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Presentation of integrins on leukocyte microvilli: a role for the extracellular domain in determining membrane localization.

Abitorabi MA, Pachynski RK, Ferrando RE, Tidswell M, Erle DJ - J. Cell Biol. (1997)

Bottom Line: Therefore, differences between the transmembrane and cytoplasmic domains of alpha4 and beta2 integrins do not account for differences in ability to support attachment under flow or in membrane localization.Integrins alpha4beta1, alpha5beta1, alpha6Abeta1, alphavbeta3, and alphaEbeta7 also localized to microvilli.Transmembrane proteins known or suspected to associate with extracellular domains of microvillous integrins, including tetraspans and CD47, were concentrated on microvilli as well.

View Article: PubMed Central - PubMed

Affiliation: The Lung Biology Center, Department of Medicine, University of California, San Francisco, California 94143, USA.

ABSTRACT
Adhesion of blood leukocytes to the endothelium involves multiple steps including initial attachment (tethering), rolling, and firm arrest. Presentation of adhesion molecules on leukocyte microvilli can substantially enhance tethering. Localization of L-selectin to microvilli and of CD44 to the planar cell body have been shown to depend upon their transmembrane and cytoplasmic domains. We investigated the role of leukocyte integrin transmembrane and cytoplasmic domains in initiating adhesion under flow and in microvillous localization. Integrins alpha4beta7, alphaLbeta2, and alphaMbeta2 were heterologously expressed in K562 cells. alpha4beta7 initiated adhesion under flow and localized to microvilli, whereas beta2 integrins did not initiate adhesion and localized to the cell body. Chimeric integrins were produced by replacing the alpha4beta7 cytoplasmic and/or transmembrane domains with the homologous domains of alphaLbeta2 or alphaMbeta2. Unexpectedly, these chimeras efficiently mediated adhesion to the alpha4beta7 ligand mucosal addressin cell adhesion molecule-1 under flow and localized to microvilli. Therefore, differences between the transmembrane and cytoplasmic domains of alpha4 and beta2 integrins do not account for differences in ability to support attachment under flow or in membrane localization. Integrins alpha4beta1, alpha5beta1, alpha6Abeta1, alphavbeta3, and alphaEbeta7 also localized to microvilli. Transmembrane proteins known or suspected to associate with extracellular domains of microvillous integrins, including tetraspans and CD47, were concentrated on microvilli as well. These findings suggest that interactions between the extracellular domains of integrins and associated proteins could direct the assembly of multimolecular complexes on leukocyte microvilli.

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Adhesion to ligands  under flow. Adhesion of various integrin transfectants to  MAdCAM-1 (top) and ICAM-1  (bottom) measured at a wall  shear stress of 1 dyne/cm2 in  the absence of Mn2+, as described in Materials and  Methods. Bars indicate SEM.
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Figure 4: Adhesion to ligands under flow. Adhesion of various integrin transfectants to MAdCAM-1 (top) and ICAM-1 (bottom) measured at a wall shear stress of 1 dyne/cm2 in the absence of Mn2+, as described in Materials and Methods. Bars indicate SEM.

Mentions: We next examined the ability of the wild-type and chimeric integrins to initiate adhesion under flow (Fig. 4). K562-α4β7 cells adhered to MAdCAM-1 under flow. This adhesion was dependent upon both α4β7 and MAdCAM-1 because K562 cells transfected with α4 alone (K562-α4β1) did not adhere to MAdCAM-1, and K562-α4β7 cells did not adhere to capillary tubes coated with other ligands, such as ICAM-1. The chimeric integrins, α4β7(αLβ2c) and α4β7 (αMβ2tc), both supported adhesion to MAdCAM-1 under flow. Wild-type α4β7 and the chimeric integrins were very similar in their ability to initiate adhesion under flow. We also examined the resistance to detachment from MAdCAM-1 at increasing shear stress conditions (up to 10 dynes/cm2). We did not find differences between wild-type and chimeric transfectants in this assay (data not shown). At a shear stress of 1 dyne/cm2, most cells remained adherent during the time interval of cell counts. Transfectants expressing a truncated α4 subunit (K562-α4Δβ7) also adhered to MAdCAM-1 under flow, although at a somewhat lower rate (perhaps related to lower levels of expression of this construct, data not shown). As expected from previous reports (von Andrian et al., 1991), K562-αLβ2 cells were unable to initiate adhesion to their ligand, ICAM-1, under flow (Fig. 4).


