Cytoplasmic Aggregates of Splicing Factor Proline-Glutamine Rich Disrupt Nucleocytoplasmic Transport and Induce Persistent Stress Granules.

Splicing factor proline-glutamine rich (SFPQ), a multifunctional RNA-binding protein (RBP), shows cytoplasmic colocalisation with stress granule (SG) markers; however, the causative relationship and mechanism underlying this coalescence of SFPQ aggregates and SGs remain unclear. In this study, we demonstrate that SFPQ lacking its nuclear localisation sequence spontaneously forms cytoplasmic aggregates that abnormally incorporate immature RNA and induce persistent SGs. mRNA profiling showed that SFPQ mislocalisation induced extensive changes in RNA processing, with a subset of alternatively spliced transcripts associated with nucleocytoplasmic transport. Notably, these altered transporters were sequestered into SFPQ aggregates, constituting aberrant protein-RNA complexes. Importantly, suppression of SG nucleation could not block cytoplasmic SFPQ aggregation with immature RNA and nucleocytoplasmic transporters, both of which, however, were moderately ameliorated by the inhibition of alternative splicing or nuclear export. Our results unveil the physiopathological role and mechanism for mislocalised SFPQ in the RNA metabolism, nucleocytoplasmic transport and pathological SGs.