Blockade of oncogenic IkappaB kinase activity in ABC DLBCL by small molecule BET protein inhibitors
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ABSTRACT: In the activated B cell-like (ABC) subtype of diffuse large B cell lymphoma (DLBCL), NF-kappaB activity is essential for viability of the malignant cells and is sustained by constitutive activity of IkappaB kinase (IKK) in the cytoplasm. Here, we report an unexpected role for the bromodomain and extraterminal domain (BET) proteins BRD2 and BRD4 in maintaining oncogenic IKK activity in ABC DLBCL. IKK activity was reduced by small molecules targeting BET proteins as well as by genetic knockdown of BRD2 and BRD4 expression, thereby inhibiting downstream NF-kappaB-driven transcriptional programs and killing ABC DLBCL cells. Using a high-throughput platform to screen for drug-drug synergy, we observed that the BET inhibitor JQ1 combined favorably with multiple drugs targeting B cell receptor signaling, one pathway that activates IKK in ABC DLBCL. The BTK kinase inhibitor ibrutinib, which is in clinical development for the treatment of ABC DLBCL, synergized strongly with BET inhibitors in killing ABC DLBCL cells in vitro and in a xenograft mouse model. These findings provide a mechanistic basis for the clinical development of BET protein inhibitors in ABC DLBCL, particularly in combination with other modulators of oncogenic IKK signaling.
Project description:In the activated B cell-like (ABC) subtype of diffuse large B cell lymphoma (DLBCL), NF-kappaB activity is essential for viability of the malignant cells and is sustained by constitutive activity of IkappaB kinase (IKK) in the cytoplasm. Here, we report an unexpected role for the bromodomain and extraterminal domain (BET) proteins BRD2 and BRD4 in maintaining oncogenic IKK activity in ABC DLBCL. IKK activity was reduced by small molecules targeting BET proteins as well as by genetic knockdown of BRD2 and BRD4 expression, thereby inhibiting downstream NF-kappaB-driven transcriptional programs and killing ABC DLBCL cells. Using a high-throughput platform to screen for drug-drug synergy, we observed that the BET inhibitor JQ1 combined favorably with multiple drugs targeting B cell receptor signaling, one pathway that activates IKK in ABC DLBCL. The BTK kinase inhibitor ibrutinib, which is in clinical development for the treatment of ABC DLBCL, synergized strongly with BET inhibitors in killing ABC DLBCL cells in vitro and in a xenograft mouse model. These findings provide a mechanistic basis for the clinical development of BET protein inhibitors in ABC DLBCL, particularly in combination with other modulators of oncogenic IKK signaling. For JQ1 time course gene expression profiling, HBL1 and LP1 cells were treated with either DMSO or 100nM JQ1 for 1h, 3h, 8h, and 24h. For shRNA gene expression profiling, HBL1 cells were infected with either a Ctrl shRNA or with shRNA targeting BRD2 or BRD4. Following puromycin selection, shRNA expression was induced for 1 day and 2 days.
