Human Myeloma Cell Line RPMI Research Articles

Effect of BECN1 Expression on Proliferation and Invasion of Human Myeloma Cell Line RPMI-8226

To investigate the effect of BECN1 expression on proliferation and invasion of human multiple myeloma (MM) cell line RPMI-8226. RPMI-8226 cells were cultured in vitro, the recombinant plasmid pcDNA3.1-BECN1 was constructed and transfected into RPMI-8226 cells, then the cells were divided into three groups: control group, negative transfection group and BECN1 transfection group. The expression of BECN1 mRNA in cells of each group was detected by real-time fluorescent quantitative polymerase chain reaction (qRT-PCR); the effect of BECN1 overexpression on cell proliferation inhibition rate was detected by cell counting kit 8 (CCK-8); the effect of BECN1 overexpression on the colony formation rate was detected by plate cloning assay; the effect of BECN1 overexpression on cell invasion was detected by Transwell assay; the effects of BECN1 overexpression on the expression of cell proliferation, invasion and autophagy-related proteins were detected by Western blot. The expression of BECN1 mRNA in BECN1 transfection group was significantly higher than that in control group and negative transfection group (P<0.05); the inhibition rate of cell proliferation and the expression of autophagy-related proteins Beclin1, Atg5 and invasion-related protein E-cadherin in BECN1 transfection group were significantly higher than those in control group and negative transfection group; the colony formation rate, invasion number and the expression of proliferation-related proteins CyclinD1, β-catenin and invasion-related protein N-cadherin were significantly lower than those in control group and negative transfection group (P<0.05). Overexpression of BECN1 can inhibit the proliferation and invasion of human MM cells RPMI-8226, which may be a potential research target of MM.

Mechanism of Targeting the Hedgehog Signaling Pathway against Chemotherapeutic Resistance in Multiple Myeloma.

Objective The aim of this study was to explore the relationship between the Hedgehog signaling pathway and drug resistance in multiple myeloma. Methods The human myeloma cell line RPMI 8266 was taken as the research object. An azithromycin (AZM)-resistant cell line RPMI 8226/R was constructed, and GENT61 was used to block the Hedgehog signaling pathway. Cells were rolled into RPMI 8226/S (S group), RPMI 8226/R (R group), GENT61+RPMI 8226/S (GENT61+S group), and GENT61+RPMI 8226/R (GENT61+R group). The proliferation of cells in each group was assessed, and the expression of patched homolog 1 (PTCH1), zinc finger-containing transcription factors 1 (GLI1), GLI2, hair-division associated enhancer 1 (Hes1), and sonic hedgehog factor (SHH) in each group was detected. Interleukin (IL)-6 and vascular endothelial growth factor (VEGF) were measured. Results Compared with the S group, the expression levels of PTCH1, GLI2, Hes1, and SHH and the contents of IL-6 and VEGF in the R group were greatly increased, while the expression level of GLI1 was notably decreased (P < 0.05). Compared with the R group, the GENT61+R group greatly increased cell proliferation inhibition. However, the expression levels of PTCH1, GLI2, Hes1, and SHH, and the contents of IL-6 and VEGF were notably decreased, while GLI1 expression levels were greatly increased (P < 0.05). Conclusion AZM-resistant multiple myeloma was closely associated with the Hedgehog signaling pathway activation, and blocking the Hedgehog signaling pathway can be used as a therapeutic target to improve drug resistance in multiple myeloma.

Selective purging of human multiple myeloma cells from peripheral blood mononuclear cells: a preliminary study.

