Background and Purpose
It is well known that microsatellite instability‐high (MSI‐H) is associated with 5‐fluorouracil (5‐FU) resistance in colorectal cancer. MSI‐H is the phenotype of DNA mismatch repair deficiency (MMR‐D), mainly occurring due to hypermethylation of MLH1 promoter CpG island. However, the mechanisms of MMR‐D/MSI‐H are unclear. We aim to investigate the pathway of MMR‐D/MSI‐H involved in 5‐FU resistance.
Experimental Approach
Human colorectal cancer specimens were diagnosed for MSI‐H by immunohistochemistry and western blotting. Proteome microarray interactome assay was performed to screen nuclear proteins interacting with ATG5. Nuclear ATG5 and ATG5‐Mis18α overexpression were analysed in ATG5high colorectal cancer bearing mice. The methylation assay determined the hypermethylation of hMLH1 promoter CpG island in freshly isolated human colorectal cancer tissue samples and HT29atg5 and SW480atg5 cancer cells.
Key Results
In ATG5high colorectal cancer patients, 5‐FU‐based therapy resulted in nuclear translocation of ATG5, leading to MSI‐H. Colorectal cancer in Atg5 Tg mice demonstrated 5‐FU resistance, compared to Atg5+/− and WT mice. Proteome microarray assay identified Mis18α, a protein localized on the centromere and a source for methylation of the underlying chromatin, which responded to the translocated nuclear ATG5 leading to ATG5‐Mis18α conjugate overexpression. This resulted in MLH1 deficiency due to hypermethylation of hMLH1 promoter CpG island, while the deletion of nuclear Mis18α failed to induce ATG5‐Mis18α complex and MMR‐D/MSI‐H.
Conclusions and Implications
Nuclear ATG5 resulted in MMR‐D/MSI‐H through its interaction with Mis18α in ATG5high colorectal cancer cells. We suggest that ATG5‐Mis18α or Mis18α may be a therapeutic target for treating colorectal cancer.
Background
Previous studies revealed that Myricetin and derivative M10, Myricetin-3-O-β-d-lactose sodium salt, prevented chronic ulcerative colitis (UC) in mice. We investigated whether the inhibitory effects of Myricetin and M10 on UC were associated to the modification of intestinal microbiota. Samples of intestinal microbiota were collected from the ileocecum of UC mice which demonstrated response to the treatment of Myricetin and M10. Gut microbiota was analyzed by 16S rDNA sequencing assay.
Results
UC model mice demonstrated the increases of Firmicutes and Actinobacteria as compared to healthy control mice. Oral M10 and Myricetin normalized the composition of Firmicutes and Actinobacteria. At genus level, the effect of M10 and Myricetin on ulcerative colitis was strongly associated to the increase of probiotics, such as Akkermansia, and the inhibition of pathogenic microorganisms, such as Ruminococcus and Parabacteroides. Myricetin’s derivative M10 significantly increased both biosynthesis and degradation activities, resulting to strong improvements of the metabolism of sulfur, pyruvate, steroid biosynthesis and unsaturated fatty acid biosynthesis in gut microenvironment.
Conclusions
Natural product Myricetin and its derivative M10 could modify the modification of gut microbiota in UC mice. Combined with pharmacologic effects of Myricetin and M10 in these UC mice, we conclued that the effects of Myricetin and M10 on UC were associated to the modification of intestinal microbiota in the environment of chronic ulcerative colitis.
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