Project description:Chronic active B cell receptor (BCR) signaling, a hallmark of the ABC subtype of diffuse large B cell lymphoma (DLBCL), engages the CARD11-MALT1-BCL10 (CBM) adapter complex to activates IkappaB kinase (IKK) and the classical NF-kappaB pathway. Here we show that the CBM complex includes the E3 ubiquitin ligases cIAP1 and cIAP2, which are essential mediators of BCR-dependent NF-kappaB activity in ABC DLBCL. cIAP1/2 attach K63-linked polyubiquitin chains on themselves and on BCL10, resulting in the recruitment of IKK and the linear ubiquitin chain ligase LUBAC, which is essential for IKK activation. SMAC mimetic drugs target cIAP1/2 for destruction, and consequently suppress NF-kappaB and selectively kill BCR-dependent ABC DLBCL lines, supporting their clinical evaluation in patients with ABC DLBCL. Four ABC DLBCL tumor biopsy samples and one ABC DLBCL cell line (YM) (n=5) were analysed for copy number gains using the Affymetrix Genome-Wide Human SNP 6.0 Array. CEL files are being made available through dbGaP
Project description:Chronic active B cell receptor (BCR) signaling, a hallmark of the ABC subtype of diffuse large B cell lymphoma (DLBCL), engages the CARD11-MALT1-BCL10 (CBM) adapter complex to activates IkappaB kinase (IKK) and the classical NF-kappaB pathway. Here we show that the CBM complex includes the E3 ubiquitin ligases cIAP1 and cIAP2, which are essential mediators of BCR-dependent NF-kappaB activity in ABC DLBCL. cIAP1/2 attach K63-linked polyubiquitin chains on themselves and on BCL10, resulting in the recruitment of IKK and the linear ubiquitin chain ligase LUBAC, which is essential for IKK activation. SMAC mimetic drugs target cIAP1/2 for destruction, and consequently suppress NF-kappaB and selectively kill BCR-dependent ABC DLBCL lines, supporting their clinical evaluation in patients with ABC DLBCL.
Project description:Chronic active B cell receptor (BCR) signaling, a hallmark of the ABC subtype of diffuse large B cell lymphoma (DLBCL), engages the CARD11-MALT1-BCL10 (CBM) adapter complex to activates IkappaB kinase (IKK) and the classical NF-kappaB pathway. Here we show that the CBM complex includes the E3 ubiquitin ligases cIAP1 and cIAP2, which are essential mediators of BCR-dependent NF-kappaB activity in ABC DLBCL. cIAP1/2 attach K63-linked polyubiquitin chains on themselves and on BCL10, resulting in the recruitment of IKK and the linear ubiquitin chain ligase LUBAC, which is essential for IKK activation. SMAC mimetic drugs target cIAP1/2 for destruction, and consequently suppress NF-kappaB and selectively kill BCR-dependent ABC DLBCL lines, supporting their clinical evaluation in patients with ABC DLBCL.
Project description:Chronic active B cell receptor (BCR) signaling, a hallmark of the ABC subtype of diffuse large B cell lymphoma (DLBCL), engages the CARD11-MALT1-BCL10 (CBM) adapter complex to activates IkappaB kinase (IKK) and the classical NF-kappaB pathway. Here we show that the CBM complex includes the E3 ubiquitin ligases cIAP1 and cIAP2, which are essential mediators of BCR-dependent NF-kappaB activity in ABC DLBCL. cIAP1/2 attach K63-linked polyubiquitin chains on themselves and on BCL10, resulting in the recruitment of IKK and the linear ubiquitin chain ligase LUBAC, which is essential for IKK activation. SMAC mimetic drugs target cIAP1/2 for destruction, and consequently suppress NF-kappaB and selectively kill BCR-dependent ABC DLBCL lines, supporting their clinical evaluation in patients with ABC DLBCL. Samples from four ABC DLBCL cell lines (HBL1, TMD8, OCILY3, and OCILY10) were exposed to 2.5 uM birinapant for 2, 4, 6, and 24 hours (n=16). Samples from 2 ABC DLBCL cell lines (HBL1 and TMD8) were transduced with shRNA and induced with doxycycline for 3 and 4 days (n=4).
Project description:Natural killer cells are innate lymphocytes that play a pivotal role in the immune surveillance and elimination of transformed or virally infected cells. Using a combined chemico-genetic approach, we have identified that BET bromodomains BRD2 and BRD4 are central regulators of NK cell responses. We show that both BRD2 and BRD4 play a key regulatory function in controlling NK cell specific inflammatory responses. However, knockdown of BRD2 but not BRD4 impairs NK cell cytolytic response, highlighting a redundant role for BRD4 in regulating NK cell killing. We further show that the prototypic monovalent BET inhibitor impairs in vitro NK cell mediated killing of cancer target cells, while the bivalent BET bromodomain AZD5153 does not. We ascribe these differences to the preferential affinity of JQ1(+) to BRD2, while AZD5153 has a higher affinity for BRD4. Our work suggests that inhibiting BET bromodomains may be an effective therapeutic strategy for controlling inflammatory function. Given that BRD2 but not BRD4 inhibition can impair NK cell mediated killing, our findings also have clinical significance in light of the ongoing clinical application of BET bromodomains in oncology.