BackgroundHigh-dose chemotherapy followed by autologous peripheral blood stem-cell transplantation are standards of therapy for patients diagnosed with multiple myeloma. The purging process to remove contaminating residual myeloma cells could improve patient outcomes. In this study, a purging method of human multiple myeloma cells from peripheral blood mononuclear cells was evaluated.Materials and methodsThe human myeloma cell line RPMI-8226 (Seoul, Korea) was treated with bortezomib (Selleck Chemicals, Houston, TX, USA) or lenalidomide (Sigma Aldrich, St. Louis, MO, USA). The mixture of the human peripheral blood mononuclear cell line PCS-800-011 (ATCC, USA) and RPMI-8226 was treated with bortezomib or lenalidomide for 24 hours. The efficacy of purging myeloma cells was evaluated by 8-color flow cytometric analysis.ResultsThe cytotoxicity of bortezomib (10–160 nmol/L) and lenalidomide (200–3,200 nmol/L) was investigated on RPMI-8226 myeloma cell line. A 24-hour incubation with bortezomib at 10, 20, 40, 80, 160 nmol/L induced 5.45%±0.07%, 47.15%±1.20%, 57.15%±0.21%, 72.35%±0.07%, and 84.75%±0.49% growth inhibition in RPMI-8226 cells, respectively. A 24-hour incubation with lenalidomide at 200, 400, 800, 1,600, and 3,200 nmol/L induced 5.45%±0.07%, 7.55%±0.07%, 9.75%±0.35%, 18.25%±0.21%, and 39.75%±0.78% growth inhibition in RPMI-8226 cells, respectively. Bortezomib (40 nmol/L, 24 hours) and lenalidomide (3,200 nmol/L, 24 hours) effectively removed CD38+CD138+ cells from peripheral mononuclear cells. RPMI-8226 cells showed abberant phenotype CD56+/CD45−.ConclusionThe results of the present study demonstrated that the bortezomib and lenalidomide treatment in RPMI-8226 multiple myeloma cells effectively removed the contaminated plasma cells.

Bortezomib could down-regulate the expression of RANKL, inhibit cell proliferation and induce cell apoptosis in the human myeloma cell line RPMI 8226 by activating casepase-3.

In spite of bortezomib being developed and demonstrated as a safe drug therapy for multiple myeloma (MM), the role of bortezomib-induced receptor activator of nuclear factor (NF)-κB ligand (RANKL) in the MM cell lines remains to be understood. Thus the present study aims to explore the impact of bortezomib on RANKL expression, cell growth and apoptosis in human myeloma cell line RPMI 8226. Four experiment groups were set according to different concentrations of bortezomib, namely blank group (treated with DMEM solution free of other drugs), low-dose group (treated with 10 nmol/L bortezomib), middle-dose group (treated with 20 nmol/L bortezomib) and high-dose group (treated with 40 nmol/L bortezomib). Western blotting was adopted to detect RANKL protein expression. MTT assay was performed to detect cell proliferation. Flow cytometry was used to analyze cell cycle and apoptosis. Spectrophotometry was applied to determine caspases-3 activity. Compared with the blank group, the RANKL protein expression, cell number at the S stage was reduced while cell inhibition rate, cell apoptosis rate and caspase-3 activity enhanced remarkably in the low-dose, middle-dose and high-dose groups with dose-dependent manner. Compared with those treated with bortezomib (20 nmol/L and 40 nmol/L) for 6 h, the RANKL expression was down-regulated, cell inhibition rate was increased, cells at the S stage were reduced, cell apoptosis rate was enhanced, and caspase-3 activity elevated in the RPMI 8226 cells as treated with bortezomib for 24 h, with a dose- and time-dependent manner. Bortezomib could reduce the RANKL expression, inhibit cell proliferation and activate caspase-3 activity to induce cell apoptosis in RPMI 8266 cells.

Potent in vitro and in vivo effects of polyclonal anti-human-myeloma globulins.

IntroductionMultiple myeloma is still incurable in most cases. Polyclonal anti T lymphocyte globulins (ATG) have been reported to kill human myeloma cells in vitro and in mouse models.MethodsAnti-human-myeloma globulins (AMG) were produced by immunizing rabbits with human myeloma cell lines RPMI-8226 (AMG-8226) or KMS-12-BM (AMG-12-BM). Cytotoxicity of the polyclonal antibodies was analyzed in vitro and in a xenograft NOD-SCID mouse model.ResultsBoth AMG had stronger cytotoxicity against myeloma cells compared to ATG. In primary T cells, AMG-8226 showed greater complement-dependent cytotoxicity (CDC) than ATG, whereas complement-independent cytotoxicity did not differ. Effects on non-hematopoietic cell lines were also similar. Competitive blocking assays revealed fourfold more antibodies against CD38 in AMG-8226 compared to ATG. Low concentrations of AMG-8226 and ATG increased ADCC. At higher concentrations, ATG inhibited ADCC more potently than AMG-8226. Combinations of ATG and AMG-8226 with melphalan or bortezomib showed additive to synergistic cytotoxicity on myeloma cells. The cytotoxic effects of AMG and ATG were confirmed in the xenograft NOD-SCID mouse model.ConclusionOur data show more potent antimyeloma effects of AMG compared to ATG. These results lay the ground for the development of polyclonal antibodies for the treatment of multiple myeloma.

