Fig. 6

Overexpressed EP4 feedback antagonized the effect of solamargine on phosphorylation of Akt and cell growth inhibition. a A549 and H1299 cells were transfected with control and EP4 overexpression vectors for 24 h before exposing the cells to solamargine (6 μM) for an additional 2 h and 24 h. Afterwards, phosphorylation of Akt and EP4 protein expressions were determined by Western blot. b A549 and H1975 cells were transfected with control and EP4 overexpression vectors for 24 h before exposing the cells to solamargine (6 μM) for an additional 24 h. Afterwards, EP4 protein expressions and cell viability were determined using Western blot and MTT assays, respectively. Values in bar graphs were given as the mean ± SD from three independent experiments performed in triplicate. *Indicates significant difference as compared to the untreated control group (P < 0.05). **Indicates significant difference from the solamargine or plus control vector group (P < 0.01). c-d A549 and H1299 cells were transfected with control (pCMV6) and EP4 overexpression vector for 24 h before exposing the cells to solamargine (6 μM) for an additional 24 h. Afterwards, expressions of SP1, p65 and EP4 protein were determined by Western blot. e The diagram the shows that solamargine inhibits the growth of lung cancer cells through inactivation of Akt, followed by reduction of SP1 and p65. This results in the inhibition of expression of EP4 gene. The cross-talk between SP1 and p65, and the positive feedback regulatory loop of PI3-K/Akt signaling by EP4 contribute to the overall responses of solamargine in this process