miR-155 Is Downregulated in Familial Adenomatous Polyposis and Modulates WNT Signaling by Targeting AXIN1 and TCF4.

Adenomatous Polyposis Coli (APC) gene mutations are responsible for the onset of familial adenomatous polyposis (FAP) and sporadic colorectal cancer and have been associated with miRNAs dysregulation. The capacity of miR-155, a cancer-related miRNA, to target components of the WNT/ß-CATENIN pathway suggests that APC gene mutations, controlling miRNAs expression, may critically regulate WNT/ß-CATENIN signaling. To this end, APC gene target sequencing was performed on colonic adenomatous polyps and paired normal mucosa clinical specimens from FAP patients (n = 9) to elucidate the role of miR-155-5p in APC-mutant setting. The expression of selected miRNAs and WNT/ß-CATENIN signaling components was characterized in FAP patients and non-FAP control subjects (n = 5). miR-155-5p expression and functional effects on WNT cascade, cell survival, growth, and apoptosis were investigated in different colorectal cancer cell lines. A somatic second hit in the APC gene was found in adenomatous polyps from 6 of 9 FAP patients. Heterozygous APC gene mutations in FAP patients were associated with altered expression of candidate miRNAs and increased levels of AXIN1 and AXIN2 mRNAs. miR-155-5p was downregulated in FAP patients and in the APC and ß-CATENIN-mutant colorectal cancer cell lines, and critically regulates WNT/ß-CATENIN cascade by targeting both AXIN1 and TCF4. Importantly, miR-155-5p may sustain long-term WNT/ß-CATENIN activation in colorectal cancer cells upon WNT3A stimulation. IMPLICATIONS: This study supports a key role of miR-155-5p in modulating WNT/ß-CATENIN signaling in colorectal cancer and unravels a new mechanism for AXIN1 regulation which represents a potential therapeutic target in specific tumor subtypes.

Inflammation increases NOTCH1 activity via MMP9 and is counteracted by Eicosapentaenoic Acid-free fatty acid in colon cancer cells.

Aberrant NOTCH1 signalling is critically involved in multiple models of colorectal cancer (CRC) and a prominent role of NOTCH1 activity during inflammation has emerged. Epithelial to Mesenchymal Transition (EMT), a crucial event promoting malignant transformation, is regulated by inflammation and Metalloproteinase-9 (MMP9) plays an important role in this process. Eicosapentaenoic Acid (EPA), an omega-3 polyunsaturated fatty acid, was shown to prevent colonic tumors in different settings. We recently found that an extra-pure formulation of EPA as Free Fatty Acid (EPA-FFA) protects from colon cancer development in a mouse model of Colitis-Associated Cancer (CAC) through modulation of NOTCH1 signalling. In this study, we exposed colon cancer cells to an inflammatory stimulus represented by a cytokine-enriched Conditioned Medium (CM), obtained from THP1-differentiated macrophages. We found, for the first time, that CM strongly up-regulated NOTCH1 signalling and EMT markers, leading to increased invasiveness. Importantly, NOTCH1 signalling was dependent on MMP9 activity, upon CM exposure. We show that a non-cytotoxic pre-treatment with EPA-FFA antagonizes the effect of inflammation on NOTCH1 signalling, with reduction of MMP9 activity and invasiveness. In conclusion, our data suggest that, in CRC cells, inflammation induces NOTCH1 activity through MMP9 up-regulation and that this mechanism can be counteracted by EPA-FFA.

A combination of eicosapentaenoic acid-free fatty acid, epigallocatechin-3-gallate and proanthocyanidins has a strong effect on mTOR signaling in colorectal cancer cells.

Colorectal cancer (CRC) is one of the major causes of cancer death worldwide. The development of novel anti-CRC agents able to overcome drug resistance and/or off-target toxicity is of pivotal importance. The mammalian target of rapamycin (mTOR) plays a critical role in CRC, regulating protein translation and controlling cell growth, proliferation, metabolism and survival. The aim of this study was to explore the effect of a combination of three natural compounds, eicosapentaenoic acid-free fatty acid (EPA-FFA), epigallocatechin-3-gallate (EGCG) and proanthocyanidins (grape seed [GS] extract) at low cytotoxic concentrations on CRC cells and test their activity on mTOR and translational regulation. The CRC cell lines HCT116 and SW480 were treated for 24h with combinations of EPA-FFA (0-150 µM), EGCG (0-175 µM) and GS extract (0-15 µM) to evaluate the effect on cell viability. The low cytotoxic combination of EPA-FFA 150 µM, EGCG 175 µM and GS extract 15 µM completely inhibited the mTOR signaling in HCT116 and SW480 cells, reaching an effect stronger than or comparable to that of the mTOR inhibitor Rapamycin in HCT116 or SW480 cells, respectively. Moreover, the treatment led to changes of protein translation of ribosomal proteins, c-Myc and cyclin D1. In addition, we found a reduction of clonal capability in both cell lines, with block of cell cycle in G0G1 and induction of apoptosis. Our data suggest that the low cytotoxic combination of EPA-FFA, EGCG and GS extract, tested for the first time here, inhibits mTOR signaling and thus could be considered for CRC treatment.

Eicosapentaenoic acid free fatty acid prevents and suppresses colonic neoplasia in colitis-associated colorectal cancer acting on Notch signaling and gut microbiota.

Inflammatory bowel diseases are associated with increased risk of developing colitis-associated colorectal cancer (CAC). Epidemiological data show that the consumption of ω-3 polyunsaturated fatty acids (ω-3 PUFAs) decreases the risk of sporadic colorectal cancer (CRC). Importantly, recent data have shown that eicosapentaenoic acid-free fatty acid (EPA-FFA) reduces polyp formation and growth in models of familial adenomatous polyposis. However, the effects of dietary EPA-FFA are unknown in CAC. We tested the effectiveness of substituting EPA-FFA, for other dietary fats, in preventing inflammation and cancer in the AOM-DSS model of CAC. The AOM-DSS protocols were designed to evaluate the effect of EPA-FFA on both initiation and promotion of carcinogenesis. We found that EPA-FFA diet strongly decreased tumor multiplicity, incidence and maximum tumor size in the promotion and initiation arms. Moreover EPA-FFA, in particular in the initiation arm, led to reduced cell proliferation and nuclear ß-catenin expression, whilst it increased apoptosis. In both arms, EPA-FFA treatment led to increased membrane switch from ω-6 to ω-3 PUFAs and a concomitant reduction in PGE2 production. We observed no significant changes in intestinal inflammation between EPA-FFA treated arms and AOM-DSS controls. Importantly, we found that EPA-FFA treatment restored the loss of Notch signaling found in the AOM-DSS control and resulted in the enrichment of Lactobacillus species in the gut microbiota. Taken together, our data suggest that EPA-FFA is an excellent candidate for CRC chemoprevention in CAC.