The F-actin bundler SWAP-70 promotes tumor metastasis

Cancers, 2021

In cancer cells, a vital cellular process during metastasis is the transformation of epithelial cells towards motile mesenchymal cells called the epithelial to mesenchymal transition (EMT). The cytoskeleton is an active network of three intracellular filaments: actin cytoskeleton, microtubules, and intermediate filaments. These filaments play a central role in the structural design and cell behavior and are necessary for EMT. During EMT, epithelial cells undergo a cellular transformation as manifested by cell elongation, migration, and invasion, coordinated by actin cytoskeleton reorganization. The actin cytoskeleton is an extremely dynamic structure, controlled by a balance of assembly and disassembly of actin filaments. Actin-binding proteins regulate the process of actin polymerization and depolymerization. Microtubule reorganization also plays an important role in cell migration and polarization. Intermediate filaments are rearranged, switching to a vimentin-rich network, and th...

Cancer Research, 2010

A key cellular process associated with the invasive or metastatic program in many cancers is the transformation of epithelial cells toward a mesenchymal state, a process called epithelial to mesenchymal transition or EMT. Actin-dependent protrusion of cell pseudopodia is a critical element of mesenchymal cell migration and therefore of cancer metastasis. However, whether EMT occurs in human cancers and, in particular, whether it is a prerequisite for tumor cell invasion and metastasis, remains a subject of debate. Microarray and proteomic analysis of actin-rich pseudopodia from six metastatic human tumor cell lines identified 384 mRNAs and 64 proteins common to the pseudopodia of six metastatic human tumor cell lines of various cancer origins leading to the characterization of 19 common pseudopod-specific proteins. Four of these (AHNAK, septin-9, eIF4E, and S100A11) are shown to be essential for pseudopod protrusion and tumor cell migration and invasion. Knockdown of each of these p...

Seminars in cell & developmental biology, 2017

Metastatic cancer cells invading through dense tumor stroma experience internal and external forces that are sensed through a variety of mechanosensory proteins that drive adaptations for specific environments. Alpha-actinin-4 (ACTN4) is a member of the α-actinin family of actin crosslinking proteins that is upregulated in several types of cancers. It shares 86% protein similarity with α-actinin-1, another non-muscle ACTN isoform, which appears to have a more modest role, if any, in cancer progression. While they share regulatory mechanisms, such as phosphorylation, calcium binding, phosphatidyl inositol binding, and calpain cleavage, α-actinin-4 exhibits a unique mechanosensory regulation that α-actinin-1 does not. This behavior is mediated, at least in part, by each protein's actin-binding affinity as well as the catch-slip-bond behavior of the actin binding domains. We will discuss currently known modes of ACTN4 regulation, their interactions, and how mechanosensation may pro...

The International Journal of Biochemistry & Cell Biology, 2004

Cell motility is crucial for tissue formation and for development of organisms. Later on cell migration remains essential throughout the lifetime of the organism for wound healing and immune responses. The actin cytoskeleton is the cellular engine that drives cell motility downstream of a complex signal transduction cascade. The basic molecular machinery underlying the assembly and disassembly of actin filaments consists of a variety of actin binding proteins that regulate the dynamic behavior of the cytoskeleton in response to different signals. The multitude of proteins and regulatory mechanisms partaking in this system makes it vulnerable to mutations and alterations in expression levels that ultimately may cause diseases. The most familiar one is cancer that in later stages is characterized by active aberrant cell migration. Indeed tumor invasion and metastasis are increasingly being associated with deregulation of the actin system.

Journal of cellular and molecular medicine, 2015

Cancer metastasis occurs via a progress involving abnormal cell migration. Cell migration, a dynamic physical process, is controlled by the cytoskeletal system, which includes the dynamics of actin organization and cellular adhesive organelles, focal adhesions (FAs). However, it is not known whether the organization of actin cytoskeletal system has a regulatory role in the physiologically relevant aspects of cancer metastasis. In the present studies, it was found that lung adenocarcinoma cells isolated from the secondary lung cancer of the lymph nodes, H1299 cells, show specific dynamics in terms of the actin cytoskeleton and FAs. This results in a higher level of mobility and this is regulated by an immature FA component, β-PIX (PAK-interacting exchange factor-β). In H1299 cells, β-PIX's activity was found not to be down-regulated by sequestration onto stress fibres, as the cells did not bundle actin filaments into stress fibres. Thus, β-PIX mainly remained localized at FAs, wh...

Breast Cancer Research, 2013

Introduction: Aberrant turnover of the actin cytoskeleton is intimately associated with cancer cell migration and invasion. Frequently however, evidence is circumstantial, and a reliable assessment of the therapeutic significance of a gene product is offset by lack of inhibitors that target biologic properties of a protein, as most conventional drugs do, instead of the corresponding gene. Proteomic studies have demonstrated overexpression of CapG, a constituent of the actin cytoskeleton, in breast cancer. Indirect evidence suggests that CapG is involved in tumor cell dissemination and metastasis. In this study, we used llama-derived CapG single-domain antibodies or nanobodies in a breast cancer metastasis model to address whether inhibition of CapG activity holds therapeutic merit.

