Synthesis of lipid-linked oligosaccharides is dependent on the cell cycle in rat 3Y1 cells

Synchronized cultures of rat 3Y1 cells, prepared by the density-arrested method, were used to investigate the relationship of N-glycosylation to the cell cycle. Although total cellular proteins were synthesized independently of the cell cycle, the synthesis of membrane-bound proteins was found to be dependent on the cell cycle, the time of maximum synthesis being just before that of maximum DNA synthesis. The synthesis of lipid-linked oligosaccharides (LLO), which are utilized as intermediates in N-glycosylation, increased in the S phase to a level at least ten times higher than in the G1, G2, and M periods. Moreover, the activities of dehydrodolichyl diphosphate synthase and farnesyl diphosphate synthase, which synthesize the precursors of dolichol, also increased in the S phase concomitantly with LLO synthesis. However, since the cell cycle dependency curves of these two enzyme activities were somewhat broader than that of LLO synthesis, the rate-limiting enzyme in the regulation of LLO synthesis might be another one such as dehydrodolichol reductase. These results suggest that LLO synthesis is regulated by multiple synthetic enzymes which are activated in a cell cycle dependent manner.