EXPRESSING MURINE BETA-1,4-GALACTOSYLTRANSFERASE IN HELA-CELLS PRODUCES A CELL-SURFACE GALACTOSYLTRANSFERASE-DEPENDENT PHENOTYPE

beta 1,4-Galactosyltransferase is traditionally viewed as a biosynthet ic component of the Gels complex, but a portion of galactosyltransfera se is also expressed on the cell surface, where it has been suggested to function as a receptor for extracellular oligosaccharide Ligands. A lthough results from a variety of studies are consistent with a cell a dhesion function for galactosyltransferase, the most rigorous test of surface galactosyltransferase function is to produce a surface galacto syltransferase-dependent phenotype in cells that normally express negl igible levels of surface galactosyltransferase. In agreement with prev ious reports, human HeLa cells were found to express low levels of gal actosyltransferase on their surface and, therefore, were stably transf ected with cDNAs encoding murine galactosyltransferase. Murine galacto syltransferase was expressed both within the presumed Golgi complex an d on the cell surface, as assayed by enzyme activity and with antiseru m raised against the bacterially expressed murine enzyme. HeLa cell tr ansfectants adhered more strongly to their extracellular substrates th an did control transfectants, as evidenced by a natter morphology in c ulture and a more rapid spreading upon plating. In contrast, cell spre ading was low and similar among all cell types when plated on extracel lular substrates that did not contain binding sites for galactosyltran sferase. Antibodies and Fab fragments against recombinant murine galac tosyltransferase inhibited the increased cell spreading characteristic of galactosyltransferase transfectants, as did soluble recombinant ga lactosyltransferase and a variety of galactosyltransferase perturbants . Thus, expression of heterologous galactosyltransferase produces a su rface galactosyltransferase-dependent phenotype, confirming its functi on as a cell adhesion molecule.