The subcellular topology of the RNAi machinery is multifaceted and reveals adherens junctions as an epithelial hub.

The RNA interference (RNAi) machinery is a key cellular mechanism catalyzing biogenesis and function of miRNAs to post-transcriptionally regulate mRNA expression. The RNAi machinery includes a set of protein complexes with subcellular localization traditionally presented in a uniform fashion: the microprocessor processes miRNAs in the nucleus, whereas the DICER and the RNA-induced silencing complex (RISC) further process and enable activity of miRNAs in the cytoplasm. However, several studies have identified subcellular patterns of RNAi components that deviate from this model. We have particularly shown that RNAi complexes associate with the adherens junctions of well-differentiated epithelial cells, through the E-cadherin partner PLEKHA7. To assess the extent of these subcellular topological patterns, we examined subcellular localization of the microprocessor and RISC in a series of human cell lines and normal human tissues. Our results show that junctional localization of RNAi components is a broad characteristic of differentiated epithelia, but it is absent in transformed or mesenchymal cells and tissues. We also find extensive localization of the microprocessor in the cytoplasm, as well as of RISC in the nucleus. These findings expose a RNAi machinery with multifaceted subcellular topology that may inform its physiological role and calls for updating of the current models.