scholarly journals Cell surface proteoglycan of mouse mammary epithelial cells is shed by cleavage of its matrix-binding ectodomain from its membrane-associated domain.

1987 ◽  
Vol 105 (6) ◽  
pp. 3087-3096 ◽  
Author(s):  
M Jalkanen ◽  
A Rapraeger ◽  
S Saunders ◽  
M Bernfield
Keyword(s):  
Epithelial Cells ◽  
Cell Surface ◽  
Mammary Epithelial Cells ◽  
Core Protein ◽  
Buoyant Density ◽  
Deae Cellulose ◽  
Kinetic Studies ◽  
Mammary Epithelial ◽  
The Matrix ◽  
Cell Surface Proteoglycan

The cell surface proteoglycan on normal murine mammary gland (NMuMG) epithelial cells consists of a lipophilic domain, presumably intercalated into the plasma membrane, and an ectodomain that binds via its glycosaminoglycan chains to matrix components, is released intact by proteases and is detected by monoclonal antibody 281-2. The antibody 281-2 also detects a proteoglycan in the culture medium conditioned by NMuMG cells. This immunoactive proteoglycan was purified to homogeneity using DEAE-cellulose chromatography, isopycnic centrifugation, and 281-2 affinity chromatography. Comparison of the immunoreactive medium proteoglycan with the trypsin-released ectodomain revealed that these proteoglycans are indistinguishable by several criteria as both: (a) contain heparan sulfate and chondroitin sulfate chains; and (b) are similar in hydrodynamic size and buoyant density; (c) have the same size core protein (Mr approximately 53 kD); (d) are nonlipophilic as studied by liposomal intercalation and transfer to silicone-treated paper. Kinetic studies of the release of proteoglycan from the surface of suspended NMuMG cells are interpreted to indicate that the immunoreactive medium proteoglycan is derived directly from the cell surface proteoglycan. Suspension of the cells both augments the release and inhibits the replacement of cell surface proteoglycan. These results indicate that the cell surface proteoglycan of NMuMG cells can be shed by cleavage of its matrix-binding ectodomain from its membrane-associated domain, providing a mechanism by which the epithelial cells can loosen their proteoglycan-mediated attachment to the matrix.

scholarly journals Cell surface proteoglycan associates with the cytoskeleton at the basolateral cell surface of mouse mammary epithelial cells.

1986 ◽  
Vol 103 (6) ◽  
pp. 2683-2696 ◽  
Author(s):  
A Rapraeger ◽  
M Jalkanen ◽  
M Bernfield
Keyword(s):  
Epithelial Cells ◽  
Cell Surface ◽  
Basal Cell ◽  
Mammary Epithelial Cells ◽  
Apical Cell ◽  
Mammary Epithelial ◽  
Filament Bundles ◽  
Matrix Components ◽  
Cell Surface Proteoglycan

The cell surface proteoglycan on normal murine mammary gland mouse mammary epithelial cells consists of an ectodomain bearing heparan and chondroitin sulfate chains and a lipophilic domain that is presumed to be intercalated into the plasma membrane. Because the ectodomain binds to matrix components produced by stromal cells with specificity and high affinity, we have proposed that the cell surface proteoglycan is a matrix receptor that binds epithelial cells to their underlying basement membrane. We now show that the proteoglycan surrounds cells grown in subconfluent or newly confluent monolayers, but becomes restricted to the basolateral surface of cells that have been confluent for a week or more; Triton X-100 extraction distinguishes three fractions of cell surface proteoglycan: a fraction released by detergent and presumed to be free in the membrane, a fraction bound via a salt-labile linkage, and a nonextractable fraction; the latter two fractions co-localize with actin filament bundles at the basal cell surface; and when proteoglycans at the apical cell surface are cross-linked by antibodies, they initially assimilate into detergent-resistant, immobile clusters that are subsequently aggregated by the cytoskeleton. These findings suggest that the proteoglycan, initially present on the entire surface and free in the plane of the membrane, becomes sequestered at the basolateral cell surface and bound to the actin-rich cytoskeleton as the cells become polarized in vitro. Binding of matrix components may cross-link proteoglycans at the basal cell surface and cause them to associate with the actin cytoskeleton, providing a mechanism by which the cell surface proteoglycan acts as a matrix receptor to stabilize the morphology of epithelial sheets.

scholarly journals Translational suppression of syndecan-1 expression in Ha-ras transformed mouse mammary epithelial cells.

1993 ◽  
Vol 4 (8) ◽  
pp. 849-858 ◽  
Author(s):  
J Kirjavainen ◽  
S Leppä ◽  
N E Hynes ◽  
M Jalkanen
Keyword(s):  
Epithelial Cell ◽  
Epithelial Cells ◽  
Cell Surface ◽  
Mammary Epithelial Cells ◽  
Core Protein ◽  
Mammary Epithelial ◽  
Epithelial Cell Line ◽  
Mrna Levels ◽  
Ras Gene ◽  
Mmtv Ltr

A cell surface proteoglycan, syndecan-1, has been shown to participate in the maintenance of the epithelial cell morphology. A point mutated activated c-Ha-ras gene under the control of the glucocorticoid inducible MMTV-LTR promoter was transfected into the mouse mammary epithelial cell line, NOG-8. The NOG-8 ras cells were used to study changes in syndecan-1 expression during epithelial transformation. NOG-8 ras cells, when induced to express Ha-ras, transformed and formed foci in monolayer cultures and colonies in suspension cultures. Expression of syndecan-1 at the cell surface was markedly reduced in cells showing the transformed phenotype. The accumulation of newly synthesized core protein of syndecan-1 was suppressed in these cells, whereas mRNA levels remained unchanged. This novel finding indicates that syndecan-1 expression is translationally suppressed in the Ha-ras-transformed epithelial cells. Hence, syndecan-1 loss during epithelial transformation could take place without altering syndecan gene transcription and, on the other hand, could be one of the critical events involved in malignant transformation.

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