GSK3β and Gli3 play a role in activation of Hedgehog-Gli pathway in human colon cancer — Targeting GSK3β downregulates the signaling pathway and reduces cell proliferation

• GSK3β staining in colon cancer tissues is positively correlated with DUKES' stage.
• GSK3β is the main molecular switch for Hh-Gli activation in colon cancer cells.
• GSK3β inhibition with LiCl enhances Gli3 processing.
• GSK3β inhibition with LiCl downregulates Hh-Gli signaling and induces cell death.
• Hh-Gli signaling stimulation rescues LiCl effects on cell proliferation.

The role of Hedgehog-Gli (Hh-Gli) signaling in colon cancer tumorigenesis has not yet been completely elucidated. Here we provide strong evidence of Hh-Gli signaling involvement in survival of colon cancer cells, with the main trigger of activation being deregulated GSK3β.Our clinical data reveals high expression levels of GSK3β and Gli3 in human colon cancer tissue samples, with positive correlation between GSK3β expression and DUKES' stage. Further experiments on colon cancer cell lines have shown that a deregulated GSK3β upregulates Hh-Gli signaling and positively affects colon cancer cell survival. We show that inhibition of GSK3β with lithium chloride enhances Gli3 processing into its repressor form, consequently downregulating Hh-Gli signaling, reducing cell proliferation and inducing cell death. Analysis of the molecular mechanisms revealed that lithium chloride enhances Gli3–SuFu–GSK3β complex formation leading to more efficient Gli3 cleavage and Hh-Gli signaling downregulation. This work proposes that activation of the Hh-Gli signaling pathway in colon cancer cells occurs non-canonically via deregulated GSK3β. Gli3 seems to be the main pathway effector, highlighting the activator potential of this transcription factor, which is highly dependent on GSK3β function and fine tuning of the Gli3–SuFu–GSK3β platform.