Altered Composition of Membrane Glycoconjugates in Rat Hepatoma Tissue Culture Cells after Dexamethasone Treatment or in Vivo Growth

Abstract

The influence of dexamethasone or in vivo growth on the composition of glycoproteins and glycolipids in membranes of rat hepatoma tissue culture cells (HTC cells) was studied. The fucose-containing glycoproteins were labeled by incubation of HTC cells or tumor tissue for 24 hr in the presence of [³H]-fucose. The glycoproteins were isolated from the total membrane fractions by concanavalin A-Sepharose chromatography and analyzed by two-dimensional gel electrophoresis. Tumor tissue contains the same set of fucose-containing glycoproteins as do the in vitro cultured cells, plus three additional fucoglycoproteins. Crossed immunoelectrophoretic analysis of these glycoproteins using antisera, raised against total glycoprotein fractions in goats, also revealed three additional precipitation lines for tumor tissue. Treatment of HTC cells with dexamethasone resulted in the appearance of two new glycoproteins. When rats bearing a hepatoma derived from HTC cells were treated with dexamethasone, the same hormone-inducible glycoproteins as found in HTC cells appear in the tumor cells. In addition, a third glycoprotein was induced in the tumor cells of the rat. Besides the appearance of hormone-inducible glycoproteins in the HTC cells growing in vitro culture and in vivo in rats, other glycoproteins were reduced in amount. No qualitative and only minor quantitative differences in the composition of both the gangliosides and the neutral glycolipids could be detected when hepatoma cells grown in vitro and in vivo were compared. Dexamethasone treatment, however, caused in HTC cells as well as in the tumor a reduction in the ganglioside G_MI and a simultaneous appearance of a new band, probably G_Dla.

These results indicate that the membrane phenotype of HTC cells is a function of the growth environment of the cell. Some of the observed alterations in the composition of the membrane-associated glycoconjugates could be related to coincident changes in plasma membrane functions, such as cell-cell interactions and transport of small molecules.