Folic Acid Supplementation Promotes Hypomethylation in Both the Inflamed Colonic Mucosa and Colitis-Associated Dysplasia

PURPOSE

The purpose of this study was to assess the effect of folic acid (FA) supplementation on colitis-associated colorectal cancer (CRC) using the azoxymethane/dextran sulfate sodium (AOM/DSS) model.

METHODS

Mice were fed a chow containing 2 mg/kg FA at baseline and randomized after the first DSS treatment to receive 0, 2, or 8 mg/kg FA chow for 16 weeks. Colon tissue was collected for histopathological evaluation, genome-wide methylation analyses (Digital Restriction Enzyme Assay of Methylation), and gene expression profiling (RNA-Seq).

RESULTS

A dose-dependent increase in the multiplicity of colonic dysplasias was observed, with the multiplicity of total and polypoid dysplasias higher (64% and 225%, respectively) in the 8 mg FA vs. the 0 mg FA group (p < 0.001). Polypoid dysplasias were hypomethylated, as compared to the non-neoplastic colonic mucosa (p < 0.05), irrespective of FA treatment. The colonic mucosa of the 8 mg FA group was markedly hypomethylated as compared to the 0 mg FA group. Differential methylation of genes involved in Wnt/β-catenin and MAPK signaling resulted in corresponding alterations in gene expression within the colonic mucosa.

CONCLUSIONS

High-dose FA created an altered epigenetic field effect within the non-neoplastic colonic mucosa. The observed decrease in site-specific DNA methylation altered oncogenic pathways and promoted colitis-associated CRC.

Dysregulation of miR-1-3p: An Early Event in Colitis-Associated Dysplasia

Detection of colorectal dysplasia during surveillance colonoscopy remains the best method of determining risk for colitis-associated colorectal cancer (CAC). miRNAs (miRs) show great promise as tissue-specific biomarkers of neoplasia. The goal of this study was to explore the miR expression profile of precancerous dysplastic lesions in the AOM/DSS mouse model and identify early molecular changes associated with CAC. Epithelial cells were laser-microdissected from the colonic mucosa (inflamed versus dysplastic) of mice with AOM/DSS-induced colitis. A miR signature that can distinguish inflamed non-neoplastic mucosa from dysplasia was identified. Bioinformatic analyses led to the discovery of associated miR gene targets and enriched pathways and supported the construction of a network interaction map. miR-1a-3p was one of the miRs with the highest number of predicted targets, including Cdk6. Interestingly, miR-1a-3p and Cdk6 were down- and up-regulated in dysplastic lesions, respectively. Transfection of HCT116 and RKO cells with miR-1a-3p mimics induced apoptosis and cell cycle arrest in G1, suggesting its biological function. A slight reduction in the level of CDK6 transcripts was also observed in cells transfected with miR-1. These data provide novel insight into the early molecular alterations that accompany the development of CAC and identify a miR signature that represents a promising biomarker for the early detection of colitis-associated dysplasia.

Abstract 1553: miR-1 targets Cdk6 and controls cell cycle progression and apoptosis in colitis-associated dysplasia

