scholarly journals CTCF functions as a critical regulator of cell-cycle arrest and death after ligation of the B cell receptor on immature B cells

2003 ◽  
Vol 100 (2) ◽  
pp. 633-638 ◽  
Author(s):  
C.-F. Qi ◽  
A. Martensson ◽  
M. Mattioli ◽  
R. Dalla-Favera ◽  
V. V. Lobanenkov ◽  
...  
Keyword(s):  
Cell Cycle ◽  
B Cells ◽  
B Cell ◽  
Cell Cycle Arrest ◽  
Cell Receptor ◽  
B Cell Receptor ◽  
Cycle Arrest ◽  
Immature B Cells

scholarly journals Murine γ-Herpesvirus 68 Latency Protein M2 Binds to Vav Signaling Proteins and Inhibits B-cell Receptor-induced Cell Cycle Arrest and Apoptosis in WEHI-231 B Cells

2005 ◽  
Vol 280 (45) ◽  
pp. 37310-37318 ◽  
Author(s):  
Patrícia A. Madureira ◽  
Paulo Matos ◽  
Inês Soeiro ◽  
Linda K. Dixon ◽  
J. Pedro Simas ◽  
...  
Keyword(s):  
Cell Cycle ◽  
B Cells ◽  
B Cell ◽  
Cell Cycle Arrest ◽  
Cell Receptor ◽  
B Cell Receptor ◽  
Signaling Proteins ◽  
Cycle Arrest ◽  
Wehi 231

IKAROS and BCL6 Limit Pre-B Cell Expansion and Prevent Leukemogenesis Downstream of the Pre-B Cell Receptor

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 146-146
Author(s):  
Rahul Nahar ◽  
Parham Ramezani-Rad ◽  
Cihangir Duy ◽  
Sinisa Dovat ◽  
B. Hilda Ye ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Tumor Suppressor ◽  
B Cell ◽  
Cell Cycle Arrest ◽  
Cell Receptor ◽  
B Cell Receptor ◽  
Receptor Signaling ◽  
Cycle Arrest ◽  
B Cell Receptor Signaling ◽  
Cell Receptor Signaling

