BRD4-Regulated Molecular Targets in Mantle Cell Lymphoma: Insights into Targeted Therapeutic Approach

Abstract

Background: Since bromodomain-containing protein 4 (BRD4) facilitates the transcription of genes important for neoplastic cells in a cancer-type specific manner, BRD4-regulated molecules may also include therapeutic targets for mantle cell lymphoma (MCL), a treatment-refractory subtype of malignant lymphoma. Materials and Methods: In order to uncover direct BRD4regulated targets in MCL, we performed integrated analysis using the pathway database and the results of both geneexpression profiling and chromatin immunoprecipitation with parallel sequencing for BRD4. Results: Treatment with BRD4 inhibitor I-BET151 exerted a dose-dependent inhibitory effect on cell proliferation in MCL cell lines. BRD4 was found to directly regulate series of genes involved in the B-cell receptor (BCR) signaling pathway, including B-cell linker (BLNK), paired box 5 (PAX5), and IKAROS family zinc finger 3 (IKZF3), and several oncogenes, such as MYB. Indeed, the combinatory inhibition of BCR pathway and IKZF showed an additive antitumor effect. Conclusion: Concomitant targeting multiple BRD4regulated molecules may constitute a rational therapeutic strategy for MCL. The advent of immunochemotherapy consisting of cytotoxic agents and monoclonal antibodies, such as the antibody to CD20 rituximab, has markedly improved treatment outcomes for the majority of patients with B-cell lymphomas (BCLs). However, several hard-to-treat disease subtypes still exist for which the treatment outcome needs to be improved (1, 2). Mantle cell lymphoma (MCL), originating from CD5positive naïve B-lymphocytes, is such a treatment-refractory disease subtype which comprises approximately 3% of all non-Hodgkin lymphomas (NHLs). In addition to the diseasespecific chromosomal translocation t(11;14)(q13;q32) leading to cyclin D1 (CCND1) overexpression in approximately 90% of patients with MCL, there are additional genetic alterations. Abnormal overexpression of sex-determining region Y-box 11 (SOX11), a transcription factor, and cross talk with aberrant activation of several cell signaling pathways, including B-cell receptor (BCR), nuclear factor-kappa B (NF-ĸB), mitogen-activated protein kinase (MAPK), and NOTCH, coordinately promote MCL development and progression (3, 4). Despite the involvement of those known molecular pathways and abnormalities, a promising therapeutic molecular target for MCL has not been defined. The sole inhibition of CCND1 is insufficient for the 77 This article is freely accessible online.

Anticancer Effects of I-BET151, an Inhibitor of Bromodomain and Extra-Terminal Domain Proteins

“…BRD4 directly regulates a series of genes related to the B cell receptor signaling pathway. I-BET151 promotes the G1/S cell cycle arrest and apoptosis in BRD4-induced MCL cells, which represents a new strategy for treating MCL disease ( 44 ).…”

Ikaros Proteins in Tumor: Current Perspectives and New Developments

“…STAT5 regulates the super-enhancer of the myc gene by means of competition for binding to target sites or regulating histone acetylation in an opposing way to Ikaros ( Katerndahl et al, 2017 ). It was revealed that the genes related to the BCR signal pathway and the IKZF family are presumed to be upstream of the MYC/IRF4 axis ( Tsukamoto et al, 2020 ). In patients with trisomy 12 CLL, IRF4 by means of inducing Ikaros mediates the overexpression of CD49d, which was considered to identify those patients treated with ibrutinib with the characteristics of inferior nodal responses and shorter clinical outcomes ( Fiorcari et al, 2019 ).…”

“…BRD4 inhibitors were suggested to enhance the anti-MCL effect of Len or ibrutinib synergistically. It works even in BTZ-resistant MCL cells ( Tsukamoto et al, 2020 ).…”

Aberrant BUB1 Overexpression Promotes Mitotic Segregation Errors and Chromosomal Instability in Multiple Myeloma

“…Total RNA extraction and quantitative RT-PCR (qRT-PCR) were performed, as described elsewhere [27,32,52,53]. Primer sequences for qRT-PCR were as follows: BUB1 FW: 5 -ACC ATT CCA CAA GCT TCC AGT G-3 , BUB1 RV: 5 -TGA AGG CAC CAC CAT GTT TTC C-3 , β-Actin (ACTB) FW: 5 -TTC TAC AAT GAG CTG CGT GTG G-3 , and ACTB RV: 5 -TGG GGT GTT GAA GGT CTC AAA C-3 .…”

“…Western blotting was performed, as described previously [27,32,52,53], using rabbit anti-BUB1 (Abcam Cat#ab9000, Cambridge, UK) and mouse anti-ACTB (Sigma-Aldrich Cat# A2228, St. Louis, MO, USA) primary antibodies.…”