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European Journal of Cell Biology Jun 2020Podosomes are prominent actin-based adhesion structures in a variety of cell types. They feature an extensive repertoire of functions, which requires exquisite... (Review)
Review
Podosomes are prominent actin-based adhesion structures in a variety of cell types. They feature an extensive repertoire of functions, which requires exquisite spatiotemporal fine-tuning. Accordingly, podosomes consist of hundreds of different components, which fulfill specific structural and regulatory functions. Moreover, it has become apparent that podosome architecture is more intricate than previously believed. The classical model of an actin-rich core surrounded by a ring structure containing adhesion plaque proteins thus had to be expanded, and several additional substructures have been described, most notably the podosome cap on top of the actin-rich core. Here, we discuss the known components of the podosome cap, the history of their detection and their potential regulatory roles in podosome turnover and function. We also point out strategies for identifying further cap components and present a new model for the podosome cap as a multilayered module that fine-tunes actomyosin contractility, a central requirement for podosome architecture, dynamics and function.
Topics: Actins; Actomyosin; Humans; Microfilament Proteins; Podosomes
PubMed: 32646641
DOI: 10.1016/j.ejcb.2020.151087 -
Cell Adhesion & Migration 2014Osteoclasts are the cells responsible for physiological bone resorption. A specific organization of their most prominent cytoskeletal structures, podosomes, is crucial... (Review)
Review
Osteoclasts are the cells responsible for physiological bone resorption. A specific organization of their most prominent cytoskeletal structures, podosomes, is crucial for the degradation of mineralized bone matrix. Each podosome is constituted of an F-actin-enriched central core surrounded by a loose F-actin network, called the podosome cloud. In addition to intrinsic actin dynamics, podosomes are defined by their adhesion to the extracellular matrix, mainly via core-linking CD44 and cloud-linking integrins. These properties allow podosomes to collectively evolve into different patterns implicated in migration and bone resorption. Indeed, to resorb bone, osteoclasts polarize, actively secrete protons, and proteases into the resorption pit where these molecules are confined by a podosome-containing sealing zone. Here, we review recent advancements on podosome structure and regulatory pathways in osteoclasts. We also discuss the distinct functions of different podosome patterns during the lifespan of a single osteoclast.
Topics: Actin Cytoskeleton; Animals; Bone Resorption; Cell Adhesion; Cell Differentiation; Humans; Osteoclasts
PubMed: 24714644
DOI: 10.4161/cam.27840 -
European Journal of Cell Biology Apr 2006The bone resorption function of osteoclasts is dependent on the integrity of the actin cytoskeleton. Depending on the substratum upon which the osteoclasts are spread,... (Comparative Study)
Comparative Study Review
The bone resorption function of osteoclasts is dependent on the integrity of the actin cytoskeleton. Depending on the substratum upon which the osteoclasts are spread, there are two different structures of actin known as podosomes and the sealing zone. To understand the specific properties and relationship of podosomes and the sealing zone, we used live-cell imaging of cultured osteoclasts. When cultured on extracellular matrix components, podosomes in these cells are organized in higher-ordered structures. These are clustered podosomes that will arrange later into dynamic short-lived rings which finally expand to the cell periphery to form a stable long-lived podosome belt in fully differentiated cells. In osteoclasts, this specific podosome patterning is under the control of microtubules (MTs). Indeed, nocodazole treatment does not affect podosome formation but only the transition between clusters/rings and belts. During this transition, MTs accumulate a specific post-translational modification of tubulin by acetylation. This process is repressed by an inhibitory pathway involving the GTPase Rho, its effector mDIA2 and the recently discovered tubulin deacetylase HDAC6. The specific function of this acetylation is still unknown but is also observed in active osteoclasts forming a sealing zone which is also MT dependent. Thus, it appears that the podosome belt is reminiscent of the sealing zone. Indeed, podosome belts and sealing zones are characterized by their overall stability. Despite their similar behavior, a sealing zone is not formed by fusion of podosomes. The formation of a podosome belt or a sealing zone is controlled by the external environment. Indeed, only the bone mineral fraction, known as apatite crystal, is able to induce sealing zone formation in mature osteoclasts. Contact of osteoclasts with apatite stimulates the non-receptor tyrosine kinase c-Src and the GTPase Rho in order to form the sealing zone. As we will discuss in this review, it appears that podosomes and the sealing zone are strikingly linked.