Cinnamon extract exhibits potent anti-proliferative activity by modulating angiogenesis and cyclooxygenase in myeloma cells

Cinnamon is one of the most widely used herbal medicines with diverse bioactive effects. However, there is no report in regard to the potential anti-proliferative effects of cinnamon on myeloma cells. In this study, the authors investigated the anti-proliferative potential of cinnamon bark powder extract (CBPE) on myeloma cells specifically focusing on its anti-angiogenic and anti-inflammatory properties. The authors observed inhibition of myeloma cell proliferation by CBPE along with anti-inflammatory and anti-angiogenic effects in a human myeloma cell line RPMI 8226. After 24h of treatment, CBPE caused approximately 50% inhibition of cell growth in RPMI 8226 cells at a concentration of 72μg/mL (IC50), compared with the untreated controls. CBPE treatment strongly inhibited expression of angiogenic factors and cyclooxygenase at mRNA as well as at protein level in a time-dependent manner. Treatment with the CBPE resulted in cell cycle arrest in the G0/G1 phase in a time-dependent manner. CBPE besides altering growth kinetics of cells, induces DNA fragmentation resulting in apoptosis. In the treated group, DNA fragmentation increased in a time dependent manner with maximum intensity of labeled nucleotides in cells treated for 72h as compared to 24h and 48h. In conclusion, the anticancer effects of cinnamon extract appear to be mediated by multiple mechanisms. These include inhibition of angiogenesis, inflammation and induction of apoptosis in myeloma cells. CBPE could be considered as a promising candidate for restricting the growth of myeloma cells. Hence, CBPE could lead to the development of an effective anti-cancer agent or herbal medicine for the treatment of MM.

Thromboxane A2 Receptor Inhibition Suppresses Multiple Myeloma Cell Proliferation by Inducing p38/c-Jun N-terminal Kinase (JNK) Mitogen-activated Protein Kinase (MAPK)-mediated G2/M Progression Delay and Cell Apoptosis

Multiple myeloma (MM) is a plasma cell malignancy without effective therapeutics. Thromboxane A2 (TxA2)/TxA2 receptor (T prostanoid receptor (TP)) modulates the progression of some carcinomas; however, its effects on MM cell proliferation remain unclear. In this study, we evaluated cyclooxygenase (COX) enzymes and downstream prostaglandin profiles in human myeloma cell lines RPMI-8226 and U-266 and analyzed the effects of COX-1/-2 inhibitors SC-560 and NS-398 on MM cell proliferation. Our observations implicate COX-2 as being involved in modulating cell proliferation. We further incubated MM cells with prostaglandin receptor antagonists or agonists and found that only the TP antagonist, SQ29548, suppressed MM cell proliferation. TP silencing and the TP agonist, U46619, further confirmed this finding. Moreover, SQ29548 and TP silencing promoted MM cell G2/M phase delay accompanied by reducing cyclin B1/cyclin-dependent kinase-1 (CDK1) mRNA and protein expression. Notably, cyclin B1 overexpression rescued MM cells from G2/M arrest. We also found that the TP agonist activated JNK and p38 MAPK phosphorylation, and inhibitors of JNK and p38 MAPK depressed U46619-induced proliferation and cyclin B1/CDK1 protein expression. In addition, SQ29548 and TP silencing led to the MM cell apoptotic rate increasing with improving caspase 3 activity. The knockdown of caspase 3 reversed the apoptotic rate. Taken together, our results suggest that TxA2/TP promotes MM cell proliferation by reducing cell delay at G2/M phase via elevating p38 MAPK/JNK-mediated cyclin B1/CDK1 expression and hindering cell apoptosis. The TP inhibitor has potential as a novel agent to target kinase cascades for MM therapy.

Synthesis and Evaluation of 2-Alkylthio-4-(N-substituted sulfonamide)pyrimidine Hydroxamic Acids as Anti-myeloma Agents.

