Staufen1 is Essential for Cell-Cycle Transitions and Cell Proliferation Via the Control of E2F1 Expression.

Cell cycle is a highly regulated process that is finely coordinated by a plethora of interconnected regulators. In this paper, we report that post-transcriptional mechanisms mediated by the RNA-binding protein Staufen1 (STAU1) are essential for the proliferation of non-transformed cells (hTERT-RPE1 and IMR90). Cell sorting quantification and time-lapse video microscopy using FUCCI-hTERT-RPE1 cells identified the G/S and G/M phase transitions of the cell cycle as crucial steps for STAU1 functions. The level of expression of 35 transcripts coding for cell-cycle regulators is up- or down-regulated following STAU1 depletion. Among others, expression of E2F1, a transcription factor essential for the G/S transition, is decreased in STAU1 depleted cells, dependent on a STAU1-binding site in the 3' untranslated region of E2F1 mRNA. Interestingly, E2F1, in turn, increases STAU1 transcription, highlighting a regulatory loop that enhances expression of both STAU1 and E2F1. Our results indicate that a STAU1-mediatedpost-transcriptional mechanism of gene regulation controls an mRNA regulon involved in decision making during cell-cycle phase transitions and that this mechanism is essential for cell-cycle progression in non-tumor cells.