PAF1c links S-phase progression to immune evasion and MYC function in pancreatic carcinoma [BLISS]
In pancreatic ductal adenocarcinoma (PDAC), MYC is required for S-phase progression and escape from immune surveillance. Here we show that recruitment of the PAF1c transcription elongation complex to RNA polymerase depends on MYC and that depletion of CTR9, a PAF1c subunit, enables long-term survival of PDAC-bearing mice. PAF1c is largely dispensable for unperturbed proliferation and regulation of MYC target genes. Instead, PAF1c limits DNA damage associated with transcription-replication conflicts by being essential for expression of long DNA repair genes. Surprisingly, the survival benefit conferred by CTR9 depletion is not due to DNA damage, but to restoration of immune surveillance. This occurs because CTR9 depletion releases RNA polymerase and the histone chaperone SPT6 from the body of long genes, promoting transcription of short genes that include MHC class-I genes. The data show that functionally distinct gene sets compete for elongation factors and directly link MYC-driven S-phase progression to tumor immune evasion. Overall design: Sequencing of double-strand breaks in cells exposed to AZD6738 with or without MYC depletion