OBJECTIVE: We have previously shown GM3 to positively regulate TNF-alpha expression via a PI3K/Akt pathway in mouse melanoma B16 cells [Wang et al.: Biochem Biophys Res Commun 2007;356:438-443]. The GM3 signal was shown to be located upstream of Akt, but whether it is located upstream of PI3K and which molecule is the effector of PI3K remain to be clarified. METHODS: We used inhibitors of PI3K and mTOR, and siRNA directed to Rictor, Raptor and Rho-GDP dissociation inhibitor beta (Arhgdib). RESULTS: PI3K inhibitors LY294002 and LY303511 were shown to suppress TNF-alpha expression that is stimulated by GM3 in B16 cells, suggesting that the GM3 signal is located upstream of the PI3K-Akt pathway. Rapamycin suppressed TNF-alpha expression, indicating mTOR to be involved in the pathway. Either siRNA Raptor or siRNA Rictor suppressed TNF-alpha expression, but the latter suppressed the effects of GM3 on TNF-alpha expression and Akt phosphorylation at Ser(473), indicating the GM3 signal to be transduced via Rictor/mTOR and Akt (Ser(473)), leading to TNF-alpha stimulation. Finally, Arhgdib, the tumor suppressor gene whose expression is associated with GM3, was shown to be upstream of TNF-alpha. CONCLUSIONS: The GM3 signal is thus transduced in B16 cells through a PI3K, Rictor/mTOR, Akt, Arhgdib pathway, leading to stimulated expression of TNF-alpha. 2008 S. Karger AG, Basel.
OBJECTIVE: We have previously shown GM3 to positively regulate TNF-alpha expression via a PI3K/Akt pathway in mousemelanoma B16 cells [Wang et al.: Biochem Biophys Res Commun 2007;356:438-443]. The GM3 signal was shown to be located upstream of Akt, but whether it is located upstream of PI3K and which molecule is the effector of PI3K remain to be clarified. METHODS: We used inhibitors of PI3K and mTOR, and siRNA directed to Rictor, Raptor and Rho-GDP dissociation inhibitor beta (Arhgdib). RESULTS: PI3K inhibitors LY294002 and LY303511 were shown to suppress TNF-alpha expression that is stimulated by GM3 in B16 cells, suggesting that the GM3 signal is located upstream of the PI3K-Akt pathway. Rapamycin suppressed TNF-alpha expression, indicating mTOR to be involved in the pathway. Either siRNA Raptor or siRNA Rictor suppressed TNF-alpha expression, but the latter suppressed the effects of GM3 on TNF-alpha expression and Akt phosphorylation at Ser(473), indicating the GM3 signal to be transduced via Rictor/mTOR and Akt (Ser(473)), leading to TNF-alpha stimulation. Finally, Arhgdib, the tumor suppressor gene whose expression is associated with GM3, was shown to be upstream of TNF-alpha. CONCLUSIONS: The GM3 signal is thus transduced in B16 cells through a PI3K, Rictor/mTOR, Akt, Arhgdib pathway, leading to stimulated expression of TNF-alpha. 2008 S. Karger AG, Basel.
Authors: Luigi Boccuto; Kazuhiro Aoki; Heather Flanagan-Steet; Chin-Fu Chen; Xiang Fan; Frank Bartel; Marharyta Petukh; Ayla Pittman; Robert Saul; Alka Chaubey; Emil Alexov; Michael Tiemeyer; Richard Steet; Charles E Schwartz Journal: Hum Mol Genet Date: 2013-09-10 Impact factor: 6.150