A plasma membrane integral sialoglycoprotein (Sgp 130) molecularly distinguishes nonjunctional dense plaque sites of microfilament attachment.

Abstract

Abstract. An integral sialoglycoprotein with Mr ,x,130,000 (Sgp 130) and highest expression in adult chicken gizzard smooth muscle has been recently identified as an excellent candidate for classification as a plasma membrane protein natively associated (directly or indirectly) with actin microfilaments (Rogalski, A. A., and S. J. Singer, 1985, J. Cell Biol., 101:785-801). In this study, the relative in situ distributions of the Sgp 130 integral species (a designation that also includes non-smooth muscle molecular forms) and the peripheral protein, vinculin, have been simultaneously revealed for the first time in selected cultured cells and tissues abundant in microfilament-membrane attachment sites, particularly, smooth and cardiac muscle. Specific antibody probes against Sgp 130 (mouse mAb 30B6) and vinculin (affinitypurified rabbit antibody) were used in double indirect immunofluorescent and immunoelectron microscopic experiments. In contrast to the widespread distributions of vinculin at microfilament-membrane attachment sites, Sgp 130 has been shown to exhibit striking site-specific variation in its abundancy levels in the plasma membrane. Sgp 130 and vinculin were found coincidentally concentrated at focal contact sites in cultured chick embryo fibroblasts and endothelial cells, membrane dense plaques of smooth muscle, and sarcolemma dense plaque sites overlying the Z line in cardiac muscle. However, at the fascia adherens junctional sites of cardiac muscle where vinculin is sharply confined, Sgp 130 was immunologically undetectable in both intact and EGTA-uncoupled tissue. This latter result was confirmed with immunoblotting experiments using isolated forms of the fascia adherens.The double immunolabeling studies of this report establish Sgp 130 as a major integral protein component of nonjunctional membrane dense plaque structures and raise the possibility that the 130-kD integral sialoglycoprotein (Sgp 130) and vinculin assume stable transmembrane associations at these particular microfilament-membrane attachment sites. Nonjunctional dense plaques are further suggested to be a molecularly distinct class of plasma membrane structures rather than a subgroup of adherens junctions. Our data also support a hypothesis that Sgp 130 is involved in plasma membrane force coupling events but not in junctional-related cell-cell coupling.T hE role of the cytoskeleton in spatially and functionally organizing the cytoplasm of nonerythrocyte cell types has been a subject of broad experimental interest. An important and challenging issue in this area concerns the mechanisms by which cytoskeletal elements, particularly actin microfilaments, assume both specific associations with the plasma membrane and key roles in basic cellular processes (20,22,29,31,42,45,52).Numerous studies have shown actin microfilament-plasma membrane associations to be either (a) highly specialized at discrete attachment sites, such as, for example, the membrane dense plaque of smooth muscle (16,18), the fascia adherens of cardiac muscle (48) or...

Focal Adhesions: Transmembrane Junctions Between the Extracellular Matrix and the Cytoskeleton

“…The 30B6 antigen shares many properties with integrin. Analysis of this antigen has been performed primarily in chicken gizzard, where it has a molecular weight of 130,000 and it is associated with a 175-kDa polypeptide (Rogalski & Singer 1985;Rogalski 1987). Although molecular weights distinguish this complex from the avian integrins originally isolated from fi broblasts or eviscerated embryos, an integrin isolated fr om chicken smooth muscle has polypeptides of molecular weights similar to those identifi ed by the 30B6 mab (Kelly et al 19 87).…”

Desmin in Muscle Formation and Maintenance: Knockouts and Consequences.

“…There is also a strong correspondence between the presence of costameres with attached IFs and extracellular filaments enriched overlying the costameres (105). The linkage of the extracellular matrix and the costamere/cytoskeletal complex appears to involve a number of proteins including the integral membranesialoglycoprotein Sgpl30 (95) and several integrins, the receptor of a variety of extracellular matrix componentsincluding fibronectin, vitronectin, laminin and different collagen types (for review see 1). It seems that costameres might require this cell-EC matrix interaction to be organized.…”

Immunolocalization of vinculin in the heart of the early developing rat embryo

“…Vinculin, therefore, appeared to contribute to formation of the truncal septum. Previous reports have shown that vinculin assembles stress fiber and the cytoskeleton and is connected to the adherent junctions that play a role in cell-cell coupling (Beckerle, 1986;Rogalski, 1987). These reports suggest that vinculin is strongly expressed in regions of stress (Rogalski, 1987).…”

“…Previous reports have shown that vinculin assembles stress fiber and the cytoskeleton and is connected to the adherent junctions that play a role in cell-cell coupling (Beckerle, 1986;Rogalski, 1987). These reports suggest that vinculin is strongly expressed in regions of stress (Rogalski, 1987). However, if vinculin expression detected in our present study in the dividing and septated outflow tract just depended on the stress induced by blood pressure, one might expect vinculin immunoreactivity to be expressed more prominently each day and to be diffusely distributed in the outflow tract as well as in the aortic arches.…”

“…Many studies have evaluated the diversification of transmembrane molecules during the migration, proliferation, and linkage of cells, or during physical stress (Beckerle et al, 1986;Duband, 1986;Rogalski, 1987;Tokuyasu, 1989;Terracio et al, 1990). The migration of embryonic cells was found to be associated with a diffuse and mobile organization of fibronectin receptors on the cell surface in labile adhesions, with a weak contact of nonorganized microfilament bundles to dissociate the F-actidalpha-actinidvinculin complexes, which was one of the adhesion plaques associated with paxillin, talin, integrin, and other proteins (Duband et al, 1986;Wilkins et al, 1986; al., 1989;Schultheiss et al, 1990;Lu et al, 1992).…”