Lacking of Aiolos accelerates pre-mature B cell apoptosis mediated by BCR signaling through elevation in cytochrome c release

Phosphoproteomic analysis of lung tissue from patients with pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a rare disorder associated with high morbidity and mortality despite currently available treatments. We compared the phosphoproteome of lung tissue from subjects with idiopathic PAH (iPAH) obtained at the time of lung transplant with control lung tissue. The mass spectrometry-based analysis found 60,428 phosphopeptide features from which 6622 proteins were identified. Within the subset of identified proteins there were 1234 phosphopeptides with q < 0.05, many of which are involved in immune regulation, angiogenesis, and cell proliferation. Most notably there was a marked relative increase in phosphorylated (S378) IKZF3 (Aiolos), a zinc finger transcription factor that plays a key role in lymphocyte regulation. In vitro phosphorylation assays indicated that GSK3 alpha and/or GSK3 beta could phosphorylate IKZF3 at S378. Western blot analysis demonstrated increased pIKZF3 in iPAH lungs compared to controls. Immunohistochemistry demonstrated phosphorylated IKZF3 in lymphocytes surrounding severely hypertrophied pulmonary arterioles. In situ hybrization showed gene expression in lymphocyte aggregates in PAH samples. A BCL2 reporter assay showed that IKZF3 increased BCL2 promoter activity and demonstrated the potential role of phosphorylation of IKZF3 in the regulation of BCL mediated transcription. Kinase network analysis demonstrated potentially important regulatory roles of casein kinase 2, cyclin-dependent kinase 1 (CDK1), mitogen-associated protein kinases (MAPKs), and protein kinases (PRKs) in iPAH. Bioinformatic analysis demonstrated enrichment of RhoGTPase signaling and the potential importance of cGMP-dependent protein kinase 1 (PRKG). In conclusion, this unbiased phosphoproteomic analysis demonstrated several novel targets regulated by kinase networks in iPAH, and reinforced the potential role of immune regulation in the pathogenesis of iPAH. The identified up- and down-regulated phosphoproteins have potential to serve as biomarkers for PAH and to provide new insights for therapeutic strategies.

Redox cycling of copper by coumarin-di(2-picolyl)amine hybrid molecule leads to ROS-mediated modulation of redox scavengers, DNA damage and cell death in diethylnitrosamine induced hepatocellular carcinoma

Targeted therapy is a new strategy for cancer treatment that targets chemical entities specific to cancer cells than normal ones. One of the features associated with malignancy is the elevated copper which plays an integral role in angiogenesis. Work is in progress in our lab to identify new copper chelators to target elevated copper under targeted therapy for the killing of cancer cells. Recently, a coumarin-based copper chelator, di(2-picolyl)amine-3(bromoacetyl)coumarin hybrid molecule (ligand-L) has been synthesized by us, and also studied its copper-dependent macromolecular damage response in copper overloaded lymphocytes. The present study investigates the anticancer activity of ligand-L and its mode of action in rat model of diethylnitrosamine (DEN) induced hepatocellular carcinoma. It has been found that liver tissue has a marked increase in copper levels in DEN induced hepatocellular carcinoma. Ex vivo results showed that ligand-L inhibited cell viability, induced reactive oxygen species (ROS) generation, DNA damage, loss of mitochondrial membrane potential and caspase-3 activation in isolated hepatocellular carcinoma cells (HCC). All these effects induced by ligand-L were abrogated by neocuproine and N-acetylcysteine (ROS scavenger). Further, ligand-L treatment of animals bearing hepatocellular carcinoma results in an increment in the cellular redox scavengers, lipid peroxidation and DNA breakage in malignant hepatocytes. In vivo studies using ligand-L also showed that ligand-L possesses anticancer properties as evidenced by improvement in liver marker enzymes and liver surface morphology, and reduced alpha-fetoprotein in the treated group compared to untreated cancer-induced group. Overall, this study suggests that copper-ligand-L interaction leads to ROS generation which caused DNA damage and apoptosis in malignant cells. This study provides enough support to establish ligand-L as a clinically relevant lead molecule for the treatment of different malignancies.

Paired box gene 5 isoforms A and B have different functions in transcriptional regulation of B cell development-related genes in immature B cells

The transcription factor paired box gene 5 (Pax5) is essential for B cell development. In this study, complementation analyses in Pax5-deficient DT40 cells showed that three Pax5 isoforms Pax5A, Pax5B and Pax5BΔEx8 (another spliced isoform of Pax5B lacking exon 8) exhibit distinct roles in transcriptional regulation of six B cell development-related genes (activation-induced cytidine deaminase, Aiolos, BTB and CNC homology 2, B cell lymphoma-6, early B cell factor 1, origin binding factor-1 genes), transcriptions of which are remarkably down-regulated by Pax5-deficiency. Moreover, ectopic expression study shows that these Pax5 isoforms may regulate themselves and each other at the transcriptional level.

