Secretory autophagy machinery and vesicular trafficking are involved in HMGB1 secretion

Abstract

Nuclear protein HMGB1 is secreted in response to various stimuli and functions as a danger-associated molecular pattern. Extracellular HMGB1 induces inflammation, cytokine production, and immune cell recruitment via activation of various receptors. As HMGB1 does not contain an endoplasmic reticulumtargeting signal peptide, HMGB1 is secreted via the endoplasmic reticulum-Golgi independently via an unconventional secretion pathway. However, the mechanism underlying HMGB1 secretion remains largely unknown. Here, we investigated the role of secretory autophagy machinery and vesicular trafficking in HMGB1 secretion. We observed that HSP90AA1 (heat shock protein 90 alpha family class A member 1), a stress-inducible protein, regulates the translocation of HMGB1 from the nucleus to the cytoplasm and its secretion through direct interaction. Additionally, geldanamycin, an HSP90AA1 inhibitor, reduced HMGB1 secretion. GORASP2/GRASP55 (golgi reassembly stacking protein 2), ARF1 Q71L (ADP ribosylation factor 1), and SAR1A T39N (secretion associated Ras related GTPase 1A), which promoted unconventional protein secretion, increased HMGB1 secretion. HMGB1 secretion was inhibited by an early autophagy inhibitor and diminished in ATG5-deficient cells even when GORASP2 was overexpressed. In contrast, a late autophagy inhibitor increased HMGB1 secretion under the same conditions. The multivesicular body formation inhibitor GW4869 dramatically decreased HMGB1 secretion under HMGB1 secretion-inducing conditions. Thus, we demonstrated that secretory autophagy and multivesicular body formation mediate HMGB1 secretion.

Release mechanisms of major DAMPs

“…The first step, translocation from the nucleus to cytoplasm, is induced by JAK/STAT-1 mediated acetylation of the nuclear localization sequences (NLS) within HMGB1 [ 39 ]. The translocation has also shown to be mediated by the interaction with HSP90AA1 (heat shock protein 90 alpha family class A member 1) and XPO1 [ 49 ]. The second step, secretion from the cytoplasm to the extracellular space, is dependent on the activation of inflammasomes and caspases as described earlier under pyroptosis [ 34 – 36 ].…”

“…HMGB1 has been found inside secretory lysosomes and it has also reported to be released via exosomes in a TLR4 and caspase-11/gasdermin D dependent manner [ 36 , 47 , 48 ]. Another study has shown that HMGB1 secretion was induced by autophagy machinery and MVB formation, resulting in its release in the form of exosomes [ 49 ].…”

The Road Less Traveled? Unconventional Protein Secretion at Parasite–Host Interfaces

“…This protein, which is usually found in the nucleus where it acts as a DNA chaperone, has the function of a danger-associated molecular pattern when transported to the extracellular space and induces inflammation and cell migration (Andersson and Tracey, 2011). For its transport across the plasma membrane, a similar vesicular trafficking machinery is involved as has been found in IL-1b, including GRASP (GORASP2/GRASP55) and heat shock protein (HSP90AA1; Dupont et al, 2011;Zhang et al, 2015;Kim et al, 2020).…”

“…in studies on UPS is increasing. Involved in the most central mechanisms of disease such as inflammation and cancer cell proliferation and, specifically for this review, secretion of virulence factors in parasites, it is of crucial importance FGF2, HIV- TAT Temmerman et al, 2008;Zeitler et al, 2015;Legrand et al, 2020 Type II No ABC-transporters, N-terminal domain HASPB, PfAK2 Denny et al, 2000;Stegmayer et al, 2005;MacLean et al, 2012;Thavayogarajah et al, 2015;Kim et al, 2018 Type III No Vesicles, inflammasome, heat shock protein, GRASP, ESCRTs IL-1β, Acb1, HMGB1 Nickel and Rabouille, 2009;Dupont et al, 2011;Curwin et al, 2016;Cruz-Garcia et al, 2020;Kim et al, 2020 Type IV Yes Golgi bypass via pericentrosomal intermediate compartment, transmembrane domain CFTR Rabouille et al, 2012;Gee et al, 2018;Kim et al, 2018 Pore formation No Gasdermin D, perforin-2 IL-1β, IL-33 Martín-Sánchez et al, 2016;Heilig et al, 2017;Lieberman et al, 2019;Hung et al, 2020 IL-1β is highlighted to emphasize its known use of two different UPS pathways. FGF2, fibroblast growth factor 2; HASPB, hydrophilic acylated surface protein B; GRASP, Golgi reassembly stacking protein; PI(4,5)P 2 , phosphatidylinositol-4,5-bisphosphate; CFTR cystic fibrosis transmembrane conductance regulator; PfAK2, Plasmodium falciparum adenylate kinase 2; ESCRT, endosomal sorting complex required for transport.…”

Metabolic Syndrome and Autophagy: Focus on HMGB1 Protein

“…Accumulating evidence supports the relationship between autophagy and HMGB1. There is a mutual regulation where one's inhibition affects the release of the other (Zhang et al, 2017), while uncontrolled autophagy increases the HMGB1 release (Tang et al, 2010b;Kim et al, 2020). HMGB1 is crucial for normal autophagy functioning (Tang et al, 2010a;Foglio et al, 2019).…”