Topics: Actin Cytoskeleton; Animals; Bone Resorption; CSK Tyrosine-Protein Kinase; Cell Adhesion; Cell Differentiation; Cell Surface Extensions; Humans; Microtubules; Models, Biological; Osteoclasts; Protein-Tyrosine Kinases; rho GTP-Binding Proteins; src-Family Kinases
PubMed: 16546562
DOI: 10.1016/j.ejcb.2005.09.008 -
Journal of Cell Science Dec 2019Podosomes are dynamic adhesion structures formed constitutively by macrophages, dendritic cells and osteoclasts and transiently in a wide variety of cells, such as... (Review)
Review
Podosomes are dynamic adhesion structures formed constitutively by macrophages, dendritic cells and osteoclasts and transiently in a wide variety of cells, such as endothelial cells and megakaryocytes. They mediate numerous functions, including cell-matrix adhesion, extracellular matrix degradation, mechanosensing and cell migration. Podosomes present as micron-sized F-actin cores surrounded by an adhesive ring of integrins and integrin-actin linkers, such as talin and vinculin. In this Review, we highlight recent research that has considerably advanced our understanding of the complex architecture-function relationship of podosomes by demonstrating that the podosome ring actually consists of discontinuous nano-clusters and that the actin network in between podosomes comprises two subsets of unbranched actin filaments, lateral and dorsal podosome-connecting filaments. These lateral and dorsal podosome-connecting filaments connect the core and ring of individual podosomes and adjacent podosomes, respectively. We also highlight recent insights into the podosome cap as a novel regulatory module of actomyosin-based contractility. We propose that these newly identified features are instrumental for the ability of podosomes to generate protrusion forces and to mechanically probe their environment. Furthermore, these new results point to an increasing complexity of podosome architecture and have led to our current view of podosomes as autonomous force generators that drive cell migration.
Topics: Animals; Cell Movement; Endothelial Cells; Humans; Megakaryocytes; Myosin Type II; Podosomes
PubMed: 31836688
DOI: 10.1242/jcs.236828 -
European Journal of Cell Biology Apr 2022Podosomes are highly dynamic actin-rich structures in a variety of cell types, especially monocytic cells. They fulfill multiple functions such as adhesion,... (Review)
Review
Podosomes are highly dynamic actin-rich structures in a variety of cell types, especially monocytic cells. They fulfill multiple functions such as adhesion, mechanosensing, or extracellular matrix degradation, thus allowing cells to detect and respond to a changing environment. These abilities are based on an intricate architecture that enables podosomes to sense mechanical properties of their substratum and to transduce them intracellularly in order to generate an appropriate cellular response. These processes are enabled through the tightly orchestrated interplay of more than 300 different components that are dynamically recruited during podosome formation and turnover. In this review, we discuss the different phases of the podosome life cycle and the current knowledge on regulatory factors that impact on the genesis, activity, dissolution and reemergence of podosomes. We also highlight mechanoregulatory processes that become important during these different stages, on the level of individual podosomes, and also at podosome sub- and superstructures.
Topics: Actins; Podosomes
PubMed: 35334303
DOI: 10.1016/j.ejcb.2022.151218 -
Nature Communications Sep 2023The activation and accumulation of lung fibroblasts resulting in aberrant deposition of extracellular matrix components, is a pathogenic hallmark of Idiopathic Pulmonary...
