Application of the RNA interference technique to Xenopus embryos: Specific reduction of the β-catenin gene products by short double-stranded RNA produced by recombinant human Dicer

Prkra dimer senses double-stranded RNAs to dictate global translation efficiency

Double-stranded RNAs (dsRNAs), known as conserved pathogen-associated molecular patterns, activate the integrated stress response via interferon-induced protein kinase R (PKR), leading to global translation inhibition. However, the interferon system is inactive in pluripotent cells, leaving the mechanisms of dsRNA sensing and translational control unclear. In this study, we utilized early zebrafish embryos as a model of pluripotent cells and discovered a PKR-independent blockage of translation initiation by dsRNA stimulation. Prkra dimer was identified as the genuine dsRNA sensor. Upon dsRNA binding, the dimerized dsRNA-binding domain 3 of Prkra becomes activated to sequester the eIF2 complexes from the translation machinery, inhibiting global protein synthesis. This distinctive embryonic stress response restricts RNA virus replication in zebrafish embryos, is conserved in mouse embryonic stem cells, and compensates PKR function in differentiated cells. Therefore, the Prkra-mediated dsRNA sensing and translation control may serve as a common strategy for cells to adapt to environmental stresses.

UVB radiation suppresses Dicer expression through β-catenin

Ultraviolet (UV) rays prompt a natural response in epidermal cells, particularly within melanocytes. The changes in gene expression and related signaling pathways in melanocytes following exposure to UV radiation are still not entirely understood. Our findings reveal that UVB irradiation suppresses the expression of Dicer (also known as Dicer1). This repression is intricately linked to the activation of the phosphoinositide 3-kinase (PI3K), ribosomal S6 kinase (RSK) and Wnt-β-catenin signaling pathways, and is directly associated with transcriptional repression by β-catenin (also known as CTNNB1). Notably, we have identified specific binding sites for the TCF/LEF-β-catenin complex in the Dicer promoter. Collectively, these results emphasize the significance of the UV-induced pathway involving the TCF/LEF-β-catenin complex, which impacts Dicer expression. UV radiation also reduced the levels of specific microRNAs known to be important in the biology of melanocytes. This pathway holds potential importance in governing melanocyte physiology.