Overexpression of Aiolos in Nalm-6 acute lymphoblastic leukaemia cells reduces apoptosis by suppressing phosphatase and tensin homologue deleted on chromosome 10 and activating the phosphatidylinositol-3-kinase/Akt signalling pathway

The aim of the present study was to elucidate the molecular mechanism of Aiolos in the regulation of B‑cell leukaemia. A lentiviral system was used for overexpression of the Aiolos gene in Nalm‑6 cells to determine the effects of Aiolos on proliferation, apoptosis and the cell cycle. The expression and activation of phosphatase and tensin homolog deleted on chromosome ten (PTEN) and Akt were also investigated. Upregulation of Aiolos inhibited cell growth and arrested an increased number of Nalm‑6 cells at the G0/G1 phase. The apoptotic cell quantities were also significantly lower in the Aiolos‑transfected Nalm‑6 cells. In addition, Aiolos overexpression downregulated PTEN, but increased the expression and phosphorylation of Akt in the Nalm‑6 cells. The Akt inhibitor, Akti‑1/2, reduced the percentage of viable Aiolos‑overexpressed Nalm‑6 cells, however, it had no effect on cell cycle arrest or proliferation. Aiolos upregulation in the Nalm‑6 cells inhibited cell proliferation, suppressed apoptosis and arrested the cell cycle at the G0/G1 phase. Aiolos improved the survival of Nalm‑6 cells via PTEN‑ and Akt‑dependent processes.

Protein kinase Cθ gene expression is oppositely regulated by GCN5 and EBF1 in immature B cells

In this study, we revealed that GCN5 and early B cell factor 1 (EBF1) participate in regulation of protein kinase Cθ (PKCθ) gene expression in an opposite manner in immature B cells. GCN5-deficiency in DT40 caused drastic down-regulation of transcription of PKCθ. In contrast, EBF1-deficiency brought about remarkable up-regulation of that of PKCθ, and re-expression of EBF1 dramatically suppressed transcription of PKCθ. Chromatin immunoprecipitation assay revealed that GCN5 binds to the 5'-flanking region of the chicken PKCθ gene and acetylates histone H3, and EBF1 binds to the 5'-flanking region of the gene surrounding putative EBF1 binding motifs.

Overexpression of AIOLOS inhibits cell proliferation and suppresses apoptosis in Nalm-6 cells

The AIOLOS gene is important in the control of mature B-lymphocyte differentiation and proliferation. Previous research has shown that deregulated AIOLOS expression is associated with adult B-cell acute lymphoblastic leukemia (ALL) and chronic lymphocytic leukemia in human patients. However, the function of AIOLOS in childhood B-cell precursor (BCP)-ALL is not fully understood. In the present study, Nalm-6 cells were divided into three groups: the untransfected control (UT), the lentiviral vector control (Lenti-Mock) and the AIOLOS-overexpressing (Lenti-AIOLOS) group. Lenti-AIOLOS Nalm-6 cells were constructed by lentiviral transduction, followed by cell proliferation assay, cell-cycle analysis and apoptosis assay, to evaluate the effects of AIOLOS on proliferation, cell cycle distribution and apoptosis of Nalm-6 cells in vitro. Moreover, the expression levels of genes associated with apoptosis and the cell cycle, as well as the transcription factors IKZF1 and NF-κB, were investigated by quantitative reverse transcription-polymerase chain reaction and western blot analysis. The results showed that the proliferation of Nalm-6 cells in the Lenti-AIOLOS group was reduced by 16% on day 8 compared with cells in the UT group (P>0.05). The reduction peaked at 29% on day 10 (P<0.05). The percentage of Nalm-6 cells in the G0/G1 phase increased from 70.4 (UT) to 84.1% (Lenti-AIOLOS) (P<0.01), and the S-phase cells decreased from 20.3 (UT) to 11.7% (Lenti-AIOLOS) (P<0.01). Total apoptotic cells significantly decreased in AIOLOS-transfected Nalm-6 cells (10.75%) compared with those in the Lenti-Mock (17.00%) or UT group (19.05%) (P<0.01). In particular, the difference between the groups in the percentage of late apoptotic cells was significant (2.85 vs. 7.95%; P<0.01). In addition, overexpression of AIOLOS resulted in upregulation of BCL-2 and downregulation of CCND3, BAX, IKZF1 and NF-κB. No changes were detected on C-MYC and P27. Our findings indicate that lentivirus-mediated overexpression of AIOLOS in Nalm-6 cells could inhibit cell proliferation, suppress cell apoptosis and arrest the cell cycle at the G0/G1 phase in vitro.

