Induction of Apoptosis in Plasma Cells by B Lymphocyte–Induced Maturation Protein-1 Knockdown

Abstract

B lymphocyte-induced maturation protein-1 (Blimp-1) is a transcriptional repressor that plays an important role during plasmacytic differentiation and is expressed in normal and transformed plasma cells. We here investigated the importance of continuous Blimp-1 expression. We found that knockdown of Blimp-1 expression by lentiviral vector-delivered short hairpin RNA causes apoptosis in multiple myeloma cell lines and plasmacytoma cells, indicating that continued expression of Blimp-1 is required for cell survival. We examined the mechanism underlying Blimp-1 knockdown-mediated apoptosis and found that the Blimp-1 knockdown neither reversed the phenotypic markers of plasma cells nor caused cell cycle arrest. Instead, our results show that knockdown of Blimp-1 induced the proapoptotic protein Bim, reduced the antiapoptotic protein Mcl-1, and activated caspase-9 and caspase-3. We further link apoptosis in transformed plasma cells mediated by proteasome inhibitors, the effective therapeutic agent for multiple myeloma patients, with reduced expression of Blimp-1. Lastly, we show that Blimp-1-dependent cell survival may act downstream of IFN regulatory factor 4 (IRF4) because IRF4 knockdown leads to down-regulation of Blimp-1 and apoptosis in multiple myeloma cells and plasmacytoma cells. Together, our data suggest that Blimp-1 ensures the survival of transformed plasma cells.

Aiolos collaborates with Blimp-1 to regulate the survival of multiple myeloma cells

“…We sought to identify the interacting partners of Blimp-1 that may contribute to the maintenance of the survival of MM cells, where Blimp-1 is expressed. 3 Nuclear extracts from the human MM line H929 were used to immunoprecipitate Blimp-1-interacting complexes using polyclonal anti-Blimp-1. Mass spectrometric analysis of differentially expressed proteins derived from Blimp-1 immunoprecipitates relative to immunoprecipitates from a control antibody revealed 10 peptide sequences that corresponded to Aiolos (Supplementary Figure 1).…”

“…1 Blimp-1 is not only essential for the generation of plasma cells but also important for ensuring their survival. 2,3 Accordingly, antigen-specific long-lived plasma cells in the bone marrow cannot be maintained when Prdm1, the Blimp-1 gene, is ablated in immunized mice. 4 The action of Blimp-1 in regulating gene repression has been revealed by the identification of several histonemodifying enzymes or co-repressors that physically interact with Blimp-1.…”

Antineoplastic effects of liposomal short interfering RNA treatment targeting BLIMP1/PRDM1 in primary effusion lymphoma

“…Interestingly, our data are in agreement with the results of an in vitro study on multiple myeloma, reporting that the infection of myeloma cell lines with lentiviral vectors expressing anti-BLIMP1 short hairpin RNA may directly cause tumor apoptosis, without triggering a process of de-differentiation or reprogramming the molecular network of neoplastic plasma cells. 15 We next tested the therapeutic potential of anti-BLIMP1 siRNA/DOTAP lipoplexes in vivo, using a previously described PEL xenograft murine model. 14 Briefly, 24 severe combined immunodeficiency (SCID)/CB17 mice were intraperitoneally (i.p.)…”

“…PEL viability and cell concentration were assessed daily by staining with annexin V/propidium iodide (Miltenyi Biotech, Bergisch Gladbach, Germany), in accordance with the manufacturer's instructions, and by using an AcT8 automated cell counter (Beckman Coulter Inc., Brea, CA, USA), respectively. Caspase-3 activity was assayed (Calbiochem, EMD Biosciences, San Diego, CA, USA) as previously reported, 15 to detect the activation of the apoptotic pathway. The cell cycle was analyzed using a commercial BrdU/7-AAD assay (BD Biosciences, San Jose, CA, USA), according to the manufacturer's instructions.…”

“…The cell cycle was analyzed using a commercial BrdU/7-AAD assay (BD Biosciences, San Jose, CA, USA), according to the manufacturer's instructions. Quantitative real-time polymerase chain reaction and western blot assays were performed, as previously described, 15 to evaluate mRNA levels and protein expression, respectively, for Blimp-1 and other relevant B-cell transcription factors.…”