Colorectal cancers comprise a complex mixture of malignant cells, nontransformed cells, and microorganisms. Fusobacterium nucleatum is among the most prevalent bacterial species in colorectal cancer tissues. Here we show that colonization of human colorectal cancers with Fusobacterium and its associated microbiome—including Bacteroides , Selenomonas , and Prevotella species—is maintained in distal metastases, demonstrating microbiome stability between paired primary and metastatic tumors. In situ hybridization analysis revealed that Fusobacterium is predominantly associated with cancer cells in the metastatic lesions. Mouse xenografts of human primary colorectal adenocarcinomas were found to retain viable Fusobacterium and its associated microbiome through successive passages. Treatment of mice bearing a colon cancer xenograft with the antibiotic metronidazole reduced Fusobacterium load, cancer cell proliferation, and overall tumor growth. These observations argue for further investigation of antimicrobial interventions as a potential treatment for patients with Fusobacterium -associated colorectal cancer.

Analysis of Fusobacterium persistence and antibiotic response in colorectal cancer

Colorectal cancer (CRC) is the third most common cancer and the fourth most common cause of cancer-related death. Most cases of CRC are detected in Western countries, with its incidence increasing year by year. The probability of suffering from colorectal cancer is about 4%–5% and the risk for developing CRC is associated with personal features or habits such as age, chronic disease history and lifestyle. In this context, the gut microbiota has a relevant role, and dysbiosis situations can induce colonic carcinogenesis through a chronic inflammation mechanism. Some of the bacteria responsible for this multiphase process include Fusobacterium spp, Bacteroides fragilis and enteropathogenic Escherichia coli. CRC is caused by mutations that target oncogenes, tumour suppressor genes and genes related to DNA repair mechanisms. Depending on the origin of the mutation, colorectal carcinomas can be classified as sporadic (70%); inherited (5%) and familial (25%). The pathogenic mechanisms leading to this situation can be included in three types, namely chromosomal instability (CIN), microsatellite instability (MSI) and CpG island methylator phenotype (CIMP). Within these types of CRC, common mutations, chromosomal changes and translocations have been reported to affect important pathways (WNT, MAPK/PI3K, TGF-β, TP53), and mutations; in particular, genes such as c-MYC, KRAS, BRAF, PIK3CA, PTEN, SMAD2 and SMAD4 can be used as predictive markers for patient outcome. In addition to gene mutations, alterations in ncRNAs, such as lncRNA or miRNA, can also contribute to different steps of the carcinogenesis process and have a predictive value when used as biomarkers. In consequence, different panels of genes and mRNA are being developed to improve prognosis and treatment selection. The choice of first-line treatment in CRC follows a multimodal approach based on tumour-related characteristics and usually comprises surgical resection followed by chemotherapy combined with monoclonal antibodies or proteins against vascular endothelial growth factor (VEGF) and epidermal growth receptor (EGFR). Besides traditional chemotherapy, alternative therapies (such as agarose tumour macrobeads, anti-inflammatory drugs, probiotics, and gold-based drugs) are currently being studied to increase treatment effectiveness and reduce side effects.

/pdf/colorectal-carcinoma-a-general-overview-and-future-2e96vugrtz.pdf

Colorectal Carcinoma: A General Overview and Future Perspectives in Colorectal Cancer

Fusobacterium nucleatum has long been found to cause opportunistic infections and has recently been implicated in colorectal cancer; however, it is a common member of the oral microbiota and can have a symbiotic relationship with its hosts. To address this dissonance, we explore the diversity and niches of fusobacteria and reconsider historic fusobacterial taxonomy in the context of current technology. We also undertake a critical reappraisal of fusobacteria with a focus on F. nucleatum as a mutualist, infectious agent and oncogenic microorganism. In this Review, we delve into recent insights and future directions for fusobacterial research, including the current genetic toolkit, our evolving understanding of its mechanistic role in promoting colorectal cancer and the challenges of developing diagnostics and therapeutics for F. nucleatum.

/pdf/fusobacterium-nucleatum-symbiont-opportunist-and-1rnank755u.pdf

Fusobacterium nucleatum - symbiont, opportunist and oncobacterium.