GCN5 protects vertebrate cells against UV-irradiation via controlling gene expression of DNA polymerase η

By UV-irradiation, cells are subjected to DNA damage followed by mutation, cell death and/or carcinogenesis. DNA repair systems such as nucleotide excision repair (NER) and translesion DNA synthesis (TLS) protect cells against UV-irradiation. To understand the role of histone acetyltransferase GCN5 in regulation of DNA repair, we studied the sensitivity of GCN5-deficient DT40, GCN5(-/-), to various DNA-damaging agents including UV-irradiation, and effects of GCN5-deficiency on the expression of NER- and TLS-related genes. After UV-irradiation, cell death and DNA fragmentation of GCN5(-/-) were appreciably accelerated as compared with those of DT40. Interestingly, GCN5(-/-) showed a remarkable sensitivity to only UV-irradiation but not to other DNA-damaging agents tested. Semiquantitative RT-PCR showed that transcription of DNA polymerase η (POLH) gene whose deficiency is responsible for a variant form of xeroderma pigmentosum was drastically down-regulated in GCN5(-/-) (to ∼25%). In addition, ectopic expression of human POLH in GCN5(-/-) dramatically reversed the sensitivity to UV-irradiation of GCN5(-/-) to almost the same level of wild type DT40. Moreover, chromatin immunoprecipitation assay revealed that GCN5 binds to the chicken POLH gene 5'-flanking region that contains a typical CpG island and acetylates Lys-9 of histone H3, but not Lys-14 in vivo. These data suggest that GCN5 takes part in transcription regulation of POLH gene through alterations in the chromatin structure by direct interaction with its 5'-flanking region, and protects vertebrate cells against UV-induced DNA damage via controlling POLH gene expression.

EBF1 acts as a powerful repressor of Blimp-1 gene expression in immature B cells

The transcription factor, early B cell factor 1 (EBF1) with an atypical zinc-finger and helix-loop-helix motif, is essential for development and differentiation of lymphocytes. In mice, EBF1 is involved in the generation of pre-pro B cells (the first specified progenitors of B cells) from common lymphoid progenitors (CLPs) and transcription regulations of various genes involved in B cell-development, for instance, mb-1 and Pax5. During B lymphopoiesis, interestingly, EBF1 is detected throughout from CLPs to mature B cells. However, in immature B cells, the physiological role of EBF1 remains to be elucidated. Here, by analyzing EBF1-deficient DT40 cells, EBF1(-/-), generated by us, we show that EBF1-deficiency caused significant increases (to ∼800%) in both mRNA and protein levels of B lymphocyte-induced maturation protein-1 (Blimp-1), the master gene for plasma cell differentiation. In addition, both transcription and protein synthesis of Blimp-1 were remarkably down-regulated (to ∼20%) by re-expression (over-expression) of EBF1. Chromatin immunoprecipitation assay revealed that EBF1 binds to proximal 5'-upstream regions around two putative EBF1 binding motifs of the gene in vivo. These results suggest that EBF1 takes part in transcriptional regulations of the Blimp-1 gene in immature B cells, and may play a key role in B cell differentiation. This is the first report on a novel EBF1 function in immature B cells as a powerful repressor of Blimp-1 gene expression.

Possible involvement of Helios in controlling the immature B cell functions via transcriptional regulation of protein kinase Cs

