Expression of the cereblon binding protein argonaute 2 plays an important role for multiple myeloma cell growth and survival

Abstract CD27, a member of tumor necrosis factor receptor superfamily that lacks a death domain in its cytoplasmic region, and its interaction with its ligand, CD70, is crucial for differentiation into plasma cells. In malignant B cells, aberrant expression and reverse signaling of CD70 might contribute to disease progression. Recent studies showed that CD27 is heterogeneously expressed on multiple myeloma (MM) plasma cells and the expression is reduced with the progression of MM. However, a possible role for the loss of CD27-CD70 interaction in myelomagenesis was never defined. In this study, we identify functional significance of CD27-CD70 interaction in 4 CD27-expressing MM lines and define mechanisms regulating CD27-mediated MM cell death. Using RT-PCR and flow cytometric analysis, we first found that all of MM lines highly express CD70 (n=10) and 4 MM lines 12BM, 12PE, 28BM, 28PE express CD27 on the cell surface. We next evaluated the effect of CD27 ligation, by CD70-transfected NIH3T3 cells (CD70 transfectant), on [3H] thymidine incorporation by CD27-expressing MM lines. CD27 ligation by CD70 transfectants inhibited DNA synthesis in these 4 CD27-expressing MM lines, but not the control transfectants. Conversely, a blocking anti-CD70 mAb blocked CD27-mediated growth inhibition in a dose-dependent manner, indicating induced growth inhibition specific triggered by CD27-CD70 interaction. Using MTT assay, CD27 ligation by CD70 transfectant also inhibited MM cell survival. IL-6 (20 ng/ml) could overcome the inhibitory effect triggered by CD27 ligation on MM cell growth and survival. In addition, CD27 ligation further enhanced Dex-induced MM cell death. Importantly, CD27-mediated MM cell death was also observed in 2 CD27-expressing patient MM cells. Since Siva is a death domain-containing proapoptotic protein identified as an intracellular ligand of CD27, we investigated its role in CD27-mediated apoptosis in MM cells. Overexpression of Siva by transducing adenovirus-expressing Siva (Ad-Siva-GFP) in 12BM MM line is sufficient to induce cell death whereas control adenovirus (Ad-GFP) transduction did not alter 12BM cell growth and survival. CD27 ligation by CD70 transfectants on Siva-overexpressing 12BM cells further enhanced Siva-induced apoptosis, as evidenced by increased subG0 fraction in cell cycle analysis. Thus, the apoptosis triggered by Siva overexpression was related to the CD27-mediated apoptotic pathway. We further determined caspase involvement in the Siva-induced apoptosis in the absence and presence of CD70 transfectants. Caspase 8 and caspase 9 activities were detected 24h following Ad-Siva-GFP transduction in 12BM cells, whereas caspas-3 activity was detected 48h after transduction. Coculture of Ad-Siva-GFP-transduced 12BM cells with CD70 transfectant further enhanced caspase activities. Therefore, overexpression of Siva is sufficient to induce apoptosis and CD27-mediated apoptosis is mediated by Siva-dependent caspase activation in MM. Furthermore, these results suggest that lack of CD27 may lead to evasion of apoptosis in human MM.

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Aptamer TY04 Inhibits Multiple Myeloma Cell Growth Via Cell Cycle Arrest

Blood ◽

10.1182/blood.v122.21.5390.5390 ◽

2013 ◽

Vol 122 (21) ◽

pp. 5390-5390

Author(s):

Jing Liu ◽

Hong-Juan Dai ◽

Bian-Ying Ma ◽

Jian-Hui Song ◽

Hui-yong Chen ◽

...

Keyword(s):

Cell Cycle ◽

Multiple Myeloma ◽

Flow Cytometry ◽

Cell Growth ◽

Cell Lines ◽

Myeloma Cell ◽

Multiple Myeloma Cell ◽

Cycle Arrest ◽

M Phase ◽

Target Molecules

Abstract Multiple myeloma (MM), also known as plasma cell myeloma, is characterized by accumulation of clonal plasma cells in the bone marrow and overproduction of monoclonal immunoglobulin (Ig) in the blood or urine. MM accounts for approximately 10% of all hematologic malignancies. Despite recent advances in the understanding and treatment of this disease, MM remains an incurable disease in the vast majority. With conventional chemotherapy, the 5-year median survival rate for MM patients is approximately 25%. Aptamers are single-stranded RNA or DNA sequences that bind to target molecules with high affinity and specificity. Compared with antibodies, aptamers have unique advantages including easy chemical synthesis and modification, low toxicity, lack of immunogenicity, and rapid tissue penetration, Based on these advantages, aptamers show great potential for therapeutic application. The aptamer TY04 is a single-stranded DNA (ssDNA) generated by a method named cell-based systematic evolution of ligands by exponential enrichment (cell-SELEX), We found TY04 strongly inhibited the growth of multiple myeloma cell lines including MM1.S, NCI-H929, KM3 and OPM2,The concentration of TY04 to inhibit 50% cell growth (IC50) on MM1.S was 3.89 μM. In contrast, TY04 had no effect on the growth of non-tumor cell lines — immortal B lymphoblastoid cell lines. Next, we used MM1.S cell line as the model to study the mechanism of TY04 anti- multiple myeloma. Flow cytometry analysis showed that TY04 with the sequence specifically bind to MM1.S cells when compared with unselected ssDNA library control. To investigate whether the target molecules of TY04 are membrane proteins on cell surface, MM1.S cells were treated with trypsin and proteinase k for 2 or 10 minutes before incubation with TY04. The result revealed that TY04 lost partly recognition ability on treated cells, indicating that the target molecules were most likely membrane proteins. Furthermore, we evaluated the cell cycle distribution of MM1.S after TY04 treatment. We found that TY04 significantly caused cell-cycle arrest in G2/M phase. The percentage of G2/M phase cells increased from 30.1±1.56 to 53.2±6.36. To identify the underlying molecular mechanism, G2/M-related proteins were assayed by flow cytometry. Following TY04 treatment, a concomitant inhibition of ERK1/2, cyclin B, CDK1 and γ-tubulin expression occurred. Meanwhile, human cell cycle PCR array was used to analyze the expression of 84 genes key to cell cycle regulation in TY04-treated MM1.S cells. Our results indicated that aptamer TY04 decreased the genes expression of CCNB1, CCNB2, BIRC5, BRCA1 and CCNH, which were involved in the progress of G2/M phase. All these results are significant in that they provide a framework for further exploring the use of TY04 as a novel anti-multiple myeloma agent. Disclosures: No relevant conflicts of interest to declare.

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