Modulation by Retinoic Acid of Cellular, Surface-Exposed, and Secreted Glycoconjugates in Cultured Human Sarcoma Cells

Abstract

The effect of β-all-trans-retinoic acid (RA) on the synthesis of cellular, cell surface, and secreted glycoconjugates by human Hs705 chondrosarcoma and Hs791 osteosarcoma cells was investigated in vitro. Untreated and RA-treated cells were labeled either metabolically with radioactive precursors or by oxidation of externally exposed cell membrane glycoprotein(s) (GP) by treatment with NalO₄ or neuraminidase and galactose oxidase followed by reduction with NaB[³H]₄. The cells were solubilized and analyzed by Polyacrylamide gel electrophoresis followed by fluorography. RA enhanced the labeling of sialic acid and galactose residues on the GP of relative molecular weight(s) (M_r) in the range 95,000-300,000 on the surfaces of both cell types. [³H]glycosamine incorporation into GP with M_r of 100,000, 150,000, and 190,000 in both cell lines was also stimulated. In the Hs705 cells there was also an increase in the labeling of a 290,000-M_r GP. In contrast, [³H]glucosamine incorporation into glycoconjugates greater than 400,000 M_r in both the cells and the conditioned medium of Hs705 cells decreased. The latter glycoconjugates were susceptible to hyaluronidase and chondroitinases. [³H]glucosamine incorporation into a secreted 230,000-M_r GP, identified as fibronectin, was also reduced. Analyses of conditioned media of cells labeled with [³⁵S]methionine or [¹⁴C]proline demonstrated that RA decreased the secretion of procollagen chains and fibronectin. Immunofluorescence revealed that RA alters the distribution of cell-associated fibronectin. These results demonstrated that RA increases the glycosylation of specific cellular and cell surface GP and decreases the production of secreted GP and glycosaminoglycans by the sarcoma cells.