Direct proteasome binding and subsequent degradation of unspliced XBP-1 prevent its intracellular aggregation

Abstract 

The non-canonical splicing of XBP-1 mRNA is a hallmark of the mammalian unfolded protein response (UPR). The proteasomal degradation of unspliced XBP-1 (XBP-1u) facilitates the termination of the UPR. Thus, understanding the mechanism of XBP-1u degradation may allow control over UPR duration and intensity.

We show that XBP-1u interacts with purified 20S proteasomes through its unstructured C-terminus, which leads to its degradation in a manner that autonomously opens the proteasome gate. In living cells, the C-terminus of XBP-1u accumulates in aggresome structures in the presence of proteasome inhibitors. We propose that direct proteasomal degradation of XBP-1u prevents its intracellular aggregation.

Structured summary

MINT-7302217: XBP1-u (uniprotkb:P17861-1) binds (MI:0407) to Proteasome subunit alpha 7.2 (uniprotkb:O14818) by pull down (MI:0096)

MINT-7302148: Vimentin (uniprotkb:P08670) and XBP1-u (uniprotkb:P17861-1) colocalize (MI:0403) by fluorescence microscopy (MI:0416)

MINT-7302163: XBP1-u (uniprotkb:P17861-1) binds (MI:0407) to Proteasome subunit alpha 5 (uniprotkb:P28066) by pull down (MI:0096)

MINT-7302186: XBP1-u (uniprotkb:P17861-1) binds (MI:0407) to Proteasome subunit alpha 6 (uniprotkb:P60900) by pull down (MI:0096)

Abbreviations: AMC, 7-amido-4-methylcoumarin, ATF6, activating transcription factor 6, ER, endoplasmic reticulum, ODC, ornithine decarboxylase, PERK, PKR-like ER kinase, UPR, unfolded protein response, XBP-1, X-box-binding protein

Keywords: Unfolded protein response, ER stress, XBP-1, Proteasome, Ubiquitin, In vitro degradation