A series of pyrimidine hydroxamic acids with a sulfide substituent at the second position and a sulfonamide substituent at the fourth position have been synthesized and evaluated for their activity against human myeloma cell line RPMI 8226. Several compounds exhibited significant anti-cancer potency. It was found that representative compound 6a selectively killed cancerous but not normal cells. Moreover, compound 6a was effective in causing apoptosis in RPMI 8226 cells and exhibited promising HDAC-inhibitory activities.

Engagement of CD99 Reduces AP-1 Activity by Inducing BATF in the Human Multiple Myeloma Cell Line RPMI8226.

CD99 signaling is crucial to a diverse range of biological functions including survival and proliferation. CD99 engagement is reported to augment activator protein-1 (AP-1) activity through mitogen-activated protein (MAP) kinase pathways in a T-lymphoblastic lymphoma cell line Jurkat and in breast cancer cell lines. In this study, we report that CD99 differentially regulated AP-1 activity in the human myeloma cell line RPMI8226. CD99 was highly expressed and the CD99 engagement led to activation of the MAP kinases, but suppressed AP-1 activity by inducing the expression of basic leucine zipper transcription factor, ATF-like (BATF), a negative regulator of AP-1 in RPMI8226 cells. By contrast, engagement of CD99 enhanced AP-1 activity and did not change the BATF expression in Jurkat cells. CD99 engagement reduced the proliferation of RPMI8226 cells and expression of cyclin 1 and 3. Overall, these results suggest novel CD99 functions in RPMI8226 cells.

Autophagy is involved in doxorubicin induced resistance of human myeloma cell line RPMI8226

To explore the role of autophagy in doxorubicin (DOX)-induced resistance of human myeloma cell line RPMI8226. We established doxorubicin induced resistant subline of myeloma cell line RPMI8226/DOX by drug concentration step-elevation method. Resistant index of DOX was measured by MTT assay. Autophagy of myeloma cell lines RPMI8226/s and RPMI8226/DOX was detected by transmission electron microscopy, immunofluorescence (LC3-FITC) and western blot respectively. Apoptosis of RPMI8226/DOX cells induced by DOX combined with autophagic inhibitor hydroxychloroquine or 3-MA was identified by AnnexinV-FITC/PI double fluorescence dyeing. Resistant index of RPMI8226/DOX was approximately 10.8 fold of that of RPMI8226/S. Electron microscopic studies revealed that most of RPMI8226/DOX cells displayed viable attributes and contained numerous autophagic vacuoles. Fluorescent images of RPMI8226/DOX cells showed a punctuate distribution in LC3 protein. Increased LC3-II protein in RPMI8226/DOX cells was determined by immunoblotting. There were no differences among 8 μmol/L HCQ (3.24±1.08)%, 10 mmol/L 3-MA (2.81±0.80)% or control \[(2.12±1.24)%\] (P>0.05) in terms of AnnexinV-FITC/PI double fluorescence dyeing; Compared with apoptosis of (9.75±2.15)%, (24.36±2.16)% and (40.51±3.14)% of RPMI8226/DOX cells under 2, 4 and 6 μmol/L DOX, apoptosis increased significantly after 24 h incubation under 2, 4 and 6 μmol/L DOX combined with 8 μmol/L HCQ as of \[(16.56±1.89)%, (36.44±2.91)% and (62.68±3.75)%, respectively\], or under 2, 4 and 6 μmol/L DOX combined with 10 mmol/L 3-MA as of \[(15.47±1.85)%, (39.28±3.06)% and (55.46±4.07)%, respectively\] (P<0.05). Autophagy was involved in doxorubicin-induced resistance of myeloma cell line RPMI8226, DOX resistance in myeloma cells was reversed partly by autophagy inhibitor hydroxychloroquine or 3-MA, and autophagy may be one of mechanisms for drug resistance.

