Bidirectional effect of intestinal microbiome and host in circadian rhythm disruption: Environmental factors and breast cancer development.

Suppression of nocturnal circadian melatonin signaling amplitude, disruption of the host's circadian clock through diet or phase shifts, and imbalances in the gut microbiome are significant factors that increase the incidence of breast cancer. After host-derived mature microRNAs (miRNAs) are secreted from intestinal epithelial cells, they pass to the microbiota as faecal or exosomal miRNAs and modify the epigenetic profile of the microbiome. Subsequently, the profile of host miRNAs is altered by metabolites, which are derived from intestinal bacteria. Bidirectional epigenetic modulations of host and microbiota trigger the activation of oncogenic transcriptional pathways in extraintestinal tissues. However, the effect of the mutual epigenetic interactions between the gut microbiota and the host on the development of extraintestinal cancer is not clear. The aim of this review is to discuss the factors influencing bidirectional epigenetic regulation mechanisms between microbial dysbiosis and the host in breast cancer.