Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0079731 (B-cell lymphoma)
 16,671 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The bcl-6 proto-oncogene encodes a POZ/zinc finger transcriptional repressor expressed in germinal center (GC) B and T cells and required for GC formation and antibody affinity maturation. Deregulation of bcl-6 expression by chromosomal rearrangements and point mutations of the bcl-6 promoter region are implicated in the pathogenesis of B-cell lymphoma. The signals regulating bcl-6 expression are not known. Here we show that antigen receptor activation leads to BCL-6 phosphorylation by mitogen-activated protein kinase (MAPK). Phosphorylation, in turn, targets BCL-6 for rapid degradation by the ubiquitin/proteasome pathway. These findings indicate that BCL-6 expression is directly controlled by the antigen receptor via MAPK activation. This signaling pathway may be crucial for the control of B-cell differentiation and antibody response and has implications for the regulation of other POZ/zinc finger transcription factors in other tissues.
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PMID:Antigen receptor signaling induces MAP kinase-mediated phosphorylation and degradation of the BCL-6 transcription factor. 964

The molecular basis accounting for the peculiar clinical and biological features of hairy cell leukaemia (HCL) is currently unknown. Deregulation of cell cycle genes plays a significant role in oncogenesis and there is considerable evidence suggesting that Cdk inhibitors (Ckis) function as tumour suppressors. We and others have recently demonstrated low expression of Cki p27 in very aggressive neoplasms and high-grade lymphomas. To investigate whether HCL cases express normal p27 protein, as in other low-grade lymphomas with a low proliferation index, 58 cases of HCL were characterized using a sensitive biotin-streptavidin-immunoperoxidase technique and specific antibodies against p27. All HCL cases showed either no or very weak reactivity, in contrast to other types of low-grade B-cell lymphoma [22 cases of chronic lymphocytic leukaemia (CLL), 12 cases of gastric marginal B-cell lymphoma (MALT), 16 cases of follicular lymphomas and two cases of splenic marginal zone lymphomas]. To investigate the possible mechanism(s) accounting for the low p27 expression observed in hairy cells, multiple approaches were used. According to these molecular studies, low levels of p2 7 are not as a result of (1) increased ubiquitin-mediated degradation, (2) decreased levels of p27 transcription or (3) p27 somatic mutations and/or allelic loss. These findings suggest that low p27 protein expression in HCL may be achieved through post-transcriptional regulation. Finally, our data demonstrate that p27 expression in HCL does not correlate with either cell cycle progression or proliferation index, suggesting that low levels of p27 in hairy cells may be associated with their unique stage of B-cell differentiation and/or the activation of as yet unknown pathways.
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PMID:Low expression of p27 and low proliferation index do not correlate in hairy cell leukaemia. 1109 Dec 10

Members of the DTX (Deltex) family act as Notch signaling modifiers and may also regulate transcription through interactions with specific transcription factors. DTX proteins have a basic N terminus; a central proline-rich region; and a C-terminal RING finger domain, a motif often found in ubiquitin-protein isopeptide ligases (E3). Recently, we identified and characterized a unique diffuse large B-cell lymphoma risk-related gene named BAL (B aggressive lymphoma). Using a yeast two-hybrid screen for BAL-binding partners, we have now identified a novel protein termed BBAP (B-lymphoma- and BAL-associated protein). Although BBAP has a unique N terminus, the C-terminal region is highly homologous to that of DTX family members. Herein, we report that BBAP and the human family of DTX proteins (DTX1, DTX2, and DTX3) function as E3 ligases based on their capacity for self-ubiquitination. DTX family members homodimerize and heterodimerize in vivo, suggesting that physical interactions between various DTX family members modify E3 activity and/or substrate availability. Consistent with this idea, BBAP and DTX1 associate via their unique N termini, resulting in enhanced self-ubiquitination.
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PMID:The BAL-binding protein BBAP and related Deltex family members exhibit ubiquitin-protein isopeptide ligase activity. 1267 Sep 57

