FIGURE 1.

APC regulates glycogen synthase through GSK-3. A, APC was knocked down by siRNA in 293T cells and phosphorylation of GS at an established GSK-3 target site (GS-Ser641) was assessed by immunoblotting with a phosphospecific antibody. The same samples were immunoblotted for total GS (loading control), phospho-Akt (Ser-473), phospho-GSK-3 (Ser-9/21), and APC. Cells in lane 2 were also treated with 15 mm LiCl. Cells were also transfected with a scrambled siRNA (control). APC knockdown reduced APC protein levels and endogenous GS phosphorylation without affecting total GS or phosphorylation of Akt or GSK-3. B, to rescue GS phosphorylation in APC knockdown cells, the Myc-tagged SAMP fragment of APC was co-transfected with scrambled (control) or APC siRNAs. EV indicates empty vector control. The SAMP fragment of APC rescues phosphorylation of GS in APC knockdowns, and this rescue is blocked by LiCl.