The activation and accumulation of lung fibroblasts resulting in aberrant deposition of extracellular matrix components, is a pathogenic hallmark of Idiopathic Pulmonary Fibrosis, a lethal and incurable disease. In this report, increased expression of TKS5, a scaffold protein essential for the formation of podosomes, was detected in the lung tissue of Idiopathic Pulmonary Fibrosis patients and bleomycin-treated mice. Τhe profibrotic milieu is found to induce TKS5 expression and the formation of prominent podosome rosettes in lung fibroblasts, that are retained ex vivo, culminating in increased extracellular matrix invasion. Tks5 mice are found resistant to bleomycin-induced pulmonary fibrosis, largely attributed to diminished podosome formation in fibroblasts and decreased extracellular matrix invasion. As computationally predicted, inhibition of src kinase is shown to potently attenuate podosome formation in lung fibroblasts and extracellular matrix invasion, and bleomycin-induced pulmonary fibrosis, suggesting pharmacological targeting of podosomes as a very promising therapeutic option in pulmonary fibrosis.
Topics: Animals; Humans; Mice; Adaptor Proteins, Vesicular Transport; Bleomycin; Extracellular Matrix; Fibroblasts; Idiopathic Pulmonary Fibrosis; Podosomes; Proto-Oncogene Proteins pp60(c-src)
PubMed: 37735172
DOI: 10.1038/s41467-023-41614-x -
Nature Reviews. Molecular Cell Biology Feb 2023Cell invasion into the surrounding extracellular matrix or across tissue boundaries and endothelial barriers occurs in both physiological and pathological scenarios such... (Review)
Review
Cell invasion into the surrounding extracellular matrix or across tissue boundaries and endothelial barriers occurs in both physiological and pathological scenarios such as immune surveillance or cancer metastasis. Podosomes and invadopodia, collectively called 'invadosomes', are actin-based structures that drive the proteolytic invasion of cells, by forming highly regulated platforms for the localized release of lytic enzymes that degrade the matrix. Recent advances in high-resolution microscopy techniques, in vivo imaging and high-throughput analyses have led to considerable progress in understanding mechanisms of invadosomes, revealing the intricate inner architecture of these structures, as well as their growing repertoire of functions that extends well beyond matrix degradation. In this Review, we discuss the known functions, architecture and regulatory mechanisms of podosomes and invadopodia. In particular, we describe the molecular mechanisms of localized actin turnover and microtubule-based cargo delivery, with a special focus on matrix-lytic enzymes that enable proteolytic invasion. Finally, we point out topics that should become important in the invadosome field in the future.
Topics: Podosomes; Actins; Extracellular Matrix; Microtubules; Proteolysis
PubMed: 36104625
DOI: 10.1038/s41580-022-00530-6 -
Communications Biology Mar 2020Integrin receptors orchestrate cell adhesion and cytoskeletal reorganization. The endocytic mechanism of integrin-β3 receptor at the podosome remains unclear. Using...
Integrin receptors orchestrate cell adhesion and cytoskeletal reorganization. The endocytic mechanism of integrin-β3 receptor at the podosome remains unclear. Using viscous RGD-membrane as the model system, here we show that the formation of podosome-like adhesion promotes Dab2/clathrin-mediated endocytosis of integrin-β3. Integrin-β3 and RGD ligand are endocytosed from the podosome and sorted into the endosomal compartment. Inhibitions of podosome formation and knockdowns of Dab2 and clathrin reduce RGD endocytosis. F-actin assembly at the podosome core exhibits protrusive contact towards the substrate and results in plasma membrane invaginations at the podosome ring. BIN1 specifically associates with the region of invaginated membrane and recruits DNM2. During the podosome formation, BIN1 and DNM2 synchronously enrich at the podosome ring and trigger clathrin dissociation and RGD endocytosis. Knockdowns of BIN1 and DNM2 suppress RGD endocytosis. Thus, plasma membrane invagination caused by F-actin polymerization promotes BIN1-dependent DNM2 recruitment and facilitate integrin-β3 endocytosis at the podosome.