Abstract Abstract 146 Background: The pre-B cell receptor promotes differentiation of normal pre-B cells and induces cell cycle arrest at the transition from large cycling pre-B cells (Fraction C') to small resting pre-B cells (Fraction D). While pre-B cell receptor-induced cell cycle arrest represents a critical safeguard against pre-B cell leukemogenesis, the mechanism of pre-B cell receptor-dependent tumor suppression is only poorly understood. We recently established that pre-B cell receptor signaling leads to upregulation of Ikaros (Trageser et al., J Exp Med, 2009). Ikaros functions as a tumor suppressor in BCR-ABL1 pre-B ALL and is deleted in >80% of the cases. In addition, we recently reported that BCL6 is upregulated during pre-B cell receptor-induced cell cycle arrest (Duy et al., J Exp Med 2010). Result: To elucidate the mechanism of pre-B cell receptor-dependent tumor suppression in BCR-ABL1-driven B cell lineage leukemia, we studied regulation of Stat5-phosphorylation as a central mediator of survival and proliferation downstream of the BCR-ABL1 kinase. Forced expression of the pre-B cell receptor resulted in rapid dephosphorylation of Stat5 Y694 and concomitant upregulation of BCL6. Pre-B cell receptor-mediated upregulation of BCL6 was sensitive to expression of a constitutively active mutant of Stat5. Therefore, upregulation of BCL6 likely occurs indirectly through dephosphorylation of Stat5 downstream of the pre-B cell receptor. Upregulation of BCL6 is indeed causally linked to pre-B cell receptor-induced cell cycle arrest: By genome-wide ChIP-on-chip analysis and single-locus qChIP verification, we observed direct recruitment of the BCL6 transcriptional repressor to the promoter regions of CCND2 and MYC, which represent central mediators of cell cycle progression in BCR-ABL1 ALL. The negative effect of BCL6 on cell cycle progression was confirmed by retroviral overexpression, which induced cell cycle arrest in the vast majority of BCR-ABL1 ALL cells. In addition, overexpression of Myc could rescue BCL6-dependent cell cycle arrest downstream of the pre-B cell receptor. To verify the role of BCL6 in negative cell cycle regulation in a genetic experiment, we tested the function of the pre-B cell receptor in BCL6+/+ and BCL6-Null BCR-ABL1-transformed pre-B ALL cells. Forced expression of the pre-B cell receptor rapidly induced cell cycle arrest in BCL6+/+ but not BCL6-Null pre-B ALL cells. We conclude that upregulation of BCL6 leads to transcriptional repression of Myc/CCND2 and is required for pre-B cell receptor-mediated cell cycle arrest. Since our experiments established that BCL6 upregulation required Stat5-dephosphorylation, we next studied how pre-B cell receptor signaling leads to dephosphorylation of Stat5 and, hence, transcriptional activation of BCL6 as key effector to induce cell cycle arrest. Surprisingly, this analysis identified Ikaros as the key-mediator of Stat5-dephosphorylation is direct cooperation with the pre-B cell receptor signaling cascade. Reconstitution of Ikaros expression resulted in dramatic Stat5-dephosphorylation, which was comparable to the effect of Imatinib. Ikaros-dependent Stat5-dephosphorylation directly intersects with the pre-B cell receptor signaling pathway, because the pre-B cell receptor-associated linker molecule BLNK (SLP65) is required for Ikaros-mediated dephosphorylation. In BLNK-Null BCR-ABL1 pre-B ALL cells, Ikaros expression did neither affect Stat5-phosphorylation nor proliferation and survival of leukemia cells. As an indirect consequence of Stat5-dephosphorylation, Ikaros/BLNK signaling resulted in upregulation of BCL6 and subsequent cell cycle arrest. Conclusion: The Ikaros (IKZF1) tumor suppressor is deleted in >80% of the cases of BCR-ABL1-driven pre-B ALL, however, the mechanisms of Ikaros-dependent tumor suppression remained elusive. Here we describe for the first time that Ikaros functions as tumor suppressor via dephosphorylation of Stat5. Thereby, the Ikaros tumor suppressor requires direct interaction with the pre-B cell receptor signaling pathway including BLNK. Ikaros/BLNK inactivate Stat5 and, hence, a critical survival and proliferation signal. In addition, Ikaros/BLNK signaling leads to activation of BCL6, which functions as negative regulator of Myc/CCND2-dependent proliferation. Disclosures: No relevant conflicts of interest to declare.

scholarly journals Pre–B cell receptor–mediated cell cycle arrest in Philadelphia chromosome–positive acute lymphoblastic leukemia requires IKAROS function

2009 ◽  
Vol 206 (8) ◽  
pp. 1739-1753 ◽  
Author(s):  
Daniel Trageser ◽  
Ilaria Iacobucci ◽  
Rahul Nahar ◽  
Cihangir Duy ◽  
Gregor von Levetzow ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Acute Lymphoblastic Leukemia ◽  
Tumor Suppressor ◽  
B Cell ◽  
Cell Cycle Arrest ◽  
Lymphoblastic Leukemia ◽  
Philadelphia Chromosome ◽  
Cell Receptor ◽  
B Cell Receptor ◽  
Cycle Arrest

