GANP regulates recruitment of AID to immunoglobulin variable regions by modulating transcription and nucleosome occupancy

摘要

Somatic hypermutation in B cells is initiated by activation-induced cytidine deaminase -catalyzed C→U deamination at immunoglobulin variable regions. Here we investigate the role of the germinal centre-associated nuclear protein ( GANP ) in enhancing the access of activation-induced cytidine deaminase ( AID ) to immunoglobulin variable regions. We show that the nuclear export factor GANP is involved in chromatin modification at rearranged immunoglobulin variable loci, and its activity requires a histone acetyltransferase domain. GANP interacts with the transcription stalling protein Spt5 and facilitates RNA Pol-II recruitment to immunoglobulin variable regions. Germinal centre B cells from ganp -transgenic mice showed a higher AID occupancy at the immunoglobulin variable region, whereas B cells from conditional ganp -knockout mice exhibit a lower AID accessibility. These findings suggest that GANP -mediated chromatin modification promotes transcription complex recruitment and positioning at immunoglobulin variable loci to favour AID targeting.