RNA-mediated MYC multimerization suppresses innate immune signaling
In response to perturbed transcription elongation, the MYC oncoprotein multimerizes and undergoes a phase transition; the underlying mechanisms and their function are unknown. Here, we show that MYC re-localizes from its canonical location on DNA to RNA in response to the accumulation of intronic RNA. MYC binds RNA directly, which enhances its multimerization. MYC multimers concentrate the nuclear exosome, a 3-5 RNA exonuclease, and its targeting complexes around double-stranded RNA and R-loops, and promote exosome recruitment to R-loops. RNA binding of MYC suppresses activation of the innate immune kinase TBK1. Upon MYC depletion, intron-derived dsRNAs, including RNA derived from repetitive elements and small nucleolar RNAs, accumulate on TLR3, a pattern recognition receptor that activates TBK1. In MYC-depleted cells, TLR3-bound snoRNAs carry aberrant 3-ends, indicating defective exosomal processing. Our data show that the phase transition of MYC is a RNA-driven stress response that suppresses the accumulation of immunogenic RNAs.