Epithelial to mesenchymal transition (EMT) is a process during which cells lose their epithelial characteristics, for instance cell polarity and cell-cell contact, and gain mesenchymal properties, such as increased motility. In colorectal cancer (CRC), EMT is associated with an invasive or metastatic phenotype. In this review, we discuss recent studies exploring novel regulation mechanisms of EMT in CRC, including the identification of new CRC EMT regulators. Upregulation of inducers can promote EMT, leading to increased invasiveness and metastasis in CRC. These inducers can downregulate E-cadherin and upregulate N-cadherin and vimentin (VIM) through modulating EMT-related signaling pathways, for instance WNT/β-catenin and TGF-β, and EMT transcription factors, such as zinc finger E-box binding homeobox 1 (ZEB1) and ZEB2. In addition, several microRNAs (miRNAs), including members of the miR-34 and miR-200 families, are found to target mRNAs of EMT-transcription factors, for example ZEB1, ZEB2, or SNAIL. Downregulation of these miRNAs is associated with distant metastasis and advanced stage tumors. Furthermore, the role of EMT in circulating tumor cells (CTCs) is also discussed. Mesenchymal markers on the surface of EMT CTCs were found to be associated with metastasis and could serve as potential biomarkers for metastasis. Altogether, these studies indicate that EMT is orchestrated by a complicated network, involving regulators of different signaling pathways. Further studies are required to understand the mechanisms underlying EMT in CRC.

https://www.mdpi.com/2072-6694/9/12/171/pdf

Regulation of EMT in Colorectal Cancer: A Culprit in Metastasis.

Influence of the Gut Microbiome, Diet, and Environment on Risk of Colorectal Cancer

Association of Fusobacterium nucleatum infection with colorectal cancer in Chinese patients

MicroRNAs have emerged as crucial regulators of tumorigenesis. However, it remains unknown whether miR-181a is involved in the pathogenesis of gastric cancer. In this study, we found that miR-181a is overexpressed in human gastric cancer tissues. Ectopic expression of miR-181a mimic promoted the proliferation, colony formation, migration, and invasion and inhibited the apoptosis of SGC-7901 gastric cancer cells, whereas ectopic expression of miR-181a inhibitor inhibited the malignant phenotypes of SGC-7901 cells. Site-directed mutagenesis and luciferase reporter assay demonstrated that miR-181a repressed KLF6 expression by targeting its 3'-UTR. Western blot analysis further showed that KLF6 protein was significantly decreased or increased when miR-181a mimic or inhibitor was transfected into SGC-7901 cells, respectively. In summary, these data suggest that KLF6 gene is a direct target of miR-181a and miR-181a functions as an oncomir in gastric cancer by repressing the expression of tumor suppressor KLF6.

MicroRNA-181a promotes gastric cancer by negatively regulating tumor suppressor KLF6

MicroRNAs (miRNAs) have emerged as important regulators that potentially play critical roles in cancer cell biological processes. Previous studies have shown that miR-492 plays an important role in cell tumorigenesis in multiple kinds of human cancer cells. However, the underlying mechanisms of this microRNA in breast cancer remain largely unknown. In the present study, we investigated miR-492's role in cell proliferation of breast cancer. MiR-492 expression was markedly upregulated in breast cancer tissues and breast cancer cells. Overexpression of miR-492 promoted the proliferation and anchorage-independent growth of breast cancer cells. Bioinformatics analysis further revealed sex-determining region Y-box 7 (SOX7), a putative tumor suppressor, as a potential target of miR-492. Data from luciferase reporter assays showed that miR-492 directly binds to the 3'-untranslated region (3'-UTR) of SOX7 messenger RNA (mRNA) and repressed expression at both transcriptional and translational levels. Ectopic expression of miR-492 led to downregulation of SOX7 protein, which resulted in the upregulation of cyclin D1 and c-Myc. In functional assays, SOX7 silenced in miR-492-in-transfected ZR-75-30 cells has positive effect to promote cell proliferation, suggesting that direct SOX7 downregulation is required for miR-492-induced cell proliferation and cell cycle of breast cancer. In sum, these results suggest that miR-492 represents a potential onco-miR and participates in breast cancer carcinogenesis by suppressing SOX7 expression.

