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ELife Feb 2020Transport of fluids, molecules, nutrients or nanoparticles through coral tissues are poorly documented. Here, we followed the flow of various tracers from the external...
Transport of fluids, molecules, nutrients or nanoparticles through coral tissues are poorly documented. Here, we followed the flow of various tracers from the external seawater to within the cells of all tissues in living animals. After entering the general coelenteric cavity, we show that nanoparticles disperse throughout the tissues via the paracellular pathway. Then, the ubiquitous entry gate to within the cells' cytoplasm is macropinocytosis. Most cells form large vesicles of 350-600 nm in diameter at their apical side, continuously internalizing their surrounding medium. Macropinocytosis was confirmed using specific inhibitors of PI3K and actin polymerization. Nanoparticle internalization dynamics is size dependent and differs between tissues. Furthermore, we reveal that macropinocytosis is likely a major endocytic pathway in other anthozoan species. The fact that nearly all cells of an animal are continuously soaking in the environment challenges many aspects of the classical physiology viewpoints acquired from the study of bilaterians.
Topics: Actins; Animals; Anthozoa; Cytoplasm; Dextrans; Diffusion; Models, Biological; Nanoparticles; Pinocytosis
PubMed: 32039759
DOI: 10.7554/eLife.50022 -
International Journal of Molecular... Dec 2019Unconventional myosins are multi-potent molecular motors that are assigned important roles in fundamental cellular processes. Depending on their mechano-enzymatic... (Review)
Review
Unconventional myosins are multi-potent molecular motors that are assigned important roles in fundamental cellular processes. Depending on their mechano-enzymatic properties and structural features, myosins fulfil their roles by acting as cargo transporters along the actin cytoskeleton, molecular anchors or tension sensors. In order to perform such a wide range of roles and modes of action, myosins need to be under tight regulation in time and space. This is achieved at multiple levels through diverse regulatory mechanisms: the alternative splicing of various isoforms, the interaction with their binding partners, their phosphorylation, their applied load and the composition of their local environment, such as ions and lipids. This review summarizes our current knowledge of how unconventional myosins are regulated, how these regulatory mechanisms can adapt to the specific features of a myosin and how they can converge with each other in order to ensure the required tight control of their function.
Topics: Actins; Alternative Splicing; Animals; Humans; Myosins; Phospholipids; Phosphorylation; Protein Interaction Maps; Protein Isoforms; Protein Multimerization
PubMed: 31861842
DOI: 10.3390/ijms21010067 -
Current Opinion in Cell Biology Jun 2020Actin has essential functions both in the cytoplasm and in the nucleus, where it has been linked to key nuclear processes, from transcription to DNA damage response. The... (Review)
Review
Actin has essential functions both in the cytoplasm and in the nucleus, where it has been linked to key nuclear processes, from transcription to DNA damage response. The multifunctional nature of actin suggests that the cell must contain mechanisms to accurately control the cellular actin balance. Indeed, recent results have demonstrated that nuclear actin levels fluctuate to regulate the transcriptional activity of the cell and that controlled nuclear actin polymerization is required for transcription activation, cell cycle progression, and DNA repair. Intriguingly, aberrant nuclear actin regulation has been observed, for example, in cancer, signifying the importance of this process for cellular homeostasis. This review discussed the latest research on how nuclear actin is regulated, and how this influences actin-dependent nuclear processes.
Topics: Actins; Animals; Cell Nucleus; Gene Expression Regulation; Genome; Humans; Polymerization; Transcription, Genetic
PubMed: 32088545
DOI: 10.1016/j.ceb.2020.01.012 -
Circulation Research Aug 2023FLNC (filamin C), a member of the filamin family predominantly expressed in striated muscles, plays a crucial role in bridging the cytoskeleton and ECM (extracellular...
BACKGROUND
FLNC (filamin C), a member of the filamin family predominantly expressed in striated muscles, plays a crucial role in bridging the cytoskeleton and ECM (extracellular matrix) in cardiomyocytes, thereby maintaining heart integrity and function. Although genetic variants within the N-terminal ABD (actin-binding domain) of FLNC have been identified in patients with cardiomyopathy, the precise contribution of the actin-binding capability to FLNC's function in mammalian hearts remains poorly understood.
METHODS
We conducted in silico analysis of the 3-dimensional structure of mouse FLNC to identify key amino acid residues within the ABD that are essential for FLNC's actin-binding capacity. Subsequently, we performed coimmunoprecipitation and immunofluorescent assays to validate the in silico findings and assess the impact of these mutations on the interactions with other binding partners and the subcellular localization of FLNC. Additionally, we generated and analyzed knock-in mouse models in which the FLNC-actin interaction was completely disrupted by these mutations.
