GSE167786
BTG1 mutation yields super-competitive B cells primed for malignant transformation
Mutations in the BTG1 tumor suppressor gene are exclusive to germinal center (GC)-derived B cell lymphomas and associate with low clinical outcome. To elucidate the effect of BTG1 mutations in mature B cells, we generated a mouse model for the conditional expression of mutant Btg1 Unlike conventional lymphoma oncogenes, mutated Btg1 expression in B cells did not induce GC hyperplasia. However, placing mutant and wild-type GC B cells in direct competition revealed that mutant Btg1 provides a massive advantage during the GC reaction. Furthermore, mutant Btg1 accelerates and dramatically increases the aggressiveness of BCL2-driven lymphomas in vivo.  NGS, cellular and molecular profiling showed activation of Myc and mTORC1 anabolic programs in Btg1 mutant GC B cells, murine lymphomas and patient DLBCLs. These programs characterize T cell-selected GC B cells that enter a growth phase prior to clonal burst. We find that mutant Btg1 sensitizes GC B cells to T cell signals, resulting in a lower threshold to Myc activation, through mRNA translational biochemical mechanisms. Together, we link recurrent mutations of BTG1 to a massive fitness gain of GC B cells that confers an agressive and invasive phenotype to B cell lymphomas in vivo and associate with low clinical outcome in patients with agressive DLBCL.  This work reveals a fine-tuned metabolic regulatory network that controls normal GC development and can be hijacked by lymphoma cells during disease progression. These findings have implications for fitness processes and natural selection at a broad level by providing fundamental insight into the power of subtle biochemical shifts to enhance biological fitness of cells. Overall design: RNAseq, RIPseq scRNAseq:  BD Rhapsody Single Cell RNA sequencing in competing Btg1 Q36H and CREneg Germinal Center B cells