Proteasome Inhibitor Induced SIRT1 Deacetylates GLI2 to Enhance Hedgehog Signaling Activity and Drug Resistance in Multiple Myeloma

Multiple myeloma (MM) is still incurable despite the successful application of proteasome inhibitors in clinic. Bortezomib represents the most common chemotherapy for MM, whereas acquired drug resistance and eventually developed relapse remain the major obstruction. In the current study, we established bortezomib-resistant myeloma cell lines and screened gene expression profiles using single cell RNA-sequencing. Resistant MM cells exhibited increased clonogenic potential, specific metabolic, and epigenetic signatures, along with the self-renewal signaling characteristic of MM stem-like cells. Aberrant activation of hedgehog (Hh) signaling was correlated with drug resistance and stem cell-like transcriptional program. The key transcriptional factor GLI2 of the Hh pathway was restricted in the high acetylation and low ubiquitination states in bortezomib-resistant myeloma cells. Further investigation revealed that SIRT1 deacetylates and stabilizes GLI2 protein at lysine 757 and consequentially activates the Hh signaling, and itself serves as a direct target of Hh signaling to format a positive regulating loop. Using combination screening with an epigenetic compound library, we identified the SIRT1 specific inhibitor S1541 and S2804 had very obvious synergetic antimyeloma effect. Sirt1 inhibition could partially impeded the Hh pathway and conferred bortezomib sensitivity in vitro and in vivo. Notably, elevated SIRT1 level was also a prominent hallmark for the resistant myeloma cells, and this expression pattern was confirmed in myeloma patients, but independent of RAS/RAF mutations. Clinically, SIRT1 expression in patients with complete response was suppressed but elevated in relapsed patients, and retrospective analysis showed patients with higher SIRT1 expression had poorer outcomes. In conclusion, the cooperation of SIRT1 and Hh is an important mechanism of drug resistance in myeloma, and therapeutics combining SIRT1 inhibitors will sensitize myeloma cells to proteasome inhibitors.