Introduction
Colorectal cancer (CRC) is the 3rd most common cancer worldwide. Approximately 85% of CRC develop on a background of Wnt/β-catenin signalling impairment. Familial adenomatous polyposis (FAP), caused by inherited APC gene mutations (part of the β-catenin destruction complex), is characterized by the development of hundreds to thousands adenomatous polyps. FAP patients have up to 100% risk of developing CRC during their lifetime. The Wnt/β-catenin together with the PI3K/mTOR signalling control the self-renewal and homeostasis of intestinal stem cells and are frequently deregulated in CRC therefore representing attractive targets for chemoprevention and treatment [1], [2]. It has been shown that each pathway may be deregulated by an altered composition of the gut microbiota [3], [4], which plays an important role in the onset, development and progression of CRC thus representing potential target for prevention and potentially biomarkers for the early detection of deranged Wnt/β-catenin-driven lesions [5].
Aims & Methods
The aim of the study was to identify potential targets for the prevention and early detection of CRC in the setting of Wnt/β-catenin disruption.
Transcriptional and translational levels of Wnt/β-catenin and PI3K/mTOR pathways were evaluated by RT-qPCR and immunohistochemical analysis, respectively, in FAP adenomas (n=17 patients) and in sporadic CRC tissues (tumor stages I-III; n=15 patients). In FAP adenomas germline and somatic APC mutations were confirmed by Sanger and Targeted Next Generation Sequencing. The composition of oral, fecal and mucosal-associated microbiota was sequenced by the bacterial 16S rRNA gene. Non-diseased Faecal Immunochemical Testing positive subjects (FIT+; n=17) were included as control group.
Results
We found increased expressions of AXIN2 and cMYC, downstream targets of Wnt/β-catenin, in FAP adenomas. The activation status of PI3K/mTOR was confirmed by an increase of RPS6 gene and pS6R protein expression, indicating that germline and somatic APC mutations of FAP adenomas induce an activation of both pathways. On the other hand, compared to FAP adenomas, a higher expression of AXIN2, cMYC and cytosolic and nuclear β-catenin was found in CRC, while no changes were detected in pS6R, suggesting that the hyperactivation of Wnt/β-catenin in sporadic CRC contributes to the impairment of mTOR signalling. Importantly, we analyzed the microbiome composition in FAP and CRC settings. The oral microbiota of FAP was significantly enriched of Proteobacteria (p<0.01), which decreased in FAP adenomatous mucosal samples compared to FIT+ and CRC. In contrast, Firmicutes showed an opposite trend in FAP patients, with a decrease in the oral composition (p<0.01) and an increase in the adenomatous mucosa (p<0.05). Interestingly, a significant decrease of the CRC-protective phylum Actinobacteria was found in oral and adenomas microbiota of FAP patients compared to FIT+. In contrast, CRC fecal microbiota was enriched of Proteobacteria and a higher abundance of the well-known cancer associated families Fusobacteriaceae, Clostridiaceae and Gemellaceae was found in CRC mucosal samples compared to FIT+.
Conclusion
These findings reveal new insights into the role of Wnt/β-catenin and PI3K/mTOR pathways in influencing the homeostasis of precancerous CRC lesions. Moreover, by defining different microbial signatures in FAP patients, these results will contribute to the enhancement of non-invasive screening tools for the early detection of WNT signalling-driven colorectal cancers.
References
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