Figure 1.HSP90AA1 interacts with HMGB1.(Kim Y H,et al.,2021)
Physiological relevance and proposed model of HMGB1 secretion.
Secretory autophagy machinery and vesicular trafficking are involved in HMGB1 secretion
Paper
2020
Autophagy |
DOI
Background
This study investigates how nuclear protein HMGB1 is secreted via unconventional pathways. It shows HSP90AA1 directly binds HMGB1 and, with XPO1, promotes its nuclear-to-cytoplasmic translocation and secretion. GORASP2, SAR1A, ARF1 dominant-negative mutants, and autophagy machinery enhance HMGB1 secretion. Secretory autophagy requires ATG5 and early autophagy, while late autophagy inhibitors increase secretion. MVB formation, ESCRT components, ceramide-dependent MVB, and RAB8A/RAB11A/RAB27A are also required. The proposed model links HSP90AA1, GORASP2, secretory autophagy, and MVB trafficking to HMGB1 release.
Key Findings
The study identifies HSP90AA1 as a novel HMGB1-binding partner that facilitates HMGB1 nucleo-cytoplasmic translocation by increasing HMGB1-XPO1 interaction; geldanamycin inhibits this and reduces HMGB1 secretion. GORASP2 overexpression or knockdown respectively increases or decreases HMGB1 secretion, and HSP90AA1/GORASP2 co-expression synergistically promotes secretion. HMGB1 secretion requires secretory autophagy: it is inhibited by early autophagy inhibitor wortmannin and reduced in atg5−/− cells, even with GORASP2 overexpression, whereas late autophagy inhibitors bafilomycin A1 and chloroquine increase secretion. SAR1A^T39N and ARF1^Q71L dominant-negative mutants enhance HMGB1 secretion in an autophagy-dependent manner. MVB formation is crucial: ESCRT knockdown (HGS, TSG101) and GW4869 reduce secretion; RAB8A, RAB11A, and RAB27A knockdown decrease it. In macrophages and gorasp2−/− mice, HMGB1 secretion is impaired. The proposed model: HSP90AA1/XPO1 export HMGB1 to cytoplasm; GORASP2/autophagy packages it into autophagosomes; fusion with MVBs and RAB-mediated trafficking mediate secretion.
Contribution
Creative Biogene provided the pFlag CMV2 plasmid (VET1147) used to subclone HSP90AA1 and generate HSP90AA1 domain constructs. This reagent enabled experiments defining HSP90AA1–HMGB1 binding, HMGB1 nucleo-cytoplasmic translocation, and HMGB1 secretion. No other contribution is reported.
This study investigates how nuclear protein HMGB1 is secreted via unconventional pathways. It shows HSP90AA1 directly binds HMGB1 and, with XPO1, promotes its nuclear-to-cytoplasmic translocation and secretion. GORASP2, SAR1A, ARF1 dominant-negative mutants, and autophagy machinery enhance HMGB1 secretion. Secretory autophagy requires ATG5 and early autophagy, while late autophagy inhibitors increase secretion. MVB formation, ESCRT components, ceramide-dependent MVB, and RAB8A/RAB11A/RAB27A are also required. The proposed model links HSP90AA1, GORASP2, secretory autophagy, and MVB trafficking to HMGB1 release.
Key Findings
The study identifies HSP90AA1 as a novel HMGB1-binding partner that facilitates HMGB1 nucleo-cytoplasmic translocation by increasing HMGB1-XPO1 interaction; geldanamycin inhibits this and reduces HMGB1 secretion. GORASP2 overexpression or knockdown respectively increases or decreases HMGB1 secretion, and HSP90AA1/GORASP2 co-expression synergistically promotes secretion. HMGB1 secretion requires secretory autophagy: it is inhibited by early autophagy inhibitor wortmannin and reduced in atg5−/− cells, even with GORASP2 overexpression, whereas late autophagy inhibitors bafilomycin A1 and chloroquine increase secretion. SAR1A^T39N and ARF1^Q71L dominant-negative mutants enhance HMGB1 secretion in an autophagy-dependent manner. MVB formation is crucial: ESCRT knockdown (HGS, TSG101) and GW4869 reduce secretion; RAB8A, RAB11A, and RAB27A knockdown decrease it. In macrophages and gorasp2−/− mice, HMGB1 secretion is impaired. The proposed model: HSP90AA1/XPO1 export HMGB1 to cytoplasm; GORASP2/autophagy packages it into autophagosomes; fusion with MVBs and RAB-mediated trafficking mediate secretion.
Contribution
Creative Biogene provided the pFlag CMV2 plasmid (VET1147) used to subclone HSP90AA1 and generate HSP90AA1 domain constructs. This reagent enabled experiments defining HSP90AA1–HMGB1 binding, HMGB1 nucleo-cytoplasmic translocation, and HMGB1 secretion. No other contribution is reported.