MiR-492 contributes to cell proliferation and cell cycle of human breast cancer cells by suppressing SOX7 expression

There are conflicting reports on the correlation between serum levels of selenium (Se), copper (Cu), and magnesium (Mg) with thyroid cancer. The purpose of the present study is to clarify the association between Se, Cu, and Mg levels with thyroid cancer using a meta-analysis approach. We searched articles indexed in PubMed published as of January 2015 that met our predefined criteria. Eight eligible articles involving 1291 subjects were identified. Overall, pooled analysis indicated that subjects with thyroid cancer had lower serum levels of Se and Mg, but higher levels of Cu than the healthy controls [Se: standardized mean difference (SMD) = −0.485, 95% confidence interval (95%CI) = (−0.878, −0.092), p = 0.016; Cu: SMD = 2.372, 95%CI = (0.945, 3.799), p = 0.001; Mg: SMD = −0.795, 95%CI = (−1.092, −0.498), p < 0.001]. Further subgroup analysis found lower serum levels of Se in thyroid cancer in Norway [SMD = −0.410, 95%CI = (−0.758, −0.062), p = 0.021] and Austria [SMD = −0.549, 95%CI = (−0.743, −0.355), p < 0.001], but not in Poland (SMD = −0.417, 95%CI = (−1.724, 0.891), p = 0.532]. Further subgroup analysis also found that patients with thyroid cancer had higher serum levels of Cu in China [SMD = 1.571, 95%CI = (1.121, 2.020), p < 0.001] and Turkey [SMD = 0.977, 95%CI = (0.521, 1.432), p < 0.001], but not in Poland [SMD = 3.471, 95%CI = (−0.056, 6.997], p = 0.054]. In conclusion, this meta-analysis supports a significant association between serum levels of Se, Cu, and Mg with thyroid cancer. However, the subgroup analysis found that there was significant effect modification of Se, Cu levels by ethnic, like China and Poland. Thus, this finding needs further confirmation by a trans-regional multicenter study to obtain better understanding of causal relationship between Se, Cu, and Mg with thyroid cancer of different human races or regions.

The Association Between Serum Levels of Selenium, Copper, and Magnesium with Thyroid Cancer: a Meta-analysis

Recent evidences show that genetic polymorphisms falling in miRNA binding sites can alter the strength of miRNA binding and disturb miRNA-mediated posttranscriptional regulation. Our study aimed to investigate the role of single-nucleotide polymorphisms (SNPs) in putative miRNA binding sites in gastric cancer (GC). Based on microarray and quantitative reverse transcription PCR analyses, we found that miR-181a was significantly upregulated in GC tissues. Bioinformatics survey was used to explore SNPs within miR-181a binding sites. Three SNPs were genotyped in a case-control study (500 cases and 502 controls). The T allele genotypes (rs12537CT and TT) of MTMR3 were found associated with significantly increased GC risk [adjusted odds ratio 1.72, 95% confidence interval (CI) 1.36-2.16, P = 3.99×10(-5)] and poor overall survival [hazard ratio (HR) 1.38, 95% CI 1.03-1.83, P = 0.029], although they were not an independent prognostic factor in multivariate Cox regression analysis (HR 1.28, 95% CI 0.95-1.72, P = 0.11). We further demonstrated that the rs12537CT genotype carriers had lower MTMR3 mRNA expression levels than CC genotype carriers in GC tissues (P = 0.013), whereas no significant difference in miR-181a expression levels was found (P = 0.135). Luciferase assay revealed that miR-181a directly targeted MTMR3, and its suppressive effect was enhanced when the rs12537C allele was substituted by T variant, although the difference was not significant (P = 0.055). Our study suggested that rs12537 is associated with susceptibility and prognosis of GC in southern Han Chinese, and miR-181a and its target gene MTMR3 play important roles in GC.

/pdf/genetic-polymorphism-at-mir-181a-binding-site-contributes-to-4atuwo37b7.pdf

Jie Cao

Papers

Association of Fusobacterium nucleatum infection with colorectal cancer in Chinese patients

MicroRNA-181a promotes gastric cancer by negatively regulating tumor suppressor KLF6

MiR-492 contributes to cell proliferation and cell cycle of human breast cancer cells by suppressing SOX7 expression

The Association Between Serum Levels of Selenium, Copper, and Magnesium with Thyroid Cancer: a Meta-analysis

Genetic polymorphism at miR-181a binding site contributes to gastric cancer susceptibility