Relationship of transformation, cell density, and growth control to the cellular distribution of newly synthesized glycosaminoglycan.

Abstract

Mouse 3T3 cells and their Simian Virus 40-transformed derivatives (3T3SV) were used to assess the relationship of transformation, cell density, and growth control to the cellular distribution of newly synthesized glycosaminoglycan (GAG). Glucosamine-and galactosamine-containing GAG were labeled equivalently by [all]-glucose regardless of culture type, allowing incorporation into the various GAG to be compared under all conditions studied. Three components of each culture type were examined: the cells, which contain the bulk of newly synthesized GAG and are enriched in chondroitin sulfate and heparan sulfate; cell surface materials released by trypsin, which contain predominantly hyaluronic acid; and the media, which contain predominantly hyaluronic acid and undersulfated chondroitin sulfate.Increased cell density and viral transformation reduce incorporation into GAG relative to the incorporation into other polysaccharides. Transformation, however, does not substantially alter the type or distribution of newly synthesized GAG; the relative amounts and cellular distributions were very similar in 3T3 and 3T3SV cultures growing at similar rates at low densities. On the other hand, increased cell density as well as density-dependent growth inhibition modified the type and distribution of newly synthesized GAG. At high cell densities both cell types showed reduced incorporation into hyaluronate and an increase in cellular GAG due to enhanced labeling of chondroitin sulfate and heparan sulfate. These changes were more marked in confluent 3T3 cultures which also differed in showing substantially more GAG label in the medium and in chondroitin-6-sulfate and heparan sulfate at the cell surface.Since cell density and possibly density-dependent inhibition of growth but not viral transformation are major factors controlling the cellular distribution and type of newly synthesized GAG, differences due to GAGs in the culture behavior of normal and transformed cells may occur only at high cell density. The densityinduced GAG alterations most likely involved are increased chondroitin-6-sulfate and heparan sulfate and decreased hyaluronic acid at the cell surface.

The hyaluronate receptor is preferentially expressed on proliferating epithelial cells.

“…It also suggests that both of these components are under a similar type of control. Indeed, several studies have shown that the synthesis of hyaluronate is also much greater in proliferating cells as compared with nonproliferating cells (4,15), again paralleling what we have observed with the hyaluronate receptor.…”

Defective basal lamina formation by transformed mammary epithelial cells: A reduced effect of collagen on basal lamina (heparan sulfate‐rich) proteoglycan degradation

“…The basal lamina may contain specialized collagen types (Kefalides, 1978), specific glycoproteins (Timpl et al, 1979), hyaluronic acid (Cohn et al, 1976), and proteoglycans (Bernfield et al, 1972;Kanwar and Farquhar, 1979; Hassell et al, 1980), but little is known about the mechanisms that control its assembly.…”

Heparan sulfate proteoglycans are concentrated on the sinusoidal plasmalemmal domain and in intracellular organelles of hepatocytes.

“…They have been found in association with cell surfaces (1)(2)(3)(4)(5), intracellular organdies (6,7), and extracellular matrices (especially basement membranes) (8)(9)(10)(11), and have been proposed to participate in a variety of functions such as cell-cell interactions (12), cell migration (13), and cell adhesion (14,15). HSPGs isolated from different sources have distinct structures in terms of their overall size (70-400 kD) and the size of their glycosaminoglycan chains (14-70 kD).…”