Dynamics of ?-actinin in focal adhesions and stress fibers visualized with ?-actinin-green fluorescent protein

Podosomes, small actin-based adhesion structures, differ from focal adhesions in two aspects: their core structure and their ability to organize into large patterns in osteoclasts. To address the mechanisms underlying these features, we imaged live preosteoclasts expressing green fluorescent protein-actin during their differentiation. We observe that podosomes always form inside or close to podosome groups, which are surrounded by an actin cloud. Fluorescence recovery after photobleaching shows that actin turns over in individual podosomes in contrast to cortactin, suggesting a continuous actin polymerization in the podosome core. The observation of podosome assemblies during osteoclast differentiation reveals that they evolve from simple clusters into rings that expand by the continuous formation of new podosomes at their outer ridge and inhibition of podosome formation inside the rings. This self-organization of podosomes into dynamic rings is the mechanism that drives podosomes at the periphery of the cell in large circular patterns. We also show that an additional step of differentiation, requiring microtubule integrity, stabilizes the podosome circles at the cell periphery to form the characteristic podosome belt pattern of mature osteoclasts. These results therefore provide a mechanism for the patterning of podosomes in osteoclasts and reveal a turnover of actin inside the podosome.

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Arfophilins Are Dual Arf/Rab 11 Binding Proteins That Regulate Recycling Endosome Distribution and Are Related to Drosophila Nuclear Fallout

Molecular Biology of the Cell ◽

10.1091/mbc.e03-03-0160 ◽

2003 ◽

Vol 14 (7) ◽

pp. 2908-2920 ◽

Cited By ~ 95

Author(s):

Gilles R.X. Hickson ◽

Johanne Matheson ◽

Blake Riggs ◽

Valerie H. Maier ◽

Andrew B. Fielding ◽

...

Keyword(s):

Green Fluorescent Protein ◽

Fluorescent Protein ◽

Binding Capacity ◽

Binding Protein ◽

Focal Adhesions ◽

Dependent Manner ◽

Recycling Endosome ◽

Nuclear Fallout ◽

Endosomal Recycling ◽

Green Fluorescent

Arfophilin is an ADP ribosylation factor (Arf) binding protein of unknown function. It is identical to the Rab11 binding protein eferin/Rab11-FIP3, and we show it binds both Arf5 and Rab11. We describe a related protein, arfophilin-2, that interacts with Arf5 in a nucleotide-dependent manner, but not Arf1, 4, or 6 and also binds Rab11. Arfophilin-2 localized to a perinuclear compartment, the centrosomal area, and focal adhesions. The localization of arfophilin-2 to the perinuclear compartment was selectively blocked by overexpression of Arf5-T31N. In contrast, a green fluorescent protein-arfophilin-2 chimera or arfophilin-2 deletions were localized around the centrosome in a region that was also enriched for transferrin receptors and Rab11 but not early endosome markers, suggesting that the distribution of the endosomal recycling compartment was altered. The arfophilins belong to a conserved family that includes Drosophila melanogaster nuclear fallout, a centrosomal protein required for cellularization. Expression of green fluorescent protein-nuclear fallout in HeLa cells resulted in a similar phenotype, indicative of functional homology and thus implicating the arfophilins in mitosis/cytokinesis. We suggest that the novel dual GTPase-binding capacity of the arfophilins could serve as an interface of signals from Rab and Arf GTPases to regulate membrane traffic and integrate distinct signals in the late endosomal recycling compartment.

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Green fluorescent protein (GFP) tagged to the cytoplasmic tail of αIIb or β3 allows the expression of a fully functional integrin αIIbβ3: effect of β3GFP on αIIbβ3 ligand binding

Biochemical Journal ◽

10.1042/bj3570529 ◽

2001 ◽

Vol 357 (2) ◽

pp. 529-536 ◽

Cited By ~ 15

Author(s):

Sébastien PLANÇON ◽

Marie-Christine MOREL-KOPP ◽

Elisabeth SCHAFFNER-RECKINGER ◽

Ping CHEN ◽

Nelly KIEFFER

Keyword(s):

