Abstract 2978: PSMD6 is a promising therapeutic target in multiple myeloma

Abstract Background: The 26S proteasome is essential for maintaining protein homeostasis by degrading misfolded or unneeded proteins regulating critical cellular processes such as the cell cycle, apoptosis, and immune response. It consists of 20S catalytic core particle and 19S regulatory particle, with the PSMD family playing a key role in proteasome assembly. Multiple myeloma (MM), a plasma cell malignancy characterized by abnormal immunoglobulin production, heavily depends on proteasome function. While proteasome inhibitors (PIs) are commonly used in MM treatment, resistance to inhibitors targeting the 20S subunit frequently develops. Targetting the PSMD family of ubiquitin receptors upstream of the proteasome in the ubiquitin proteasome cascade represents a promising therapeutic target to overcome PI resistance. This study aimed to identify key PSMD subunits as therapeutic targets in MM, with a focus on validating PSMD6. Methods: Gene expression and cell line dependencies were analyzed using the Gene Expression Omnibus datasets and DepMap portal. Kaplan-Meier plotter was used to assess the correlation between PSMD expression and MM patient survival. PSMD6 was knocked down via siRNA or CRISPR/Cas9 in MM cell lines, followed by immunoblotting to evaluate K48 polyubiquitinated protein accumulation, apoptosis, endoplasmic reticulum (ER) stress, and cell cycle progression. Results: 1) DepMap identified that PSMD1-4, PSMD6-8, and PSMD11-14 as essential for MM cell line survival. 2) PSMD3, PSMD5-13, and PAAF1, are highly expressed in MM patients (GSE6691, GSE6471, GSE153380). 3) Elevated expression of PSMD1-3, PSMD6, PSMD8, PSMD9, PSMD11, and PSMD13 was correlated with poor MM patient survival. 4) Our real-time PCR and immunoblot analysis confirmed higher PSMD6 expression in MM patient samples and cell lines compared to normal controls. 5) Functional studies revealed that PSMD6 KD significantly inhibited proliferation of MM cell lines (AMO1, KMS11, H929, and RPMI-8226), independent of p53 status. 6) To assess whether PSMD6 KD disrupt proteasome function, a ubiquitin-GFP reporter cell line was used, where GFP is constitutively degraded by the proteasome. Immunoblot analysis revealed significant accumulation of GFP in PSMD6 KD cells. This was further confirmed by live-cell imaging using the IncuCyte system. 7) Mechanistic studies showed that PSMD6 KD led to increased apoptosis (early and late apoptotic phases), G0-G1 cell cycle arrest, accumulation of K48-linked polyubiquitinated proteins, caspases activation, and induction of the ER stress pathway. Conclusion: Our study highlights the potential of PSMD subunits, particularly PSMD6, as therapeutic targets in MM. Our data validate targeting PSMD6 to enhance cytotoxicity and overcome PI resistance in MM and provide the preclinical rationale for developing PSMD6 inhibitors to improve patient outcomes in MM. Keywords: PSMD6, proteasome, multiple myeloma, therapeutic target Citation Format: Minxing Wang, Arghya Ray, Teng Fang, Xueping Wan, Ting Du, Sindhu C. Pillai, Md Abu Musa, Yan Song, Kenneth C. Anderson. PSMD6 is a promising therapeutic target in multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 2978.