Mouse lymphoma cell lines resistant to pea lectin are defective in fucose metabolism

Two mutants of the BW5147 mouse lymphoma cell line have been selected for their resistance to the toxic effects of pea lectin. These cell lines, termed PL(R)1.3 and PHA(R)1.8 PL(R)7.2, have a decreased number of high affinity pea lectin-binding sites. Intact cell labelling experiments using [2-³H]mannose indicated that PL(R)1.3 cells have a block in the conversion of GDP-[³H] mannose to GDP-[³H]fucose whereas PHA(R)1.8 PL(R)7.2 cells appear to be blocked in the transfer of fucose from GDP-[³H]fucose to glycoprotein acceptors. In vitro experiments with extracts of PL(R)1.3 cells confirmed the failure to convert GDP-mannose to GDP-fucose and indicated that the defect is in GDP-mannose 4,6-dehydratase (EC 4.2.1.47), the first enzyme in the conversion of GDP-mannose to GDP-fucose. The block in the PL(R)1.3 cells could be bypassed by growing the cells in the presence of fucose, demonstrating that an alternate pathway for the production of GDP-fucose presumably via fucose 1-phosphate is functional in this line. PL(R)1.3 cells grown in 10 mM fucose showed normal high affinity pea lectin binding. PHA(R)1.8 PL(R)7.2 cells synthesize GDP-fucose and have normal or increased levels of GDP-fucose:glycoprotein fucosyltransferase when assayed in vitro. The fucosyltransferases of this clone can utilize its own glycoproteins as fucose acceptors in in vitro assays. These findings indicate that this cell line fails to carry out the fucosyltransferase reaction in vivo despite the fact that it possesses the appropriate nucleotide sugar, glycoprotein acceptors, and fucosyltransferase. The finding of decreased glycoprotein fucose in two independent isolates of pea lectin-resistant cell lines and the restoration of high affinity pea lectin binding to PL(R) 1.3 cells following fucose feeding strongly implicates fucose as a major determinant of pea lectin binding.