Current Opinion in Cell Biology, 2012

Metastasis requires tumor cell dissemination to different organs from the primary tumor. Dissemination is a complex cell motility phenomenon that requires the molecular coordination of the protrusion, chemotaxis, invasion and contractility activities of tumor cells to achieve directed cell migration. Recent studies of the spatial and temporal activities of the small GTPases have begun to elucidate how this coordination is achieved. The direct visualization of the pathways involved in actin polymerization, invasion and directed migration in dissemination competent tumor cells will help identify the molecular basis of dissemination and allow the design and testing of more specific and selective drugs to block metastasis.

Cytoskeleton, 2013

Tumor initiation and progression are accompanied by complex changes in the cytoarchitecture that at the cellular level involve remodeling of the cytoskeleton. We report on the impact of a mutant b-actin (G245Dactin) on cell structure and multicellular assembly properties. To appreciate the effects of the Gly245Asp substitution on the organization of the actin cytoskeleton, we examined the polymerization properties of G245D-actin in vitro by pyrene polymerization assays and total internal reflection fluorescence microscopy (TIRF). The mutant actin on its own has a significantly reduced polymerization efficiency compared to native actin but also modifies the polymerization of actin in copolymerization experiments. Comparison of the structure of Rat-2 fibroblasts and a stably transfected derivate called Rat-2-sm9 revealed the effects of G245D-actin in a cellular environment. The overall actin levels in Rat-2-sm9 show a 1.6-fold increase with similar amounts of mutant and wild-type actin. G245D-actin expression renders Rat-2-sm9 cells highly tumorigenic in nude mice. In Rat-2-sm9 monolayers, G245D-actin triggers the formation of extensive membrane ruffles, which is a characteristic feature of many transformed cells. To approximate complex cell-cell and cell-matrix interactions that occur in tumors and might modulate the effects of G245D-actin, we extended our studies to scaffold-free 3D spheroid cultures. Bright field and scanning electron microscopy (SEM) show that Rat-2-sm9 and Rat-2 cells share essential features of spheroid formation and compaction. However, the resulting spheroids exhibit distinct phenotypes that differ mainly in surface structure and size.

Experimental Cell Research, 2004

We have examined the role of endogenous 70-kDa S6 kinase (p70 S6K) in actin cytoskeletal organization and cell migration in Swiss 3T3 fibroblasts. Association of p70 S6K with the actin cytoskeleton was demonstrated by cosedimentation of p70 S6K with F-actin and by subcellular fractionation in which p70 S6K activity was measured in the F-actin cytoskeletal fraction. Immunocytochemical studies showed that p70 S6K , Akt1, PDK1, and p85 phosphoinositide 3-kinase (PI 3-kinase) were localized to the actin arc, a caveolin-enriched cytoskeletal structure located at the leading edge of migrating cells. Using a phospho-specific antibody to mammalian target of rapamycin (mTOR), we find that activated mTOR is enriched at the actin arc, suggesting that activation of the p70 S6K signaling pathway is important to cell migration. Using the actin arc to assess migration, epidermal growth factor (EGF) stimulation was found to induce actin arc formation, an effect that was blocked by rapamycin treatment. We show further that actin stress fibers may function to down-regulate p70 S6K. Fibronectin stimulated stress fiber formation in the absence of growth factors and caused an inactivation of p70 S6K. Conversely, cytochalasin D and the Rho kinase inhibitor Y-27632, both of which cause stress fiber disruption, increased p70 S6K activity. These studies provide evidence that the p70 S6K pathway is important for signaling at two F-actin microdomains in cells and regulates cell migration.

PLoS ONE, 2014

Cellular motility is the basis for cancer cell invasion and metastasis. In the case of breast cancer, the most common type of cancer among women, metastasis represents the most devastating stage of the disease. The central role of cellular motility in cancer development emphasizes the importance of understanding the specific mechanisms involved in this process. In this context, tumor development and metastasis would be the consequence of a loss or defect of the mechanisms that control cytoskeletal remodeling. Profilin I belongs to a family of small actin binding proteins that are thought to assist in actin filament elongation at the leading edge of migrating cells. Traditionally, Profilin I has been considered to be an essential control element for actin polymerization and cell migration. Expression of Profilin I is down-regulated in breast and various other cancer cells. In MDA-MB-231 cells, a breast cancer cell line, further inhibition of Profilin I expression promotes hypermotility and metastatic spread, a finding that contrasts with the proposed role of Profilin in enhancing polymerization. In this report, we have taken advantage of the fluorescence recovery after photobleaching (FRAP) of GFP-actin to quantify and compare actin dynamics at the leading edge level in both cancer and non-cancer cell models. Our results suggest that (i) a high level of actin dynamics (i.e., a large mobile fraction of actin filaments and a fast turnover) is a common characteristic of some cancer cells; (ii) actin polymerization shows a high degree of independence from the presence of extracellular growth factors; and (iii) our results also corroborate the role of Profilin I in regulating actin polymerization, as raising the intracellular levels of Profilin I decreased the mobile fraction ratio of actin filaments and slowed their polymerization rate; furthermore, increased Profilin levels also led to reduced individual cell velocity and directionality.