Interplay between WNT/PI3K-mTOR axis and the microbiota in APC-driven colorectal carcinogenesis: data from a pilot study and possible implications for CRC prevention.

BACKGROUND: Wnt/ß-catenin signalling impairment accounts for 85% of colorectal cancers (CRCs), including sporadic and familial adenomatous polyposis (FAP) settings. An altered PI3K/mTOR pathway and gut microbiota also contribute to CRC carcinogenesis. We studied the interplay between the two pathways and the microbiota composition within each step of CRC carcinogenesis. METHODS: Proteins and target genes of both pathways were analysed by RT-qPCR and IHC in tissues from healthy faecal immunochemical test positive (FIT+, n = 17), FAP (n = 17) and CRC (n = 15) subjects. CRC-related mutations were analysed through NGS and Sanger. Oral, faecal and mucosal microbiota was profiled by 16 S rRNA-sequencing. RESULTS: We found simultaneous hyperactivation of Wnt/ß-catenin and PI3K/mTOR pathways in FAP-lesions compared to CRCs. Wnt/ß-catenin molecular markers positively correlated with Clostridium_sensu_stricto_1 and negatively with Bacteroides in FAP faecal microbiota. Alistipes, Lachnospiraceae, and Ruminococcaceae were enriched in FAP stools and adenomas, the latter also showing an overabundance of Lachnoclostridium, which positively correlated with cMYC. In impaired-mTOR-mutated CRC tissues, p-S6R correlated with Fusobacterium and Dialister, the latter also confirmed in the faecal-ecosystem. CONCLUSIONS: Our study reveals an interplay between Wnt/ß-catenin and PI3K/mTOR, whose derangement correlates with specific microbiota signatures in FAP and CRC patients, and identifies new potential biomarkers and targets to improve CRC prevention, early adenoma detection and treatment.

Discovering the Mutational Profile of Early Colorectal Lesions: A Translational Impact.

Colorectal cancer (CRC) develops through a multi-step process characterized by the acquisition of multiple somatic mutations in oncogenes and tumor-suppressor genes, epigenetic alterations and genomic instability. These events lead to the progression from precancerous lesions to advanced carcinomas. This process requires several years in a sporadic setting, while occurring at an early age and or faster in patients affected by hereditary CRC-predisposing syndromes. Since advanced CRC is largely untreatable or unresponsive to standard or targeted therapies, the endoscopic treatment of colonic lesions remains the most efficient CRC-preventive strategy. In this review, we discuss recent studies that have assessed the genetic alterations in early colorectal lesions in both hereditary and sporadic settings. Establishing the genetic profile of early colorectal lesions is a critical goal in the development of risk-based preventive strategies.

Are Wnt/ß-Catenin and PI3K/AKT/mTORC1 Distinct Pathways in Colorectal Cancer?

Wnt/ß-catenin and phosphatidylinositol-3-kinase/protein kinase B/mammalian target of rapamycin complex 1 (PI3K/AKT/mTORC1) pathways both are critically involved in colorectal cancer (CRC) development, although they are implicated in the modulation of distinct oncogenic mechanisms. In homeostatic and pathologic conditions, these pathways show a fine regulation based mainly on feedback mechanisms, and are connected at multiple levels involving both upstream and downstream common effectors. The ability of the Wnt/ß-catenin and PI3K/AKT/mTORC1 pathways to reciprocally control themselves represents one of the main resistance mechanisms to selective inhibitors in CRC, leading to the hypothesis that in specific settings, particularly in cancer driven by genetic alterations in Wnt/ß-catenin signaling, the relationship between Wnt/ß-catenin and PI3K/AKT/mTORC1 pathways could be so close that they should be considered as a unique therapeutic target. This review provides an update on the Wnt/ß-catenin and PI3K/AKT/mTORC1 pathway interconnections in CRC, describing the main molecular players and the potential implications of combined inhibitors as an approach for CRC chemoprevention and treatment.

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.