BCL6 repression of EP300 in human diffuse large B cell lymphoma cells provides a basis for rational combinatorial therapy
Leandro C. Cerchietti, … , Gabriela Chiosis, Ari Melnick
Leandro C. Cerchietti, … , Gabriela Chiosis, Ari Melnick
Published November 1, 2010
Citation Information: J Clin Invest. 2010;120(12):4569-4582. https://doi.org/10.1172/JCI42869.
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Research Article Oncology

BCL6 repression of EP300 in human diffuse large B cell lymphoma cells provides a basis for rational combinatorial therapy

Abstract

B cell lymphoma 6 (BCL6), which encodes a transcriptional repressor, is a critical oncogene in diffuse large B cell lymphomas (DLBCLs). Although a retro-inverted BCL6 peptide inhibitor (RI-BPI) was recently shown to potently kill DLBCL cells, the underlying mechanisms remain unclear. Here, we show that RI-BPI induces a particular gene expression signature in human DLBCL cell lines that included genes associated with the actions of histone deacetylase (HDAC) and Hsp90 inhibitors. BCL6 directly repressed the expression of p300 lysine acetyltransferase (EP300) and its cofactor HLA-B–associated transcript 3 (BAT3). RI-BPI induced expression of p300 and BAT3, resulting in acetylation of p300 targets including p53 and Hsp90. Induction of p300 and BAT3 was required for the antilymphoma effects of RI-BPI, since specific blockade of either protein rescued human DLBCL cell lines from the BCL6 inhibitor. Consistent with this, combination of RI-BPI with either an HDAC inhibitor (HDI) or an Hsp90 inhibitor potently suppressed or even eradicated established human DLBCL xenografts in mice. Furthermore, HDAC and Hsp90 inhibitors independently enhanced RI-BPI killing of primary human DLBCL cells in vitro. We also show that p300-inactivating mutations occur naturally in human DLBCL patients and may confer resistance to BCL6 inhibitors. Thus, BCL6 repression of EP300 provides a basis for rational targeted combinatorial therapy for patients with DLBCL.

Authors

Leandro C. Cerchietti, Katerina Hatzi, Eloisi Caldas-Lopes, Shao Ning Yang, Maria E. Figueroa, Ryan D. Morin, Martin Hirst, Lourdes Mendez, Rita Shaknovich, Philip A. Cole, Kapil Bhalla, Randy D. Gascoyne, Marco Marra, Gabriela Chiosis, Ari Melnick

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Figure 8

EP300 genetic lesions and the impact of combinatorial therapy on primary DLBCL specimens.

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EP300 genetic lesions and the impact of combinatorial therapy on primar...
(A) Representation of the EP300 mutations found in DLBCL cell lines (n = 10) and patient samples (n = 93). The EP300 protein (N1 to C2414 terminus) is represented as a white bar with the KAT domain (1224 to 1669) in gray. Synonymous mutations are italicized. For nonsynonymous mutations, the substituted amino acid is indicated. Truncated proteins are indicated with an asterisk. The data correspondent to the cell line RC-K8 is from the literature (23). Patient samples are categorized accordingly to their DLBCL subtype as ABC, GCB, and unclassifiable (UC). (B) CD19+ single-cell suspensions from lymph node biopsies of 8 confirmed BCL6+ DLBCL specimens were cocultured with HK dendritic cells in a dual chamber separated by a 0.4-μm porous membrane. CD19+ cells were exposed to vehicle (white bars), 10 μM of RI-BPI (light gray bars), 1 μM of SAHA (dark gray bars), or the combination of RI-BPI and SAHA (black bars) for 48 hours. Cell viability (represented as percentage of control-treated cells) is shown on the y axis. Individual cases as well as the average for all the cases are shown on the x axis. The experiment was carried out in 4 replicates. (C) Similar experimental conditions as in B but for cells treated with vehicle (white bars), 10 μM of RI-BPI (light gray bars), 1 μM of PU-H71 (dark gray bars), or the combination of RI-BPI and PU-H71 (black bars) for 48 hours. Data are presented as mean with 95% CI.