Based on the presented experiments, we conclude that there was no significant glycan leakage from embedded cells, since the chromatogram obtained from the analysis of untreated cells did not contain structures other than the oligomannose. Histone acetylation at gene promoters is an important epigenetic modification controlling gene expression. Treatment with the deacetylase inhibitor Trichostatin A resulted in altered expression of glyco-genes in HepG2 cancer cells, whereas both Trichostatin A and sodium butyrate altered the composition of glycan structures in HeLa cells. However, whether the original glycan profile upon drug removal from the medium is preferentially restored or irreversibly changed is still unknown. We performed multiple independent experiments wherein, following the treatments, HeLa cells were left to grow in a drugfree medium. Major N-glycome ICI 182780 changes were not expected since the inhibition of HDAC activity affects the expression of only 2% of mammalian genes. However, a couple of glycan groups were affected. In general, sodium butyrate induced ABT-263 in vivo milder changes than TSA, probably due to its lower affinity to bind the substrate, requiring higher concentrations to have an effect. Both inhibitors induced the increased expression of biantennary glycans, and the decreased expression of disialylated glycans with core-fucose. Specifically, TSA downregulated the expression of complex, branched glycan structures from GP10, whereas sodium butyrate upregulated the expression of tetraantennary glycans from GP7. Since incorporation of fucose into glycoproteins and increased glycan branching are both associated with malignant phenotype, the observed reduction in quantity of these glycans following an epigenetic treatment is a desirable effect. However, following cell recovery in a drug-free medium we observed reversal of the induced effects and obtained similar composition of the membrane N-glycome of HeLa cells as prior to the treatments. This finding strongly argues in favor of stability of the N-glycome and corresponding epigenetic mechanisms responsible for establishment and maintenance of histone acetylation levels of glyco-genes involved in glycan biosynthesis. It also confirms transient mode of TSA action, based on reversible binding to HDACs, and demonstrates the importance of recurrent epigenetic treatments for successful reversal of potentially undesirable glycan phenotypes. The role of DNA methylation in the regulation of glycosylation has particularly been studied in the context of fucosylation, which is present mostly on secretory or membrane proteins on the cell surface, such as epidermal growth factor and transforming growth factor beta receptors. Fucosylation levels in normal liver and colon are relatively low, but increase during carcinogenesis, mediating killing of oncogenically transformed cells by natural killer cells. However, mutations in the gene GMDS coding for a key enzyme involved in the synthesis of GDP-fucose, a donor substrate for fucosyltransferases. Therefore, zebularine treatments of various cancer cell lines with relatively low fucosylation levels were performed in order to induce up-regulation of fucosylationrelated genes and consequently restore global fucosylation level. Interestingly, we observed in HeLa cells that the expression of fucosylated glycans was not altered following the 100 mM zebularine treatment.