B cell lineage acute lymphoblastic leukemia (ALL) arises in virtually all cases from B cell precursors that are arrested at pre–B cell receptor–dependent stages. The Philadelphia chromosome–positive (Ph+) subtype of ALL accounts for 25–30% of cases of adult ALL, has the most unfavorable clinical outcome among all ALL subtypes and is defined by the oncogenic BCR-ABL1 kinase and deletions of the IKAROS gene in >80% of cases. Here, we demonstrate that the pre–B cell receptor functions as a tumor suppressor upstream of IKAROS through induction of cell cycle arrest in Ph+ ALL cells. Pre–B cell receptor–mediated cell cycle arrest in Ph+ ALL cells critically depends on IKAROS function, and is reversed by coexpression of the dominant-negative IKAROS splice variant IK6. IKAROS also promotes tumor suppression through cooperation with downstream molecules of the pre–B cell receptor signaling pathway, even if expression of the pre–B cell receptor itself is compromised. In this case, IKAROS redirects oncogenic BCR-ABL1 tyrosine kinase signaling from SRC kinase-activation to SLP65, which functions as a critical tumor suppressor downstream of the pre–B cell receptor. These findings provide a rationale for the surprisingly high frequency of IKAROS deletions in Ph+ ALL and identify IKAROS-mediated cell cycle exit as the endpoint of an emerging pathway of pre–B cell receptor–mediated tumor suppression.

scholarly journals Rewiring of B cell receptor signaling by Epstein–Barr virus LMP2A

2020 ◽  
Vol 117 (42) ◽  
pp. 26318-26327
Author(s):  
Kamonwan Fish ◽  
Federico Comoglio ◽  
Arthur L. Shaffer ◽  
Yanlong Ji ◽  
Kuan-Ting Pan ◽  
...  
Keyword(s):  
Cell Cycle ◽  
B Cells ◽  
B Cell ◽  
Epstein Barr Virus ◽  
Cell Receptor ◽  
B Cell Receptor ◽  
Barr Virus ◽  
Human B Cells ◽  
Bcr Signaling ◽  
Epstein Barr

Epstein–Barr virus (EBV) infects human B cells and reprograms them to allow virus replication and persistence. One key viral factor in this process is latent membrane protein 2A (LMP2A), which has been described as a B cell receptor (BCR) mimic promoting malignant transformation. However, how LMP2A signaling contributes to tumorigenesis remains elusive. By comparing LMP2A and BCR signaling in primary human B cells using phosphoproteomics and transcriptome profiling, we identified molecular mechanisms through which LMP2A affects B cell biology. Consistent with the literature, we found that LMP2A mimics a subset of BCR signaling events, including tyrosine phosphorylation of the kinase SYK, the calcium initiation complex consisting of BLNK, BTK, and PLCγ2, and its downstream transcription factor NFAT. However, the majority of LMP2A-induced signaling events markedly differed from those induced by BCR stimulation. These included differential phosphorylation of kinases, phosphatases, adaptor proteins, transcription factors such as nuclear factor κB (NF-κB) and TCF3, as well as widespread changes in the transcriptional output of LMP2A-expressing B cells. LMP2A affected apoptosis and cell-cycle checkpoints by dysregulating the expression of apoptosis regulators such as BCl-xL and the tumor suppressor retinoblastoma-associated protein 1 (RB1). LMP2A cooperated with MYC and mutant cyclin D3, two oncogenic drivers of Burkitt lymphoma, to promote proliferation and survival of primary human B cells by counteracting MYC-induced apoptosis and by inhibiting RB1 function, thereby promoting cell-cycle progression. Our results indicate that LMP2A is not a pure BCR mimic but rather rewires intracellular signaling in EBV-infected B cells that optimizes cell survival and proliferation, setting the stage for oncogenic transformation.

SYK Is a Tumor Suppressor In Pre-B Cell Acute Lymphoblastic Leukemia and Not a Therapeutic Target

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 4199-4199
Author(s):  
Carina Ng ◽  
Rahul Nahar ◽  
Emily Elliott ◽  
Clifford A. Lowell ◽  
Markus Muschen
Keyword(s):  
Cell Cycle ◽  
B Cell ◽  
Cell Receptor ◽  
B Cell Receptor ◽  
Leukemia Cells ◽  
Imatinib Treatment ◽  
Empty Vector Control ◽  
Empty Vector ◽  
Cycle Arrest

