Fig. 5. AMPK is essential for the blockade of UVB-induced mTOR pathway by apigenin.

(A) Apigenin activates AMPK at baseline and in UVB-irradiated cells. 308 cells were treated as indicated. Apigenin (25 μM) was added 1 hr prior to irradiation. The cells were harvested at 24 h after irradiation. (B) Apigenin activates AMPK in mouse skin. SKH-1 mice were irradiated as described in Fig.1. Apigenin was given topically 1 hr prior to irradiation at 5 and 10 μmol. Whole-skin protein extracts were immunoblotted for phosphorylated and total AMPK and p44/42 MAPK was used as loading control. (C) 308 cells were pre-treated with 5 μM compound C or vehicle (DMSO) for 1 h, then 25 μM apigenin was added to the media for another 1 h and followed by UVB exposure (500 J/m²). (D) 308 cells were transfected with AMPK siRNA or non-targeting control siRNA, and 48 h later cells were exposed to apigenin and UVB irradiation as described above. (E) 308 cells were pre-treated with different doses of AMPK activator A-769662 for 1 h before subjecting to UVB irradiation. All samples in (C-D) were harvested 24 h after irradiation and phosphorylated and total p70S6K/AMPK were assessed by Western blot.