Structural and functional characterization of the TCF25/Rqc1 protein and its role in neuronal development

During translation, ribosomes can encounter obstacles, including chemical modifications of mRNA, premature poly(A) tail, and limited availability of tRNA. These challenges can disrupt the elongation and lead to ribosome stalling and collisions. Such collisions cause ribosome splitting, mRNA degradation, 40S subunit recycling, and the associated ribosome quality control (RQC) activation. The RQC complex is composed of the proteins Ltn1/Lister (yeast/mammals), Rqc1/TCF25, and Rqc2/NEMF, which, together with other proteins, remove the aberrant nascent polypeptide from the 60S ribosome subunit and are directed by proteasome degradation. It prevents protein aggregation and allows the 60S subunit recycling. Interestingly, the perturbation of RQC components causes neurodegeneration in both mice and humans. However, the function of Rqc1/TCF25 is unknown, as is the distribution of the RQC proteins in different tissues. Our research identified that RQC components exhibit widespread expression across various human tissues, with a notable decline in mRNA abundance with aging. Notably, TCF25 displayed elevated mRNA levels not corresponding to increased protein content, indicating post-translational protein regulation. Additionally, we purified the yeast Rqc1 protein and performed the structural characterization. Moreover, we investigated the effect of Rqc1/TCF25 silencing by siRNA knockdown on neuronal development in SH-SY5Y human neuroblastoma cells. Silenced cells were differentiated and visualized by fluorescence microscopy using neuronal differentiation markers. TCF25-silenced cells exhibit reduced differentiation, suggesting a role for the protein in neuronal maturation. These findings highlight the importance of TCF25/RQC1 as a functional component of the RQC and suggest potential implications for neurodevelopment and disorders related to protein homeostasis.