Study for the biological role of N-glycolylneuraminic acid-containing glycoconjugates

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NeuGc is derived from NeuAc by hydroxylation of a methyl moiety in the N-acetyl residue. This hydroxylation occurs by the conversion of CMP-N-acetylneuraminic acid (CMP-NeuAc) to CMP-N-glycolylCMP-NeuGc, which is carried out by an electron transport system involving NADH-dependent cytochrome b5 reductase, cytochrome b5, and CMP-NeuAc hydroxylase. CMP-NeuAc hydroxylase is the key enzyme in the hydroxylation of CMP-NeuAc, and functions at the final step of the electron transport system. We have previously purified CMP-NeuAc hydroxylase from the mouse liver, and isolated a cDNA for this enzyme which contains an ORF encoding a protein of 577 amino acids.In this study, we investigated the effect of the increasing amount of NeuGc in cells. In order to increase the amount of NeuGc, a vector containig CMP-NeuAc hydroxylade cDNA under the actin promoter was transfected into 3T3 cells. The cells receiving the vector had the high amount of NeuGc (about 85% of the total sialic acid), but the control cells had the small amount (about 3% of the total sialic acid). The responses for PDGF,EGF,FGF and insulin were investigated. The growth rate betweem the two cells was almost simillar in the presence of PDGF,EGF or insulin. However, the cells containing the high amount of NeuGc grew 1.8 folds faster than those with the low amount of NeuGc in the presence of FGF.