Project description:The medicinal active phenothiazine mepazine acts as a small molecule inhibitor of the MALT1 protease. Mepazine selectively inhibits cleavage activity of recombinant and cellular MALT1 by a noncompetitive mechanism. MALT1 activity is required for NF-kappaB signaling and survival of aggressive lymphoma belonging to the ABC-DLBCL (activated B-cell-type of diffuse large B-cell lymphoma) entity. Gene expression profiling was carried out in the ABC-DLBCL cell line HBL1 after treatment with mepazine (20 microM) for 6, 12, and 24 hr. Mepazine inhibits anti-apoptotic NF-kB signaling and thereby survival of these cells.
Project description:The medicinal active phenothiazine mepazine acts as a small molecule inhibitor of the MALT1 protease. Mepazine selectively inhibits cleavage activity of recombinant and cellular MALT1 by a noncompetitive mechanism. MALT1 activity is required for NF-kappaB signaling and survival of aggressive lymphoma belonging to the ABC-DLBCL (activated B-cell-type of diffuse large B-cell lymphoma) entity. Gene expression profiling was carried out in the ABC-DLBCL cell line HBL1 after treatment with mepazine (20 microM) for 6, 12, and 24 hr. Mepazine inhibits anti-apoptotic NF-kB signaling and thereby survival of these cells. Using Agilent 2-color gene expression microarrays (GPL10332) mepazine-treated HBL1 cells were compared with DMSO in the control channels.
Project description:Outcomes in activated B-cell diffuse large B-cell lymphoma (ABC-DLBCL) remain poor and new targets for treatment are needed. NF-κB signalling pathways from the B-cell receptor and Toll-like receptors bear mutations and are constitutively active in ABC-DLBCL but inhibitors of the major components of these signalling pathways have not yet entered clinical practice. The IKK related kinases, IKKε/TBK1, have essential roles in innate immunity and regulate aspects of NF-κB signalling and other pathways. TBK1 mRNA expression is associated with clinical outcome and TBK1 and IKKε are variably expressed in human DLBCL.
Project description:In the activated B-cell-like (ABC) subtype of diffuse large B cell lymphoma (DLBCL), the most frequent gain-of-function mutations target MyD88, a signaling adapter for Tolllike receptors (TLRs). The most prevalent oncogenic mutant, MyD88 L265P, occurs in 29% of cases and is the most active in engaging the NF-kappaB pathway. Here we show that MyD88 mutants do not function autonomously, but rather require TLR7, TLR9, and to a lesser extent, TLR4 to promote the survival of ABC DLBCL cells. Unlike wild type MyD88, MyD88 mutants associate constitutively with TLR7 and TLR9 in ABC DLBCL cells. Like ligand-induced TLR7/9 signaling in normal immune cells, the survival of ABC DLBCL cell lines depends upon translocation of TLR7 and TLR9 to acidic endolysosomes, where proteolytic processing of their ligand binding ectodomains is required for their oncogenic signaling. ABC DLBCL viability also depends upon CD14, a co-receptor for TLR7 and TLR9 that promotes engagement of nucleic acid ligands by these receptors. Point mutations in the TLR7 or TLR9 ectodomains that abrogate ligand binding and/or signaling were incapable of sustaining ABC DLBCL survival. An inhibitory oligonucleotide that suppresses TLR9 responses in normal B cells blocked NF-kappaB signaling and survival of ABC DLBCL lines. Together, these data suggest that an endogenous TLR ligand may play a pathogenic role in ABC DLBCL and provide a rationale for targeting TLR signaling to improve therapy of this aggressive lymphoma.