Recent advances in understanding the complex biology of the ubiquitin-proteasome pathway have led to the identification of many potentially 'drugable' targets within this pathway. One such inhibitor, bortezomib (formerly known as PS341), has proven to be an effective reversible inhibitor of the chymotryptic protease in the 26S proteasome. Proteasome inhibitors represent a new approach for the treatment of many forms of cancer, especially select hematological malignancies. The proteasome plays an important role in regulating the availability of different intracellular proteins. While only some of the consequences of inhibiting this activity are understood, a growing amount of data suggests that inhibition of the proteasome is associated with a remarkable panoply of different biological effects that include cell cycle arrest, apoptosis, changes in cell surface adhesion markers, and an increased sensitivity to standard chemotherapy and radiation therapy. Bortezomib was recently approved by the US FDA for the treatment of relapsed or refractory multiple myeloma. In addition, bortezomib has also shown encouraging results in the treatment of select types of non-Hodgkin lymphomas (NHLs). Ongoing phase II clinical trials in pretreated patients are exploring bortezomib in different histologies of NHLs and in combination with conventional chemotherapy. Preliminary data have shown interesting activity, especially in patients with follicular, marginal zone, and mantle cell lymphoma; in these populations, durable complete and partial remissions have been reported. The toxicity profile of this drug, coupled with its unusual mechanism of action, make it a potentially important agent warranting further preclinical and clinical attention. However, many unanswered questions remain regarding how best to employ bortezomib in the conventional treatment of lymphoma. The apparent lack of activity in different subtypes of lymphoma, such as small lymphocytic lymphoma/chronic lymphocytic leukemia and diffuse large B-cell lymphoma, as well as a lack of understanding about the best way to combine bortezomib with standard therapies for indolent NHLs, raises important questions regarding the mechanistic basis for its effects. We will undoubtedly need to understand these effects better in order to fully exploit the potential of this new class of drugs.
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PMID:Mechanistic rationale and clinical evidence for the efficacy of proteasome inhibitors against indolent and mantle cell lymphomas. 1657 48

The activation of T cells is tightly controlled by many positive and negative regulatory processes. This fine-tuning allows productive immunity to pathogens while minimizing the risk of autoimmunity. One negative regulatory mechanism is clonal anergy, which is a hyporesponsive state that occurs when T cells are activated through the T-cell antigen receptor in the absence of appropriate co-stimulatory signals. Recent studies have confirmed a crucial role for defective Ras activation in mediating this hyporesponsive state. Diminished Ras activation can, in part, be explained by the upregulated expression of diacylglycerol kinases (DGKs), which phosphorylate diacylglycerol and restrict Ras guanyl releasing protein 1 (RasGRP1)-dependent activation of Ras. Increased expression of DGKs is probably transcriptional and is accompanied by augmented expression of additional negative regulators, including the transcription factors early growth response (Egr) 2 and Egr3, and the E3 ubiquitin ligases known as gene related to anergy in lymphocytes (GRAIL) and Casitas B-cell lymphoma-b (Cbl-b). A model is emerging for how these factors are regulated to control T-cell responsiveness.
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PMID:Molecular regulation of T-cell anergy. 1817 97

S-phase kinase protein 2 (SKP2), an F-box protein, targets cell-cycle regulators including cycle-dependent kinase inhibitor p27KiP1 via ubiquitin-mediated degradation. SKP2 is frequently overexpressed in a variety of cancer cells and has been implicated in oncogenesis; however, its role in diffuse large B-cell lymphoma (DLBCL) has not been elucidated. Therefore, we investigated the role of SKP2 and its ubiquitin-proteasome pathway in a large series (301) of DLBCL patient samples and a panel of DLBCL cell lines. Using immunohistochemistry, SKP2 was detected in 41.6% of DLBCL tumours and was inversely associated with p27Kip1 protein level. The DLBCL subset with high SKP2 and low p27Kip1 showed a strong correlation with the proliferating index marker Ki-67 (p < 0.0001) and also with the germinal centre phenotype (p = 0.0147). Treatment of DLBCL cell lines with bortezomib or expression of SKP2-specific siRNA causes down-regulation of SKP2 and accumulation of p27Kip1, leading to suppression of growth by inducing apoptosis. Furthermore, treatment of DLBCL cells with bortezomib causes apoptosis via involving the mitochondrial pathway and activation of caspases. Finally, treatment of DLBCL cells with bortezomib down-regulated the expression of XIAP, cIAP1, and survivin. Altogether, these results suggest that SKP2 and the ubiquitin-proteasome pathway may be a potential target for therapeutic intervention in DLBCL.
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PMID:S-phase kinase protein 2 is an attractive therapeutic target in a subset of diffuse large B-cell lymphoma. 1885 May 83

