Role of stress granules and RNA-binding proteins in neurodegeneration: a mini-review

Abstract

The eukaryotic stress response involves translational suppression of non-housekeeping proteins and the sequestration of unnecessary mRNA transcripts into stress granules (SGs). This process is dependent on mRNA-binding proteins (RBPs) that interact with capped mRNA transcripts through RNA recognition motifs, and exhibit reversible aggregation through hydrophobic polyglycine domains, some of which are homologous to yeast prion proteins. The activity and aggregation of RBPs appears to be important in the context of unfolded protein diseases. The discovery that mutations in these RBPs can cause familial motoneuron diseases and familial dementias indicates the importance of these genes to neuronal degeneration. Some disorders linked to mutations in RBPs include: amyotrophic lateral sclerosis, frontotemporal dementia and spinal muscular atrophy. These RBPs also associate with pathological structures in other neurodegenerative diseases, including Huntington's chorea, Creutzfeldt-Jakob disease, and Alzheimer's disease. Interestingly, protein levels of RBPs change across the aging spectrum and may be linked to other age-related disorders, such as type 2 diabetes. The link between SG pathways and proteins linked to neurodegenerative diseases suggests a potential role for common pathways in both processes, such as those involved in translational control, and highlights potentially novel targets for therapeutic intervention in neurodegenerative diseases.

Figure 1

TIA-1, TDP-43 and many other RBPs reside in the nucleus under basal conditions. Their nuclear functions vary, but RBPs act in part to facilitate RNA transcription and to regulate RNA splicing. Stress causes these nuclear RBPs to leave the nucleus. In the cytoplasm, the RBPs bind stalled, free mRNA and aggregate to form SGs primarily through the glycine rich domains and secondarily by other domains. The process of SG formation is reversible, but prolonged stress leads to maturation and incorporation of other proteins and post-translational modifications. Mature SGs interact with P-bodies, the autophagic and apoptotic systems.