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Evidence that distinct states of the integrin alpha6beta1 interact with laminin and an ADAM.

Chen MS, Almeida EA, Huovila AP, Takahashi Y, Shaw LM, Mercurio AM, White JM - J. Cell Biol. (1999)

Bottom Line: In Ca2+-containing media, laminin E8 beads did not bind to eggs.Treatment of eggs with phorbol myristate acetate or with the actin disrupting agent, latrunculin A, inhibited fertilin bead binding, but did not induce laminin E8 bead binding.Our results provide the first evidence that different states of an integrin (alpha6beta1) can interact with an extracellular matrix ligand (laminin) or a membrane-anchored cell surface ligand (ADAM 2).

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, University of Virginia, Charlottesville, Virginia 22908, USA.

ABSTRACT
Integrins can exist in different functional states with low or high binding capacity for particular ligands. We previously provided evidence that the integrin alpha6beta1, on mouse eggs and on alpha6-transfected cells, interacted with the disintegrin domain of the sperm surface protein ADAM 2 (fertilin beta). In the present study we tested the hypothesis that different states of alpha6beta1 interact with fertilin and laminin, an extracellular matrix ligand for alpha6beta1. Using alpha6-transfected cells we found that treatments (e.g., with phorbol myristate acetate or MnCl2) that increased adhesion to laminin inhibited sperm binding. Conversely, treatments that inhibited laminin adhesion increased sperm binding. Next, we compared the ability of fluorescent beads coated with either fertilin beta or with the laminin E8 fragment to bind to eggs. In Ca2+-containing media, fertilin beta beads bound to eggs via an interaction mediated by the disintegrin loop of fertilin beta and by the alpha6 integrin subunit. In Ca2+-containing media, laminin E8 beads did not bind to eggs. Treatment of eggs with phorbol myristate acetate or with the actin disrupting agent, latrunculin A, inhibited fertilin bead binding, but did not induce laminin E8 bead binding. Treatment of eggs with Mn2+ dramatically increased laminin E8 bead binding, and inhibited fertilin bead binding. Our results provide the first evidence that different states of an integrin (alpha6beta1) can interact with an extracellular matrix ligand (laminin) or a membrane-anchored cell surface ligand (ADAM 2).

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Summary of ligand  binding states of α6β1 on the  egg. Eggs in Ca2+ strongly  prefer to bind fertilin (left).  Eggs in Mn2+ strongly prefer  to bind laminin (right).  PMA- or latrunculin-treated  eggs bind significantly less fertilin than untreated eggs, but do not  bind laminin (middle). Binding of both fertilin and laminin to  eggs is inhibited by GoH3, but not by J1B5.
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Figure 12: Summary of ligand binding states of α6β1 on the egg. Eggs in Ca2+ strongly prefer to bind fertilin (left). Eggs in Mn2+ strongly prefer to bind laminin (right). PMA- or latrunculin-treated eggs bind significantly less fertilin than untreated eggs, but do not bind laminin (middle). Binding of both fertilin and laminin to eggs is inhibited by GoH3, but not by J1B5.

Mentions: As outlined above, our data suggest that the egg α6β1 integrin can exist in a state, exemplified by native fertilization-competent eggs, that supports binding of the ADAM protein fertilin β but not laminin (Fig. 12, left). It can also exist in a state exemplified by treating eggs with Mn2+ that strongly prefers binding laminin and disfavors the ADAM (Fig. 12, right). Our data further suggest that α6β1 on the egg can exist in a third state, exemplified by treating eggs with phorbol esters or latrunculin, with limited affinity for either ligand (Fig. 12, middle). It may be that in the unfertilized egg α6β1 is tethered to the cortical actin cytoskeleton and binds the ADAM protein fertilin β (Fig. 12, left). Release from cytoskeletal anchorage (induced in vitro by treatment with either latrunculin or PMA; Fig. 12, middle) may promote lateral diffusion of the integrin (Kucik et al., 1996; Yauch et al., 1997). Increase in the lateral mobility of α6β1 may in turn disfavor binding between α6β1 and fertilin and may be a prerequisite for interaction between α6β1 and laminin. High avidity adhesion of laminin to α6β1 may require subsequent clustering of α6β1 and/or changes in its conformation (mimicked in vitro by treatment with Mn2+; Fig. 12, right). It should be noted that in addition to binding different states of the α6β1 integrin, fertilin β and laminin may bind to different sites on the integrin. Approximately 5–10-fold more GoH3 is required to inhibit binding of fertilin β than to inhibit binding of laminin.


