Tp53 deletion in B lineage cells predisposes mice to lymphomas with oncogenic translocations

Abstract

Inactivating Tp53 mutations are frequent genetic lesions in human tumors that harbor genomic instability, including B lineage lymphomas with IG translocations. Antigen receptor genes are assembled and modified in developing lymphocytes by RAG/AID-initiated genomic rearrangements that involve the induction of DNA double strand breaks (DSBs). Although TP53 inhibits the persistence of DSBs and induces apoptosis to protect cells from genomic instability and transformation, the development of spontaneous tumors harboring clonal translocations has not been reported in mice that only lack wild-type Tp53 protein or express Tp53 mutants. Tp53-deficient (Tp53 À/À ) mice succumb to T lineage lymphomas lacking clonal translocations but develop B lymphoid tumors containing immunoglobulin (Ig) translocations upon combined inactivation of DSB repair factors, RAG mutation or AID overexpression; mice expressing apoptosis-defective Tp53 mutants develop B cell lymphomas that have not been characterized for potential genomic instability. As somatic rather than germline inactivating mutations of TP53 are typically associated with human cancers and Tp53 deletion has cellular context dependent effects upon lymphocyte transformation, we generated mice with conditional Tp53 deletion in lineage-committed B lymphocytes to avoid complications associated with defective Tp53 responses during embryogenesis and/or in multilineage potential cells and, thereby, directly evaluate the potential physiological role of Tp53 in suppressing translocations in differentiated cells. These mb1-cre:Tp53 flox/flox mice succumbed to lymphoid tumors containing Ig gene rearrangements and immunophenotypes characteristic of B cells from various developmental stages. Most mb1-cre: Tp53 flox/flox tumors harbored clonal translocations, including Igh/c-myc or other oncogenic translocations generated by the aberrant repair of RAG/AID-generated DSBs.Our data indicate that Tp53 serves critical functions in B lineage lymphocytes to prevent transformation caused by translocations in cell populations experiencing physiological levels of RAG/AID-initiated DSB intermediates, and provide evidence that the somatic TP53 mutations found in diffuse large B-cell lymphoma and Burkitt's lymphoma may contribute to the development of these human malignancies.

Somatic inactivation of Tp53 in hematopoietic stem cells or thymocytes predisposes mice to thymic lymphomas with clonal translocations

“…VP and LP mice succumb to tumors at similar ages as Tp53 −/− , Lck-cre:Tp53 −/− mice, and Mb1-cre:Tp53 flox/flox mice. 32,33,36,44 In contrast to the aneuploid thymic lymphomas that arise in Tp53 −/− mice, we found that VP and LP mice developed lymphomas with aneuploidy or clonal translocations, including Ig or Tcrα/δ translocations. The distinct cancer phenotypes of these mice indicate that loss of Tp53 during embryogenesis, in cells before lymphocyte commitment, and/or in thymocytes masks development of lymphomas with oncogenic translocations in germline Tp53-deficient mice.…”

“…4B and C). Since the c-myc oncogene on chromosome 15 is activated by Igh or Tcrα/δ translocations in mouse lymphomas, 40,44 we also used a c-myc probe to identify potential Igh;c-myc and Tcrα/δ;c-myc translocations in VP lymphoma no. 421 and LP lymphoma no.…”

“…The TCRCα-232F19, TCRVδ3/Vα6-46G9, Igh C H BAC199, and c-myc-454G15 FISH probes have been described previously. 43,44 Slides were examined at room temperature under a BX61 microscope (magnification: 600×) from Olympus, controlled by a LAMBDA 10-B Smart Shutter from Sutter Instrument (Novato). Images were captured using a LAMBDA LS light source from Sutter Instrument, and a COOL-1300QS camera ASI, then analyzed through Case Data Manager Version 5.5 configured by Applied Spectral Imaging.…”

Lymphocyte lineage-specific and developmental stage specific mechanisms suppress cyclin D3 expression in response to DNA double strand breaks

“…39 Cells were stained with antibodies against surface antigens in PBS with 3% FBS and then washed before flow cytometry. The antibodies used from BD PharMingen were: anti-TCRb (553172), anti-CD4 (553653), anti-CD8a (553033), anti-CD25 (552880), anti-CD117 (553356).…”

Integrated signaling in developing lymphocytes

“…33,36 Deficiency of p53 results in a higher incidence of lymphoid malignancies with chromosomal translocations, consistent with an important role for this tumor suppressor in eliminating cells at risk for aberrant DNA repair and malignant transformation. 33,[37][38][39][40][41] However, mechanisms must exist to ensure that p53 does not induce the death of all cells attempting to assemble antigen receptor genes.…”