Identification of brain-derived neurotrophic factor as a novel angiogenic protein in multiple myeloma

Patients with multiple myeloma (MM) have increased bone marrow angiogenesis, but the angiogenic properties of myeloma cells and the mechanism of MM-induced angiogenesis have not been completely clarified. The brain-derived neurotrophic factor (BDNF) and its high-affinity receptor, TrkB, have been identified as critical factors in the regulation of vessel formation. In this study, we demonstrate that patients with MM had increased BDNF and vascular endothelial growth factor (VEGF) in their peripheral blood. We also found in particular that a decreased BDNF level was correlated with the remission of MM. BDNF was expressed by the human myeloma cell line RPMI8226 and primary myeloma cells, and TrkB was expressed by human umbilical vein endothelial cells (HUVEC) at the protein levels. In a coculture system, we observed that both RPMI8226 cells and primary myeloma cells induced the migration and formation of a net-like structure in HUVEC. The anti-BDNF monoclonal antibody significantly but partially restrained the angiogenesis effect of MM cells. Moreover, in an experimental model of angiogenesis in vivo, BDNF and VEGF significantly promoted vessel formation in Matrigel plug compared to the control. These effects were also blocked by anti-BDNF monoclonal antibody. Finally, our in vitro results were supported by the in vivo finding in human myeloma xenograft NOD/SCID models. Anti-BDNF mAb treatment resulted in inhibition of tumor growth, decreased vessel density, and tumor necrosis. Our study suggested that the BDNF/TrkB signaling pathway could be involved, at least in part, in MM-induced angiogenesis.

Phenyhexyl Isothiocyanate, a Novel Inhibitor of Histone Deacetylation and Methylation, Induce Growth Arrest and Apoptosis of Myeloma Cells.

Histone deacetylase (HDAC) inhibitors are emerging as a promising family of new agents in the therapy of hematologic malignancies. We have shown that phenyhexyl isothiocyanate(PHI) is a novel histone deacetylase inhibitor and can also modulate histone methylation in leukemia cells. In this study we investigated the effect of PHI on human myeloma cell line RPMI8226 in vitro.We have observed that cell proliferation was inhibited by PHI in a dose and time dependent manner. Cell cycle analysis indicated an arrest in G0/G1 phase, and significant apoptosis was detected in PHI treated RPMI8226 cells. The accumulation of P21 and reduced Levels of PCNA were detected. We also examined the effect of PHI on vascular endothelial growth factor (VEGF) production by the myeloma cells. Treatment with 20μM PHI for 24hrs led to a decrease of VEGF concentration by 50% of that secreted by the control cells. VEGF production further decreased to 25% when the cells were exposed to PHI for 48hrs. These data suggest that myeloma cells are sensitive to the novel HDAC inhibitor, and PHI may become a novel agent in multiple myeloma therapy. [Display omitted]

Cycloxygenase-2 (COX-2) Expression Is More in Clonal Plasma Cells.

Multiple myeloma is characterised by deregulated cytokine network with secretion of inflammatory cytokines. Recent studies have showed the independent poor prognostic value of COX-2 expression in myeloma. We have here studied the COX-2 expression in plasma cells from patients with myeloma, monoclonal gammopathy of undetermined significance (MGUS), Waldenstrom's Macroglobulinemia (WM) and compared with the COX-2 expression by normal plasma cells.Methods:Our study included bone marrow samples from 34 patients (Lymphoma: 15; myeloma: 10; MGUS: 7; WM: 1; Amyloidosis: 1). Mononuclear cells were harvested from the bone marrow samples by density gradient sedimentation using Lymphoprep TM from Axis-Shield, Norway. Mononuclear cells were stained with PE conjugated CD 38 (BD Bioscience) and APC conjugated CD138 (BD Bioscience). FITC conjugated IgG against human COX-2 (Cayman Chemical) was used to study the expression of cycloxygenase-2 following permeabilization with fix and perm kit (Caltag). Flow cytometry was performed on a Becton Dickinson FACS vantage with appropriate isotype controls. The colorectal cell line HT- 29 and human myeloma cell line RPMI 8226 were used as positive controls and the flow results are validated by western blotting and Prostaglandin E2 EIA assay (Cayman Chemical).Results:HT-29 cell line showed a peak fluorescence of 58 for COX-2, where as RPMI 8226 cell line revealed peak fluorescence of 141. Median plasma cell count in bone marrow of patients with MGUS was 2 %( range 2–6%). Plasma cells from MGUS patients revealed median peak fluorescence for COX-2 was 37(range: 9–74). Median plasma cell count in bone marrow of patients with myeloma was 25% (range: 10–59%). Median peak fluorescence for COX-2 in plasma cells from patients with myeloma was 24(range: 10–85). Median plasma cell count in bone marrow of patients with lymphoma was 1 %( range1–4%). Median peak fluorescence for COX-2 in plasma cells from patients with lymphoma was 11(range: 2–38).Conclusions:Our study reveals COX-2 expression is more in clonal plasma cells as compared to normal plasma cells. Studies are needed to ascertain the role of COX-2 in oncogenesis in myeloma and to discover how COX-2 expression leads to poor outcome in patients with myeloma. This information may lead to the therapeutic role of selective COX-2 inhibitors in the therapy of myeloma.