Abstract Abstract 4199 Background: The pre-B cell receptor promotes differentiation of normal pre-B cells and couples the immunoglobulin μ-chain to activating tyrosine kinases (e.g. SYK) via linker molecules (e.g. BLNK). We recently established that the pre-B cell receptor functions as a tumor suppressor in pre-B acute lymphoblastic leukemia (ALL) including ALL cells carrying the BCR-ABL1 oncogene (Trageser et al., J Exp Med, 2009). In virtually all cases of BCR-ABL1 ALL, pre-B cell receptor function is compromised and its reconstitution induces rapid cell cycle arrest. Given that the SYK tyrosine kinase represents a critical signaling molecule in the pre-B cell receptor pathway, one would expect that SYK tyrosine kinase activity has a tumor suppressive effect. It therefore seems counterintuitive that pharmacologic targeting of SYK was recently proposed as a new treatment approach for pre-B ALL (Uckun et al., Br J Haematol. 2010). While there is solid evidence for a role of Syk as a target in B cell lymphoma (Friedberg et al., Blood 2010) and B cell lineage CLL (Buchner et al., Blood 2010), where tonic B cell receptor signaling delivers critical survival signals, the role of Syk downstream of the pre-B cell receptor in ALL is unclear. Results: To clarify the role of SYK downstream of the pre-B cell receptor in pre-B ALL, we performed a genetic experiment to inducibly delete the Syk gene in pre-B ALL cells. To this end, pre-B cells from Syk-fl/fl mice were propagated in the presence of IL7 and then transformed with retroviral BCR-ABL1 or MLL-ENL oncogenes. After transformation, pre-B leukemia cells were transduced with 4-hydroxy-tamoxyfen (4-OHT)-inducible retroviral Cre-ERT2 or an ERT2 empty vector control. After puromycin-selection of Cre-ERT2 and ERT2 transduced leukemia cells, Cre-ERT2 or the ERT2 control were induced by addition of 4-OHT and deletion of Syk was studied at different time points. As assessed by Western blot and PCR, deletion of Syk was near complete after two days and undetectable after six days. We then studied changes in cell viability upon inducible deletion of Syk: Acute deletion of the Syk tyrosine kinase had no significant impact on the viability of pre-B ALL cells, even after prolonged cell culture over several weeks. We then reasoned that the effect of Syk-deletion may be subtle yet important, so we studied in BCR-ABL1-transformed Syk-fl/fl pre-B leukemia cells whether Syk-deletion sensitizes to Imatinib-treatment. Deletion of Syk was again confirmed by Western blot, yet the dose-response curves to Imatinib-treatment were superimposable for Syk-fl/fl and Syk-del/del pre-B leukemia cells. We conclude that SYK does not contribute important survival signals in our mouse model for pre-B ALL, nor does deletion of Syk sensitize BCR-ABL1-driven pre-B leukemia cells to Imatinib-treatment. We next investigated the counter-hypothesis that Syk functions as a tumor suppressor downstream of the pre-B cell receptor. To test this possibility, we tested the effect of forced pre-B cell receptor expression in the presence or absence of Syk. Syk-fl/fl and Syk-del/del pre-B leukemia cells were transduced with CD8/μ-chain or a CD8 empty vector control. The μ-chain represents the central component of the pre-B cell receptor. Forced expression of the CD8 empty vector control had no effect regardless of whether Syk was deleted or not. When pre-B cell receptor signaling was reconstituted in Syk-fl/fl cells by expression of CD/μ-chain, viability of the leukemia decreased by >80%. By contrast, deletion of Syk greatly attenuated the tumor suppressive effect of CD8/μ-chain expression and less than 25% of the leukemia cells underwent cell cycle arrest and cell death. Background: Genetic deletion of Syk unequivocally demonstrates that Syk does not deliver critical survival signals downstream of the pre-B cell receptor in ALL. This is unlike B cell lymphoma, where tonic signaling from the B cell receptor promotes cell survival via Syk (Friedberg et al., 2010; Buchner et al., 2010). On the contrary, in pre-B ALL, the Syk kinase mediates pre-B cell receptor-induced cell cycle arrest. These findings are in direct conflict with a recent report on the therapeutic usefulness of pharmacological inhibition of Syk in pre-B ALL cell lines (Uckun et al., Br J Haematol.; 149: 508-17; 2010). The compound (C-61) used in this study may have unrecognized off-target effects, which might account for the discrepancies. Disclosures: No relevant conflicts of interest to declare.