Detection of colorectal dysplasia during surveillance colonoscopy is currently the best method of determining risk of colitis-associated colorectal cancer (CAC). An understanding of the early molecular changes associated with the development of these lesions will inform the identification of new biomarkers for earlier detection. miRNAs (miRs), highly conserved noncoding RNAs, show great promise as stable, tissue-specific biomarkers of neoplasia. We previously identified 12 miRs that are differentially-expressed in colitis-associated dysplasias (flat and polypoid) vs. inflamed colonic mucosa from mice treated with AOM/DSS. miR-1, a putative tumor suppressor, was downregulated in colitis-associated dysplasias. Analysis of the mRNA expression profile of AOM/DSS-induced dysplasias and prediction of the interactions between the miRs and their targets led to the selection of the Cdk6 as the target of miR-1 to be further investigated, based on its: 1) upregulation in AOM/DSS-induced dysplasia; and 2) association with cell cycle progression and inflammatory signaling. The goal of the present study was to validate the predicted interaction between miR-1 and Cdk6 and assess the biological function of miR-1 in vitro. The ability of miR-1 to interact with the 3’UTR of Cdk6 mRNA was assessed using a dual luciferase assay. Co-transfection of HCT116 or RKO colon carcinoma cells with Cdk6-WT and miR-1 mimics led to a significant reduction in relative luciferase activity in both cell lines (30%, p=0.0117 and 47%, p=0.0269; respectively). Transfection with the Cdk6-Mut did not alter relative luciferase activity, confirming the Cdk6 binding site was specific for miR-1. The biological function of miR-1 was assessed in HCT116 and RKO cells reverse-transfected with miR-1 and cel-miR-67 (negative control) for 48 hrs. Apoptosis (AnnexinV+ cells) and cell cycle progression (% of cells in G0/G1, G2/M and S phase) were evaluated by flow cytometry, and proliferation by cell count (Trypan Blue). HCT116 and RKO transfected with the miR-1 mimic exhibited a higher proportion of apoptotic cells than the negative control (30% and 20% increase, p=0.0022 and 0.0013, respectively). Cell cycle analyses revealed the miR-1 mimic induced cell cycle arrest (G0/G1) in both cell lines (p&lt;0.05). In HCT116 cells, this was accompanied by a reduction in the percentage of cells in G2/M (p=0.002) and S (p&lt;0.001) phase. No effect of miR-1 on total cell number was observed. These results demonstrate that Cdk6 is a direct target of miR-1, and suggest that downregulation of this miR in dysplastic lesions contributes to CAC by inducing cell cycle progression and inhibiting apoptosis. These data provide novel insight into the early molecular changes that accompany the development of colitis-associated dysplasia and may serve as biomarkers for early detection of neoplasia. Supported by the Timothy P. and Aurora M. Hughes Fund for Colon Cancer Research.

Citation Format: Mariana F. Fragoso, Geysson J. Fernandez, Lisa Vanderveer, Harry S. Cooper, Michael Slifker, Margie L. Clapper. miR-1 targets Cdk6 and controls cell cycle progression and apoptosis in colitis-associated dysplasia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1553.

Abstract 2374: Identification of altered miRNA-gene interactions in AOM/DSS induced colitis-associated dysplasia

Although significant progress has been made in delineating the pathways that contribute to ulcerative colitis (UC)-associated tumorigenesis, the early molecular alterations that fuel disease progression remain poorly understood. microRNAs (miRs) have emerged as important modulators of inflammatory pathways and their aberrant expression has been associated with initiation and progression of malignancy. The goal of this study is to identify gene-miR interactions that occur early in experimental UC and contribute to the development of colitis-associated dysplasia. The mRNA and miR expression profile of laser microdissected colon specimens (inflamed mucosa vs. dysplasia) from Swiss Webster mice with AOM/DSS-induced colitis was interrogated using the Mouse Gene Expression Microarrays 4x44K v2 (Agilent®) and miRNA Mouse platform (NanoString®). Data were analyzed using R/Bioconductor and nSolverTM (NanoString®). Differentially expressed miRs (n=12, p&lt;0.001) were validated by RT-qPCR (n=9) and used for target prediction (TargetScan v. 7.2). The differential expression of the predicted target genes (mRNA array) vs. miRs was compared and filtered to include only those with contrasting changes in expression (e.g. downregulated miR and upregulated mRNA). The resulting list of 98 genes was subjected to pathway enrichment analysis using EnrichR. Network interactions were calculated using STRING and visualized on Cytoscape v.3.8.0. Gene ontology analyses revealed 23 terms associated with the pathogenesis and progression of UC, including TNFα signaling via NF-kB, G1 to S cell cycle control, Wnt and Hedgehog signaling. Analyses of miR targets revealed that miR-30c, miR-145a and miR-1a controlled the largest number of predicted target genes (35%, 26% and 18%, respectively). These data suggest an important role of these top miRs (putative tumor suppressors) in UC-associated tumorigenesis, based on their downregulation in dysplasias and corresponding upregulation of their oncogenic targets (Sox9, Ccnd2 and Cdk6). Consistent with our findings, Sox9 contributes to carcinogenesis through its effect on stem cells. The Ccnd2/Cdk6 complex is considered a central component of signaling pathways that regulate cell cycle G1/S transition during neoplastic development. Therefore, early interaction of these miRs with their respective target genes may contribute to the transition of inflamed colonic mucosa to dysplasia in mice with experimental colitis. Additional in vitro validation of the predicted interactions remains in progress. (Supported by a generous donation from Aurora and Timothy Hughes).