An Experimental Study of Gene Expressing Profile in Human Myeloma Cell Line RPMI8226 Induced by Thalidomide.

Multiple myeloma (MM) is one of malignant plasmacyte neoplasm in hematopietic system. Although nearly 70% patients of myeloma response to chemotherapy, but repeated therapies will induce drug resistance soon and lead to refractory or relapsed myelomas. In recent years, thalidomide is used to treat relapsed and refractory myeloma with satisfied effects and overall therapeutic rate with thalidomide is about 60%. Furthermore, the adverse effects of thalidomide is slight without myelosuppression, hepatotoxicity and renal toxicity. So thalidomide is likely to be a prospective antitumor agent. However, the mechanism of antitumor activity of the agent is still not clear. DNA microarray technology has provided us a very useful method to detect simultaneously the expression pattern of thousands of genes for investigating the molecular antitumor mechanism of thalidomide.To investigate the genes expression profiles of multiple myeloma cell line RPMI8226 treated with thalidomide, cDNA microarray were used to detect thousands of gene expression in a chip. Two cDNA probes were prepared through reverse transcription from mRNA of RPMI8226 cells with or without thalidomide treatment. The probes were labled with Cy3 and Cy5 fluorescence dyes individually,hybridized with cDNA microarray representing 1152 different human genes. Fluorescent intensity were scanned and screened by means of differential analysis between two gene expression profiles. After 72 hrs' co-culture of RPMI8226 cells and thalidomide in 100μmol/L concentration, the expression of 18 genes were up-regulated and 4 genes were down-regulated. The up-regulated genes(GeneBank Accession) included: 1) protein synthesis-related genes:NM_004184(WARS), NM_ 003335(UBE1L); 2) immune-related protein:NM_001465(FYB), NM_004341 (CAD), NM_002388(MCM3); 3) matabolism relatedgenes: BC008861, NM_001640(APEH), NM_020040(TUBB4Q), NM_001033(RRM1), NM_ 001976(ENO3), NM_003330 (TXNRD1); 4) cell signals and transducing proteins: NM_005167(ARHC), NM_001465(FYB); 5) other genes: NM_ 017432(PTOV1), NM_003564 (TAGLN2), NM_005053(RAD23A), NM_ 001033(RRM1), AK025983, NM_015685 (CLONE24904), NM_033158 (HYAL2). The down-regulated genes includes: 1) protein synthesis-related genes: NM_000994(RPL32); 2) immune-related proteins: NM_001551 (IGBP1); 3) other genes: NM_002983(SCYA3), NM_002421(MMP1).These genes were involved in preotein synthesis and degradation, cell signal transduction, cytoskeletal movement immune cell matabolism and regulation of anti-oncogene. WARS gene encoding tryptophanyl-tRNA synthetase was up-regulated by thalidomide, while MMP1 gene encoding matrix metalloprotein 1 was down-regulated. They may be related to the inhibition of angiogenesis caused by thalidomide. SCYA3 gene encoding macrophage inflammatory protein-1alpha was down-regulated by thalidomide, as well as IGBP1 gene which encoding immunoglobulin binding protein 1. They may play a role in the inhibition of cell proliferation caused by thalidomide. TUBB4Q gene encoding tubulinβ4, UBE1L gene encoding ubiquitin- activating enzyme E1-like protein and TXNRD1 gene encoding thioredoxin reductase 1 were up-regulated by thalidomide. They may involve in apoptosis of RPMI8226 cells induced by thalidomide. FYB gene encoding Fyn-binding protein was up regulated by thalidomide. The elevated expression of this gene may play a role in the killing of RPMI8226 cells by thalidomide.

