A novel in vivo model for studying conditional dual loss of BLIMP‐1 and p53 in B‐cells, leading to tumor transformation

Abstract

The tumor suppressors B-lymphocyte-induced maturation protein-1 (BLIMP-1) and p53 play a crucial role in B-cell lymphomas, and their inactivation contributes to the pathogenesis of a wide spectrum of lymphoid malignancies, including diffuse large B-cell lymphomas (DLBCLs). Patients with activated B-cell-like (ABC) DLBCL may present with loss of BLIMP-1, c-Myc over-expression, decreased p53, and poor prognosis. Nevertheless, there is a lack of in vivo models recapitulating the biology of high-grade ABC DLBCL. We therefore aimed to develop an in vivo model aiming to recapitulate the phenotype observed in this cohort of patients. A Cre-Lox approach was used to achieve inactivation of both p53 and BLIMP-1 in murine B-cells. Contextual ablation of BLIMP-1 and p53 led to development of IgM-positive B-cell lymphoma with an aggressive phenotype, supported by c-Myc up-regulation, and accumulation of somatic mutations, as demonstrated by whole exome sequencing. Sensitivity of B-tumor cells to BTK inhibition was demonstrated. This model mirrors what reported in patients with ABC DLBLC, and therefore represents a novel model for studying the biology of ABC-DLBCL harboring the dual loss of BLIMP-1/p53 and c-Myc over-expression.

Reduced IRF4 expression promotes lytic phenotype in Type 2 EBV-infected B cells

“…IRF4 is an essential survival factor for T1 EBV-transformed LCLs [ 39 , 40 ], as well as many activated diffuse large B cell lymphomas (DLBCLs) [ 54 , 55 ]. Of note, T1 EBV uses multiple different mechanisms to activate IRF4 in LCLs, including EBNA2-mediated transcriptional activation [ 56 ], LMP1-induced IRF4 phosphorylation by the SRC kinase [ 57 , 58 ] and EBNA3C-mediated IRF4 protein stabilization [ 59 ].…”

“…Furthermore, since genes that are activated more efficiently by type 1 EBNA2 versus type 2 EBNA2 (including LMP1) have been previously shown to be enriched for EICE motifs [ 19 , 20 ], the higher level of IRF4 in type 1 LCLs might also contribute to enhanced activation of these EBNA2-responsive genes in type 1 LCLs. Given the ability of IRF4 to activate plasma cell differentiation (which can result in loss of proliferation and death of the host cell), activated DLBCLs that require IRF4 for survival often contain inactivating mutations of the PRDM1 gene to prevent such differentiation [ 54 , 55 ]. Likewise, in EBV-transformed LCLs, and transgenic mouse models, the T1 EBV latency proteins, EBNA3A and EBNA3C, have been shown to inhibit PRDM1 transcription [ 61 , 62 ].…”

Evidence for immortality and autonomy in animal cancer models is often not provided, which causes confusion on key issues of cancer biology

“…For this reason, the manipulations in most in vitro transformation assays are made in a perpetual manner, such as being made as stably-expressing cell clones, to prevent the loss of the coercer. Actually, some techniques of conditional immortalization and/or transformation [744][745][746][747][748][749], along with many conditionally immortalized cell lines [743,[750][751][752][753][754][755][756][757][758][759], like the temperature-controlled ones [756,760], have been widely established to make it feasible to turn on or off the coercer gene. There are even transgenic animals established to facilitate the establishment of such conditionally immortalized cell lines [755].…”

Mutation or not, what directly establishes a neoplastic state, namely cellular immortality and autonomy, still remains unknown and should be prioritized in our research

“…Knowing that there is no way of promptly immortalizing primary cells, researchers often perpetuate the manipulations, namely the coercions, by using such as stably-expressing cell clones or transgenic animals. However, for different research needs, many systems of "conditional immortality" or "conditional transformation" have also been created [600][601][602][603][604][605], including transgenic animals [606]. Accordingly, many conditional cell lines have been established [589,[606][607][608][609][610][611][612][613][614][615], like the temperaturecontrolled ones [612,616], which show controllable immortalization or neoplastic transformation [612,615,617].…”