Cyclin D2 promoter disrupted by t(12;22)(p13;q11.2) during transformation of chronic lymphocytic leukaemia to non-Hodgkin's lymphoma

In a unique case of chronic lymphocytic leukaemia (CLL) we performed a long itudinal cytogenetic and molecular genetic study of tumour cells from diagn osis through progression and transformation to non-Hodgkin's lymphoma (NHL) and lymphomatous meningitis. CLL cells at diagnosis had trisomy 12 and a t (14;19)(q32;q13.3), At relapse, the leukaemic cells had a subclone carrying a t(12;22)(p13;q11.2) in addition to the initial changes. We cloned recipr ocal translocation junctions at the 22q11.2(-) chromosome and the 12p13(+) chromosome and the corresponding germline DNA fragments. Restriction map an alysis and nucleotide sequence analysis of the cloned DNA fragment from the 22q11.2(-) chromosome mapped the translocation break within the immunoglob ulin (Ig)-lambda-C complex at the nt3889; nts 3890, 3891 were lost from the translocation site. A probe from the 3'-end of the clone derived from the 22q11.2- chromosome showed single copy hybridization which was different fr om the Ig-h probe. Nucleotide sequence analysis of the exact junction regio n and the corresponding germline DNA showed that the translocation at 12p13 occurred in the negative regulatory region of the cyclin D2 gene at the nt -1602, and a pentamer consisting of nts -1603 to -1599 was lost at the bre ak site. We sequenced another 227 bp upstream of the known 5'-end of the pr omoter and did not find any open reading frame. From these results we hypot hesize that, in this patient, the t(12;22) disrupted the negative regulator in the promoter of cyclin D2 which in turn might have deregulated cyclin D 2.