L. Riboni et al., Basic fibroblast growth factor-induced proliferation of primary astrocytes- Evidence for the involvement of sphingomyelin biosynthesis, J BIOL CHEM, 276(16), 2001, pp. 12797-12804
We recently reported that the marked decrease in cellular ceramide in prima
ry astrocytes is an early event associated with the mitogenic activity of b
asic fibroblast growth factor (bFGF) (Riboni, L,, Viani, P,, Bassi, R,, Sta
bieini, A., and Tettamanti, G, (2000) GLIA 32, 137-145), Here we show that
a rapid activation of sphingomyelin biosynthesis appears to be the major me
chanism responsible for the fall in ceramide levels induced by bFGF, When q
uiescent astrocytes were treated with bFGF, an increased amount of newly sy
nthesized ceramide (from either L-[H-3]serine or [H-3]sphingosine) was dire
cted toward the biosynthesis of sphingomyelin, Conversely, bFGF did not app
ear to affect ceramide levels by other metabolic pathways involved in ceram
ide turnover such as sphingomyelin degradation and ceramide biosynthesis, d
egradation, and glucosylation, Enzymatic studies demonstrating a relevant a
nd rapid increase in sphingomyelin synthase activity after bFGF treatment h
ave provided a convincing explanation for the activation of sphingomyelin b
iosynthesis, The bFGF-induced increase in sphingomyelin synthase appears to
depend on a post-translational activation mechanism. Moreover, in the pres
ence of brefeldin A, the activation of sphingomyelin biosynthesis was aboli
shed, suggesting that the enzyme is located in a compartment other than the
Golgi apparatus. Also the phosphatidylcholine-specific phospholipase C inh
ibitor D609 exerted a potent inhibitory effect on sphingomyelin biosynthesi
s. Finally, we demonstrate that inhibition of sphingomyelin biosynthesis by
brefeldin A or D609 led to a significant inhibition of bFGF-stimulated mit
ogenesis. All this supports that, in primary astrocytes, the early activati
on of sphingomyelin synthase is involved in the bFGF signaling pathway lead
ing to proliferation.