Identification and Clinical Relevance of Receptor Activator of Nuclear Factor κB Ligand Expression of Myeloma Cells

Identification and Clinical Relevance of Receptor Activator of Nuclear Factor κB Ligand Expression of Myeloma Cells

Radiation-induced apoptosis in human myeloma cell line increases BCL-2/BAX dimer formation and does not result in BAX/BAX homodimerization.

A popular model of BCL-2 and BAX involvement in apoptosis suggests that upon apoptosis induction cytosolic BAX translocates to the mitochondria, where it displays the pro-apoptotic function, which involves its homodimerization. BCL-2 exerts anti-apoptotic function by forming heterodimers with BAX, thus neutralizing the pro-apoptotic activity of the latter. We have shown that irradiation of the human myeloma cell line RPMI-8226 induced apoptosis as determined by DNA degradation, cytochrome c release into cytoplasm and BCL-2 caspase-mediated cleavage. BCL-2 protein was present only in the membrane fraction, whereas BAX was found both in cytosol and membranes isolated from non-irradiated cells. Radiation induced moderate redistribution of BAX from cytosol to membranes with a concomitant increase in BCL-2/BAX heterodimer formation. Rapid and transient BCL-2 phosphorylation in membrane fractions of irradiated cells did not affect BCL-2/BAX heterodimerization. We failed to detect any BAX/BAX homodimers in apoptotic cells. Our findings show that in irradiated RPMI-8226 cells the formation of BCL-2/BAX heterodimers correlates with apoptosis. We conclude that BCL-2/BAX heterodimers are negative regulators of death protection, and our data agree with those who propose that BCL-2 does not require BAX to exert its survival function.

Induction of apoptosis by all-trans retinoic acid in the human myeloma cell line RPMI 8226 and negative regulation of some of its typical morphological features by dexamethasone.

We investigated the effects of all-trans retinoic acid (RA) and dexamethasone (Dex) on the in vitro growth of the human myeloma cell line RPMI 8226. RA inhibited RPMI 8226 cell growth by both antiproliferative effect and induction of apoptosis. Typical morphological and biochemical characteristics of apoptosis including chromatin condensation, apoptotic bodies formation and internucleosomal DNA cleavage were detected after 4 days of treatment with 1 microM RA. In situ TUNEL assay demonstrated that DNA cleavage preceded chromatin condensation. The expression of tissue transglutaminase (tTG), an enzyme proposed to play a role in apoptosis was induced with RA, as shown by both enzymatic assay and in situ immunofluorescence detection. Dex, when used alone, had no effect on cell growth and apoptosis. When combined to RA, Dex did not interfere with the RA-dependent inhibition of cell proliferation, but unexpectedly inhibited both quantitatively and qualitatively several morphological and biochemical features of the apoptosis induced by RA. Dex did not affect RA-induced DNA breaks formation but impeded the progression of chromatin condensation and the formation of apoptotic bodies. Interestingly, Dex also inhibited the RA-dependent induction of tTG. RU486, a glucocorticoid antagonist, counteracted all Dex effects. Taken together these data demonstrate that key cytoplasmic and nuclear events occurring during apoptosis are differentially regulated by RA and Dex in myeloma cell line RPMI 8226.

Evidence for the Involvement of Both Retinoic Acid Receptor- and Retinoic X Receptor-Dependent Signaling Pathways in the Induction of Tissue Transglutaminase and Apoptosis in the Human Myeloma Cell Line RPMI 8226