RESULTS
Our findings revealed that F93A/L98E mutations completely disrupted FLNC-actin interaction while preserving FLNC's ability to interact with other binding partners ITGB1 (β1 integrin) and γ-SAG (γ-sarcoglycan), as well as maintaining FLNC subcellular localization. Loss of FLNC-actin interaction in embryonic cardiomyocytes resulted in embryonic lethality and cardiac developmental defects, including ventricular wall malformation and reduced cardiomyocyte proliferation. Moreover, disruption of FLNC-actin interaction in adult cardiomyocytes led to severe dilated cardiomyopathy, enhanced lethality and dysregulation of key cytoskeleton components.
CONCLUSIONS
Our data strongly support the crucial role of FLNC as a bridge between actin filaments and ECM through its interactions with actin, ITGB1, γ-SAG, and other associated proteins in cardiomyocytes. Disruption of FLN-actin interaction may result in detachment of actin filaments from the extracellular matrix, ultimately impairing normal cardiac development and function. These findings also provide insights into mechanisms underlying cardiomyopathy associated with genetic variants in FLNC ABD and other regions.
Topics: Mice; Animals; Filamins; Actins; Muscle, Skeletal; Cardiomyopathies; Myocytes, Cardiac; Mutation; Mammals
PubMed: 37492967
DOI: 10.1161/CIRCRESAHA.123.322750 -
ELife Aug 2022Fascin is an important regulator of F-actin bundling leading to enhanced filopodia assembly. Fascin is also overexpressed in most solid tumours where it supports...
Fascin is an important regulator of F-actin bundling leading to enhanced filopodia assembly. Fascin is also overexpressed in most solid tumours where it supports invasion through control of F-actin structures at the periphery and nuclear envelope. Recently, fascin has been identified in the nucleus of a broad range of cell types but the contributions of nuclear fascin to cancer cell behaviour remain unknown. Here, we demonstrate that fascin bundles F-actin within the nucleus to support chromatin organisation and efficient DDR. Fascin associates directly with phosphorylated Histone H3 leading to regulated levels of nuclear fascin to support these phenotypes. Forcing nuclear fascin accumulation through the expression of nuclear-targeted fascin-specific nanobodies or inhibition of Histone H3 kinases results in enhanced and sustained nuclear F-actin bundling leading to reduced invasion, viability, and nuclear fascin-specific/driven apoptosis. These findings represent an additional important route through which fascin can support tumourigenesis and provide insight into potential pathways for targeted fascin-dependent cancer cell killing.
Topics: Actins; Carrier Proteins; Cell Survival; Histones; Humans; Microfilament Proteins; Neoplasms
PubMed: 36039640
DOI: 10.7554/eLife.79283 -
Journal of Clinical Immunology Nov 2022Cells of the innate and adaptive immune systems depend on proper actin dynamics to control cell behavior for effective immune responses. Dysregulated actin networks are... (Review)
Review
Cells of the innate and adaptive immune systems depend on proper actin dynamics to control cell behavior for effective immune responses. Dysregulated actin networks are known to play a pathogenic role in an increasing number of inborn errors of immunity. The WAVE regulatory complex (WRC) mediates branched actin polymerization, a process required for key cellular functions including migration, phagocytosis, vesicular transport, and immune synapse formation. Recent reports of pathogenic variants in NCKAP1L, a hematopoietically restricted gene encoding the HEM1 protein component of the WRC, defined a novel disease involving recurrent bacterial and viral infections, autoimmunity, and excessive inflammation (OMIM 141180). This review summarizes the diverse clinical presentations and immunological phenotypes observed in HEM1-deficient patients. In addition, we integrate the pathophysiological mechanisms described in current literature and highlight the outstanding questions for diagnosis and management of the HEM1 actin immunodysregulatory disorder.
Topics: Humans; Actins; Phagocytosis; Autoimmunity; Phenotype; Genotype; Membrane Proteins
PubMed: 35869404
DOI: 10.1007/s10875-022-01327-0 -
Current Biology : CB May 2021Actin filaments play multiple roles in the secretory pathway and in endosome dynamics in mammals, including maintenance of Golgi structure, release of membrane cargo... (Review)
Review
Actin filaments play multiple roles in the secretory pathway and in endosome dynamics in mammals, including maintenance of Golgi structure, release of membrane cargo from the trans-Golgi network (TGN), endocytosis, and endosomal sorting dynamics. In addition, TGN carrier transport and endocytosis both occur by multiple mechanisms in mammals. Actin likely plays a role in at least four mammalian endocytic pathways, five pathways for membrane release from the TGN, and three processes involving endosomes. Also, the mammalian Golgi structure is highly dynamic, and actin is likely important for these dynamics. One challenge for many of these processes is the need to deal with other membrane-associated structures, such as the cortical actin network at the plasma membrane or the matrix that surrounds the Golgi. Arp2/3 complex is a major actin assembly factor in most of the processes mentioned, but roles for formins and tandem WH2-motif-containing assembly factors are being elucidated and are anticipated to grow with further study. The specific role for actin has not been defined for most of these processes, but is likely to involve the generation of force for membrane dynamics, either by actin polymerization itself or by myosin motor activity. Defining these processes mechanistically is necessary for understanding membrane dynamics in general, as well as pathways that utilize these processes, such as autophagy.
