Amyotrophic lateral sclerosis (ALS) linked mutation in Ubiquilin 2 affects stress granule assembly via TIA-1

Aims: The ubiquilin-like protein ubiquilin 2 (UBQLN2) is associated with amyotrophic lateral sclerosis and frontotemporal degeneration (ALS/FTD). The biological function of UBQLN2 has previously been shown to be related to stress granules (SGs). In this study, we aimed to clarify the regulatory relationship between UBQLN2 and SGs.

Methods: In this study, we transfected UBQLN2-WT or UBQLN2-P497H plasmids into cell lines (HEK293T, HeLa), and observed the process of SG dynamics by immunofluorescence. Meanwhile, immunoblot analyses the protein changes of stress granules related components.

Results: We observed that ubiquilin 2 colocalizes with the SG component proteins G3BP1, TIA-1, ATXN2, and PABPC1. In cells expressing WT UBQLN2 or P497H mutants, in the early stages of SG formation under oxidative stress, the percentage of cells with SGs and the number of SGs per cell decreased to varying degrees. Between WT and mutant, there was no significant difference in eIF2α activity after stress treatment. Interestingly, the UBQLN2 P497H mutant downregulates the level of TIA-1. In addition, the overexpression of the UBQLN2 P497H mutant inhibited the phosphorylation of 4E-BP1 and affected the nucleoplasmic distribution of TDP-43.

Conclusions: Ubiquilin 2 colocalizes with the SG component proteins G3BP1, TIA-1, ATXN2, and PABPC1. It participates in regulating SG dynamics. And UBQLN2 mutation affects the assembly of stress granules by regulating TIA-1. In addition, the overexpression of the UBQLN2 P497H mutant inhibited the phosphorylation of 4E-BP1 and affected the nuclear and cytoplasmic distribution of TDP-43. These provide new insights into the role of UBQLN2 in oxidative stress and the pathogenesis of ALS.