Connectin: cell surface protein that binds both laminin and actin.

Brown, Susan S.; Malinoff, Herbert L.; Wicha, Max S.

doi:10.1073/pnas.80.19.5927

Cited by 114 publications

(46 citation statements)

References 28 publications

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“…In addition to the statistical association between these structures, we frequently observed the alignment of cytoskeletal filaments with extracellular matrix structures traversing the lamina lucida. These results suggest the existence of a structural interaction that could be mediated by integral membrane proteins (see also Brown et al, 1983;Hay, 1982).…”

Section: Discussionmentioning

confidence: 94%

Development of ultrastructural specializations during the formation of acetylcholine receptor aggregates on cultured myotubes

Olek¹,

Ling²,

Daniels³

1986

J. Neurosci.

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The ultrastructure of cultured rat myotubes was examined at stages in the initial assembly of acetylcholine receptor (AChR) aggregates in order to elucidate the role of cell-surface specializations in aggregate formation. Within 4-6 hr, embryonic brain extract (EBX) induces the formation of sites of AChR density elevated 5-9x above that of surrounding regions, and the appearance of these aggregates is preceded by the formation of clouds of punctate microaggregates (Olek et al., 1983). A video image-intensification system was used to monitor this redistribution of fluorescently labeled AChR, and sites of aggregation were mapped on identified myotubes. After processing the cultures for electron microscopy, thin sections were taken through identified aggregate sites at various stages in assembly. Specializations, including a basal lamina, mound-shaped plasma membrane contours with occasional deep infoldings, and a subjacent dense cytoskeletal specialization, which tended to exclude other cytoplasmic organelles, were associated with newly formed aggregates found 4-6 hr after adding EBX to the cultures. Analysis of random thin sections through EBX-treated and untreated myotubes showed that the extent of specializations of the basal lamina and cytoplasm was approximately threefold greater in cells exposed to EBX for 4 hr, suggesting a concurrent, and possibly interdependent, organization of such specializations with AChR aggregate assembly. Examination of sections through clouds of microaggregates, which formed within 90 min, revealed mound-shaped plasma membrane contours and underlying cytoplasm depleted of organelles but relatively little basal lamina and submembrane cytoskeletal density. These results suggest that the initial stage of AChR aggregate assembly involves relatively subtle changes in the structure of the cell cortex and that the evolution of microaggregates to aggregates may require the formation of additional cytoskeletal and extracellular matrix structures.A critical question in cellular neurobiology is how certain regions within neurons and their synaptic targets become organized to subserve specialized functions. A striking example of such a region is the motor endplate, where a small area (less than 0.0 1% of the cell surface) of the muscle cell becomes highly differentiated in function and structure during synapse formation. While the function of the mature motor endplate in neuromuscular transmission has been well studied, relatively little

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Section: Discussionmentioning

confidence: 94%

Development of ultrastructural specializations during the formation of acetylcholine receptor aggregates on cultured myotubes

Olek¹,

Ling²,

Daniels³

1986

J. Neurosci.

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“…A third possibility is that actin interacts directly with an integral membrane protein. Evidence has been presented for several examples of this latter type of interaction (6,13,14,29,30).…”

Section: Discussionmentioning

confidence: 99%

Isolation of an actin-binding protein from membranes of Dictyostelium discoideum.

Stratford¹,

Brown²

1985

The Journal of Cell Biology

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We prepared a probe of radiolabeled, glutaraldehyde cross-linked filamentous actin (F-actin) to study binding of actin to membranes of Dictyostelium discoideum. The probe bound to membranes or detergent extracts of membranes with a high affinity and in a saturable manner. The binding could be reduced by boiling of either the actin probe or the membranes, or by addition of excess native F-actin, but not by addition of an equivalent amount of bovine serum albumin, to the assay. The probe labeled several proteins when used to overlay sodium dodecyl sulfate gels of Dictyostelium membranes. One of these labeled proteins was a 24,000-mol-wt protein (p24), which was soluble only in the presence of a high concentration of sodium deoxycholate (5%, wt/vol) at room temperature or above. The p24 was purified by selective detergent extraction and column chromatography. When tested in a novel twophase binding assay, p24 bound both native monomeric actin (G-actin) and F-actin in a specific manner. In this assay, G-actin bound p24 with a submicromolar affinity.

