The unconventional secretion of stress-inducible protein 1 by a heterogeneous population of extracellular vesicles

Abstract

The co-chaperone stress-inducible protein 1 (STI1) is released by astrocytes, and has important neurotrophic properties upon binding to prion protein (PrP(C)). However, STI1 lacks a signal peptide and pharmacological approaches pointed that it does not follow a classical secretion mechanism. Ultracentrifugation, size exclusion chromatography, electron microscopy, vesicle labeling, and particle tracking analysis were used to identify three major types of extracellular vesicles (EVs) released from astrocytes with sizes ranging from 20-50, 100-200, and 300-400 nm. These EVs carry STI1 and present many exosomal markers, even though only a subpopulation had the typical exosomal morphology. The only protein, from those evaluated here, present exclusively in vesicles that have exosomal morphology was PrP(C). STI1 partially co-localized with Rab5 and Rab7 in endosomal compartments, and a dominant-negative for vacuolar protein sorting 4A (VPS4A), required for formation of multivesicular bodies (MVBs), impaired EV and STI1 release. Flow cytometry and PK digestion demonstrated that STI1 localized to the outer leaflet of EVs, and its association with EVs greatly increased STI1 activity upon PrP(C)-dependent neuronal signaling. These results indicate that astrocytes secrete a diverse population of EVs derived from MVBs that contain STI1 and suggest that the interaction between EVs and neuronal surface components enhances STI1-PrP(C) signaling.

PRNP/prion protein regulates the secretion of exosomes modulating CAV1/caveolin-1-suppressed autophagy

“…We previously demonstrated that EVs isolated from astrocyte CM typically express exosomal markers and exhibit classical exosome morphology and size as evidenced by electron microscopy and nanoparticle tracking analysis (NTA). 21 Additionally, our previous data showed that a dominant-negative variant of VPS4A, an AAA-ATPase essential for MVB biogenesis, reduces the release of EVs into astrocyte CM by 85%, indicating that a large fraction of these EVs are composed of exosomes. 21 Our present results pointed out that CM from prnp-null astrocytes derived from ZrchI (prnp (Fig.…”

“…21 Additionally, our previous data showed that a dominant-negative variant of VPS4A, an AAA-ATPase essential for MVB biogenesis, reduces the release of EVs into astrocyte CM by 85%, indicating that a large fraction of these EVs are composed of exosomes. 21 Our present results pointed out that CM from prnp-null astrocytes derived from ZrchI (prnp (Fig. 1A).…”

“…20 In conditioned media from astrocytes, STIP1 is found within MVB-derived extracellular vesicles (EVs) containing classical exosome markers. 21 STIP1-containing exosomes are responsible for PRNP-dependent neuronal survival. Accordingly, glioblastomas, which are tumors derived from astrocyte precursors, also secrete STIP1 whose interaction with PRNP at the cell surface modulates the in vitro and in vivo proliferation of these tumor cells.…”

Disruption of prion protein–HOP engagement impairs glioblastoma growth and cognitive decline and improves overall survival

“…[8][9][10] Despite its cytoplasmic localization, HOP is constitutively secreted mainly in extracellular vesicles. 11 Once in the extracellular milieu, HOP (at amino acids (aa) 230-245) interacts with membrane-bound PrP C (at aa 113-128). 12,13 PrP C and HOP have been implicated in cancer progression.…”

Hsp70/Hsp90 Organising Protein (Hop): Beyond Interactions with Chaperones and Prion Proteins

“…Chaperones have been found in the extracellular environment and play physiological roles such as modulation of the stress response and cell survival (Arruda-Carvalho et al 2007;Lima et al 2007;Beraldo et al 2013;Hajj et al 2013). Hop is secreted by various cells types, including neuronal stem cells (Santos et al 2011), microglia (da Fonseca et al 2012, astrocytes Arantes et al 2009) and cancerous cells such as gliomas (Erlich et al 2007) and ovarian cancer cells (Wang et al 2010;Tsai et al 2012).…”