Roles of sphingolipids and glycosphingolipids in neurite extension, adhesion and growth of neuronal cells.

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( 1 ) An inhibitor of glucosylceramide synthase, PDMP ( 1-phenyl-2-decanoylamino-3morpholino-1-propanol ), affected the cell cycle progression of murine neuroblastoma NS-20Y cells: the proportion of cells in the S phase was reduced, and that in the GO/G1 phase significantly increased. The recovery of cell growth was not found after the addition of major glycosphingolipids of NS-20Y cells, lactosylceramide, globotetraosylceramide, GM1, or GD1a. GM1 itself showed an inhibition of cell cycle progression. A flow cytometric analysis showed that the expression of GM1 on the cell surface did not change during the cell cycle progression of NS-20Y cells.( 2 ) Pathways for the biosynthesis and recycling of sphingolipids were inhibited by PDMP, N-butyldeoxygalactonojirimycin, fumonisin B l , L-cycloserine, or β -chloro-L-alanine and the effects on cell growth and GM1 expression were investigated. In NS20Y cells, ( i ) glycoshingolipids were synthesized predominantly from sphingosine and sphingani … More ne produced by hydrolysis of sphingolipids; ( ii ) de novo biosynthesis of sphinganine was used for a part of glycosphingolipid synthesis; and ( iii ) a part of native or partially hydrolyzed GM1 was recycled from the endosomal pathway through the Golgi apparatus.( 3 ) The cell surface glycoconjugates were examined for their reactivity with a series of lectins in mouse neuroblastoma cell lines and rat PC12 cell. Lectins specific for LFuc reacted only with a minor population of each cells. Most of the lectins specific for Gal GalNAc and those specific for Man Glc GlcNAc reacted well with varying intensities. Maackia amurensis ( MAM ) lectin reacted well with mouse neuroblastoma cells ( NS-20Y, Neuro2a, NIE-115 ) and rat PC12 cell, indicating the presence of Sia α2-3Gal sugar chains.( 4 ) Neurite outgrowth in tnurine neuroblastoma NS-20Y cells induced by serum deprivation was strongly inhibited by MAM lectin at the concentration above 1μ g/ml, and a characteristic change in cell morphology Was observed. Other lectins which bound to NS-20Y cells with different specificities did not show these effects. The mechanisms by which the binding of MAMlectins to cell surface sialic acids caused the inhibition of neurite extension and the morphology change are very intriguing. Less