Updated project metadata. Spinocerebellar ataxia type-1 is caused by an abnormally expanded polyglutamine (polyQ) tract in ataxin-1 protein. These expansions are responsible for protein misfolding and self-assembly into intranuclear inclusion bodies (IIBs) that are linked to neuronal death. Here, we describe a nuclear protein aggregation model of pathogenic human ataxin-1. Using an inducible Sleeping Beauty transposon system, we overexpressed ATXN1Q82 gene in human mesenchymal stem cells that are resistant to the early cytotoxic effects of the mutant protein. We characterized the structure and the protein composition of insoluble polyQ IIBs which gradually occupy the nuclei. In response to their formation, our transcriptome analysis reveals a cerebellum-specific perturbed protein interaction network, primarily affecting protein translation. Our study resolves the previously unknown architecture of insoluble polyQ IIBs and suggests that they affect the assembly and the function of the ribosome. Our inducible cell system faithfully models a human cerebellum at the end-stage of the disease.