Histone Demethylase LSD1 is required for Germinal Center formation and BCL6-driven lymphomagenesis

Germinal center (GC) B cells feature repression of many gene enhancers to establish their characteristic transcriptome. Here we show that conditional deletion of Lsd1 in GCs significantly impaired GC formation, associated with to failure to repress immune synapse genes linked to GC exit, which are also direct targets of the BCL6 transcriptional repressor. We found that BCL6 directly binds and recruits LSD1, primarily to intergenic and intronic enhancers. Conditional deletion of Lsd1 suppressed GC hyperplasia caused by constitutive expression of Bcl6, and significantly delayed Bcl6-driven lymphomagenesis. Administration of LSD1 catalytic inhibitors had little effect on GC formation or GC derived lymphoma cells. Using a CRISPR/Cas9 domain screen we found instead that the LSD1 Tower domain was critical for LSD1 dependency in GC derived B cells. These results indicate an essential role of LSD1 in the humoral immune response, where it modulates enhancer function by forming repression complexes with BCL6.