Shammas, Masood A.

Abstract Multiple myeloma (MM) is a complex hematological malignancy characterized by genomic changes and transcriptomic dysregulation. Initial exome sequencing approaches have failed to identify any single, frequent (>25%) mutation in the coding genome. However, using whole-genome sequencing, we found that one of the genomic regions most frequently mutated (62% of the patients with MM) was the 5′ untranslated region and/or intron 1 of the BCL7A gene. RNA-sequencing data from a large cohort suggest a loss of BCL7A expression in a large majority of patients with MM as compared with normal plasma cells. BCL7A loss of function in a panel of MM cell lines led to a highly proliferative phenotype in vitro and in vivo, whereas its ectopic expression significantly reduced cell viability, suggesting a tumor suppressor function for BCL7A in MM. We studied the cellular and molecular effects of BCL7A loss and observed that it endows myeloma cells with proliferative potential in cooperation with the plasma cell–defining transcription factor IRF4. BCL7A is involved in a direct protein-protein interaction with IRF4, limiting its DNA-binding activity. Loss of BCL7A thus enhances the expression of IRF4-associated cytokines and reduces mitochondrial metabolism and reactive oxygen species levels. Our study therefore suggests that BCL7A loss provides the necessary molecular change to allow IRF4-mediated transcriptional activity and MM cell growth and survival.

AbstractGenetic heterogeneity between individuals confounds the comparison of gene profiling of multiple myeloma (MM) cells versus normal plasma cells (PCs). To overcome this barrier, we compared the gene expression profile of CD138+ MM cells from a patient bone marrow (BM) sample with CD138+ PCs from a genetically identical twin BM sample using microarray profiling. Two hundred and ninety-six genes were up-regulated and 103 genes were down-regulated at least 2-fold in MM cells versus normal twin PCs. Highly expressed genes in MM cells included cell survival pathway genes such as mcl-1, dad-1, caspase 8, and FADD-like apoptosis regulator (FLIP); oncogenes/transcriptional factors such as Jun-D, Xbp-1, calmodulin, Calnexin, and FGFR-3; stress response and ubiquitin/proteasome pathway–related genes and various ribosomal genes reflecting increased metabolic and translational activity. Genes that were down-regulated in MM cells versus healthy twin PCs included RAD51, killer cell immunoglobulin-like receptor protein, and apoptotic protease activating factor. Microarray results were further confirmed by Western blot analyses, immunohistochemistry, fluorescent in situ hybridization (FISH), and functional assays of telomerase activity and bone marrow angiogenesis. This molecular profiling provides potential insights into mechanisms of malignant transformation in MM. For example, FGFR3, xbp-1, and both mcl-1 and dad-1 may mediate transformation, differentiation, and survival, respectively, and may have clinical implications. By identifying genes uniquely altered in MM cells compared with normal PCs in an identical genotypic background, the current study provides the framework to identify novel therapeutic targets.