FUS contributes to mTOR-dependent inhibition of translation

Abstract

The amyotrophic lateral sclerosis (ALS) and frontotemporal degeneration (FTD)-linked RNA-binding protein called fused in sarcoma (FUS) has been implicated in several aspects of RNA regulation, including mRNA translation. The mechanism by which FUS affects the translation of polyribosomes has not been established. Here we show that FUS can associate with stalled polyribosomes and that this association is sensitive to mTOR (mammalian Target of Rapamycin) kinase activity. Specifically, we show that FUS association with polyribosomes is increased by Torin1 treatment or when cells are cultured in nutrient-deficient media, but not when cells are treated with rapamycin, the allosteric inhibitor of mTORC1. Moreover, we report that FUS is necessary for efficient stalling of translation as FUS-deficient cells are refractory to the inhibition of mTOR-dependent signaling by Torin1. We also show that ALS-linked FUS mutants, R521G and P525L, associate abundantly with polyribosomes and decrease global protein synthesis. Importantly, the inhibitory effect on translation by FUS is impaired by mutations that reduce its RNA binding affinity. These findings demonstrate that FUS is an important RNA-binding protein that mediates translational repression through mTOR-dependent signaling, and that ALS-linked FUS-mutants can cause a toxic gain-of-function in the cytoplasm by repressing the translation of mRNA at polyribosomes.

Identification of a novel interaction of FUS and syntaphilin may explain synaptic and mitochondrial abnormalities caused by ALS mutations

“…Our data also confirms previous data showing that mutations in FUS affect protein synthesis 36 , 43 . Moreover, translation defects appear to be specific to the degree of mislocalised cytoplasmic FUS depending on the mutation present.…”

“…As with our previous data, FUS R514G led to an increase in translation in affected soma and neurites whereas FUS ΔNLS led to a decrease. Previous reports have demonstrated that mutant FUS interacts with polyribosomes and that a toxic ‘gain of function’ in the cytoplasm affects translation 43 . Therefore, it is likely that the changes in global translation alongside the mitochondrial abnormalities we observe lead to the synaptic abnormalities exhibited by each specific mutant.…”

FUS-ALS mutants alter FMRP phase separation equilibrium and impair protein translation

“…We report that expression of FUS mutants at endogenous levels impairs translation, both in physiological models of disease (heterozygous FUS mutant mice) and in MNs carrying homozygous mutations. A recent study, where FUS was overexpressed in human embryonic kidney (HEK) 293 cells, has shown that FUS-mediated translation inhibition was associated with increased cosedimentation of FUS mutants with polysomes ( 38 ). In our model, however, we find that endogenously expressed mutant FUS does not associate with the translational machinery using biochemical and imaging approaches, a difference that could be due to the overexpression of the protein or to an alternative regulation in HEK293 cells.…”

Proximity-based labeling reveals DNA damage-induced N-terminal phosphorylation of fused in sarcoma (FUS) leads to distinct changes in the FUS protein interactome

“…FUS function is closely linked to regulation of mRNA translation (Baron et al , 2013; Baron et al ., 2019; Kamelgarn et al ., 2018; Sévigny et al , 2020; Yasuda et al , 2013). In line with this, we saw that expression of FUS PM enhanced protein translation compared to FUS WT (Figure 5D).…”