Cell surface and Golgi pools of beta-1,4-galactosyltransferase are differentially regulated during embryonal carcinoma cell differentiation.

Abstract

beta-1,4-Galactosyltransferase (GalTase) has two functionally distinct subcellular distributions. In the Golgi apparatus, GalTase participates in the glycosylation of secretory and membrane-bound glycoproteins, whereas on the cell surface it mediates specific aspects of intercellular adhesion. For this study, a murine GalTase clone was obtained by screening a lambda gt10 cDNA library made from F9 embryonal carcinoma cells with a heterologous bovine GalTase cDNA probe. The murine GalTase cDNA probe was used in conjunction with assays of GalTase activity to investigate the expression and distribution of GalTase during differentiation of F9 stem cells into secretory endodermal epithelium. During the initial phase of F9 cell differentiation, GalTase mRNA levels remained relatively constant; however, as differentiation progressed, as assayed by expression of the differentiation-specific marker laminin B1, GalTase mRNA levels and enzyme activity rose dramatically. Furthermore, subcellular fractionation of these cells showed that the increased GalTase levels were specifically associated with the Golgi apparatus, whereas GalTase specific activity on the plasma membrane remained constant. These results show that levels of cell surface and Golgi GalTase change relative to one another during F9 cell differentiation and suggest that these functionally distinct pools of GalTase are independently and differentially regulated.

Isolation of a cDNA encoding a murine UDPgalactose:beta-D-galactosyl- 1,4-N-acetyl-D-glucosaminide alpha-1,3-galactosyltransferase: expression cloning by gene transfer.

“…5). These results are similar to those reported in F9 cells with ,B-1,4-galactosyltransferase (29) and suggest that the dynamic changes in cell surface oligosaccharide structures known to accompany in vitro differentiation of this cell line (10) are associated with significant changes in glycosyltransferase gene expression.…”

Transcriptional Regulation of α1,3-Galactosyltransferase in Embryonal Carcinoma Cells by Retinoic Acid

“…It has been reported that ␤1,4GT activity decreases to approximately one-third of control values during the first 3 days of differentiation of F9 cells following RA addition and then begins to rise slowly on day 4 following RA treatment (53). Consistent with this, we found that the activity of the ␤1,4GT in extracts of both F9 and RA/F9 cells is similar during the first 3 days following RA treatment (data not shown).…”

“…However, using a different assay for fucosyltransferase activity another group observed a slight increase in the activity of fucosyltransferase upon RA treatment of F9 cells (88). In the case of ␤1,4GT, it was shown that ␤1,4GT activity in F9 cells declines after 3 days of differentiation and then begins to rise around 5-6 days of differentiation, which correlates with increased levels of transcript observed after 5-6 days of treatment with RA (53). Recently, it was reported that neither the ␤1,4GT enzyme nor transcript levels change significantly in F9 cells treated with RA alone, but treatment with RA and cAMP causes a 6.5-fold induction of the transcript in 8 days (54).…”

Mutational analysis of the cytoplasmic domain of β1,4-galactosyltransferase I: influence of phosphorylation on cell surface expression

“…The level of GalT I on the cell surface is differentially regulated from that in the Golgi pool and is not the result of simple bulk flow of Golgi-derived vesicles to the cell surface (Lopez et al, 1989). This suggests that the Golgi and surface pools of GalT I result from distinct protein species and/or molecular pathways (reviewed by Shur et al, 1998).…”