Evidence that distinct states of the integrin alpha6beta1 interact with laminin and an ADAM.

Chen MS, Almeida EA, Huovila AP, Takahashi Y, Shaw LM, Mercurio AM, White JM - J. Cell Biol. (1999)

Summary of ligand  binding states of α6β1 on the  egg. Eggs in Ca2+ strongly  prefer to bind fertilin (left).  Eggs in Mn2+ strongly prefer  to bind laminin (right).  PMA- or latrunculin-treated  eggs bind significantly less fertilin than untreated eggs, but do not  bind laminin (middle). Binding of both fertilin and laminin to  eggs is inhibited by GoH3, but not by J1B5.
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2132920&req=5

Figure 12: Summary of ligand binding states of α6β1 on the egg. Eggs in Ca2+ strongly prefer to bind fertilin (left). Eggs in Mn2+ strongly prefer to bind laminin (right). PMA- or latrunculin-treated eggs bind significantly less fertilin than untreated eggs, but do not bind laminin (middle). Binding of both fertilin and laminin to eggs is inhibited by GoH3, but not by J1B5.
Mentions: As outlined above, our data suggest that the egg α6β1 integrin can exist in a state, exemplified by native fertilization-competent eggs, that supports binding of the ADAM protein fertilin β but not laminin (Fig. 12, left). It can also exist in a state exemplified by treating eggs with Mn2+ that strongly prefers binding laminin and disfavors the ADAM (Fig. 12, right). Our data further suggest that α6β1 on the egg can exist in a third state, exemplified by treating eggs with phorbol esters or latrunculin, with limited affinity for either ligand (Fig. 12, middle). It may be that in the unfertilized egg α6β1 is tethered to the cortical actin cytoskeleton and binds the ADAM protein fertilin β (Fig. 12, left). Release from cytoskeletal anchorage (induced in vitro by treatment with either latrunculin or PMA; Fig. 12, middle) may promote lateral diffusion of the integrin (Kucik et al., 1996; Yauch et al., 1997). Increase in the lateral mobility of α6β1 may in turn disfavor binding between α6β1 and fertilin and may be a prerequisite for interaction between α6β1 and laminin. High avidity adhesion of laminin to α6β1 may require subsequent clustering of α6β1 and/or changes in its conformation (mimicked in vitro by treatment with Mn2+; Fig. 12, right). It should be noted that in addition to binding different states of the α6β1 integrin, fertilin β and laminin may bind to different sites on the integrin. Approximately 5–10-fold more GoH3 is required to inhibit binding of fertilin β than to inhibit binding of laminin.

Bottom Line: In Ca2+-containing media, laminin E8 beads did not bind to eggs.Treatment of eggs with phorbol myristate acetate or with the actin disrupting agent, latrunculin A, inhibited fertilin bead binding, but did not induce laminin E8 bead binding.Our results provide the first evidence that different states of an integrin (alpha6beta1) can interact with an extracellular matrix ligand (laminin) or a membrane-anchored cell surface ligand (ADAM 2).

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, University of Virginia, Charlottesville, Virginia 22908, USA.

ABSTRACT
Integrins can exist in different functional states with low or high binding capacity for particular ligands. We previously provided evidence that the integrin alpha6beta1, on mouse eggs and on alpha6-transfected cells, interacted with the disintegrin domain of the sperm surface protein ADAM 2 (fertilin beta). In the present study we tested the hypothesis that different states of alpha6beta1 interact with fertilin and laminin, an extracellular matrix ligand for alpha6beta1. Using alpha6-transfected cells we found that treatments (e.g., with phorbol myristate acetate or MnCl2) that increased adhesion to laminin inhibited sperm binding. Conversely, treatments that inhibited laminin adhesion increased sperm binding. Next, we compared the ability of fluorescent beads coated with either fertilin beta or with the laminin E8 fragment to bind to eggs. In Ca2+-containing media, fertilin beta beads bound to eggs via an interaction mediated by the disintegrin loop of fertilin beta and by the alpha6 integrin subunit. In Ca2+-containing media, laminin E8 beads did not bind to eggs. Treatment of eggs with phorbol myristate acetate or with the actin disrupting agent, latrunculin A, inhibited fertilin bead binding, but did not induce laminin E8 bead binding. Treatment of eggs with Mn2+ dramatically increased laminin E8 bead binding, and inhibited fertilin bead binding. Our results provide the first evidence that different states of an integrin (alpha6beta1) can interact with an extracellular matrix ligand (laminin) or a membrane-anchored cell surface ligand (ADAM 2).

Show MeSH
Related in: MedlinePlus