ChIP-Seq with reference exogenous genome (ChIP-Rx) of MAX in U2OS-MYC-KO-MYC-Tet-On cells with exogenous wild-type and mutant MYC expression

Transcription factor (TF) MYC binds to thousands of gene regulatory elements in the genome such as promoters and enhancers and exerts an amplification effect on the expression of most genes, regardless of the E-box motif existence. In this study, we discovered that MYC is an RNA-binding protein with a high affinity to guanosine-rich RNAs. RNAs that bind to MYC increase MYC’s chromatin occupancy, which helps with MYC-mediated regulation of gene expression. Mechanistically, two highly conserved sequences, amino acids 355-357 and 364-367, in the basic region of MYC are essential for RNA binding. Notably, alanine substitution of Lys355, Arg356, and Arg357 of MYC abolishes its RNA binding function but does not influence its complex formation ability, and E-box binding capacity of MYC:MAX dimer in vitro. However, loss of RNA binding function alone decreases MYC recruitment at gene regulatory elements in vivo, followed by a decreased MYC:MAX chromatin binding at these regions. This process further attenuates MYC-mediated gene expression. Therefore, RNA-binding-deficient MYC is compromised in promoting cancer cell proliferation. By demonstrating the mechanism of MYC-RNA interaction and the fundamental role of RNA binding activity in MYC-centric functions, our study reveals a new paradigm to MYC function and highlights an essential and probably general role of RNA binding capacity of TFs for their gene regulatory function.