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A RIAM/lamellipodin-talin-integrin complex forms the tip of sticky fingers that guide cell migration.

Lagarrigue F, Vikas Anekal P, Lee HS, Bachir AI, Ablack JN, Horwitz AF, Ginsberg MH - Nat Commun (2015)

Bottom Line: The leading edge of migrating cells contains rapidly translocating activated integrins associated with growing actin filaments that form 'sticky fingers' to sense extracellular matrix and guide cell migration.Here we utilized indirect bimolecular fluorescence complementation to visualize a molecular complex containing a Mig-10/RIAM/lamellipodin (MRL) protein (Rap1-GTP-interacting adaptor molecule (RIAM) or lamellipodin), talin and activated integrins in living cells.These data reveal the molecular basis of the formation of 'sticky fingers' at the leading edge of migrating cells and show that an MIT complex drives these protrusions.

View Article: PubMed Central - PubMed

Affiliation: Department of Medicine, University of California San Diego, La Jolla, California 92093, USA.

ABSTRACT
The leading edge of migrating cells contains rapidly translocating activated integrins associated with growing actin filaments that form 'sticky fingers' to sense extracellular matrix and guide cell migration. Here we utilized indirect bimolecular fluorescence complementation to visualize a molecular complex containing a Mig-10/RIAM/lamellipodin (MRL) protein (Rap1-GTP-interacting adaptor molecule (RIAM) or lamellipodin), talin and activated integrins in living cells. This complex localizes at the tips of growing actin filaments in lamellipodial and filopodial protrusions, thus corresponding to the tips of the 'sticky fingers.' Formation of the complex requires talin to form a bridge between the MRL protein and the integrins. Moreover, disruption of the MRL protein-integrin-talin (MIT) complex markedly impairs cell protrusion. These data reveal the molecular basis of the formation of 'sticky fingers' at the leading edge of migrating cells and show that an MIT complex drives these protrusions.

No MeSH data available.


Related in: MedlinePlus

The MIT complex forms without ligand engagement.(a) U2-OS cells expressing VN-RIAM and ligand-binding defective integrin αIIb-VCβ3(D119A) were plated on fibrinogen for 2 h. The cells were imaged with TIRFM. Note lack of spreading documents lack of ligand engagement and because the cells are not spread, filopodia are at varying angles to the TIRF plane. Scale bar, 5 μm. (b,c) U2-OS cells expressing VN-RIAM and integrin αIIb-VCβ3 were plated on fibrinogen (b) or BSA (c) for 2 h. The cells were imaged with TIRFM. Cells appear well spread with discernible actin stress fibers on fibrinogen. Unspread cells on BSA still exhibit filopodia and BiFC. Scale bar, 5 μm.
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f7: The MIT complex forms without ligand engagement.(a) U2-OS cells expressing VN-RIAM and ligand-binding defective integrin αIIb-VCβ3(D119A) were plated on fibrinogen for 2 h. The cells were imaged with TIRFM. Note lack of spreading documents lack of ligand engagement and because the cells are not spread, filopodia are at varying angles to the TIRF plane. Scale bar, 5 μm. (b,c) U2-OS cells expressing VN-RIAM and integrin αIIb-VCβ3 were plated on fibrinogen (b) or BSA (c) for 2 h. The cells were imaged with TIRFM. Cells appear well spread with discernible actin stress fibers on fibrinogen. Unspread cells on BSA still exhibit filopodia and BiFC. Scale bar, 5 μm.

Mentions: One of the hallmarks of ‘sticky fingers' is that they contain activated unoccupied integrins. As noted above, BiFC that reported formation of the αIIbβ3 MIT complex co-localized with PAC1 (Fig. 4c), a ligand-mimetic antibody, suggesting that the MIT complex forms without ligand binding. To directly test this idea, we used β3(D119A), a ligand binding-defective mutant40. Even though cells expressing αIIb-VC β3(D119A) did not spread on fibrinogen, they still formed actin-containing microspikes that exhibited bright BiFC at their tips (Fig. 7a; Supplementary Movie 11). Alternatively, we examined cells expressing αIIb-VCβ3 plated on non-adhesive bovine serum albumin (BSA). Cells on fibrinogen spread well (Fig. 7b), but cells on BSA did not. Nevertheless, BiFC was still evident at the tips of actin-based protrusions in cells (Fig. 7c) plated on BSA. Thus, the MIT complex forms without ligand engagement to generate activated but unoccupied integrins at the tips of actin-based protrusions.


