Limits...
Marching at the front and dragging behind: differential alphaVbeta3-integrin turnover regulates focal adhesion behavior.

Ballestrem C, Hinz B, Imhof BA, Wehrle-Haller B - J. Cell Biol. (2001)

Bottom Line: We have analyzed alphaVbeta3-integrin dynamics in migrating cells using a green fluorescent protein-tagged beta3-integrin chain.Photobleaching experiments demonstrated a slow turnover of beta3-integrins in low-density contacts, which may account for their stationary nature.In contrast, the fast beta3-integrin turnover observed in high-density contacts suggests that their apparent sliding may be caused by a polarized renewal of focal contacts.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology, Centre Médical Universitaire, Geneva, Switzerland.

ABSTRACT
Integrins are cell-substrate adhesion molecules that provide the essential link between the actin cytoskeleton and the extracellular matrix during cell migration. We have analyzed alphaVbeta3-integrin dynamics in migrating cells using a green fluorescent protein-tagged beta3-integrin chain. At the cell front, adhesion sites containing alphaVbeta3-integrin remain stationary, whereas at the rear of the cell they slide inward. The integrin fluorescence intensity within these different focal adhesions, and hence the relative integrin density, is directly related to their mobility. Integrin density is as much as threefold higher in sliding compared with stationary focal adhesions. High intracellular tension under the control of RhoA induced the formation of high-density contacts. Low-density adhesion sites were induced by Rac1 and low intracellular tension. Photobleaching experiments demonstrated a slow turnover of beta3-integrins in low-density contacts, which may account for their stationary nature. In contrast, the fast beta3-integrin turnover observed in high-density contacts suggests that their apparent sliding may be caused by a polarized renewal of focal contacts. Therefore, differential acto-myosin-dependent integrin turnover and focal adhesion densities may explain the mechanical and behavioral differences between cell adhesion sites formed at the front, and those that move in the retracting rear of migrating cells.

Show MeSH

Related in: MedlinePlus

Model of cell migration based on differential integrin turnover. Cell migration is driven by Rac1- and Cdc42-dependent actin polymerization in the advancing lamellipodium. Integrin αVβ3 is incorporated in the lamellipodial actin filament lattice (gray shading) to form low-density integrin focal adhesions (focal complexes) (large and irregular shaped dots). These low-density focal adhesions remain stationary in respect to the substrate, firmly anchored in the cytoskeletal scaffold due to their slow turnover rate. These stabilized focal adhesions support the advancing lamellipodium. At the rear of the zone of transient clustering (circumferenced by dotted line), stationary focal adhesions rapidly disperse due to the depolymerization of the lamellipodial actin filament lattice (gray shading). While the cell moves forward, low-density focal adhesions at the lateral edges of the lamellipodium transform into high-density integrin focal adhesions (focal contacts) (accumulation of small dots). This transformation is directed by the acto-myosin–driven local collapse of the lamellipodial actin filaments into stress fibers and provides a means to sense the rigidity of the substrate. Integrins localized in high-density focal adhesions loose their firm cytoskeletal anchor and begin to show fast turnover, creating a great degree of plasticity for modulation of the contact. This plasticity can lead to polarized renewal of focal adhesions, the loss of integrins from the distal edge and their addition at the proximal edge of the contact, giving the illusion of sliding (small arrows).
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2199321&req=5

fig8: Model of cell migration based on differential integrin turnover. Cell migration is driven by Rac1- and Cdc42-dependent actin polymerization in the advancing lamellipodium. Integrin αVβ3 is incorporated in the lamellipodial actin filament lattice (gray shading) to form low-density integrin focal adhesions (focal complexes) (large and irregular shaped dots). These low-density focal adhesions remain stationary in respect to the substrate, firmly anchored in the cytoskeletal scaffold due to their slow turnover rate. These stabilized focal adhesions support the advancing lamellipodium. At the rear of the zone of transient clustering (circumferenced by dotted line), stationary focal adhesions rapidly disperse due to the depolymerization of the lamellipodial actin filament lattice (gray shading). While the cell moves forward, low-density focal adhesions at the lateral edges of the lamellipodium transform into high-density integrin focal adhesions (focal contacts) (accumulation of small dots). This transformation is directed by the acto-myosin–driven local collapse of the lamellipodial actin filaments into stress fibers and provides a means to sense the rigidity of the substrate. Integrins localized in high-density focal adhesions loose their firm cytoskeletal anchor and begin to show fast turnover, creating a great degree of plasticity for modulation of the contact. This plasticity can lead to polarized renewal of focal adhesions, the loss of integrins from the distal edge and their addition at the proximal edge of the contact, giving the illusion of sliding (small arrows).

Mentions: To conclude, we propose a model of dynamic integrin clustering and dispersal in motile cells (Fig. 8). Rac1 and Cdc42 become activated and induce filopodia and lamellipoda that exhibit many stationary, low-density focal adhesions. Maximal cell motility is maintained by their ability to form firm adhesions due to slow integrin turnover and rapid dispersal at the rear of the zone of “transient integrin clustering,” possibly caused by the depolymerization of lamellipodial actin filaments. Low-density focal adhesions form independent of intracellular tension, but transform into integrin dense focal adhesions at the lateral edge of the lamellipodium in response to RhoA induced acto-myosin–dependent intracellular tension. During this contraction, the actin integrin linkage senses the mechanical condition of the contacted ECM substrate resulting in the enforcement of focal adhesions on rigid substrates. High-density focal adhesions maintained by high traction forces at the lateral borders, begin to slide and subsequently detach due to their fast integrin turnover, a prerequisite for cell migration. Therefore, acto-myosin induced integrin turnover would offer a crucial therapeutic target to control migratory behavior of many cell types and might be relevant for pathological situations involving excessive migration of cells.