AbstractIn this study, we show that both all-trans-retinoic acid (atRA) and 9-cis-retinoic acid (9-cis-RA) are potent inducers of tissue transglutaminase (TGase II), an enzyme involved in apoptosis, at the level of both enzyme activity and mRNA in the human myeloma cell line RPMI 8226. RPMI 8226 cells were shown to express mRNAs for all the retinoid receptors subtypes, ie, RARα, RARβ, RARγ, RXRα, RXRβ, and RXRγ. To identify which of these receptors are involved in regulating TGase II expression, several receptor-selective synthetic retinoids were used. Neither CD367, a very potent retinoid that selectively binds and activates receptors of the RAR family, nor CD2425, an RXR-selective agonist, induced TGase II when used alone. However, combination of CD367 and CD2425 resulted in nearly full induction of the enzyme. Moreover, when used in combination with atRA, CD367 partially inhibited the atRA-dependent induction of TGase II, whereas CD2425 enhanced it. The effects of Am 580, CD417, and CD437, three synthetic retinoids selective for the RARs subtypes RARα, RARβ, and RARγ, respectively, were also investigated. None of these compounds was able to induce TGase II when used alone; however, the combination of each of them with CD2425 resulted in strong induction of the enzyme activity, reaching 30% to 50% of the values obtained in the presence of retinoic acid and suggesting functional redundancy between the RAR subtypes. Finally, treatment with atRA or the combination of CD367 and CD2425, but not with CD367 or CD2425 alone, was also shown to trigger apoptosis in RPMI 8226 cells, with prominent accumulation of TGase II immunoreactivity in apoptotic cells. Taken together these data suggest that the induction of TGase II expression and apoptosis in the RPMI 8226 myeloma cell line required ligand-dependent activation of both the RAR and RXR receptors.

Evidence for the Involvement of Both Retinoic Acid Receptor- and Retinoic X Receptor-Dependent Signaling Pathways in the Induction of Tissue Transglutaminase and Apoptosis in the Human Myeloma Cell Line RPMI 8226

In this study, we show that both all-trans-retinoic acid (atRA) and 9-cis-retinoic acid (9-cis-RA) are potent inducers of tissue transglutaminase (TGase II), an enzyme involved in apoptosis, at the level of both enzyme activity and mRNA in the human myeloma cell line RPMI 8226. RPMI 8226 cells were shown to express mRNAs for all the retinoid receptors subtypes, ie, RARα, RARβ, RARγ, RXRα, RXRβ, and RXRγ. To identify which of these receptors are involved in regulating TGase II expression, several receptor-selective synthetic retinoids were used. Neither CD367, a very potent retinoid that selectively binds and activates receptors of the RAR family, nor CD2425, an RXR-selective agonist, induced TGase II when used alone. However, combination of CD367 and CD2425 resulted in nearly full induction of the enzyme. Moreover, when used in combination with atRA, CD367 partially inhibited the atRA-dependent induction of TGase II, whereas CD2425 enhanced it. The effects of Am 580, CD417, and CD437, three synthetic retinoids selective for the RARs subtypes RARα, RARβ, and RARγ, respectively, were also investigated. None of these compounds was able to induce TGase II when used alone; however, the combination of each of them with CD2425 resulted in strong induction of the enzyme activity, reaching 30% to 50% of the values obtained in the presence of retinoic acid and suggesting functional redundancy between the RAR subtypes. Finally, treatment with atRA or the combination of CD367 and CD2425, but not with CD367 or CD2425 alone, was also shown to trigger apoptosis in RPMI 8226 cells, with prominent accumulation of TGase II immunoreactivity in apoptotic cells. Taken together these data suggest that the induction of TGase II expression and apoptosis in the RPMI 8226 myeloma cell line required ligand-dependent activation of both the RAR and RXR receptors.

IFN-γ Upregulates Anti-Apoptotic Gene Expression and Inhibits Apoptosis in IL-3-Dependent Hematopoietic Cells

IFN-γ is a cytokine which functions in a wide range of biological activities by inducing a number of early and delayed genes. In murine IL-3-dependent cell lines BAF-B03 and 32D, IFN-γ upregulatedbag-1 andbcl-xLgene expression. These cells revealed prolonged cell survival against IL-3-deprivation by IFN-γ stimulation. In contrast, human myeloma cell line RPMI8226, despite expression of IFN-γ receptor, showed neither induction of their expressions nor prolonged cell survival against serum starvation-induced apoptosis by IFN-γ stimulation. Gene-transfer-mediated overexpression of BAG-1 protein in BAF-B03 cells led to prolonged cell survival against IL-3-deprived apoptosis compared with control BAF-B03 transfectants, indicating that levels of BAG-1 expression are crucial for cell survival in BAF-B03 cells. Taken together, these studies suggest that induction of anti-apoptotic gene expression is a crucial factor for the anti-apoptotic function of IFN-γ in IL-3-dependent immature hematopoietic cells.