A RIAM/lamellipodin-talin-integrin complex forms the tip of sticky fingers that guide cell migration.

Lagarrigue F, Vikas Anekal P, Lee HS, Bachir AI, Ablack JN, Horwitz AF, Ginsberg MH - Nat Commun (2015)

The MIT complex forms without ligand engagement.(a) U2-OS cells expressing VN-RIAM and ligand-binding defective integrin αIIb-VCβ3(D119A) were plated on fibrinogen for 2 h. The cells were imaged with TIRFM. Note lack of spreading documents lack of ligand engagement and because the cells are not spread, filopodia are at varying angles to the TIRF plane. Scale bar, 5 μm. (b,c) U2-OS cells expressing VN-RIAM and integrin αIIb-VCβ3 were plated on fibrinogen (b) or BSA (c) for 2 h. The cells were imaged with TIRFM. Cells appear well spread with discernible actin stress fibers on fibrinogen. Unspread cells on BSA still exhibit filopodia and BiFC. Scale bar, 5 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4589889&req=5

f7: The MIT complex forms without ligand engagement.(a) U2-OS cells expressing VN-RIAM and ligand-binding defective integrin αIIb-VCβ3(D119A) were plated on fibrinogen for 2 h. The cells were imaged with TIRFM. Note lack of spreading documents lack of ligand engagement and because the cells are not spread, filopodia are at varying angles to the TIRF plane. Scale bar, 5 μm. (b,c) U2-OS cells expressing VN-RIAM and integrin αIIb-VCβ3 were plated on fibrinogen (b) or BSA (c) for 2 h. The cells were imaged with TIRFM. Cells appear well spread with discernible actin stress fibers on fibrinogen. Unspread cells on BSA still exhibit filopodia and BiFC. Scale bar, 5 μm.
Mentions: One of the hallmarks of ‘sticky fingers' is that they contain activated unoccupied integrins. As noted above, BiFC that reported formation of the αIIbβ3 MIT complex co-localized with PAC1 (Fig. 4c), a ligand-mimetic antibody, suggesting that the MIT complex forms without ligand binding. To directly test this idea, we used β3(D119A), a ligand binding-defective mutant40. Even though cells expressing αIIb-VC β3(D119A) did not spread on fibrinogen, they still formed actin-containing microspikes that exhibited bright BiFC at their tips (Fig. 7a; Supplementary Movie 11). Alternatively, we examined cells expressing αIIb-VCβ3 plated on non-adhesive bovine serum albumin (BSA). Cells on fibrinogen spread well (Fig. 7b), but cells on BSA did not. Nevertheless, BiFC was still evident at the tips of actin-based protrusions in cells (Fig. 7c) plated on BSA. Thus, the MIT complex forms without ligand engagement to generate activated but unoccupied integrins at the tips of actin-based protrusions.

Bottom Line: The leading edge of migrating cells contains rapidly translocating activated integrins associated with growing actin filaments that form 'sticky fingers' to sense extracellular matrix and guide cell migration.Here we utilized indirect bimolecular fluorescence complementation to visualize a molecular complex containing a Mig-10/RIAM/lamellipodin (MRL) protein (Rap1-GTP-interacting adaptor molecule (RIAM) or lamellipodin), talin and activated integrins in living cells.These data reveal the molecular basis of the formation of 'sticky fingers' at the leading edge of migrating cells and show that an MIT complex drives these protrusions.

View Article: PubMed Central - PubMed

Affiliation: Department of Medicine, University of California San Diego, La Jolla, California 92093, USA.

ABSTRACT
The leading edge of migrating cells contains rapidly translocating activated integrins associated with growing actin filaments that form 'sticky fingers' to sense extracellular matrix and guide cell migration. Here we utilized indirect bimolecular fluorescence complementation to visualize a molecular complex containing a Mig-10/RIAM/lamellipodin (MRL) protein (Rap1-GTP-interacting adaptor molecule (RIAM) or lamellipodin), talin and activated integrins in living cells. This complex localizes at the tips of growing actin filaments in lamellipodial and filopodial protrusions, thus corresponding to the tips of the 'sticky fingers.' Formation of the complex requires talin to form a bridge between the MRL protein and the integrins. Moreover, disruption of the MRL protein-integrin-talin (MIT) complex markedly impairs cell protrusion. These data reveal the molecular basis of the formation of 'sticky fingers' at the leading edge of migrating cells and show that an MIT complex drives these protrusions.

No MeSH data available.


Related in: MedlinePlus