bcl-2 translocation in Japanese B cell lymphoma: novel bcl-2 translocation with immunoglobulin heavy chain diversity segment.

Breakpoints of a lymphoma case with bcl-2 gene rearrangement that did not show comigration of immunoglobulin (Ig) heavy chain joining (JH) fragment were cloned. Sequence analysis revealed that the translocation broke the 3' side of the Ig heavy chain diversity (DH) segment at the heptamer recombination signal and each end was ligated to the bcl-2 locus. Since Southern blot demonstrated that both alleles of JH were rearranged, this translocation was suggested to have occurred at the step of VH-DH, or DH-DHJH recombination, one step later than that of DH-JH recombination where the common pattern of bcl-2 rearrangement generally occurs. Cases that showed comigration with JH fragment were also studied by polymerase chain reaction with 5' bcl-2 oligomer and 3' JH consensus anti-sense oligomer since it has been demonstrated that bcl-2 translocation at the major breakpoint clustering region (mbr) in American cases clusters within an about 150 bp region in the mbr. The results demonstrated that four out of five cases studied were amplified, indicating that the same clustering mechanism exists for Japanese cases. The present study, together with our previous report on Ig kappa-bcl-2, indicated that bcl-2 translocation in Japanese B cell lymphomas might occur at a later stage of B cell development, as compared with that in American cases. Less involvement of bcl-2 in Japanese B cell lymphoma may also be in part explainable by low susceptibility to bcl-2 rearrangement at the step of DH-JH recombination.