FIGURE 5.

STAT3 promotes GSK3β activity to induce degradation of SNAI. A, GSK3β suppresses SNAI expression in CRC lines. The indicated protein levels were measured by immunoblotting 3 days after siRNA transfection. B, GSK3β suppresses SNAI via its kinase activity. HCT116 cells were treated with either LiCl (4 mm) or SB216763, GSK3β inhibitors as indicated for 4 h, and the indicated proteins were measured by immunoblotting. C, STAT3 interacts with GSK3β. GSK3β in isolated mouse tumor cells or in HCT116 cells was immunoprecipitated and immunoblotted for STAT3 (S3, STAT3; G3, GSK3β). D, STAT3 regulates phosphorylation levels of GSK3β. Lysates from HCT116 cells transfected with the indicated siRNA were divided and separated by either traditional SDS-PAGE or Phos-tag SDS-PAGE, and the indicated proteins were measured by immunoblotting. E, STAT3 inhibits phosphorylation at Ser-9 of GSK3β. HCT116 cells were transfected with the indicated siRNA (C, control; S3, STAT3), total cell lysates were collected 1 or 3 days after transfection, and the levels of indicated proteins were measured by immunoblotting. F, GSK3β-CA reverses the effects of STAT3 depletion. HCT116 cells were transfected with control siRNA (C), STAT3 siRNA (S3), GSK3β-CA plasmid, or STAT3 siRNA (S3) plus GSK3β-CA plasmid. Cell invasion assay (n = 3) and immunoblotting were performed 3 days after transfection.