Topics: Actins; Adaptor Proteins, Signal Transducing; Adaptor Proteins, Vesicular Transport; Animals; Cell Adhesion; Cell Membrane; Cells, Cultured; Clathrin; Dynamin II; Endocytosis; Fibroblasts; Gene Knockdown Techniques; Humans; Integrin beta3; Ligands; Membranes, Artificial; Mice; Nerve Tissue Proteins; Oligopeptides; Podosomes; Polymerization; Rats; Transfection; Tumor Suppressor Proteins
PubMed: 32170110
DOI: 10.1038/s42003-020-0843-2 -
Nature Communications Jul 2022Actin filaments assemble into force-generating systems involved in diverse cellular functions, including cell motility, adhesion, contractility and division. It remains...
Actin filaments assemble into force-generating systems involved in diverse cellular functions, including cell motility, adhesion, contractility and division. It remains unclear how networks of actin filaments, which individually generate piconewton forces, can produce forces reaching tens of nanonewtons. Here we use in situ cryo-electron tomography to unveil how the nanoscale architecture of macrophage podosomes enables basal membrane protrusion. We show that the sum of the actin polymerization forces at the membrane is not sufficient to explain podosome protrusive forces. Quantitative analysis of podosome organization demonstrates that the core is composed of a dense network of bent actin filaments storing elastic energy. Theoretical modelling of the network as a spring-loaded elastic material reveals that it exerts forces of a few tens of nanonewtons, in a range similar to that evaluated experimentally. Thus, taking into account not only the interface with the membrane but also the bulk of the network, is crucial to understand force generation by actin machineries. Our integrative approach sheds light on the elastic behavior of dense actin networks and opens new avenues to understand force production inside cells.
Topics: Actin Cytoskeleton; Actins; Cell Movement; Elasticity; Podosomes
PubMed: 35789161
DOI: 10.1038/s41467-022-30652-6 -
Journal of Cell Science Jun 2020Podosomes play crucial roles in macrophage adhesion and migration. Wiskott-Aldrich syndrome protein (WASP; also known as WAS)-mediated actin polymerization is one of the...
Podosomes play crucial roles in macrophage adhesion and migration. Wiskott-Aldrich syndrome protein (WASP; also known as WAS)-mediated actin polymerization is one of the key events initiating podosome formation. Nevertheless, membrane signals to trigger WASP activation at macrophage podosomes remain unclear. Here, we show that phosphatidylinositol (3,4,5)-trisphosphate [PI(3,4,5)P3] lipids are enriched at the podosome and stably recruit WASP rather than the WASP-5KE mutant. Phosphatidylinositol 4,5-bisphosphate 3-kinase catalytic subunit β (PIK3CB) is spatially located at the podosome core. Inhibition of PIK3CB and overexpression of phosphatase and tensin homolog (PTEN) impede F-actin polymerization of the podosome. PIK3CB activation is regulated by Abl1 and Src family kinases. At the podosome core, Src and Hck promote the phosphorylation of Tyr488 in the consensus Y-x-x-M motif of Abl1, which enables the association of phosphoinositide 3-kinase (PI3K) regulatory subunits. Knockdown of Abl1 rather than Abl2 suppresses the PI3K/Akt pathway, regardless of Src and Hck activities. Reintroduction of wild-type Abl1 rather than the Abl1-Y488F mutant rescues PI3KR1 recruitment and PI3K activation. When PIK3CB, Abl1 or Src/Hck is suppressed, macrophage podosome formation, matrix degradation and chemotactic migration are inhibited. Thus, Src/Hck-mediated phosphorylation of Abl1 Tyr488 triggers PIK3CB-dependent PI(3,4,5)P3 production and orchestrates the assembly and function of macrophage podosomes.
Topics: Actins; Macrophages; Phosphatidylinositol 3-Kinase; Phosphatidylinositol 3-Kinases; Phosphorylation; Podosomes
PubMed: 32393599
DOI: 10.1242/jcs.234385