Ubiquitylation of MYC couples transcription elongation with double-strand break repair at active promoters (ChIPseq_DS)

MYC family proteins are oncogenic transcription factors that can globally affect the function of RNA Polymerase II (RNAPII). The ability of MYC proteins to promote transcription elongation depends on their ubiquitination, but the underlying mechanism and its biological relevance are unknown. Here we show that MYC and the Polymerase II associated factor, PAF1c, interact directly and their function is mutually dependent, since the specific binding of MYC to active promoters depends on PAF1c and, conversely, PAF1c is required for MYC-dependent pause release. Upon binding, PAF1c is rapidly transferred from MYC onto RNAPII and this transfer is driven by the HUWE1 ubiquitin ligase. Both MYC and HUWE1 globally control histone H2B ubiquitylation, which promotes transcriptional elongation and alters chromatin structure for double-strand break repair. Consistently, MYC suppresses the accumulation of double-strand breaks at promoters in response to topoisomerase II inhibition. While depletion of PAF1c has only minor effects on MYC-dependent gene expression, MYC induces rampant transcription-dependent DNA damage in PAF1c-depleted cells. We propose that the HUWE1-dependent transfer of PAF1c from MYC onto RNAPII is critical for absorbing the topological stress accompanied with deregulated and oncogenic transcription. Overall design: U2OS cells expressing doxycycline-inducible MYC. Treated with/without doxycycline for 24 hrs and with or without BI8626 for 4 hrs