Development of B Cell Lymphoma in E_μ-Cyclin D1 X Mutant p53 Transgenic Mice.

Background: Mantle cell lymphoma (MCL) is characterized by t(11;14) which dysregulates cyclin D1 expression. E_μ-cyclinD1 transgenic mice, however, are healthy. Additional genetic events must be necessary for lymphomagenesis, and knowledge of these would enhance understanding and therapy of MCL. In addition, a mouse model of MCL would be helpful in drug development. Alterations in p53 have been described in MCL, often associated with the blastic variant.

Objectives and Methods: To determine whether p53 and cyclin D1 can cooperate in lymphomagenesis, we cross bred E_μ-cyclinD1 transgenic mice (Bodrug et al EMBO J, 1996, courtesy of Alan Harris) with mice transgenic for mutant p53 (Jackson Labs, Jacks et al Curr Biol, 1994). Progeny mice were monitored for presence of the transgenes by PCR of tail vein DNA and observed for development of disease.

Results: Of mice carrying both aberrant genes, 24 of 38 developed B cell lymphoma. Mice did not become visibly ill until at least 12 months of age, with median age at sacrifice 15.5 (range 12–23) months. The lymphoma was generally disseminated, involving spleen, liver, diffuse adenopathy and marrow with occasional extranodal sites. Histology varied between small and large cell, with some having a vaguely follicular growth pattern. T cell lymphomas occurred in 2 other mice, while 5 developed osteosarcoma (1 of these in a mouse that also had B cell lymphoma). The B cell lymphomas were clonal by C_μ-V_H PCR. Cyclin D1 expression was documented by Western analysis. A cell line has also been developed from one of the B cell lymphomas and this line rapidly grows into disseminated lymphoma in syngeneic mice. These B cell lymphomas differ from the thymic T cell lymphomas seen in heterozygous p53 mutant mice that do not co-express cyclin D1. The latency period differs from cyclin D1 x myc double transgenic mice.

Conclusions: This model demonstrates cooperation between p53 and cyclin D1 pathways in B cell lymphomagenesis and should prove useful in delineating how these signals interact. The cell line may prove useful in pre-clinical testing of new agents for MCL.