Green Fluorescent Protein ◽

Fluorescent Protein ◽

Chinese Hamster ◽

Focal Adhesions ◽

Cytoplasmic Tail ◽

Receptor Activation ◽

Living Cells ◽

Cell Surface Expression ◽

Β3 Integrin ◽

Green Fluorescent

Using green fluorescent protein (GFP) as an autofluorescent tag, we report the first successful visualization of a β3 integrin in a living cell. GFP fused in frame to the cytoplasmic tail of either αIIb or β3 allowed normal expression, heterodimerization, processing and surface exposure of αIIbGFPβ3 and αIIbβ3GFP receptors in Chinese hamster ovary (CHO) cells. Direct microscopic observation of the autofluorescent cells in suspension following antibody-induced αIIbβ3 capping revealed an intense autofluorescent cap corresponding to unlabelled immunoclustered GFP-tagged αIIbβ3. GFP-tagged αIIbβ3 receptors mediated fibrinogen-dependent cell adhesion, were readily detectable in focal adhesions of unstained living cells and triggered p125FAK tyrosine phosphorylation similar to wild-type αIIbβ3 (where FAK corresponds to focal adhesion kinase). However, GFP tagged to β3, but not to αIIb, induced spontaneous CHO cell aggregation in the presence of soluble fibrinogen, as well as binding of the fibrinogen mimetic monoclonal antibody PAC1 in the absence of αIIbβ3 receptor activation. Time-lapse imaging of living transfectants revealed a characteristic redistribution of GFP-tagged αIIbβ3 during the early stages of cell attachment and spreading, starting with αIIbβ3 clustering at the rim of the cell contact area, that gradually overlapped with the boundary of the attached cell, and, with the onset of cell spreading, to a reorganization of αIIbβ3 in focal adhesions. Taken together, our results demonstrate that (1) fusion of GFP to the cytoplasmic tail of either αIIb or β3 integrin subunits allows normal cell surface expression of a functional receptor, and (2) structural modification of the β3 integrin cytoplasmic tail, rather than the αIIb subunit, plays a major role in αIIbβ3 affinity modulation. With the successful direct visualization of functional αIIbβ3 receptors in living cells, the generation of autofluorescent integrins in transgenic animals will become possible, allowing new approaches to study the dynamics of integrin functions.

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Zyxin Is not Colocalized with Vasodilator-stimulated Phosphoprotein (VASP) at Lamellipodial Tips and Exhibits Different Dynamics to Vinculin, Paxillin, and VASP in Focal Adhesions

Molecular Biology of the Cell ◽

10.1091/mbc.12.10.3103 ◽

2001 ◽

Vol 12 (10) ◽

pp. 3103-3113 ◽

Cited By ~ 71

Author(s):

Klemens Rottner ◽

Matthias Krause ◽

Mario Gimona ◽

J. Victor Small ◽

Jürgen Wehland

Keyword(s):

Focal Adhesion ◽

Actin Polymerization ◽

Fluorescent Protein ◽

Protein Complexes ◽

Focal Adhesions ◽

Stress Fibers ◽

Live Cells ◽

Fusion Construct ◽

Focal Adhesion Protein ◽

Green Fluorescent

Actin polymerization is accompanied by the formation of protein complexes that link extracellular signals to sites of actin assembly such as membrane ruffles and focal adhesions. One candidate recently implicated in these processes is the LIM domain protein zyxin, which can bind both Ena/vasodilator-stimulated phosphoprotein (VASP) proteins and the actin filament cross-linking protein α-actinin. To characterize the localization and dynamics of zyxin in detail, we generated both monoclonal antibodies and a green fluorescent protein (GFP)-fusion construct. The antibodies colocalized with ectopically expressed GFP-VASP at focal adhesions and along stress fibers, but failed to label lamellipodial and filopodial tips, which also recruit Ena/VASP proteins. Likewise, neither microinjected, fluorescently labeled zyxin antibodies nor ectopically expressed GFP-zyxin were recruited to these latter sites in live cells, whereas both probes incorporated into focal adhesions and stress fibers. Comparing the dynamics of zyxin with that of the focal adhesion protein vinculin revealed that both proteins incorporated simultaneously into newly formed adhesions. However, during spontaneous or induced focal adhesion disassembly, zyxin delocalization preceded that of either vinculin or paxillin. Together, these data identify zyxin as an early target for signals leading to adhesion disassembly, but exclude its role in recruiting Ena/VASP proteins to the tips of lamellipodia and filopodia.

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α4β1 Integrin Regulates Lamellipodia Protrusion via a Focal Complex/Focal Adhesion-independent Mechanism

Molecular Biology of the Cell ◽

10.1091/mbc.02-05-0086 ◽

2002 ◽

Vol 13 (9) ◽

pp. 3203-3217 ◽

Cited By ~ 35

Author(s):

Karen A. Pinco ◽

Wei He ◽

Joy T. Yang

Keyword(s):

Green Fluorescent Protein ◽

Fluorescent Protein ◽

Chinese Hamster Ovary Cells ◽

Chinese Hamster ◽

Focal Adhesions ◽

Leading Edge ◽

Time Lapse ◽

Random Motility ◽

Protein Fusion ◽

Green Fluorescent

α4β1 integrin plays an important role in cell migration. We show that when ectopically expressed in Chinese hamster ovary cells, α4β1 is sufficient and required for promoting protrusion of broad lamellipodia in response to scratch-wounding, whereas α5β1 does not have this effect. By time-lapse microscopy of cells expressing an α4/green fluorescent protein fusion protein, we show that α4β1 forms transient puncta at the leading edge of cells that begin to protrude lamellipodia in response to scratch-wounding. The cells expressing a mutant α4/green fluorescent protein that binds paxillin at a reduced level had a faster response to scratch-wounding, forming α4-positive puncta and protruding lamellipodia much earlier. While enhancing lamellipodia protrusion, this mutation reduces random motility of the cells in Transwell assays, indicating that lamellipodia protrusion and random motility are distinct types of motile activities that are differentially regulated by interactions between α4β1 and paxillin. Finally, we show that, at the leading edge, α4-positive puncta and paxillin-positive focal complexes/adhesions do not colocalize, but α4β1 and paxillin colocalize partially in ruffles. These findings provide evidence for a specific role of α4β1 in lamellipodia protrusion that is distinct from the motility-promoting functions of α5β1 and other integrins that mediate cell adhesion and signaling events through focal complexes and focal adhesions.

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