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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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Effects of PMA and  Mn2+ on binding of laminin E8– coated beads to eggs. Beads  were coated with laminin E8 as  described in Materials and  Methods. Eggs were collected  and freed of their zonae pellucidae as described in the legend  to Fig. 7 and Materials and  Methods. (a) Eggs were pretreated with either 100 ng/ml  PMA or 1 mM MnCl2, incubated with laminin E8–coated  beads for 1 h at 37°C, and  washed and observed with a  confocal microscope. (b) Eggs  were incubated with laminin  E8–coated beads for 1 h at 37°C  in Puck's saline A containing increasing amounts of MnCl2 as  indicated. Eggs were washed  and observed with a confocal  microscope. Paired fluorescence and phase-contrast images  from representative experiments are shown.
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Figure 8: Effects of PMA and Mn2+ on binding of laminin E8– coated beads to eggs. Beads were coated with laminin E8 as described in Materials and Methods. Eggs were collected and freed of their zonae pellucidae as described in the legend to Fig. 7 and Materials and Methods. (a) Eggs were pretreated with either 100 ng/ml PMA or 1 mM MnCl2, incubated with laminin E8–coated beads for 1 h at 37°C, and washed and observed with a confocal microscope. (b) Eggs were incubated with laminin E8–coated beads for 1 h at 37°C in Puck's saline A containing increasing amounts of MnCl2 as indicated. Eggs were washed and observed with a confocal microscope. Paired fluorescence and phase-contrast images from representative experiments are shown.

Mentions: We next assessed the effects of integrin avidity/affinity modulators on the binding of fertilin- (Figs. 7 and 10) and laminin E8– (see Figs. 8–10) coated fluorescent beads to mouse eggs. Because beads coated with whole laminin formed large aggregates in suspension, we used the elastase digestion fragment, E8, which contains the major integrin α6β1 binding domain (Goodman, 1992; Yurchenco and O'Rear, 1994). We first analyzed fertilin- (Fig. 7) and laminin E8– (see Figs. 8 and 9) bead binding individually. We then analyzed fertilin and laminin E8 bead binding in a competition experiment (see Fig. 10). As seen in Fig. 7 a, PMA (middle) and Mn2+ (right) inhibited binding of fertilin β–coated beads to mouse eggs (fertilin-bead binding in the presence of Mg2+ alone [1 mM] was similar to that seen in the Ca2+/Mg2+ control media; Almeida, E., M. Chen, and J. White, unpublished data). As seen in Fig. 7 b, the effect of PMA on fertilin bead binding was dose-dependent.


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)

Effects of PMA and  Mn2+ on binding of laminin E8– coated beads to eggs. Beads  were coated with laminin E8 as  described in Materials and  Methods. Eggs were collected  and freed of their zonae pellucidae as described in the legend  to Fig. 7 and Materials and  Methods. (a) Eggs were pretreated with either 100 ng/ml  PMA or 1 mM MnCl2, incubated with laminin E8–coated  beads for 1 h at 37°C, and  washed and observed with a  confocal microscope. (b) Eggs  were incubated with laminin  E8–coated beads for 1 h at 37°C  in Puck's saline A containing increasing amounts of MnCl2 as  indicated. Eggs were washed  and observed with a confocal  microscope. Paired fluorescence and phase-contrast images  from representative experiments are shown.
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Related In: Results  -  Collection

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Figure 8: Effects of PMA and Mn2+ on binding of laminin E8– coated beads to eggs. Beads were coated with laminin E8 as described in Materials and Methods. Eggs were collected and freed of their zonae pellucidae as described in the legend to Fig. 7 and Materials and Methods. (a) Eggs were pretreated with either 100 ng/ml PMA or 1 mM MnCl2, incubated with laminin E8–coated beads for 1 h at 37°C, and washed and observed with a confocal microscope. (b) Eggs were incubated with laminin E8–coated beads for 1 h at 37°C in Puck's saline A containing increasing amounts of MnCl2 as indicated. Eggs were washed and observed with a confocal microscope. Paired fluorescence and phase-contrast images from representative experiments are shown.
Mentions: We next assessed the effects of integrin avidity/affinity modulators on the binding of fertilin- (Figs. 7 and 10) and laminin E8– (see Figs. 8–10) coated fluorescent beads to mouse eggs. Because beads coated with whole laminin formed large aggregates in suspension, we used the elastase digestion fragment, E8, which contains the major integrin α6β1 binding domain (Goodman, 1992; Yurchenco and O'Rear, 1994). We first analyzed fertilin- (Fig. 7) and laminin E8– (see Figs. 8 and 9) bead binding individually. We then analyzed fertilin and laminin E8 bead binding in a competition experiment (see Fig. 10). As seen in Fig. 7 a, PMA (middle) and Mn2+ (right) inhibited binding of fertilin β–coated beads to mouse eggs (fertilin-bead binding in the presence of Mg2+ alone [1 mM] was similar to that seen in the Ca2+/Mg2+ control media; Almeida, E., M. Chen, and J. White, unpublished data). As seen in Fig. 7 b, the effect of PMA on fertilin bead binding was dose-dependent.

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