF-1α significantly induced the activation of LIMK1 in Jurkat human leukemic T cells and peripheral blood lymphocytes. SDF-1α also induced cofilin phosphorylation, actin reorganization, and activation of small GTPases, Rho, Rac, and Cdc42, in Jurkat cells. Pretreatment with pertussis toxin inhibited SDF-1α-induced LIMK1 activation, thus indicating that Gi protein is involved in LIMK1 activation. Expression of dominant negative Rac (DN-Rac), but not DN-Rho or DN-Cdc42, blocked SDF-1α-induced activation of LIMK1, which means that SDF-1α-induced LIMK1 activation is mediated by Rac but not by Rho or Cdc42. We used a cell-permeable peptide (S3 peptide) that contains the phosphorylation site (Ser-3) of cofilin to inhibit the cellular function of LIMK1. S3 peptide inhibited the kinase activity of LIMK1 in vitro. Treatment of Jurkat cells with S3 peptide inhibited the SDF-1α-induced cofilin phosphorylation, actin reorganization, and chemotactic response of Jurkat cells. These results suggest that the phosphorylation of cofilin by LIMK1 plays a critical role in the SDF-1α-induced chemotactic response of T lymphocytes.