Abnormal expression of DLBCL-derived mutant BCL6 alleles.

(A) Schematic diagram of the pLA/S5 wild-type reporter containing the BCL6 5′ noncoding region. Mutant constructs were generated by exchanging the 2.7-kb NdeI/SpeI fragment with the corresponding region of mutant BCL6 alleles derived from GC B cells or various lymphoma types. (B) Ly1 cells were transfected by electroporation with equimolar amounts of the indicated pLA/S5 reporter constructs and the pRL-TK plasmid as an internal control for transfection efficiency. In each tumor case, identified by a bracket, both alleles were tested (solid bars indicate mutated alleles; white bars, wild-type alleles). After 48 hours, cells were harvested and the luciferase activities were measured. One representative experiment of 3 to 8 independent transfections performed in duplicate with similar results is shown. Average luciferase activity (± SD) is expressed as relative increases with respect to the wild-type construct (set as 1), after normalization for Renilla activity; differences in activity were defined as significant when greater than 2-fold (dotted line). The DLBCL-derived alleles Ly1A, 93-611A, 93-611B, and 93-2889A were found overexpressed (4- to 18-fold), whereas no significant changes were observed in transfectants deriving from normal GC cells or other lymphoma types. DLBCL indicates diffuse large B-cell lymphoma; FL, follicular lymphoma; BL, Burkitt lymphoma; B-CLL, B-cell chronic lymphocytic leukemia.