Marching at the front and dragging behind: differential alphaVbeta3-integrin turnover regulates focal adhesion behavior.

Ballestrem C, Hinz B, Imhof BA, Wehrle-Haller B - J. Cell Biol. (2001)

Model of cell migration based on differential integrin turnover. Cell migration is driven by Rac1- and Cdc42-dependent actin polymerization in the advancing lamellipodium. Integrin αVβ3 is incorporated in the lamellipodial actin filament lattice (gray shading) to form low-density integrin focal adhesions (focal complexes) (large and irregular shaped dots). These low-density focal adhesions remain stationary in respect to the substrate, firmly anchored in the cytoskeletal scaffold due to their slow turnover rate. These stabilized focal adhesions support the advancing lamellipodium. At the rear of the zone of transient clustering (circumferenced by dotted line), stationary focal adhesions rapidly disperse due to the depolymerization of the lamellipodial actin filament lattice (gray shading). While the cell moves forward, low-density focal adhesions at the lateral edges of the lamellipodium transform into high-density integrin focal adhesions (focal contacts) (accumulation of small dots). This transformation is directed by the acto-myosin–driven local collapse of the lamellipodial actin filaments into stress fibers and provides a means to sense the rigidity of the substrate. Integrins localized in high-density focal adhesions loose their firm cytoskeletal anchor and begin to show fast turnover, creating a great degree of plasticity for modulation of the contact. This plasticity can lead to polarized renewal of focal adhesions, the loss of integrins from the distal edge and their addition at the proximal edge of the contact, giving the illusion of sliding (small arrows).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2199321&req=5

fig8: Model of cell migration based on differential integrin turnover. Cell migration is driven by Rac1- and Cdc42-dependent actin polymerization in the advancing lamellipodium. Integrin αVβ3 is incorporated in the lamellipodial actin filament lattice (gray shading) to form low-density integrin focal adhesions (focal complexes) (large and irregular shaped dots). These low-density focal adhesions remain stationary in respect to the substrate, firmly anchored in the cytoskeletal scaffold due to their slow turnover rate. These stabilized focal adhesions support the advancing lamellipodium. At the rear of the zone of transient clustering (circumferenced by dotted line), stationary focal adhesions rapidly disperse due to the depolymerization of the lamellipodial actin filament lattice (gray shading). While the cell moves forward, low-density focal adhesions at the lateral edges of the lamellipodium transform into high-density integrin focal adhesions (focal contacts) (accumulation of small dots). This transformation is directed by the acto-myosin–driven local collapse of the lamellipodial actin filaments into stress fibers and provides a means to sense the rigidity of the substrate. Integrins localized in high-density focal adhesions loose their firm cytoskeletal anchor and begin to show fast turnover, creating a great degree of plasticity for modulation of the contact. This plasticity can lead to polarized renewal of focal adhesions, the loss of integrins from the distal edge and their addition at the proximal edge of the contact, giving the illusion of sliding (small arrows).
Mentions: To conclude, we propose a model of dynamic integrin clustering and dispersal in motile cells (Fig. 8). Rac1 and Cdc42 become activated and induce filopodia and lamellipoda that exhibit many stationary, low-density focal adhesions. Maximal cell motility is maintained by their ability to form firm adhesions due to slow integrin turnover and rapid dispersal at the rear of the zone of “transient integrin clustering,” possibly caused by the depolymerization of lamellipodial actin filaments. Low-density focal adhesions form independent of intracellular tension, but transform into integrin dense focal adhesions at the lateral edge of the lamellipodium in response to RhoA induced acto-myosin–dependent intracellular tension. During this contraction, the actin integrin linkage senses the mechanical condition of the contacted ECM substrate resulting in the enforcement of focal adhesions on rigid substrates. High-density focal adhesions maintained by high traction forces at the lateral borders, begin to slide and subsequently detach due to their fast integrin turnover, a prerequisite for cell migration. Therefore, acto-myosin induced integrin turnover would offer a crucial therapeutic target to control migratory behavior of many cell types and might be relevant for pathological situations involving excessive migration of cells.

Bottom Line: We have analyzed alphaVbeta3-integrin dynamics in migrating cells using a green fluorescent protein-tagged beta3-integrin chain.Photobleaching experiments demonstrated a slow turnover of beta3-integrins in low-density contacts, which may account for their stationary nature.In contrast, the fast beta3-integrin turnover observed in high-density contacts suggests that their apparent sliding may be caused by a polarized renewal of focal contacts.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology, Centre Médical Universitaire, Geneva, Switzerland.

ABSTRACT
Integrins are cell-substrate adhesion molecules that provide the essential link between the actin cytoskeleton and the extracellular matrix during cell migration. We have analyzed alphaVbeta3-integrin dynamics in migrating cells using a green fluorescent protein-tagged beta3-integrin chain. At the cell front, adhesion sites containing alphaVbeta3-integrin remain stationary, whereas at the rear of the cell they slide inward. The integrin fluorescence intensity within these different focal adhesions, and hence the relative integrin density, is directly related to their mobility. Integrin density is as much as threefold higher in sliding compared with stationary focal adhesions. High intracellular tension under the control of RhoA induced the formation of high-density contacts. Low-density adhesion sites were induced by Rac1 and low intracellular tension. Photobleaching experiments demonstrated a slow turnover of beta3-integrins in low-density contacts, which may account for their stationary nature. In contrast, the fast beta3-integrin turnover observed in high-density contacts suggests that their apparent sliding may be caused by a polarized renewal of focal contacts. Therefore, differential acto-myosin-dependent integrin turnover and focal adhesion densities may explain the mechanical and behavioral differences between cell adhesion sites formed at the front, and those that move in the retracting rear of migrating cells.

Show MeSH
Related in: MedlinePlus