Abstract 679: Dual conditional loss of BLIMP-1 and p53 in B-cells drives B-cell lymphomagenesis
Authors: Roccaro Aldo M. , Kawano Yawara , Sacco Antonio , Park Jihye , Moschetta Michele , Mishima Yuji , Morgan Elizabeth , Carrasco Ruben , Ghobrial Irene 
Published: July 2016

Abstract
The transcription factor p53 is a well defined tumor suppressor involved in the modulation of cell proliferation, cell cycle progression and programmed cell death. BLIMP-1 plays a crucial role in modulating B-cell terminal differentiation towards Ig-secreting plasma cells, and it also acts as a tumor suppressor, as documented in both diffuse large B-cell lymphoma and Burkitt lymphoma. Whether B-cell specific loss of both p53 and BLIMP-1 may favor a B-cell lymphoma phenotype remains unanswered. Therefore, we aimed to define the functional relevance of both p53 and BLIMP-1 n B-cell lymphomagenesis in vivo, and generated dual p53/BLIMP-1-floxed conditional inactivation in B-cells, using mice expressing Cre recombinase under the control of CD19 promoter. 100% of the generated CD19Cre/Cre/BLIMPF/F/p53F/F transgenic mice (referred as CD19/Bl-/p53-) presented with diffuse lymphadenomegalies, marked splenomegaly, and hepatomegaly, observed in 90.3% and 77.4% of the cases, respectively. Other clinical manifestations included presence of ascites and hind lymb paralysis that were documented in 12.9% and 19.3% of the cases. The CD19/Bl-/p53- showed worse survival compared to BLIMPF/F/p53F/F mice non-expressing the CD19/Cre recombinase, CD19Cre/Cre/p53F/F, or CD19Cre/Cre/BLIMPF/F (363, 469.5, 460.5, and 770 days, respectively).
H.E. staining of CD19/Bl-/p53–derived lymph nodes, defined a nodal architecture completely effaced by a relatively monomorphic population of large sized atypical lymphoid cells with finely clumped and dispersed chromatin, and multiple basophilic medium sized, paracentrally situated nucleoli. A “starry sky” pattern was also observed. Overall, these features are compatible with a BL-like or high-grade lymphomas. IHC analysis confirmed a marked positivity for B220 staining, whit negativity for TdT, Bcl6, CD138 and CD4, CD8. Tumors were confirmed to be B220+/IgM+, with either Igk- or Ig-lambda-restriction as demonstrated by flow cytometry. Moreover, tumors were shown to be either mono- or bi-clonal, as demonstrated by Southern blotting, thus further confirming the clonal transformation induced by dual BLIMP/p53 deletion in B cells.
Whole exome sequencing was performed from B220-selected cells obtained from pathological lymph nodes of CD19/Bl-/p53- mice (n: 3) and from matched tail-derived tissues, used as germline. Agilent SureSelectXT was used for library prep. WES was performed on the Illumina HiSeq 2500 platform. Tumor and matched normal DNA sequencing data were processed using the Broad Institute best practices pipeline. We have identified 213 SNVs. Among them, somatic mutations were mapped on genes involved in the regulation of focal adhesion, PDGF singaling, p53-downstream pathway, and lipoprotein metabolism.
These studies demonstrate that the specific dual inactivation of p53 and BLIMP in B-cells promotes oncogenic transformation, resulting in aggressive B-cell lymphoma development.
Citation Format: Aldo M. Roccaro, Yawara Kawano, Antonio Sacco, Jihye Park, Michele Moschetta, Yuji Mishima, Elizabeth Morgan, Ruben Carrasco, Irene Ghobrial. Dual conditional loss of BLIMP-1 and p53 in B-cells drives B-cell lymphomagenesis. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 679.