Autophagic flux is essential for the downregulation of D-dopachrome tautomerase by atractylenolide I to ameliorate intestinal adenoma formation.

Abstract

Colorectal cancer is generally believed to progress through an adenoma - carcinoma sequence. Adenomatous polyposis coli (APC) mutations serve as the initiating event in adenoma formation. The ApcMin/+ mouse harbors a mutation in the APC gene, which is similar or identical to the mutation found in individuals with familial adenomatous polyposis and 70% of all sporadic CRC cases. Autophagy is a constitutive process required for proper cellular homeostasis. However, its role in intestinal adenoma formation is still controversial. Atractylenolide I (AT1) is a sesquiterpenoid that possesses various clinically relevant properties such as anti-tumor and anti-inflammatory activities. The role of AT1 on adenoma formation was tested in ApcMin/+ mice and its underlying mechanism in regulating autophagy was documented. D-dopachrome tautomerase (D-DT) was identified as a potential target of AT1 by an proteomics-based approach. The effects of p53 modification on autophgic flux was monitored in p53-/- and p53+/+ HCT116 cells. Small interfering RNA was used to investigate the function of Atg7 and D-DT on autophagy programme induce by AT1. AT1 effectively reduced the formation of adenoma and downregulated the tumorigenic proteins in ApcMin/+ mice. Importantly, AT1 stimulated autophagic flux through downregulating acetylation of p53. Activation of Sirt1 by AT1 was essential for the deacetylation of p53 and downregulation of D-DT. The lowered expression of COX-2 and β-catenin by AT1 were partly recovered by Atg7 knockdown. AT1 activates autophagy machinery to downregulate D-DT and reduce intestinal adenoma formation. This discovery provides evidence in vivo and in vitro that inducing autophagy by natural products maybe a potential therapy to ameliorate colorectal adenoma formation.