Citation Format: Mariana F. Fragoso, Geysson J. Fernandez, Lisa Vanderveer, Harry S. Cooper, Wen-Chi Chang, Michael Slifker, Karthik Devarajan, Yan Zhou, Eric Ross, Margie L. Clapper. Identification of altered miRNA-gene interactions in AOM/DSS induced colitis-associated dysplasia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2374.

Açai (Euterpe oleracea Mart.) feeding attenuates dimethylhydrazine-induced rat colon carcinogenesis

This study investigated the protective effect of spray-dried açaí powder (AP) intake on colon carcinogenesis induced by 1,2-dimethylhydrazine (DMH) in male Wistar rats. After 4 weeks of DMH administrations, the groups were fed with standard diet, a diet containing 2.5% or 5.0% AP or a diet containing 0.2% N-acetylcysteine (NAC) for 10 weeks, using aberrant crypt foci (ACF) as the endpoint. Additionally, two groups were fed with standard diet or a diet containing 5.0% AP for 20 weeks, using colon tumors as the endpoint. In ACF assay, a reduction in the number of aberrant crypts (ACs) and ACF (1-3 AC) were observed in the groups fed with 5.0% AP (37% AC and 47% ACF inhibition, p=0.036) and 0.2% NAC (39% AC and 41% ACF inhibition, p=0.042). In tumor assay, a reduction in the number of invasive tumors (p<0.005) and tumor multiplicity (p=0.001) was observed in the group fed with 5.0% AP. Also, a reduction in tumor Ki-67 cell proliferation (p=0.003) and net growth index (p=0.001) was observed in the group fed with 5.0% AP. Therefore the findings of this study indicate that AP feeding may reduce the development of chemically-induced rat colon carcinogenesis.

Inhibition of mouse urinary bladder carcinogenesis by açai fruit (Euterpe oleraceae Martius) intake

Açai, fruit from Euterpe oleraceae Martius, is consumed in natura and in a variety of beverages and food preparations and possesses several potential antioxidant compounds. In a first study for anticarcinogenicity screening, male Swiss mice (n = 20/per group) were chemically-induced to urothelial bladder carcinogenesis for 10 weeks and received a standard diet or a standard diet containing 2.5 and 5 % spray-dried açai pulp (AP) for 10 weeks. At week 20, the incidence of simple and nodular hyperplasia and the incidence and multiplicity of transitional cell carcinoma (TCC) were evaluated. In a second study for antigenotoxicity screening, male Swiss mice (n = 6/per group) were fed standard diet or standard diet containing 5 % AP for three weeks. Urothelial cell suspensions were obtained and challenged with H(2)O(2) for induction of DNA damage and analyzed by comet assay. Overall, dietary 5 % AP reduced TCC incidence and multiplicity (p = 0.019 and p = 0.015, respectively) and tumor cell proliferation and p63 expression (p = 0.02 and p = 0.007, respectively), Furthermore, the group fed the 5 % AP presented a significant reduction (p < 0.01) in DNA damage induced by H(2)O(2), a notable oxidant agent. The results suggest that the spray-dried açai pulp used here inhibits the TCC development in male Swiss mice, probably due to its potential antioxidant action.