Dynamic Supercoiling Sponsors Transcription Amplification by MYC

MYC dysregulation occurs in most cancers provoking, profound changes in gene expression. Although sometimes considered to be an E-box-dependent transcription factor, an alternate model posits MYC to be a universal amplifier of active genes. Although MYC is associated with accelerated pause release, the full extent of its participation in the transcription cycle remains poorly illuminated. MYC also stimulates topoisomerases to resolve topological issues that complicate DNA transactions; whether and how this stimulation is coordinated with or independent of its transcriptional role has not been examined. We have developed a genetic tool that discriminates between MYCs ability to activate versus amplify reporter gene expression in any cell. This system enables the interrogation of genes, cofactors, and compounds that execute or modulate MYC activity. Using a combination of biochemical and cellular assays, we reveal the dynamic interplay between MYC-driven transcription amplification and DNA supercoiling. The early stages of transcription are highly sensitive to the level of DNA supercoiling. Reducing the activity of TOP1 either through genetic knockdown or low-dose inhibition potentiates transcription amplification by MYC. This enhancement is associated with pre-initiation complex (PIC) stabilization by DNA supercoiling. MYC helps to mobilize these stabilized PICs. Significance StatementMYC is dysregulated in most cancers, yet its precise functions in transcription are poorly understood. Using a genetic system that distinguishes transcriptional activation from amplification, we reveal a functional interplay between MYC-driven amplification and DNA supercoiling. Reduced topoisomerase I activity increases DNA-supercoiling that in turn stabilizes PICs to provide more substrate for MYC-dependent transcription amplification. Thus, DNA topology as a critical regulator of MYC-dependent transcription.