Background & Aims Nearly 20% of the global cancer burden can be linked to infectious agents. Fusobacterium nucleatum promotes tumor formation by epithelial cells via unclear mechanisms. We aimed to identify microRNAs (miRNAs) induced by F nucleatum and evaluate their ability to promote colorectal carcinogenesis in mice. Methods Colorectal cancer (CRC) cell lines were incubated with F nucleatum or control reagents and analyzed in proliferation and would healing assays. HCT116, HT29, LoVo, and SW480 CRC cell lines were incubated with F nucleatum or phosphate buffer saline (PBS control) and analyzed for miRNA expression patterns and in chromatin immunoprecipitation assays. Cells were incubated with miRNAs mimics, control sequences, or small interfering (si) RNAs; expression of reporter constructs was measured in luciferase assays. CRC cells were incubated with F nucleatum or PBS and injected into BALB/C nude mice; growth of xenograft tumors was measured. C57BL APCmin/+, C57BL miR21a−/−, and C57BL mice with full-length miR21a (controls) were given F nucleatum by gavage; some mice were given azoxymethane (AOM) and dextran sodium sulfate (DSS) to induce colitis and colon tumors. Intestinal tissues were collected and tumors were counted. Serum samples from mice were analyzed for cytokine levels by ELISAs. We performed in situ hybridization analyses to detect enrichment of F nucleatum in CRC cells. F nucleatum DNA in 90 tumor and matched non-tumor tissues from patients in China were explored for the expression correlation analysis; levels in 125 tumor tissues from patients in Japan were compared with their survival times. Results F nucleatum increased proliferation and invasive activities of CRC cell lines, compared with control cells. CRC cell lines infected with F nucleatum formed larger tumors, more rapidly, in nude mice than uninfected cells. APCmin/+ mice gavaged with F nucleatum developed significantly more colorectal tumors than mice given PBS and had shorter survival times. We found several inflammatory factors to be significantly increased in serum from mice given F nucleatum (interleukin 17F [IL17F], IL21, IL22, and MIP3A). We found 50 miRNAs to be significantly upregulated and 52 miRNAs to be significantly downregulated in CRCs incubated with F nucleatum vs PBS; levels of miR21 increased by the greatest amount (more than 4-fold). Inhibitors of miR21 prevented F nucleatum from inducing cell proliferation and invasion in culture. miR21a−/− mice had a later appearance of fecal blood and diarrhea after administration of AOM and DSS, and had longer survival times, compared with control mice. The colorectum of miR21a−/− mice had fewer tumors, of smaller size, and the miR21a−/− mice survived longer than control mice. We found RASA1, which encodes a RAS GTPase, to be one of the target genes consistently downregulated in cells that overexpressed miR21 and upregulated in cells exposed to miR21 inhibitors. Infection of cells with F nucleatum increased expression of miR21 by activating TLR4 signaling to MYD88, leadi...
Purpose Colorectal cancer (CRC) is one of the most common malignancies worldwide. Recently, a novel circular RNA, ciRS-7, was proposed to be a potential miR-7 sponge. Since miR-7 regulates the expression of several important drivers of CRC, we analyzed the clinical significance of ciRS-7 in CRC patients. Experimental Design Initially, we evaluated the expression levels of ciRS-7 in a training cohort comprising of 153 primary CRC tissues and 44 matched normal mucosae. We subsequently confirmed its clinical relevance in an independent validation cohort (n=165), and evaluated the effect of ciRS-7 on miR-7, and its targets genes EGFR and RAF1. Functional analysis were performed in cell lines and an animal model to support clinical findings. Results Our data revealed that ciRS-7 was significantly up-regulated in CRC tissues compared with matched normal mucosae (P=0.0018), and its overexpression was associated with poor patient survival (P=0.0224 and 0.0061 in the training and validation cohorts, respectively). Multivariate survival analysis revealed that ciRS-7 emerged as an independent risk factor for overall survival (P=0.0656 and 0.0324 in the training and validation cohorts, respectively). Overexpression of ciRS-7 in HCT116 and HT29 cells led to blocking of tumor suppressive effects of miR-7 and resulted in a more aggressive oncogenic phenotype, and ciRS-7 overexpression permitted inhibition of miR-7 and subsequent activation of EGFR and RAF1 oncogenes. Conclusions CiRS-7 is a promising prognostic biomarker in CRC patients and may serve as a therapeutic target for reducingEGFR-RAF1 activity in CRC patients.
Our results suggest that CCAL is a crucial oncogenic regulator involved in CRC tumorigenesis and progression.
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