The transcription factor Ikaros family consists of five zinc-finger proteins: Ikaros, Aiolos, Helios, Eos and Pegasus; these proteins except Pegasus are essential for development and differentiation of lymphocytes. However, in B lymphocytes, the physiological role of Helios remains to be elucidated yet, because its expression level is very low. Here, we generated the Helios-deficient DT40 cells, Helios (-/-), and showed that the Helios-deficiency caused significant increases in transcriptions of four protein kinase Cs (PKCs); PKC-δ, PKC-ε, PKC-η and PKC-ζ, whereas their expressions were drastically down-regulated in the Aiolos-deficient DT40 cells, Aiolos (-/-). In addition, Helios (-/-) was remarkably resistant against phorbol 12-myristate 13-acetate (PMA)/ionomycin treatment, which mimics the B cell receptor (BCR)-mediated stimulation. In the presence of PMA/ionomycin, their viability was remarkably higher than that of DT40, and their DNA fragmentation was less severe than that of DT40 in the opposite manner for the Aiolos-deficiency. The resistance against the PMA/ionomycin-induced apoptosis of Helios (-/-) was sensitive to Rottlerin but not to Go6976. In addition, the Helios-deficiency caused remarkable up-regulation of the Rottlerin-sensitive superoxide (O2 (-))-generating activity. These data suggest that Helios may contribute to the regulation of the BCR-mediated apoptosis and O2 (-)-generating activity, via transcriptional regulation of these four PKCs (especially PKC-δ) in immature B lymphocytes. Together with previous data, our findings may significantly help in the understanding of the B lymphocyte-specific expressions of PKC genes and molecular mechanisms of both the BCR-mediated apoptosis involved in negative selection and the O2 (-)-generating system in immature B lymphocytes.

Pathogenesis of myeloma

Multiple myeloma (MM) is a neoplasm of post-germinal center, terminally differentiated B cells. It is characterized by a multifocal proliferation of clonal, long-lived plasma cells within the bone marrow (BM) and associated skeletal destruction, serum monoclonal gammopathy, immune suppression, and end-organ sequelae. MM is preceded by an age-progressive premalignant condition termed monoclonal gammopathy of undetermined significance. Unlike the genomes of most hematological malignancies, and similar to those of solid-tissue neoplasms, MM genomes are typified by numerous structural and numerical chromosomal aberrations as well as mutations in a number of oncogenes and tumor-suppressor genes, some of which have been linked to disease pathogenesis and clinical behavior. Recent studies have also defined the importance of interactions between the MM cells and their BM microenvironment, dysregulation in signaling pathways and in a specialized subpopulation of cells within the tumor (termed myeloma cancer stem cells) for tumor cell growth and survival, and the development of resistance to therapy.

Deregulation of Aiolos expression in chronic lymphocytic leukemia is associated with epigenetic modifications

Chronic lymphocytic leukemia (CLL) is characterized by a clonal accumulation of mature neoplastic B cells that are resistant to apoptosis. Aiolos, a member of the Ikaros family of zinc-finger transcription factors, plays an important role in the control of mature B lymphocyte differentiation and maturation. In this study, we showed that Aiolos expression is up-regulated in B-CLL cells. This overexpression does not implicate isoform imbalance or disturb Aiolos subcellular localization. The chromatin status at the Aiolos promoter in CLL is defined by the demethylation of DNA and an enrichment of euchromatin associated histone markers, such as the dimethylation of the lysine 4 on histone H3. These epigenetic modifications should allow its upstream effectors, such as nuclear factor-κB, constitutively activated in CLL, to gain access to promoter, resulting up-regulation of Aiolos. To determine the consequences of Aiolos deregulation in CLL, we analyzed the effects of Aiolos overexpression or down-regulation on apoptosis. Aiolos is involved in cell survival by regulating the expression of some Bcl-2 family members. Our results strongly suggest that Aiolos deregulation by epigenetic modifications may be a hallmark of CLL.

Curcumin dramatically enhances retinoic acid-induced superoxide generating activity via accumulation of p47-phox and p67-phox proteins in U937 cells

The membrane bound cytochrome b558 composed of large gp91-phox and small p22-phox subunits, and cytosolic proteins p40-, p47- and p67-phox are important components of superoxide (O(2)(-))-generating system in phagocytes and B lymphocytes. A lack of this system in phagocytes is known to cause serious life-threatening infections. Here, we describe that curcumin, a polyphenol responsible for the yellow color of curry spice turmeric, dramatically activates the O(2)(-)-generating system during retinoic acid (RA)-induced differentiation of human monoblastic leukemia U937 cells to macrophage-like cells. When U937 cells were cultured in the presence of RA and curcumin, the O(2)(-)-generating activity increased more than 4-fold compared with that in the absence of the latter. Semiquantitative RT-PCR showed that co-treatment with RA and curcumin slightly enhanced gene expressions of the five components compared with those of the RA-treatment only. On the other hand, immunoblot analysis revealed that co-treatment with RA and curcumin caused remarkable accumulation of protein levels of p47-phox (to 7-fold) and p67-phox (to 4-fold) compared with those of the RA-treatment alone. These results suggested that curcumin dramatically enhances RA-induced O(2)(-)-generating activity via accumulation of cytosolic p47-phox and p67-phox proteins in U937 cells. Therefore, it should have the potential as an effective modifier in therapy of leukemia and/or as an immunopotentiator.