Selective Enhancer Dependencies inMYC-Intact andMYC-Rearranged Germinal Center B-cell Diffuse Large B-cell Lymphoma

Abstract

AbstractHigh expression ofMYCand its target genes define a subset of germinal center B-cell diffuse large B-cell lymphoma (GCB-DLBCL) associated with poor outcomes. Half of these high-grade cases show chromosomal rearrangements between theMYClocus and heterologous enhancer-bearing loci, while focal deletions of the adjacent non-coding genePVT1are enriched inMYC-intact cases. To identify genomic drivers ofMYCactivation, we used high-throughput CRISPR-interference (CRISPRi) profiling of candidate enhancers in theMYClocus and rearrangement partner loci in GCB-DLBCL cell lines and mantle cell lymphoma (MCL) comparators that lacked common rearrangements betweenMYCand immunoglobulin (Ig) loci. Rearrangements betweenMYCand non-Ig loci were associated with unique dependencies on specific enhancer subunits within those partner loci. Notably, fitness dependency on enhancer modules within theBCL6super-enhancer (BCL6-SE) cluster regulated by a transcription factor complex of MEF2B, POU2F2, and POU2AF1 was higher in cell lines bearing a recurrentMYC::BCL6-SE rearrangement. In contrast, GCB-DLBCL cell lines withoutMYCrearrangement were highly dependent on a previously uncharacterized 3’ enhancer within theMYClocus itself (GCBME-1), that is regulated in part by the same triad of factors. GCBME-1 is evolutionarily conserved and active in normal germinal center B cells in humans and mice, suggesting a key role in normal germinal center B cell biology. Finally, we show that thePVT1promoter limitsMYCactivation by either native or heterologous enhancers and demonstrate that this limitation is bypassed by 3’ rearrangements that removePVT1from its position inciswith the rearrangedMYCgene.Key pointsCRISPR-interference screens identify a conserved germinal center B cellMYCenhancer that is essential for GCB-DLBCL lackingMYCrearrangements.Functional profiling ofMYCpartner loci reveals principles ofMYCenhancer-hijacking activation by non-immunoglobulin rearrangements.