NEMF mutations that impair ribosome-associated quality control are associated with neuromuscular disease

A hallmark of neurodegeneration is defective protein quality control. The E3 ligase Listerin (LTN1/Ltn1) acts in a specialized protein quality control pathway—Ribosome-associated Quality Control (RQC)—by mediating proteolytic targeting of incomplete polypeptides produced by ribosome stalling, and Ltn1 mutation leads to neurodegeneration in mice. Whether neurodegeneration results from defective RQC and whether defective RQC contributes to human disease have remained unknown. Here we show that three independently-generated mouse models with mutations in a different component of the RQC complex, NEMF/Rqc2, develop progressive motor neuron degeneration. Equivalent mutations in yeast Rqc2 selectively interfere with its ability to modify aberrant translation products with C-terminal tails which assist with RQC-mediated protein degradation, suggesting a pathomechanism. Finally, we identify NEMF mutations expected to interfere with function in patients from seven families presenting juvenile neuromuscular disease. These uncover NEMF’s role in translational homeostasis in the nervous system and implicate RQC dysfunction in causing neurodegeneration

NEMF mutations that impair ribosome-associated quality control are associated with neuromuscular disease.

A hallmark of neurodegeneration is defective protein quality control. The E3 ligase Listerin (LTN1/Ltn1) acts in a specialized protein quality control pathway-Ribosome-associated Quality Control (RQC)-by mediating proteolytic targeting of incomplete polypeptides produced by ribosome stalling, and Ltn1 mutation leads to neurodegeneration in mice. Whether neurodegeneration results from defective RQC and whether defective RQC contributes to human disease have remained unknown. Here we show that three independently-generated mouse models with mutations in a different component of the RQC complex, NEMF/Rqc2, develop progressive motor neuron degeneration. Equivalent mutations in yeast Rqc2 selectively interfere with its ability to modify aberrant translation products with C-terminal tails which assist with RQC-mediated protein degradation, suggesting a pathomechanism. Finally, we identify NEMF mutations expected to interfere with function in patients from seven families presenting juvenile neuromuscular disease. These uncover NEMF's role in translational homeostasis in the nervous system and implicate RQC dysfunction in causing neurodegeneration

Vms1 and ANKZF1 peptidyl-tRNA hydrolases release nascent chains from stalled ribosomes

Ribosomal surveillance pathways scan for ribosomes that are transiently paused or terminally stalled owing to structural elements in mRNAs or nascent chain sequences. Some stalls in budding yeast are sensed by the GTPase Hbs1, which loads Dom34, a catalytically inactive member of the archaeo-eukaryotic release factor 1 superfamily. Hbs1–Dom34 and the ATPase Rli1 dissociate stalled ribosomes into 40S and 60S subunits. However, the 60S subunits retain the peptidyl-tRNA nascent chains, which recruit the ribosome quality control complex that consists of Rqc1–Rqc2–Ltn1–Cdc48–Ufd1–Npl4. Nascent chains ubiquitylated by the E3 ubiquitin ligase Ltn1 are extracted from the 60S subunit by the ATPase Cdc48–Ufd1–Npl4 and presented to the 26S proteasome for degradation. Failure to degrade the nascent chains leads to protein aggregation and proteotoxic stress in yeast and neurodegeneration in mice. Despite intensive investigations on the ribosome quality control pathway, it is not known how the tRNA is hydrolysed from the ubiquitylated nascent chain before its degradation. Here we show that the Cdc48 adaptor Vms1 is a peptidyl-tRNA hydrolase. Similar to classical eukaryotic release factor 1, Vms1 activity is dependent on a conserved catalytic glutamine. Evolutionary analysis indicates that yeast Vms1 is the founding member of a clade of eukaryotic release factor 1 homologues that we designate the Vms1-like release factor 1 clade

A novel RING finger protein, Znf179, modulates cell cycle exit and neuronal differentiation of P19 embryonal carcinoma cells

Znf179 is a member of the RING finger protein family. During embryogenesis, Znf179 is expressed in a restricted manner in the brain, suggesting a potential role in nervous system development. In this report, we show that the expression of Znf179 is upregulated during P19 cell neuronal differentiation. Inhibition of Znf179 expression by RNA interference significantly attenuated neuronal differentiation of P19 cells and a primary culture of cerebellar granule cells. Using a microarray approach and subsequent functional annotation analysis, we identified differentially expressed genes in Znf179-knockdown cells and found that several genes are involved in development, cellular growth, and cell cycle control. Flow cytometric analyses revealed that the population of G0/G1 cells decreased in Znf179-knockdown cells. In agreement with the flow cytometric data, the number of BrdU-incorporated cells significantly increased in Znf179-knockdown cells. Moreover, in Znf179-knockdown cells, p35, a neuronal-specific Cdk5 activator that is known to activate Cdk5 and may affect the cell cycle, and p27, a cell cycle inhibitor, also decreased. Collectively, these results show that induction of the Znf179 gene may be associated with p35 expression and p27 protein accumulation, which lead to cell cycle arrest in the G0/G1 phase, and is critical for neuronal differentiation of P19 cells

Molecular interactions between Hel2 and RNA supporting ribosome-associated quality control

Ribosome-associated quality control (RQC) pathways monitor and respond to stalling of the translating ribosome. Here the authors show that the ribosome associated RQC factor Hel2/ZNF598, an E3 ubiquitin ligase, generally interacts with mRNAs in the vicinity of stop codons

The disruption of proteostasis in neurodegenerative diseases

Cells count on surveillance systems to monitor and protect the cellular proteome which, besides being highly heterogeneous, is constantly being challenged by intrinsic and environmental factors. In this context, the proteostasis network (PN) is essential to achieve a stable and functional proteome. Disruption of the PN is associated with aging and can lead to and/or potentiate the occurrence of many neurodegenerative diseases (ND). This not only emphasizes the importance of the PN in health span and aging but also how its modulation can be a potential target for intervention and treatment of human diseases.info:eu-repo/semantics/publishedVersio

Mutations in RNF135, a gene within the NF1 microdeletion region, cause phenotypic abnormalities including overgrowth

17q11 microdeletions that encompass NF1 cause 5%-10% of cases of neurofibromatosis type 1, and individuals with microdeletions are typically taller than individuals with intragenic NF1 mutations, suggesting that deletion of a neighboring gene might promote human growth. We identified mutations in RNF135, which is within the NF1 microdeletion region, in six families characterized by overgrowth, learning disability, dysmorphic features and variable additional features. These data identify RNF135 as causative of a new overgrowth syndrome and demonstrate that RNF135 haploinsufficiency contributes to the phenotype of NF1 microdeletion cases