B-Aggressive Lymphoma Gene (BAL) Is a Risk-Related, γIFN-Inducible Gene That Is Expressed in Primary Diffuse Large B-Cell Lymphomas with a Brisk Host Inflammatory Response.

Although diffuse large B-cell lymphoma (DLBCL) is potentially curable with current therapy, a significant number of DLBCL patients still die of their disease. In a broad-based screen for genes and pathways associated with poor DLBCL outcome, we previously identified a novel risk-related gene, termed BAL (B-aggressive lymphoma). Thereafter, we cloned and characterized a major BAL partner protein, BBAP (B-aggressive lymphoma and BAL binding partner), described the nuclear trafficking patterns of both proteins and demonstrated that BAL functions as a modulator of transcription. In the current study, we characterized BAL expression in normal tonsil and primary DLBCLs and defined BAL regulation and potential functions in both cell types. Immunohistochemical staining of normal tonsil revealed that BAL was expressed by small numbers of germinal center (GC) cells and interfollicular cells with the morphologic features of centroblasts (with the GC) and immunoblasts (within the interfollicular areas). In primary DLBCLs, BAL was expressed by the malignant B cells. To gain insights regarding the regulation of BAL and BBAP expression in DLBCLs, we analyzed a series of 176 primary tumor biopsies transcriptionally profiled an U133A/B Affymetrix microarrays. BAL/BBAP high-expressing DLBCLs had evidence of a brisk host immune response, including increased expression of T/NK-cell receptor and activation pathway components, complement cascade members, macrophage/dendritic cells markers and γIFN-induced transcripts, raising the possibility that BAL was induced by γIFN. Consistent with this hypothesis, γIFN treatment of DLBCL cell lines with low basal levels of BAL markedly increased BAL expression. In silico analysis revealed that the BAL and BBAP genes are located in 3q21 in head-to-head orientation and share the same CpG-related promoter. This shared promoter contains a conserved γIFN-responsive module composed of IRF and STAT binding elements. The BAL/BBAP bidirectional promoter was cloned into a pGL3 luciferase promoterless reporter vector and found to increase luciferase activity > 20-fold following γIFN stimulation. To gain further insights into regulation of BAL transcription, mutant versions of BAL promoter were generated and cloned. Luciferase assays demonstrated that the IRF binding site was necessary for γIFN-induced BAL transcription, whereas the STAT1 binding site had an accessory role. Taken together, these results demonstrate that BAL and BBAP genes are transcriptionally activated by γIFN in DLBCLs with features of a brisk host immune response including γIFN signaling. Preliminary studies suggest that BAL limits the efficacy of the observed host inflammatory response.