Abstract
This study examined if the anti-tumorigenesis effect of Exendin-4 in HT29 and HCT116 colorectal cancer (CRC) involves modulation of SIRT1 and Akt/GSR3K/beta-catenin/NF-kappa B axis. HT29 and HCT116 cells were treated either with increasing levels of Exendin-4 (0.0-200 mu M) or with Exendin-4 (at its IC50) in the presence or absence of EX-527 (10 mu M/a selective SIRT1 inhibitor) or Exendin-4 (9-39) amide (E (9-39) A) (1 mu M/an Exendin-4 antagonist). In a dose-dependent manner, Exendin-4 inhibited cell survival, but enhanced levels of lactate dehydrogenase (LDH) and single-stranded DNA (ssDNA) in both HT29 and HCT116. In both cell lines and at it has an IC50 (45 mu M for HT29 and 35 mu M for HCT1165), Exendin-4 also significantly reduced cell survival, migration, and invasion of both cell types, with no effect on the expression GLP-1 receptors (GLPRs) nor of the activity of Akt. At these doses, Exendin-4 also increased the expression of SIRT1 but reduced the acetylation of NF-kappa B and the expression of Bax and cleaved caspase-3 and in both cell lines. Concomitantly, protein levels of p-GS3K beta (Ser(9)), total and acetylated beta-catenin, and Anix2 were significantly decreased, but levels of p-GS3K beta (Ser9) and p-beta-catenin (Ser(33/37)/Thr(41)) were significantly increased in both HT29 and HCT116-exendin-4 treated cells. All the effects exerted by Exendin-4 were completely prevented by Ex527 or E (9-39) A. In conclusion, Exendin-4 suppresses the tumorigenesis of HT29 and HCT116 CRC cell activation of GS3K beta-induced inhibition of beta-catenin and NF-kappa beta in a SIRT1-dependent mechanism.