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“…However, the increase in 8-casein message in cells cultured on HSPG without an obvious morphological change argues against a simple correlation between shape and mRNA levels. Cellassociated HSPG has been shown to span the plasma membrane, connecting the ECM and the cytoskeleton (30), and laminin also has been reported to have connections to actin via a cell-surface receptor (31). Perhaps HSPG and laminin in our cultures can increase 83-casein mRNA levels by altering cytoskeletal interactions with polysomes, leading to increased message stability (24).…”

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confidence: 99%

Influence of a reconstituted basement membrane and its components on casein gene expression and secretion in mouse mammary epithelial cells.

Li¹,

Aggeler²,

Farson³

et al. 1987

Proc. Natl. Acad. Sci. U.S.A.

526

309

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When primary mouse mammary epithelial cells are cultured on plastic, they rapidly lose their ability to synthesize and secrete most milk proteins even in the presence of lactogenic hormones, whereas cells cultured on released type I collagen gels show greatly enhanced mRNA levels and secretion rates of ,B-casein and of some other milk proteins. We show here that culture on a reconstituted basement membrane from Engelbreth-Holm-Swarm tumor (EHS) allows >90% of cells to produce high levels of 13-casein. By 1-3). Until a decade ago, most investigators cultured cells on plastic surfaces, which led to drastic alterations of morphology and function from the parent tissue (4). Following the example of Emerman and Pitelka (5), we and others have shown that several aspects of functional epithelium can be maintained when primary mouse mammary epithelial cells (PMME) are cultured on "released" (RG or "floating") collagen type I gels instead of plastic. These include polarization of organelles, appearance of apical microvilli, formation of a basal lamina (5, 6), changes in glucose metabolite pattern (7), lumina formation (8), altered synthesis and compartmentalization of extracellular matrix (ECM) components (9, 10), enhancement ofmost milk protein synthesis and secretion (11), and increases in p-casein (12) and transferrin (13,14) mRNA levels. These results signify the importance of cell-substratum interactions in regulating tissue-specific functions and point to a possible regulatory role for ECM in vivo.Cells on released gels (and not on plastic or flat gels) were shown to synthesize an intact basement membrane (5) containing high levels of heparan sulfate and other sulfated glycosaminoglycans (9), type IV collagen, and laminin (10). We reasoned that the released gel may act through the influence of newly synthesized basement membrane components. To test the mechanism of cell-ECM interaction more directly, we have analyzed the consequences of culturing PMME cells on a reconstituted basal lamina derived from Engelbreth-Holm-Swarm (EHS) tumor (15) and on some of its individual components.MATERIALS AND METHODS PMME from 14-to 17-day pregnant BALB/c mice and collagen from rat tail tendon were prepared as described (5, 10, 11). Tumors (EHS) from normal or lathyritic mice were extracted with high salt and 2 M urea as described by Kleinman et al. (15). Dialyzed EHS extract (100-200 1.d) was spread either directly on 35-mm dishes or on top of rat-tail collagen gels. Collagen gels were released 3-4 days after seeding. Matrigel, an EHS preparation from Collaborative Research (Waltham, MA), was used for some experiments. Laminin and type IV collagen (Bethesda Research Laboratories) were spread at 2.5-10 pug/cm2. Heparan sulfate proteoglycan (HSPG; low density form) was prepared from EHS tumors as described by Hassell et al. (16) and was spread at 1-5 ,ug/cm2 or was added to the medium at 5 ,ug/ml every other day. The latter was less toxic but also less effective. EHS (10 ,ug/ml) and individual substrata other than HSPG we...

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Connectin: cell surface protein that binds both laminin and actin.

Cited by 114 publications

References 28 publications

Development of ultrastructural specializations during the formation of acetylcholine receptor aggregates on cultured myotubes

Development of ultrastructural specializations during the formation of acetylcholine receptor aggregates on cultured myotubes

Isolation of an actin-binding protein from membranes of Dictyostelium discoideum.

Influence of a reconstituted basement membrane and its components on casein gene expression and secretion in mouse mammary epithelial cells.

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