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Sialyl cholesterol is translocated into cell nuclei and it promotes neurite outgrowth in a mouse neuroblastoma cell line.
To determine the mechanisms of the neuritogenesis induced by synthetic sialyl cholesterol (SC) in a mouse neuroblastoma cell line, Neuro2a, the biochemical fate of SC and ganglioside GM1 (IV3NeuAc-GgOse4Cer) was investigated. The kinetics of incorporation of SC and GM1 into cells for the two compounds were similar. SC was not degraded nor modified for at least 24 h after the incorporation, indicating that SC itself and not its metabolites were responsible for the neuritogenic activity. Cell fractionation experiments showed that approximately 40% of the incorporated SC was localized in the nucleus, 25% in the plasma membrane fractions, and 11-14% in the granule fraction. This distribution was different from that of GM1. The nuclear SC was found to affect de novo RNA synthesis, indicating its biological effect may be mediated at the level of transcription. SC also increased the rates of both Ca2+ influx and efflux, although the intracellular level of total Ca2+ remained unchanged. Levels of inositol 1,4,5-triphosphate (IP3) also remained unchanged and the SC dependent neuritogenesis was not inhibited by an excess amount of W-7, an inhibitor of Ca2+/CaM kinases. These results again accord with the suggestion that SC and GM1 do not utilize Ca2+, IP3 or Ca2+/CaM as a second messenger for neuritogenesis. Rather it appears very likely that the nuclear localized SC may play a key role in neuritogenesis.
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