Bacteroides fragilis toxin induces epithelial-to-mesenchymal transition and stem-like phenotype in breast epithelial cells and concomitantly activates Notch and βcatenin axes

ABSTRACT: Aided by deep sequencing techniques, recent studies suggest the existence of distinct breast microbiota and a shift in microbial community composition in diseased breast compared to normal breast. However, their functional impact and underlying mechanisms are unknown. Present study examines the contribution of pro-carcinogenic bacteria in breast cancer initiation, growth and progression. Extensive data mining and metagenomic analyses of existing datasets revealed the presence of toxin producing Bacteriodes fragilis in malignant breast. B. fragilis is a pro-carcinogenic bacterium known for its potential to initiate and promote colon cancer; its pathogenicity has been attributed to its unique toxin ‘BFT’. About 35% of human population asymptomatically harbor ETBF colonization in the gut. Mice with enteric B fragilis infection exhibited a significant amount of circulating BFT and distinct morphological alterations in mammary gland similar to focal hyperplasia. Histological analysis revealed inflammation, fibrosis, breast duct thickening and hyperproliferation of breast epithelial cells. In vitro, upon treatment with BFT, prominent cytoskeletal reorganization, significant increase in migration and invasion potential and decreased adhesion of MCF10A and MCF7 cells were observed along with molecular markers of epithelial-to-mesenchymal transition. Decreased expression of epithelial marker, E-cadherin along with elevated levels of mesenchymal markers, N-cadherin and vimentin were observed. BFT also increased the expression of EMT-related transcription factors, Snail, Slug and Twist. BFT-treated cells attained stem cell-like phenotype exhibiting an increased ability to form secondary and tertiary mammospheres. Mechanistic studies showed that BFT induced expression and nuclear translocation of NICD and β-catenin resulting in activation of downstream targets. Inhibition of Notch1 and β-catenin using γ-secretase and β-catenin inhibitors successfully inhibited functional effects of BFT. Mammary gland implantation and in vivo limiting dilution assays were utilized to corroborate the in vitro findings. BFT-pretreated MCF7 cells exhibit increased tumor growth and form multifocal tumors in mice. In vivo limiting dilution assay using breast tumors from BFT-pretreated MCF7 cells exhibited a striking increase in tumor-initiating cells. Follow-up analyses of these tumors demonstrated increased migratory, invasive, and -mammospheres-forming behavior confirming that brief BFT exposure elicits long-term molecular changes. Altered expression of stemness markers was also confirmed by RNA sequencing.

ORGANISM(S): Homo sapiens

PROVIDER: GSE149241 | GEO | 2023/04/10

REPOSITORIES: GEO