Suppression of focus formation by bovine papillomavirus-transformed cells by contact with non-transformed cells: involvement of sugar(s) and phosphorylation.

Focus formation by bovine papilloma virus-transformed C127 cells was inhibited by direct contact with non-transformed C127 cells. The suppressive capacity of C127 cells was abolished by introduction of the neomycin resistance gene (neor) but not by that of the hygromycin resistance gene (hygrr). Though both genes code for phosphotransferase which inactivates the aminoglycoside antibiotics, their substrates are different, i.e., there is no cross-resistance between them. As the neomycin phosphotransferase phosphorylates the specific hydroxyl group of the sugar in the aminoglycosides, such as 3'OH of the glucose residue of kanamycin A, some specific sugar(s) on the molecules exposed on the cell surface must be responsible for the suppressive signal and their phosphorylation must have resulted in the loss of that signal. The sugar must have the structure shared by kanamycin, neomycin or G418 but not by hygromycin B. Involvement of sugar was also suggested by the observation that concanavalin A partially abrogated the suppressive capacity of C127 cells.