Abstract
BACKGROUND: Multiple myeloma (MM) is a hematologic cancer marked by clonal expansion of plasma cells in the bone marrow. Although its genomic landscape has been extensively characterized, the transcriptional mechanisms that govern malignant progression and long-term tumor cell survival remain incompletely understood. METHODS: We integrated single-cell RNA sequencing (scRNA-seq) data from healthy donors (HD), monoclonal gammopathy of undetermined significance (MGUS), smoldering multiple myeloma (SMM), and newly diagnosed multiple myeloma (NDMM) patients, retrieved from GEO datasets GSE124310 and GSE271107, to construct a comprehensive transcriptional landscape of plasma cell differentiation. Pseudotime and enrichment analyses identified PDIA4 as a terminal-state-associated gene. The prognostic significance of PDIA4 was validated using the multiple myeloma research foundation (MMRF) CoMMpass cohort. Functional analyses were performed in vitro and in vivo to validate the role of PDIA4 in MM cell survival and therapeutic response. RESULTS: Pseudotime trajectory analysis revealed progressive upregulation of genes involved in protein processing in the endoplasmic reticulum (ER), with PDIA4 identified as a top candidate in terminal-stage plasma cells. Survival analysis in the MMRF CoMMpass cohort further demonstrated that high PDIA4 expression correlated with poor overall survival. In RPMI-8226 cells, PDIA4 knockout activated the IRE1α/XBP1s branch of the unfolded protein response (UPR), impaired proliferation, and induced G1-phase arrest. PDIA4 depletion also sensitized cells to bortezomib. In vivo, sg-PDIA4 suppressed tumor growth in RPMI-8226 xenografts. CONCLUSIONS: PDIA4 is a key regulator of the unfolded protein response and MM cell survival. Targeting PDIA4 may enhance the efficacy of proteasome inhibitors and offers a potential strategy to overcome therapeutic resistance in multiple myeloma.