MANF promotes cell fitness and attenuates bortezomib sensitivity in multiple myeloma

BACKGROUND: Multiple myeloma (MM) is a clonal plasma cell malignancy in which disease relapse and treatment resistance remain major clinical challenges. Identifying molecular dependencies that support myeloma cell fitness may reveal therapeutic vulnerabilities beyond recurrent genomic alterations. Mesencephalic astrocyte-derived neurotrophic factor (MANF) is an endoplasmic reticulum-resident, stress-responsive protein, but its clinical and biological significance in MM remains poorly defined. METHODS: Publicly available DepMap CRISPR dependency data were analyzed to identify candidate MM-preferential dependencies. MANF expression and prognostic associations were examined in the MMRF CoMMpass cohort. Single-cell RNA sequencing and in silico perturbation analyses characterized its cellular distribution and predicted functional associations. MANF knockdown and genetic rescue using an siRNA-resistant MANF construct were performed in RPMI-8226 and OPM-2 cells to assess proliferation, cell-cycle distribution, and bortezomib sensitivity. Transcriptomic profiling characterized gene expression changes following MANF knockdown, while measurements at multiple time points assessed the temporal patterns of IRE1α-XBP1s-associated readouts. RESULTS: MANF was identified as a candidate MM-preferential dependency. Higher MANF expression was associated with advanced ISS stage and inferior overall survival, with the survival association retained after adjustment for established clinical and cytogenetic risk factors. Single-cell analysis localized MANF expression predominantly to plasma cells, while virtual knockout predicted changes involving ER protein processing, proteasome function, and metabolism. MANF knockdown inhibited proliferation, increased G0/G1 accumulation, and reduced MYC/E2F-associated transcriptional programs and cell-cycle regulatory proteins. Time-course analyses revealed early enhancement followed by later attenuation in selected IRE1α-XBP1s-associated readouts. MANF knockdown also increased bortezomib-induced apoptosis and reduced its IC₅₀. MANF re-expression partially reversed proliferation and cell-cycle phenotypes, restored IRE1α-XBP1s-associated protein abundance, and attenuated bortezomib sensitization. CONCLUSION: These findings identify MANF as a previously underexplored candidate myeloma-associated dependency that supports proliferative fitness and modulates bortezomib sensitivity in the tested MM models. MANF depletion is associated with dynamic changes in IRE1α-XBP1s-related readouts. These results support further investigation of MANF as a candidate therapeutic vulnerability in MM.