Casitas B-cell lymphoma (Cbl)-family E3 ubiquitin ligases are negative regulators of tyrosine kinase signaling. Recent work has revealed a critical role of Cbl in the maintenance of hematopoietic stem cell (HSC) homeostasis, and mutations in CBL have been identified in myeloid malignancies. Here we show that, in contrast to Cbl or Cbl-b single-deficient mice, concurrent loss of Cbl and Cbl-b in the HSC compartment leads to an early-onset lethal myeloproliferative disease in mice. Cbl, Cbl-b double-deficient bone marrow cells are hypersensitive to cytokines, and show altered biochemical response to thrombopoietin. Thus, Cbl and Cbl-b play redundant but essential roles in HSC regulation, whose breakdown leads to hematological abnormalities that phenocopy crucial aspects of mutant Cbl-driven human myeloid malignancies.
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PMID:Rapidly fatal myeloproliferative disorders in mice with deletion of Casitas B-cell lymphoma (Cbl) and Cbl-b in hematopoietic stem cells. 2080 96

ALK-positive large B-cell lymphoma is a rare subtype of lymphoma, and most cases follow an aggressive clinical course with a poor prognosis. We examined an ALK-positive large B-cell lymphoma case showing an anti-ALK immunohistochemistry pattern distinct from those of 2 known ALK fusions, CLTC-ALK and NPM-ALK, for the presence of a novel ALK fusion; this led to the identification of SQSTM1-ALK. SQSTM1 is an ubiquitin binding protein that is associated with oxidative stress, cell signaling, and autophagy. We showed transforming activities of SQSTM1-ALK with a focus formation assay and an in vivo tumorigenicity assay using 3T3 fibroblasts infected with a recombinant retrovirus encoding SQSTM1-ALK. ALK-inhibitor therapies are promising for treating ALK-positive large B-cell lymphoma, especially for refractory cases. SQSTM1-ALK may be a rare fusion, but our data provide novel biological insights and serve as a key for the accurate diagnosis of this rare lymphoma.
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PMID:Identification of a novel fusion, SQSTM1-ALK, in ALK-positive large B-cell lymphoma. 2113 80

We previously showed that Bcl-2 (B-cell lymphoma 2) is down-regulated in a kainate (KA)-induced rat epileptic seizure model. The underlying mechanism had remained largely unknown, but we here report for the first time that denitrosylation and ubiquitination are involved. Our results show that the S-nitrosylation levels of Bcl-2 are down-regulated after KA injection and that the GluR6 (glutamate receptor 6) antagonist NS102 can inhibit the denitrosylation of Bcl-2. Moreover, the ubiquitin-dependent degradation of Bcl-2 was found to be promoted after KA treatment, which could be suppressed by the proteasome inhibitor MG132 and the NO donors, sodium nitroprusside and S-nitrosoglutathione. In addition, experiments based on siRNA transfections were performed in the human SH-SY5Y neuroblastoma cell line to verify that the stability of Bcl-2 is causal to neuronal survival. At the same time, it was found that the exogenous NO donor GSNO could protect neurons when Bcl-2 is targeted. Subsequently, these mechanisms were morphologically validated by immunohistochemistry, cresyl violet staining, and in situ TUNEL staining to analyze the expression of Bcl-2 as well as the survival of CA1 and CA3/DG pyramidal neurons. NS102, GSNO, sodium nitroprusside, and MG132 contribute to the survival of CA1 and CA3/DG pyramidal neurons by attenuating Bcl-2 denitrosylation. Taken together, our data reveal that Bcl-2 ubiquitin-dependent degradation is induced by Bcl-2 denitrosylation during neuronal apoptosis after KA treatment.
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PMID:Activation of GluR6-containing kainate receptors induces ubiquitin-dependent Bcl-2 degradation via denitrosylation in the rat hippocampus after kainate treatment. 2114 65

E3 ubiquitin ligases have been placed among the essential molecules involved in the regulation of T cell functions and T cell tolerance. However, it has never been experimentally proven in vivo whether these functions indeed depend on the catalytic E3 ligase activity. The Casitas B-cell lymphoma (Cbl) family protein Cbl-b was the first E3 ubiquitin ligase directly implicated in the activation and tolerance of the peripheral T cell. In this study, we report that selective genetic inactivation of Cbl-b E3 ligase activity phenocopies the T cell responses observed when total Cbl-b is ablated, resulting in T cell hyperactivation, spontaneous autoimmunity, and impaired induction of T cell anergy in vivo. Moreover, mice carrying a Cbl-b E3 ligase-defective mutation spontaneously reject tumor cells that express human papilloma virus Ags. These data demonstrate for the first time, to our knowledge, that the catalytic function of an E3 ligase, Cbl-b, is essential for negative regulation of T cells in vivo. Thus, modulation of the E3 ligase activity of Cbl-b might be a novel modality to control T cell immunity in vaccination, cancer biology, or autoimmunity.
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PMID:Essential role of E3 ubiquitin ligase activity in Cbl-b-regulated T cell functions. 2124 50


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