Promiscuous Rearrangements of the MYC Locus Hijack Enhancers and Super-Enhancers to Dysregulate MYC Expression in Multiple Myeloma

Abstract

MYC locus rearrangements – often complex combinations of translocations, insertions, deletions, and inversions - in multiple myeloma (MM) were thought to be a late progression event, which often did not involve immunoglobulin genes. Yet germinal center activation of MYC expression has been reported to cause progression to MM in an MGUS prone mouse strain. Although previously detected in 16% of MM, we find MYC rearrangements in nearly 50% of MM, including smoldering MM, and they are heterogeneous in some cases. Rearrangements reposition MYC near a limited number of genes associated with conventional enhancers, but mostly with super-enhancers (e.g., IGH, IGL, IGK, NSMCE2, TXNDC5, FAM46C, FOXO3, IGJ, PRDM1). MYC rearrangements are associated with a significant increase of MYC expression that is monoallelic, but MM tumors lacking a rearrangement have bi-allelic MYC expression at significantly higher levels than in MGUS. We also show that germinal center activation of MYC does not cause MM in a mouse strain that rarely develops spontaneous MGUS. It appears that increased MYC expression at the MGUS/MM transition usually is bi-allelic, but sometimes can be mono-allelic if there is a MYC rearrangement. Our data suggests that MYC rearrangements, regardless of when they occur during MM pathogenesis, provide one event that contributes to tumor autonomy.