Expression of cyclin D1 in mouse B cell lymphomas of different histologic types and differentiation stages

The G1 cyclin, cyclin D1, has been implicated in the development of human and mouse tumors. Here we describe immunohistochemical analyses of cyclin D1 for a large panel of mouse B cell tumors. In addition, we characterize cyclin D1 expression in a series of cultured cell lines that represent transformed B cells at different stages of development. Immunohistochemical analysis showed that for low-grade lymphomas, cyclin D1 was expressed by 83% of centroblastic centrocytic (CBCC) and 14% of small lymphocytic lymphomas (SLL). For high-grade tumors, 28% of B lymphoblastic and 23% of centroblastic tumors expressed cyclin D1, while all immunoblastic lymphomas were negative. Studies of RNA and protein prepared from cultured B lineage tumors showed that cyclin D1 was expressed by all pre-B and most B cell tumors but not by cell lines representative of late B cell differentiation or by plasma cells. Expression of cyclin D1 in the lymphomas was not associated with alterations in the genomic structure of the Fis-1 (Bcl-1) common proviral integration site or cyclin D1 itself or with cell growth activity as assessed by expression of proliferating cell nuclear antigen (PCNA).