The Transcriptional Network Governed by Interferon Regulatory Factor (IRF8) In Germinal Center B Cell Lymphomas.

Abstract 3638

The transcription factor IRF8, is highly expressed in germinal center (GC) centroblastic B cells and diffuse large B cell lymphomas (DLBCL). IRF8 is known to play roles in GC formation as well as in early B cell fate commitment, functioning both as a transcriptional activator and repressor; however, the transcriptional network regulated by IRF8 has not been elucidated yet. To identify direct targets of IRF8 on a genome-wide scale, we used ChIP-chip and expression profiling to study human and mouse lymphoma cell lines of GC origin – human Ly1, Odh1 and Val and mouse NFS201, NFS202, and NFS205. The IRF8-negative human multiple myeloma cell line, MMS1, and mouse plasmacytoma cell line, MPC11, were used as negative controls. For the human lines, 271 IRF8 target genes with common binding sites in all three cell lines, but not in negative cell line, were highly enriched for genes involved in innate immunity and adaptive immunity. Two well-established IRF8 target motifs- GAAANNGAAA and GGAANNGAAA - were significantly enriched in promoters of these genes compared to sequences 1kb upstream. Studies of the mouse lines identified 871 IRF8 targets with the lowest number found in NFS205. NFS205 expressed little PU.1, a common partner of IRF8 in DNA binding. PU.1 ChIP-chip analyses of the mouse lines allowed us to classify IRF8 targets into those that are PU.1-associated and PU.1-independent. Analyses of expression profiling of siIRF8-treated cells were used to identify transcriptionally active IRF8 targets. Gene Set Enrichment Analysis (GSEA) revealed significantly high enrichment of IRF8 ChIP targets as well as significant enrichment of genes involved in hematopoietic development. Finally 52 IRF8 targets common to human and mouse GC neoplasms were identified and characterized as contributing to antigen presentation, BCR and CD40 signaling, and interferon signaling, which can contribute differentially to the normal GC reaction and B cells transformation. These results define the contribution of IRF8 to the transcriptional network in GC B cells and provide new insights into the workings of the GC reaction in health and disease.

This work was supported by the Intramural Research Program of the NIH, National Institute of Allergy and Infectious Diseases.