Nucleolar aggresomes as counterparts of cytoplasmic aggresomes in proteotoxic stress

The nucleolus may represent a key stress response organelle in the nucleus following proteotoxic stress by serving as a platform for protein aggregates. Aggregation of proteins often results from insufficient protein degradation by the ubiquitin-proteasome system (UPS), occurring in inclusion diseases, upon treatment by proteasome inhibitors (PIs) or due to various forms of stress. As the nucleolar inclusions resemble cytoplasmic aggresomes in gathering ubiquitin and numerous UPS components and targets, including cancer-related transcription factors and cell cycle regulators (e.g. p53 and cyclin D) and proteins involved in neurodegenerative diseases (e.g. ataxin-1, Malin), these organelles are termed herein as nucleolar aggresomes. These nucleolar aggresomes contain polyadenylated RNA, and seem to be linked to defects in nuclear export. Nucleolar aggresomes have been identified in non-neuronal cells, but prominent similarities with nuclear ubiquitin and/or ribonuclear foci detected in triplet and other repeat disease pathologies are revealed here, creating a common interest between research in cancer and neurodegeneration.