ALS mutations in TLS/FUS disrupt target gene expression

Abstract

Amyotrophic lateral sclerosis (ALS) is caused by mutations in a number of genes, including the gene encoding the RNA/DNA-binding protein translocated in liposarcoma or fused in sarcoma (TLS/FUS or FUS). Previously, we identified a number of FUS target genes, among them MECP2. To investigate how ALS mutations in FUS might impact target gene expression, we examined the effects of several FUS derivatives harboring ALS mutations, such as R521C (FUS C ), on MECP2 expression in transfected human U87 cells. Strikingly, FUS C and other mutants not only altered MECP2 alternative splicing but also markedly increased mRNA abundance, which we show resulted from sharply elevated stability. Paradoxically, however, MeCP2 protein levels were significantly reduced in cells expressing ALS mutant derivatives. Providing a parsimonious explanation for these results, biochemical fractionation and in vivo localization studies revealed that MECP2 mRNA colocalized with cytoplasmic FUS C in insoluble aggregates, which are characteristic of ALS mutant proteins. Together, our results establish that ALS mutations in FUS can strongly impact target gene expression, reflecting a dominant effect of FUS-containing aggregates.

Sequestration of PRMT1 and Nd1-L mRNA into ALS-linked FUS mutant R521C-positive aggregates contributes to neurite degeneration upon oxidative stress

“…Consistent with our data, recent evidence showed that FUS-R521C can form stable FUS- Bdnf mRNA or FUS- MECP2 mRNA complexes, which impair transcription and/or RNA splicing suggesting that FUS mutants could disrupt target gene expression at a post-transcriptional level4960. Recent RNA-seq transcriptome analyses have identified more target genes that are differentially regulated in FUS-WT and ALS-linked FUS mutants in cellular and animal models49.…”

RNA-binding proteins in neurodegeneration: mechanisms in aggregate

“…The mRNA was found to be present with mutant FUS in cytoplasmic aggregates by both biochemical analysis and FISH, suggesting that the transcript is sequestered. These results suggest that mutant FUS aggregation can affect the stability and translation of mRNA targets through direct sequestration of RNAs as well as pre-mRNA splicing through sequestration of splicing factors (Coady and Manley 2015).…”

“…DNA FUS-responsive elements were later found enriched within promoter regions of genes shown to respond transcriptionally to FUS levels (Tan et al 2012). One such gene, MECP2, biologically interesting due to its relationship to the neuroregressive disease Rett syndrome, was found to be misspliced in cells transfected with mutant, but not wild-type, FUS (Coady and Manley 2015). Interestingly, the splice isoform of MECP2 promoted by mutant FUS was found to have increased RNA stability yet express lower protein levels.…”

Widespread Translational Remodeling during Human Neuronal Differentiation

“…Dysregulation of RNA and protein expression in neurons has deleterious consequences and contributes to numerous neurological and psychiatric diseases (Darnell, 2013; Pilaz and Silver, 2015). For example, expression of variants of the TLS/ FUS RNA binding protein found in amyotrophic lateral sclerosis patients causes aberrant gene expression in human cells, including of MECP2 (Coady and Manley, 2015). Similarly, copy-number variations in the NUDT21 gene found in patients with neurological disease increase the fraction of MECP2 mRNA molecules with long 3′ UTRs (Gennarino et al, 2015).…”

“…Similarly, copy-number variations in the NUDT21 gene found in patients with neurological disease increase the fraction of MECP2 mRNA molecules with long 3′ UTRs (Gennarino et al, 2015). Total MECP2 mRNA levels are elevated in patient-derived cells (Gennarino et al, 2015) or human cells expressing TLS/FUS variants (Coady and Manley, 2015), but MeCP2 protein levels are decreased in both cases. Thus, measuring translation changes in the manner described here that can detect and quantify alternative transcripts and 3′ UTRs is essential when studying diseases involving genetic alterations to post-transcriptional control factors.…”