scholarly journals RAG-mediated DNA double-strand breaks activate a cell type–specific checkpoint to inhibit pre–B cell receptor signals

2016 ◽  
Vol 213 (2) ◽  
pp. 209-223 ◽  
Author(s):  
Jeffrey J. Bednarski ◽  
Ruchi Pandey ◽  
Emily Schulte ◽  
Lynn S. White ◽  
Bo-Ruei Chen ◽  
...  
Keyword(s):  
Cell Cycle ◽  
B Cells ◽  
B Cell ◽  
Cell Receptor ◽  
B Cell Receptor ◽  
Cell Cycle Checkpoint ◽  
Double Strand Breaks ◽  
Chain Gene ◽  
Dna Double Strand Breaks ◽  
Strand Breaks

DNA double-strand breaks (DSBs) activate a canonical DNA damage response, including highly conserved cell cycle checkpoint pathways that prevent cells with DSBs from progressing through the cell cycle. In developing B cells, pre–B cell receptor (pre–BCR) signals initiate immunoglobulin light (Igl) chain gene assembly, leading to RAG-mediated DNA DSBs. The pre–BCR also promotes cell cycle entry, which could cause aberrant DSB repair and genome instability in pre–B cells. Here, we show that RAG DSBs inhibit pre–BCR signals through the ATM- and NF-κB2–dependent induction of SPIC, a hematopoietic-specific transcriptional repressor. SPIC inhibits expression of the SYK tyrosine kinase and BLNK adaptor, resulting in suppression of pre–BCR signaling. This regulatory circuit prevents the pre–BCR from inducing additional Igl chain gene rearrangements and driving pre–B cells with RAG DSBs into cycle. We propose that pre–B cells toggle between pre–BCR signals and a RAG DSB-dependent checkpoint to maintain genome stability while iteratively assembling Igl chain genes.

scholarly journals Interferon regulatory factors 4 and 8 induce the expression of Ikaros and Aiolos to down-regulate pre–B-cell receptor and promote cell-cycle withdrawal in pre–B-cell development

Blood ◽  
2008 ◽  
Vol 111 (3) ◽  
pp. 1396-1403 ◽  
Author(s):  
Shibin Ma ◽  
Simanta Pathak ◽  
Long Trinh ◽  
Runqing Lu
Keyword(s):  
Cell Cycle ◽  
B Cells ◽  
B Cell ◽  
Light Chain ◽  
Cell Receptor ◽  
B Cell Receptor ◽  
Regulatory Factors ◽  
Surrogate Light Chain ◽  
Interferon Regulatory Factors ◽  
Molecular Events

Abstract Pre-B lymphocytes consist of 2 distinct cell populations: large pre-B and small pre-B. The large pre-B cells are newly generated pre-B cells that express pre–B-cell receptor (pre-BCR) on the surface and are highly proliferative; small pre-B cells are derived from large pre-B cells that have down-regulated pre-BCR and withdrawn from cell cycle. The molecular events that mediate the transition from cycling pre-B to small, resting pre-B have not been fully elucidated. Here, we show that interferon regulatory factors 4 and 8 (IRF4,8) suppress surrogate light chain expression and down-regulate pre-BCR in pre-B cells. Our studies further reveal that IRF4,8 induce the expression of Ikaros and Aiolos in pre-B cells, and reconstitution of expression of either one is sufficient to suppress surrogate light chain expression and down-regulate pre-BCR in pre-B cells lacking IRF4,8. Interestingly, our results also indicate that pre-B cells undergo growth inhibition and cell-cycle arrest in the presence of IRF4,8. Moreover, we provide evidence that Ikaros and Aiolos are indispensable for the down-regulation of pre-BCR and the cell-cycle withdrawal mediated by IRF4,8. Thus, IRF4,8 orchestrate the transition from large pre-B to small pre-B cells by inducing the expression of Ikaros and Aiolos.

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