Topics: Actins; Animals; Biological Transport; Endocytosis; Endosomes; Protein Transport; trans-Golgi Network
PubMed: 34033793
DOI: 10.1016/j.cub.2021.03.038 -
Transfusion Apr 2020During platelet storage, there are extensive changes in cytoskeleton and phosphatidylserine exposure. The intrinsic mitochondrial pathway of apoptosis, activated in...
BACKGROUND
During platelet storage, there are extensive changes in cytoskeleton and phosphatidylserine exposure. The intrinsic mitochondrial pathway of apoptosis, activated in stored platelets, is a major mediator these changes. Cofilin-1 is an effector of actin reorganization. We examined the effect of cofilin-1 deficiency on cytoskeleton and phosphatidylserine exposure during storage and following activation of apoptosis.
METHODS AND RESULTS
We assessed actin filaments by Alexa-647-phalloidin and phosphatidylserine exposure by fluorescein isothiocyanate-lactadherin by fluorescence microscopy. In fresh platelets, actin filaments are distributed in the subcortical region, and they do not express phosphatidylserine in the outer surface. In stored platelets, there is retraction of actin filaments from the subcortical region with increased phosphatidylserine expression. These changes are seen in 20% of platelets of 6 days old and increases further with storage. Treatment with ABT-737, which activates the mitochondrial apoptosis, induces similar cytoskeletal changes in actin filaments with increased phosphatidylserine. Cofilin-1 is activated in stored platelets as well as in ABT-737 treated platelets by dephosphorylation. In cofilin-1 deficient murine platelets actin filaments are abnormal and ABT-737 induces less phosphatidylserine. Despite these changes in vitro, platelet survival of cofilin-1 deficient platelets in mice was not significantly different from their wild-type controls.
CONCLUSION
These results show that cofilin-1 plays a role in apoptosis-induced actin rearrangement and phosphatidylserine exposure during storage. Despite the defects in platelet cytoskeleton and phosphatidylserine exposure in cofilin-1-deficient platelets, the in vivo life span of platelets is similar to littermate controls, indicating multiple redundant pathways for the clearance of platelets in vivo.
Topics: Actins; Animals; Apoptosis; Biphenyl Compounds; Blood Platelets; Blood Preservation; Cofilin 1; Cytoskeleton; Humans; Mice; Nitrophenols; Phosphatidylserines; Piperazines; Sulfonamides
PubMed: 32159862
DOI: 10.1111/trf.15747 -
Trends in Biochemical Sciences May 2023Actin, one of the most abundant proteins in nature and a key component of the cytoskeleton, undergoes a unique multistep N-terminal (Nt) maturation. In a recent report,...
Actin, one of the most abundant proteins in nature and a key component of the cytoskeleton, undergoes a unique multistep N-terminal (Nt) maturation. In a recent report, Haahr et al. identified actin maturation protease (ACTMAP) as the dedicated actin aminopeptidase and showed that its absence is associated with abnormal muscle physiology.
Topics: Actins; Cytoskeleton; Actin Cytoskeleton
PubMed: 36804256
DOI: 10.1016/j.tibs.2023.02.002 -
Journal of Biosciences 2023Eukaryotic cell migration requires continuous supply of actin polymers at the leading edges to make and extend lamellipodia or pseudopodia. Linear and branched... (Review)
Review
Eukaryotic cell migration requires continuous supply of actin polymers at the leading edges to make and extend lamellipodia or pseudopodia. Linear and branched filamentous actin polymers fuel cell migration. Branching of actin polymers in the lamellipodia/pseudopodia is facilitated by the actin-related protein (Arp) 2/3 complex, whose function is essentially controlled by the Scar/WAVE complex. In cells, the Scar/WAVE complex remains inactive, and its activation is a highly regulated and complex process. In response to signalling cues, GTP-bound Rac1 associates with Scar/WAVE and causes activation of the complex. Rac1 is essential but not sufficient for the activation of the Scar/ WAVE complex, and it requires multiple regulators, such as protein interactors and modifications (phosphorylation, ubiquitylation, etc.). Although our understanding of the regulation of the Scar/WAVE complex has improved over the last decade, it remains enigmatic. In this review, we have provided an overview of actin polymerization and discussed the importance of various regulators of Scar/WAVE activation.
Topics: Actin Cytoskeleton; Actins; Cell Movement; rac1 GTP-Binding Protein
PubMed: 37204155
DOI: No ID Found