Sphingomyelin Synthase 1 Regulates Neuro-2a Cell Proliferation and Cell Cycle Progression Through Modulation of p27 Expression and Akt Signaling.

Sphingomyelin synthase (SMS) is a key enzyme involved in the generation of sphingomyelin (SM) and regulation of cell growth and survival. However, the effects of SMS on neuronal cell proliferation and cell cycle progression are not completely elucidated. In this study, we examined the direct effects of SMS1 in regulating cell cycle progression and proliferation of Neuro-2a cells that exhibit neuronal characteristics. Neuro-2a cells transfected with SMS-specific small hairpin RNA (shRNA) expressed significantly lower levels of SMS1. RNA interference-mediated depletion of SMS1 in Neuro-2a cells caused a significant decrease in SM levels. Decreased SMS1 levels resulted in reduced proliferation rate and morphological changes including neurite-like outgrowth. Also, silencing of SMS1 induced cell cycle arrest as shown by the increased percentage of cells in G0/G1 and decreased proportion of cells in S phase. These changes were accompanied by upregulation of cyclin-dependent kinase inhibitor p27 and decreased levels of cyclin D1 and phospho-Akt. Nuclear accumulation of p27 was also evident in SMS1-deficient cells. Furthermore, loss of SMS1 inhibited the migratory potential of Neuro-2a cells in association with decreased levels of matrix metalloproteinases. These results indicate that SMS1 plays an important role in mediating the key signaling pathways that are involved in the tight coordination of multiple cellular activities, including neuronal cell proliferation, cell cycle progression, and migration, and therefore may have significant implications in neurodegenerative diseases.