RESUMO
The MYCN oncoprotein binds active promoters in a heterodimer with its partner protein MAX. MYCN also interacts with the nuclear exosome, a 3'-5' exoribonuclease complex, suggesting a function in RNA metabolism. Here, we show that MYCN forms stable high-molecular-weight complexes with the exosome and multiple RNA-binding proteins. MYCN binds RNA in vitro and in cells via a conserved sequence termed MYCBoxI. In cells, MYCN associates with thousands of intronic transcripts together with the ZCCHC8 subunit of the nuclear exosome targeting complex and enhances their processing. Perturbing exosome function results in global re-localization of MYCN from promoters to intronic RNAs. On chromatin, MYCN is then replaced by the MNT(MXD6) repressor protein, inhibiting MYCN-dependent transcription. RNA-binding-deficient alleles show that RNA-binding limits MYCN's ability to activate cell growth-related genes but is required for MYCN's ability to promote progression through S phase and enhance the stress resilience of neuroblastoma cells.
Assuntos
Proteína Proto-Oncogênica N-Myc , Proteínas Nucleares , Proteínas Oncogênicas , Proteínas de Ligação a RNA , Proteína Proto-Oncogênica N-Myc/metabolismo , Proteína Proto-Oncogênica N-Myc/genética , Humanos , Proteínas de Ligação a RNA/metabolismo , Proteínas de Ligação a RNA/genética , Proteínas Nucleares/metabolismo , Proteínas Nucleares/genética , Proteínas Oncogênicas/metabolismo , Proteínas Oncogênicas/genética , Regiões Promotoras Genéticas , Linhagem Celular Tumoral , Neuroblastoma/metabolismo , Neuroblastoma/genética , Neuroblastoma/patologia , Exossomos/metabolismo , Exossomos/genética , Íntrons , Ligação Proteica , Núcleo Celular/metabolismo , Complexo Multienzimático de Ribonucleases do Exossomo/metabolismo , Complexo Multienzimático de Ribonucleases do Exossomo/genética , Regulação Neoplásica da Expressão Gênica , RNA/metabolismo , RNA/genética , Proteínas Repressoras/metabolismo , Proteínas Repressoras/genética , Proliferação de CélulasRESUMO
Oncoproteins of the MYC family drive the development of numerous human tumours1. In unperturbed cells, MYC proteins bind to nearly all active promoters and control transcription by RNA polymerase II2,3. MYC proteins can also coordinate transcription with DNA replication4,5 and promote the repair of transcription-associated DNA damage6, but how they exert these mechanistically diverse functions is unknown. Here we show that MYC dissociates from many of its binding sites in active promoters and forms multimeric, often sphere-like structures in response to perturbation of transcription elongation, mRNA splicing or inhibition of the proteasome. Multimerization is accompanied by a global change in the MYC interactome towards proteins involved in transcription termination and RNA processing. MYC multimers accumulate on chromatin immediately adjacent to stalled replication forks and surround FANCD2, ATR and BRCA1 proteins, which are located at stalled forks7,8. MYC multimerization is triggered in a HUWE16 and ubiquitylation-dependent manner. At active promoters, MYC multimers block antisense transcription and stabilize FANCD2 association with chromatin. This limits DNA double strand break formation during S-phase, suggesting that the multimerization of MYC enables tumour cells to proliferate under stressful conditions.