SerpinB2 (PAI-2) Modulates Proteostasis via Binding Misfolded Proteins and Promotion of Cytoprotective Inclusion Formation

Abstract

SerpinB2 (PAI-2), a member of the clade B family of serine protease inhibitors, is one of the most upregulated proteins following cellular stress. Originally described as an inhibitor of urokinase plasminogen activator, its predominant cytoplasmic localisation suggests an intracellular function. SerpinB2 has been reported to display cytoprotective properties in neurons and to interact with intracellular proteins including components of the ubiquitin-proteasome system (UPS). In the current study we explored the potential role of SerpinB2 as a modulator of proteotoxic stress. Initially, we transiently transfected wild-type SerpinB2 and SerpinB2-/- murine embryonic fibroblasts (MEFs) with Huntingtin exon1-polyglutamine (fused C-terminally to mCherry). Inclusion body formation as result of Huntingtin aggregation was evident in the SerpinB2 expressing cells but significantly impaired in the SerpinB2-/- cells, the latter concomitant with loss in cell viability. Importantly, recovery of the wild-type phenotype and cell viability was rescued by retroviral transduction of SerpinB2 expression. SerpinB2 modestly attenuated Huntingtin and amyloid beta fibril formation in vitro and was able to bind preferentially to misfolded proteins. Given the modest chaperone-like activity of SerpinB2 we tested the ability of SerpinB2 to modulate UPS and autophagy activity using a GFP reporter system and autophagy reporter, respectively. Activity of the UPS was reduced and autophagy was dysregulated in SerpinB2-/- compared to wild-type MEFs. Moreover, we observed a non-covalent interaction between ubiquitin and SerpinB2 in cells using GFP-pulldown assays and bimolecular fluorescence complementation. We conclude that SerpinB2 plays an important role in proteostasis as its loss leads to a proteotoxic phenotype associated with an inability to compartmentalize aggregating proteins and a reduced capacity of the UPS.

SERPINB2 is regulated by dynamic interactions with pause-release proteins and enhancer RNAs

“…It can comprise up to 1% of total cellular protein in monocytes [6, 7]. Recent data have implicated SERPINB2, also known as PAI-2 (plasminogen activator inhibitor-2), in type III angioedema and a new functional analysis revealed one of its key functions is to modulate proteotoxic stress [8, 9]. …”

‘Cell cycle’ and ‘cell death’- related genes are differentially expressed during long – term in vitro real-time cultivation of porcine oviductal epithelial cells

“…It was shown that it exhibits cytoprotective propertiesin neurons. It is one of the most regulated proteins after cellular stress [24]. The TXNIP gene encodes thioredoxininteracting proteins, which are important for glucose metabolism [25].…”

Resolution of Deep Venous Thrombosis: Proposed Immune Paradigms

“…Experimental models of PAI-2 deficiency exhibit accelerated DVT resolution without significantly affecting fibrinolysis [205,206]. PAI-2 is primarily retained intercellularly where it binds misfolded proteins, but can be abundantly secreted by pro-inflammatory macrophages [207,208], and acts to regulate many aspects of circulating monocyte and macrophage behavior [209,210]. Within apolipoprotein E gene-deleted mice, hyperlipidemia resulted in a significantly elevated level of PAI-1 and an undetectable uPA concentration, so fibrinolysis and thrombus resolution were severely impaired [211].…”