Abstract
BACKGROUND: Resistance to the proteasome inhibitor bortezomib (BTZ) poses a formidable therapeutic challenge in multiple myeloma (MM). Our study aims to analyze the mechanism by which exosomes heat shock 70 kDa protein 9 (HSPA9) secreted by BTZ-resistant MM cells disseminate resistance to BTZ-sensitive MM cells. METHODS: The serum exosomes were identified by nanoparticle tracking analysis and transmission electron microscopy. Liquid chromatography-mass spectrometry and public databases were performed to screen exosomes HSPA9. Cell counting kit-8, western blotting and colony formation assay were used to detected the role of HSPA9 protein in vitro. Co-immunoprecipitation, immunofluorescence and protein truncation test experiments were used to determine the regulatory network of the HSPA9-USP1-TRIP13 complex. Optical imaging in vivo and xenograft mouse models were performed to investigate that exosomes HSPA9 promoted MM proliferation and BTZ resistance. RESULTS: We demonstrated that HSPA9 was highly expressed in serum exosomes and BTZ-resistant MM patients. Knockdown of HSPA9 significantly suppressed tumorigenesis and reversed BTZ resistance in vitro. As a downstream molecular of HSPA9, thyroid hormone receptor-interacting protein 13 (TRIP13) was also highly expressed in BTZ-resistant MM patients. Mechanistically, the carboxyl-terminal peptide-binding domain of HSPA9, provides a platform for recruiting the deubiquitinating enzyme ubiquitin-specific peptidase 1 (USP1), which prevents TRIP13 protein degradation. The HSPA9-USP1-TRIP13 complex exhibits stability in the cytoplasm, and its inhibition remarkably enhances BTZ resistance in vito. CONCLUSION: Our findings propose a pioneering molecular regulatory network in which MM-cell-derived exosomes HSPA9 transmitted BTZ resistance through the USP1/TRIP13 signaling pathway. This research highlights exosomes HSPA9 as a promising target to overcome MM BTZ resistance.