Presentation of integrins on leukocyte microvilli: a role for the extracellular domain in determining membrane localization.

Abitorabi MA, Pachynski RK, Ferrando RE, Tidswell M, Erle DJ - J. Cell Biol. (1997)

Adhesion to ligands  under flow. Adhesion of various integrin transfectants to  MAdCAM-1 (top) and ICAM-1  (bottom) measured at a wall  shear stress of 1 dyne/cm2 in  the absence of Mn2+, as described in Materials and  Methods. Bars indicate SEM.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2139798&req=5

Figure 4: Adhesion to ligands under flow. Adhesion of various integrin transfectants to MAdCAM-1 (top) and ICAM-1 (bottom) measured at a wall shear stress of 1 dyne/cm2 in the absence of Mn2+, as described in Materials and Methods. Bars indicate SEM.
Mentions: We next examined the ability of the wild-type and chimeric integrins to initiate adhesion under flow (Fig. 4). K562-α4β7 cells adhered to MAdCAM-1 under flow. This adhesion was dependent upon both α4β7 and MAdCAM-1 because K562 cells transfected with α4 alone (K562-α4β1) did not adhere to MAdCAM-1, and K562-α4β7 cells did not adhere to capillary tubes coated with other ligands, such as ICAM-1. The chimeric integrins, α4β7(αLβ2c) and α4β7 (αMβ2tc), both supported adhesion to MAdCAM-1 under flow. Wild-type α4β7 and the chimeric integrins were very similar in their ability to initiate adhesion under flow. We also examined the resistance to detachment from MAdCAM-1 at increasing shear stress conditions (up to 10 dynes/cm2). We did not find differences between wild-type and chimeric transfectants in this assay (data not shown). At a shear stress of 1 dyne/cm2, most cells remained adherent during the time interval of cell counts. Transfectants expressing a truncated α4 subunit (K562-α4Δβ7) also adhered to MAdCAM-1 under flow, although at a somewhat lower rate (perhaps related to lower levels of expression of this construct, data not shown). As expected from previous reports (von Andrian et al., 1991), K562-αLβ2 cells were unable to initiate adhesion to their ligand, ICAM-1, under flow (Fig. 4).

Bottom Line: Therefore, differences between the transmembrane and cytoplasmic domains of alpha4 and beta2 integrins do not account for differences in ability to support attachment under flow or in membrane localization.Integrins alpha4beta1, alpha5beta1, alpha6Abeta1, alphavbeta3, and alphaEbeta7 also localized to microvilli.Transmembrane proteins known or suspected to associate with extracellular domains of microvillous integrins, including tetraspans and CD47, were concentrated on microvilli as well.

View Article: PubMed Central - PubMed

Affiliation: The Lung Biology Center, Department of Medicine, University of California, San Francisco, California 94143, USA.

ABSTRACT
Adhesion of blood leukocytes to the endothelium involves multiple steps including initial attachment (tethering), rolling, and firm arrest. Presentation of adhesion molecules on leukocyte microvilli can substantially enhance tethering. Localization of L-selectin to microvilli and of CD44 to the planar cell body have been shown to depend upon their transmembrane and cytoplasmic domains. We investigated the role of leukocyte integrin transmembrane and cytoplasmic domains in initiating adhesion under flow and in microvillous localization. Integrins alpha4beta7, alphaLbeta2, and alphaMbeta2 were heterologously expressed in K562 cells. alpha4beta7 initiated adhesion under flow and localized to microvilli, whereas beta2 integrins did not initiate adhesion and localized to the cell body. Chimeric integrins were produced by replacing the alpha4beta7 cytoplasmic and/or transmembrane domains with the homologous domains of alphaLbeta2 or alphaMbeta2. Unexpectedly, these chimeras efficiently mediated adhesion to the alpha4beta7 ligand mucosal addressin cell adhesion molecule-1 under flow and localized to microvilli. Therefore, differences between the transmembrane and cytoplasmic domains of alpha4 and beta2 integrins do not account for differences in ability to support attachment under flow or in membrane localization. Integrins alpha4beta1, alpha5beta1, alpha6Abeta1, alphavbeta3, and alphaEbeta7 also localized to microvilli. Transmembrane proteins known or suspected to associate with extracellular domains of microvillous integrins, including tetraspans and CD47, were concentrated on microvilli as well. These findings suggest that interactions between the extracellular domains of integrins and associated proteins could direct the assembly of multimolecular complexes on leukocyte microvilli.

Show MeSH
Related in: MedlinePlus